ROOTSTOCKS FOR PE a a S .. WITH SPECIAL REFERENCE TO SCION ROOTING AND COMPATIBILITY By GURCHAR a N SINGH RANDHa WA A THESIS Submitted to the School of Graduate Studies of Michigan State College of Agriculture and Applied Science in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Horticulture 1949 ACKHOWLEDG|iMEW TS The writer wishes to express his deep gratitude to Dr. H. B. Tukey, Head of the Department of Horticulture, Michigan State College and to Dr. W. H. Upshall, Chief in Research, Vineland Station, Canada for their guidance, unfailing help, and encouragement throughout the course of these investigations. He also wishes to extend his appreciation to Dr. E. J. Benne of Michigan Agricultural Experiment Station for his advice and cooperation. Thanks are also due to many staff members of the Department of Horticulture, Ontario Agricultural College, Guelph, and the Vineland Station, Ontario, Canada for their cooperation. C 0 U T E N T S Page Part 1. Rootstocks for pears Introduction 1 Pyrus communis Historical Botany Propagation Soil adaptation Climatic requirements Diseases Insects Value as a rootstock 4 46 7 8 10 12 18 19 Pyrus pyrifolia (Japanese pear) Historical Botany Propagation Soil adaptation Climatic requirements Diseases Insects Value as a rootstock 24 25 25 26 27 28 50 50 Pyrus ussuriensis Historical Botany Soil adaptation Climatic requirements Diseases and insects Value as a rootstock 54 54 55 35 56 37 38 Pyrus betulaefolia Historical Botany Propagation Soil adaptation Climatic requirements Diseases and insects Value as a rootstock 41 41 41 42 45 44 44 46 Pyrus calleryana Historical Botany Propagation 24 49 49 50 50 Soil adaptation Climatic requirements Diseases and insects Value as a rootstock 51 52 55 54 •» Pyrus serrulata Historical Botany Soil adaptation and Climatic requirements Value as a rootstock 59 59 59 60 60 Quince 62 Historical Botany Propagation Climatic requirements Diseases and insects Value as a rootstock Some other 62 62 65 65 66 67 rootstocks for pears 74 apple 74 Hawthorn or white thorn 74 Mountain ash 74 White beam 75 Summary and conclusions Part II 76 Effect of scion rooting on growth and cropping of 14-year dwarf pear trees. Introduction 77 Review of literature 78 Experimental Material and Layout 81 Methods 85 Observations on tree growth Technique of excavations Observations on root growth Washing the roots Number of roots Measurements of roots and Determination of age of scion roots 83 85 84 84 84 84 Identification of pear and quince rootstocks from rootpieces. Macroscopic tests Chemical tests Presentation 85 85 85 of Data Observation on tree growth Observations on root growth Number of scion roots Capacity of scion rooting age when scion roots originated Effect of scion rooting on growth Bartlett an jou Vermont Beauty Clapp Favorite Bose Effect of scion rooting on cropping Bartlett Anjou Vermont Beauty Clapp Favorite Bose 86 86 86 88 90 91 92 92 95 9o 94 94 95 95 95 96 96 97 Effect of scion rooting on weight per fruit 97 Identification of Pear and Quince rootstocks from rootpieces 98 Macroscopic characters Colour of bark General growth characters Colour of inner bark Colour of bark on exposure to air Through Chemicals Discussion 'Summary 98 98 99 99 99 99 101 107 Part III. Studies in Incompatibility between stock and scion of dwarf pear trees Introduction 108 Review of Literature 1Q9 Experimental Materials and Liethods 117 Field methods General observations in the nursery Swelling at Union Laboratory methods water conductivity Starch accumulation Bark and wood continuity Strength-at-union Nature of fracture at the union 117 117 117 117 117 118 118 118 119 Results General growth behaviour in the nursery Swelling at Union Obstruction to the passage of water and elaborated foods in the region of the union Water conductivity Starch accumulation Bark and wood continuity Strength-at-union and nature of fracture Premature autumn leaf colora­ tion and early defoliation Swelling at union Obstruction to the passage of water and elaborated foods in the region of the union Water conductivity Starch accumulation Bark and wood continuity 3trength-at-union and nature of fracture 120 120 120 122 122 125 125 128 129 129 152 lo2 152 lo5 lo4 Discussion 156 Summary and conclusions 143 Part IV. Relationship between the graft-union, autumnal leaf colors, and growth and fruiting of standard Kieffer pear trees. Introduction la4 Experimental Materials and Methods 145 Hesuits 147 Orchard trees 147 relationship between leaf colora­ tion tree size, fruit size and quality 147 Chemical analysis of leaves Ontario orchards Michigan orchards Soil analysis 149 149 150 151 Nursery trees 155 Behaviour of red-leaved nursery trees after planting in the orch­ ard. Chemical analysis of tops Swelling at the graft-union Obstruction to the passage of water and carbohydrates in the region of the union vVater conductivity Starch accumulation Strength at union and nature of fracture 155 155 156 158 158 159 160 Discussion 161 Summarv and conclusions 164 Bibliography 165 Appendix PART I ROOTSTOCKS FOR PKARS INTRODUCTION It is a matter of common knowledge that the pear, like other tree fruits, does not reproduce true to vari­ ety from seed. For this reason, it is propagated on seedling roots by budding or grafting. The seedling roots employed are commonly designated as '’rootstocks1'. ' The fruit industry in many new regions of the World, with wide variations in soil and climatic conditions, has been greatly expanded recently in order to meet local market requirements, and many improved commercial varie­ ties have been produced. As a result, new rootstocks have been required in order to adapt these varieties to conditions of soil, winter cold, drought, and resistance to diseases and insect pests. The pear has numerous diseases and insect pests. Of all these, fire-blight (Erwinia amylovora; is most serious, causing enormous mortality in pear orchards each year, unfortunately, seedlings of the French pear (Pyrus communis, L.) are quite susceptible to this malady. Some Oriental stocks are reputed to be more blight-resistant, but some varieties of pear develop "black-end" fruits on most of these stocks. Pacific Coast, This trouble is especially common on the -2Until about World War I, France was the exclusive source of both pear seed and seedlings. The seed was easy to procure in quantity from the fruit-juice (perry) mills. These seedlings were commonly known as "French pear". Like most of the pear varieties, such as, Bart­ lett, Bose, and Hardy, these seedlings are botanically identical, i.e., they are also Pyrus communis. Until 1930, much dependence was placed upon French pear seed­ lings imported from Europe. However, an embargo placed against the importation of rootstocks in 1930, induced the production of a domestic supply of seedlings. Today, 'Domestic" pear seedlings are employed almost exclusively as pear stocks in North America, Due to scarcity of French stock during and after World War I, the Japanese stock (Pyrus pyrifolia), came into prominence. It was considered more blight-resistant than French pear seedling stock. Ten years after its general introduction approximately 30 per cent of the pear orchards in California were on this stock. However, twenty five years' experience with this stock revealed Its unsuit­ ability. xhe varieties grown on it developed black-end fruits, and consequently most of the orchards on this stock were removed. -5The Angers quince iCydonia vulgari3, Lindl) is commonly used for dwarfing pears. The early French and English settlers took a fancy to dwarf-pear culture but it was not long before they realized that this venture was of questionable merit from the commercial point of view. Dwarf pear trees are comparatively short-lived, and need better care than standard trees. susceptible to fire-blight. They are also Dwarf trees are, however, well suited for home gardens where they occupy limited space and produce high quality fruit. Many other Oriental stocks such as Pyrus calleryana, P. betulaefolia, and P. ussuriensis have also been tried but with limited success. undoubtedly, a better rootstock for pears is required, xt should be blight-resistant, adaptable to various soil and climatic conditions, and, at the same time, congenial with most of the leading commercial pear varieties. An attempt has been made to review the literature on rootstocks for pears with the idea of exploring the pos­ sibility of obtaining this better rootstock. -4pyrus communis. L. Historical Pyrus comnmnis, L. the common cultivated, pear, is found in Southern Europe and Southwestern Asia as far East as Kashmir, ±ndia. It includes the leading com­ mercial pear varieties of America and also the French seedlings used as rootstock. Homer, ahout 1,000 years before the Christian era, mentioned the pear as one of the fruits in the gardens of Alicinous. Even prior to this period a few varie­ ties were known. Theophrastus (370-286 B.C.) described both wild and cultivated pears, thods of grafting the pear. ne also described me­ Pliny, in his natural his­ tory, named more than 40 varieties of pears. The con­ quests of the Romans were further responsible for the distribution of pears throughout temperate Europe,, During the eighteenth and nineteenth centuries a .D. a considerable interest arose in France and Belgium in the improvement of the pear by breeding. of great value were developed. Many varieties Among the leaders in breeding were nardenpont (1705-74;, a Belgian worker, who produced about a dozen high quality pear varieties, and Van Mons (1765-1842/ of the same country who did extensive work in pear breeding. Of the 400 pear varieties origi­ nated or distributed by Van Mons, about 40 proved to be of significant merit. Pears came to the North American continent along 'with the French and English settlers. Pear seeds were imported to this country as early as 1629, Pears were among the first luxuries available to the Franch and English settlers, from Canada to Florida. English travellers in 1638-39 remarked that pear trees were prospering abundantly. Hedrick (1921y mentions that the pear was also introduced into Maine at a very early date by French settlers. Most of the early pear or­ chards sprang from seed imported from France. A nursery in Massachussetts began to sell pear trees as early as 1641. These trees were, probably raised from the im­ ported seed since no trees had been imported to this country by that time. Paul Dudley (1726> remarked that American pears were as good as those of England. Hence it might be concluded that the pear was quite a promi­ nent fruit in the early history of Massachusetts. Many horticulturists of that time did marvellous work to popularize this fruit by breeding new varieties and in­ troducing some fine European varieties. A nursery in Long Island, began to sell budded or grafted pear trees for the first time in the year 1730. xn 1771 this nursery sold trees of 43 different varie­ ties. Close to 1794, pear blight became a factor in pear culture. This malady was prominent in the orchards of the Hudson Valley, and the damage caused was signifi- -6cant. However, it did not shake the confidence of the lovers of this fruit. In 1825, Robert Manning began the collection of as many pear varieties as possible, both native and foreign, for varietal trials. By the time of his death in 1842 he had collected about 2,000 varieties. While the Colonies on the Eastern Coast were figh­ ting for their independence the Franciscan monks were busy in establishing their missions in California. With them, they brought many cultivated fruits of Europe and, for­ tunately, the pear was one of them. Today this region on the pacific Coast is the greatest center of commercial pear enterprise in the worth American Continent. Some hardy strains of pyrus communis were first im­ ported from Russia in 187 9. They continued for a few years with the hope that they might be suited for very cold regions. Unfortunately, the quality of the fruit was very poor and the trees were highly susceptible to fire-blight. Botany; The trees of this species are upright and vigorous growers with a central leader. stout with medium sized thorns. purplish brown in color. The branches are usually The bark is brown or The leaves are medium-sized, oval or oblong-ovate, apex acuminate, margins entire or 3 -7crenate-serrate. The petiole is slender varying in length from 1 to 2 inches. Flowers are white or some­ times with pinkish tinge, medium sized, with rounded pe­ tals, 15 to 20 stamens, and 5 pistils. They are borne usually on fruit spurs in dense or loose clusters. The fruit is usually pyriform, green or greenishyellow with persistant calyx and fleshy pedicels. The flesh is white, yellowish or pink, soft, and juicy. The seeds are large, brownish and usually tufted at the top. Propagation; The propagation of commercial varieties of this species is by budding or grafting desired varieties on­ to seedlings imported from France or raised in American nurseries, until 1930, great dependence was placed upon seedlings imported from Europe. However, an embargo placed against the importation of rootstocks in 1930, induced the development of a domestic supply of seedlings. Most of these seedlings were produced in the States of Washington, Oregon, and Kansas, though a few were raised in Connecticut, IMew York, and other states. nedrick ^1921/ reports that the pear can be propagated readily by hardwood cuttings in the tropics and in some Southern states like Florida, xexas, Mississippi, Alabama, and ^eorgia. It is possible to root the cuttings elsewhere, -8also, by providing suitable temperature to the rooting media. Kieffer and Le Conte root especially well al­ though some other varieties may also show satisfactory results. On the whole, however, vegetative propagation is not of little consequence commercially. The French pear seedlings used in america are usu­ ally raised from seed of the Bartlett or Vifinter Nelis varieties, and the desired varieties are budded or graf­ ted onto them, shield budding being the common practice. Experiments conducted at Davis, California, indicate that Winter Nelis makes most vigorous and satisfactory stock followed by Hardy and Bartlett in order of their importance. Day (1947; mentions that whether the Winter Nelis rootstock eventually makes a better, long-lived orchard tree as compared to Hardy or Bartlett seedlings is controversial. There are, however, several fine Bartlett orchards on Winter Nelis rootstocks growing in Lake County, California. Soil adaptation: This species thrives very well on a variety of soils ranging from sandy loams to heavy clays with a good humus content and water holding capacity. However, it prefers well drained, fertile, moist, cool, and rather heavy type soils with a porous subsoil. -9Reimer (1925> suggests that the Bartlett and Howell varieties can he successfully grown on a wider range of soils than the Anjou, Bose, and Cornice. He further re­ ports that in Southern Oregon Bartlett, Bose, Howell, and Winter Wells are very successfully grown on heavy adobe soils which are unsuited for the cultivation of other fruits. On such fertile adobe soils the above mentioned varieties are productive, develop a nice fla­ vor, and have better keeping quality. Hedrick (1921; contends that Kieffer, a hybrid between the common pear and Oriental pear, prefers sands and gravels over clays and heavy loams provided such soils are well supplied with nutritive plant food materials, m other words the pear trees are not long-lived on poor soils. The flavor and texture of pears vary with the type of soil. j.n general the pear trees located on uncongen­ ial soils produce sour, dry or gritty fruits. Some va­ rieties like Bartlett, Clapp, and Seckel, however, can succeed on a variety of soils and the quality of the fruit is also satisfactory. Some varieties, not adapted to a particular soil can be made to grow satisfactorily by grafting them onto a stock adapted to that soil. Pyrus communis can tolerate wet soils much better than any other species of pear with the possible excep­ tions of P. calleryana and P. betulaefolia. Nevertheless it is worth mentioning here that water logged conditions are not suited to pears. The different commercial pear -10varieties on French pear seedlings rootstock cannot tole­ rate excess of lime in the soil and are less affected by lime-induced chlorisis than those on Pyrus calleryana and Qydonia vulgaris. Further, they tolerate less alkali than P. betulaefolia seedlings. Day (1947; contends that excess of boron dwarfs the pear trees or reduces their productivity but characteristic leaf and twig symptoms do not become evident. Climatic requirements; Pyrus communis is well suited for the milder regions of the temperate zones. Generally speaking the pear cannot be grown profitably in the regions where the temperature falls below -15°F. during winter. Winter killing begins at this temperature and the fruit buds are sometimes des­ troyed even at -10°F. Nursery trees are more tender than mature trees in the orchard. The climate in most parts of North America is unsui­ ted for pear culture, however, it reaches its perfection in Northern States located east or adjacent to the Great Lakes and on the Pacific Coast, it is not known to be very hardy in the extreme north or in the upper Mississippi Valley. The trees grow satisfactorily in the Southern States but are unproductive and most susceptible to fire­ blight. -11- The common pear varieties on French pear seedling rootstock's cannot endure extremes of heat or cold, or wetness or dryness. On the whole the pear is less re­ sistant to cold than the apple. In fact, apples can be better grown in the colder regions where pears may not thrive. Many varieties, such as anjou, Clapp, and Flemish Beauty are quite resistant to cold and can be successfully grown in almost all except the coldest apple growing regions. Hedrick (1921) states that some hybrids, like Kieffer and Le Conte, can tolerate hot summers of the culf States and can be grown as far south as Central Florida and Southern Texas. He further mentions that Tyson, Flemish Beauty and Beurre Superfin are much har­ dier than Bartlett, Seckel and Clapp, and, therefore, well suited for colder regions of New York. Some pear varieties which are native of Central and Northern Russia show remarkable resistance to extremes of climate and can be successfully grown in the coldest agricultural regions of North America, although as previously mentioned, the quality of the fruit is inferior* Of the common commercial pear varieties of Pyrus communis the wood of Bartlett is the least resistant to low winter temperature. The buds of the pear need as much chilling to break the rest period as do apple buds. -12Fur the r the pear fruit can tolerate much higher summer temperature than that of most apple varieties. The Bartlett pear is successfully grown over a wider range of climate than any other variety. Some of the hottest valleys of California produce better quality Bartletts (better in flavor and in evenness of ripening/ than the cooler sections where the fruits have a tendency to ripen unevenly. This, however, does not seem to hold good with other pear varieties. Diseases: Fire-blight, a most virulent and contagious disease, is caused by a bacterium known as hrwinia amylovora (Burrill). This malady is of American origin and was first noticed in the Hudson river valley in 1780. it had reached California by 1900 and was noticed in Southern uregon in 1906. Today, it is prevalent in al­ most all the pear growing regions of America. Besides attacking pears it also attacks apples, quinces, and other pomes. The disease is especially disasterous in the Mississippi Valley and along the Atlantic Coast from sou­ thern rennsylvania southward, where the early summer is hot and humid. The pear industry was completely par­ alyzed in Southern States 75 years ago. nowever, in some parts of America and Canada, around the Oreat Lakes, where summers are cooler, fire-blight is not as serious. These -13- regions are still producing good quality pears. On the Pacific Coast the disease is also severe, but has been held in check by heroic treatment. Almost all the parts of the tree, namely, blossoms, fruits, branches including trunk and water sprouts and the roots are damaged by this malady. The disease is often designated after the name of the infected part, for example, blossom-blight, root blight, and so on. Blight rapidly invades the infected parts and turn them dark, ending in their death, hence the name, fireblight. The organism lives in the delicate tissues of the inner bark, it is, therefore, impossible to control it by spraying. The organism is very active during spring and early summer when cue plane tissues are tender and sappy. The conditions which favor the tree growth are also known to favor the development of the organism. During winter the bacterium either perisnes entirely or it remains dor­ mant m tne inner Dark of tne trunk or roots and in the cankers formed on the large branches. The' infection in­ creases during the spring, producing an ooze which con­ tains this organism and from whicn tne infection is spread by honey bees, thrips, and otner carriers, ror example, if blossom blight takes place, these insects especially tne bees, distribute tne infection in the orchard. Acci­ dentally these insects distribute the malady so effective- -14ly that fireblight has become a limiting factor in pear production in the United States. R a m s often wasn tne organisms from the upper portions of the tree to the lower branches. Unfortunately, Pyrus communis, is extremely susceptiole to fire-light as compared with the other pear species in this country. Losses sustained are enormous and this malady has therefore proved to be a great hindrance to the pear industry in America. The French pear seedlings used universally as a stock in this country, sucker badly thus exposing the stock more to the danger of fire-blight. Chandler (1928; mentions that Old Home and surprise are highly resistant to this disease, xie further re­ ports that Seckel is more resistant than Bose and Bart­ lett but not significantly so. Some hybrids, like Kieffer, are more resistant to blight than Seckel, still quite susceptible, experiments at Georgia reveal that Sewega, a high quality pear variety, is fairly resistant to blight. Day il947,) contends that old Home seedlings are not resistant to fire/blight unless their parent flowers are hybridized with the pollen of another blight resistant variety at the blossoming stage. Reimer (1925; reports that seedlings of Old Home X Parmingdale are resistant to blight, experiments conducted by jjay at Davis, -15Calif ornia, confirm the Reimer's results. Reimer fur­ ther states that Old Home and a hybrid, Variolosa (P. Pashia X p. communis; make strong union with most pear varieties and hence serve as a satisfactory body stock in Southern Oregon. These two varieties are bud­ ded or grafted onto common pear stock at ground level* The trees are transplanted to the orchard when one-year old. after a few years, when the trees have formed well ' branched, symmetrical, and strong framework, the branches are top worked with the desirable pear varieties. Day (1947; holds that Old Home makes wide-angled crotches and hence is used as a blight-resistant framework successfully in many commercial pear orchards of California. Argles ^1937; reports that Jistella, a seedling of Kieffer, also makes a good body stock for Bartlett and Anjou. The Bose variety is, however, known to be incompatible on this stock. Reimer (1925; holds that Kieffer (P. communis X P. pyrifolia; makes a good union with most of the pear varieties grown in Southern Oregon and is successfully used as a body stock, nowever, Tukey (1928; stresses that, in Northeastern America, Kieffer makes a poor orchard plant on French pear seedlings and suggests that if the Kieffer pear is grown commercially for fruit pro­ duction it should be grown on its own roots. Tukey and Brase (1934;, however, report that 6 to 7 year-old Kieffer trees on French pear seedlings were making satis-, factory growth at that age. -16- Leaf blight (Fabraea maculataj This disease is particularly common and disasterous in the eastern States where summers are attended with high humidity, unfortunately, again, French pear seed­ lings are highly susceptible to this fungus. The disease is particularly destructive to nursery trees and also, sometimes, affects orchard trees. pome fruits. It also attacks other Quince suffers even more than the pears. The fungus first appears in the spring in the form of reddish brown circular spots on the upper surface of the leaves and then slowly penetrates to the lower surface turning them dark brown, it stunts the growth of the in­ fected trees and defoliates them prematurely. The fun­ gus lives over the vvinter among the fallen leaves, xt seems desirable, therefore, to collect and burn the fallen leaves. Tear Scab (Venturia pirinaj Pear scab, another destructive disease of pears, is caused by a fungus known as, Venturia pirina. It attacks branches, leaves, flowers, and fruits of old and young pear trees in almost all the pear-growing regions of North America. Black spots become evident on the twigs, leaves and fruits in the form of "green velvety spots". Usually, the young fruits drop but, if they persist, they do not grow further in size. The leaves are simi- -17larly attacked, usually the lower* surface. not show up conspicuously on the twigs, Scab does it passes the winter on the twigs and among fallen leaves. Chandler (1928; writes that some of the varieties, like Flemish Beauty, are so seriously infected by this disease that spraying is a necessity even for other pear varieties nearby, nedrick (1921; reports that / Flemish Beauty and Summer Doyenne are most susceptible and that it is impossible to obtain a "clean cheek" fruit. Other diseases: Most of the pear varieties and French stock, ryrus communis, are resistant to Mushroom Root Rot and Black End, The former attacks the roots of many cultivated fruit trees on the racific Coast and destroys them com­ pletely. The latter turns the tissues hard and gritty at the blossom end of the fruit. these fruits turns black. The infected tissue of Black mold (Pumago vagans), a fungus, produces a sooty covering on the pear fruit, it spreads to the leaves and twigs and thus impedes their* growth, Rink-rot (Cephalothecium roseum; causes consi­ derable damage to fruits in cold storage. The fungus enters the fruit through the injuries caused either by mishandling at harvest time or by pear scab and other fungi, rear trees on French stock are resistant to Oak root fungus yArmillaria mellea;. -18insects; Pear root aphis (Eriosoma languinosa) This insect is most common in pear orchards located on the Pacific Coast. highly susceptible, The French pear seedlings are its roots, particularly, are the favorite food of this pest and the infected trees are weakened considerably. The trees in the nurseries or in the young orchards are particularly damaged. kills, mostly, the small roots. The insect Further no tumors or galls are observed on the pear roots as is the case in Wooly aphis of apples. The Japanese stock (Pyrus pyrlfolia; is quite resistant and had replaced the French stock in the Pacific Coast states until the Black end disease showed up seriously in pear varieties on this rootstock. This pest also attacks apples and quinces. The pear psylla yPsylla pyricola; This insect attacks the foliage of pear trees in nursery and orchard and is very serious in Eastern parts of the United States. The young nymphs suck the juice from the buds and young leaves and thereby weaken the trees. Codling moth (Carpocapsa pomonella; The Codling moth causes considerable damage to pears in JUew York State, it makes a cavity in the pear es­ pecially around the core and eats its way out to the sur- -19face of the fruit. The French roots are also considered resistant to .Nematode (Heterodera marioni). Day and -rufts (1944; write that, of the 15 varieties tested by them, the seedlings of Winter Nelis are the least susceptible, seedlings of master and nardy are also lightly infec­ ted while those of Bartlett, Bose, Comice, and Howell are moderately attacked. Value as a rootstock; The French pear seedlings are used almost ex­ clusively as a rootstock for standard pears in America and many other countries, xerkes (1929; states that it makes a strong and smooth union with European pear varieties and the trees are vigorous, healthy, and hence long-lived. However, there is some evidence to show that Kleffer, a hybrid between Pyrus communis and P. pyrifolia, is slightly incompatible on French roots0 Reimer (1925; holds that Kieffer makes a good union writh most of the pear varieties grown in Southern Ore­ gon. Tukey (1928; reports that Kieffer makes a poor union with French pear seedlings in Northeastern United States. Comparing two rows of Kieffer pear trees, one on French pear and the other on its own roots praised from cuttings;, he concludes that own rooted trees are uniform and vigorous whereas those on French roots are -20less vigorous, less uniform, with some mortality, tie, therefore, suggests that Kieffer should be grown on its own roots. The Kieffer roots readily in G-eorgia and some other Southern States. It is less susceptible to blight, tolerates adverse soil and climatic conditions and is quite vigorous. On French roots, this variety often shows overgrowth of scion and a conspicuous swelling at the union, it does not exhibit this ab­ normality when own-rooted. Such Kieffer trees sucker sparingly and obviously would be more resistant to fire blight than those on French roots. Tukey and Brase ^1934; report that their 6 to 7 year-old Kieffer trees on French roots were satisfactory in growth, uniformity, and longevity, suggesting that union may be satisfactory in young trees. The Geneva Experiment Station published a brief re­ port of the 3rd Annual Rootstock Conference in the American Nurseryman (1940/. It is reported there that Kieffer does better on its own roots than on French pear, and confirms the suggestion of questionable longevity of the Kieffer trees in the experiment of Tukey and Brase (1934; on French roots. Bailey (1929; mentions that the four varieties, Le Conte, Kieffer, Garber, and Smith are vigorous growers and therefore overgrow the French stock. For this rea­ son these varieties are propagated by cuttings in the South. -21No variety of Pyrus communis has ever been reported as Incompatible with French roots. Under certain con­ ditions, however, some varieties may grow less satis­ factorily. For example, Tukey (1928; in 11The Pear and its Culture" lists six varieties which, in his opinion, are better suited on quince than on pear. Quinn (1955; states that four varieties which, according to Tukey, succeed better on quince than on pear, show quite op­ posite results in South Australia. There the trees on quince were less vigorous and in some cases proved worthless. These wide differences in these two root- stock experiments may be due to difference in quince strains used by the two workers or to difference in soil and climatic conditions prevailing at the two places from time to time. Pyrus communis is the only satisfactory stock for pears today, m many pear regions, at least, where fireblight is not a menace this rootstock is of signific­ ant value, in others, where blight is serious, the pear varieties are put on French roots with Old Home as the intermediate or body stock. However, mention need be made here that French roots are non-resistant to blight and hence form a weak link, it seems desirable that some blight resistant seedlings should be used in place of the French roots. Day (1947; suggests that the best plan is to produce Old Home on its own roots by the following -22two methods: Firstly, by vegetative propagation such as layering, root cutting, or trench layering; secondly, by growing Old Home on French or some other roots with the bud or graft union buried deep in the ground. After a period of time scion roots originate, stock roots become less and less important or ultimately die, and the tree is wholly on its own roots. Regarding the vegetative propagation of Old Home, experiments at Davis, Cali­ fornia, indicate negligible success by stem and root cuttings. It, however, roots readily by trench layering but commercial production is considered to be uneconomic. Seedlings from a cross between Old Home and Farmingdale gave fair results from root cuttings as did also the seedlings of Winter Nelis, Seckel, and Easter. Day (1947) further mentions that many pear varie­ ties of commercial importance, such as Bartlett, Hardy, Bose, Winter Nelis, Comice, and Wilder have been suc­ cessfully grown on Old Home scaffold for the last 15 to 25 years in California orchards. The Old Home scaffold which is resistant to blight checks the downward move­ ment of the blight from the scion to the roots. Reimer (1925) mentions that three varieties of Pyrus communis, namely Old Home, Farmingdale and longworth are fairly resistant to pear-blight and can be of significant value as a trunk or body stock for most of the commercial pear varieties. These three varieties when used as -25trunk or framework stock become less susceptible to winter injury than the other pear species especially F. Ussuriensls. Further, out of these three, Old. Home is the most vigorous, blight resistant, hardy, forms a nice frame work, and. hence considered to be the best. In California Old Home is susceptible to a disease known as bacterial canker. It is particularly active during the dormant season. Lemon, a vigorous and can­ ker resistant stock, has been used. It propagates easily and exhibit upright spreading growth. It makes a congenial union with Bartlett but, unfortunately, it is less resistant to blight in contrast to the Old Home. Day (1947), however, promises it a better stock than Old Home provided it proves resistant to blast,. -24Pyrus pyrifolla (Japanese pear): Historical: Pyrus pyrifolla formerly (P. serotlna) is a native of central and. western China. Reimer (1925) thinks that it is also a native of central and northern Japan because he found this species widely distributed in these regions of the country. Tukey and Brase (1954) consider it to be a native of Ch ina and Japan. Reimer (1925) found it growing in the upper Yangtze river Valley and central and western China where the summers are attended by heavy rains and the winters are dry. Tukey (1928) states that it is growing wild in Mongolia from where it spread to China and Japan. This species came to America from Asia through Europe where it was imported by the Royal Horticultural Society in 1820. It was first noticed in Prince's Nur­ sery, Flushing, New York, in 1840 under the name, Chinese pear o r Sha Lea. This oriental pear species hybridized w i t h Pyrus communis and the first hybrid, Le Conte, was recorded in 1846* The important hybrid, Kieffer, originated in 1873 and proved to be better than Le Conte except in certain southern parts of this country. Another valuable hybrid, Garber, came into being during 1880. munis . These hybrids are more blight resistant than P.com­ In the past, considerable quantities of seeds and seedlings of P. pyrifolia were imported to this country -25for propagating nursery stock for cultivated pear varieties. However, about 1920, the pear varieties on this stock began to develop black-end or hard-end in the fruits. After 1926 few trees were propagated on this stock. Botany: The trees are large, vigorous, long-lived, and productive. The young shoots have glossy green bark and this color deepens with age. deep furrows. The old trunks have The leaves are large, pointed, ovate or ovate-oblong, base subcordate, and the margins are setose serrate. It blooms early in spring. The flowers are large, white, and borne in loose clusters of 5 to 8 on slender pedicels. The petals are oval; stamens 20, styles 4 to 5 and glabrous. The fruit is brown, apple shaped, calyx not deciduous, flesh hard or gritty flavor sweet or insipid, and keeping quality is good. The seeds are dark brown or black. Propagation: The seeds of Pyrus pyrifolia are imported from the Orient. Gourley (192^) reports that Japanese stock is either directly imported from Japan or the seedlings are first grown in France. He further records that some American nurserymen believe that this stock is superior to the French stock but French nurserymen think it in­ -26ferior to the French stock. The seeds to be exported are packed in finely ground charcoal or any other dry mater­ ial in order to insure protection against mold while in transit. Else, the best method is to place them in boxes in sawdust, moist sand, or dry sphagnum moss. These boxes should be stored in a suitable low temperature during transit. It insures a sort of stratification,, The seedlings are mostly grown in Kansas and Pacific Coast states, where they are budded to various varieties. Soil adaptation: Pyrus pyrifolia can be grown on a variety of soils but not on as wide a range as P. communis. It behaves as well on the deep fertile, and well drained soils as the French pear. The trees are extremely vigorous and healthy on such congenial soils, in part perhaps, due to its resistance to pear root aphid in such soils. On the other hand, the shallow and wet soils are not congenial; the youn6 trees may grow satisfactorily for a period of time but later in life they exhibit stunted growth. On such soils P. communis and P. calleryana rootstocks do better than P. pyrifolia. excess lime in the soil. Further, it does not favor Under such conditions P. betu- laefolia gives the best results. This species develops a strong and extensive root system. -27Sorae pyrifolia seedlings, however, produce very deep but less branching root systems than French pear. By transplanting the seedlings of this species at least once in the nursery after having trimmed the tap roots it may be possible to obtain a well branched root system. Day (1947) states that some pear varieties on Pyrus pyrifolia are more susceptible to lime-induced chlorosis than those on P. communis but less so than those on Gydonia vulgaris (Quince). Climatic requirements: This species is not as winter-hardy as Pyrus communis. Yerkes (1929) holds that it cannot tolerate as much cold as the French pear. For this reason, it should not be used as a stock in the colder regions of America, it is quite popular in the Southern States and on the Pacific Coast and at one time was even more commonly used as a pear stock than the French pear seedlings. Carrick (1920) holds that Kieffer roots are more resistant to cold than the French pear roots. He ob­ serves that at -9° C. the Kieffer roots have been slight­ ly injured whereas 2-year French roots were killed. Childs and Brown (1951) state that the common European pear varieties are more susceptible to winter injury in the trunk on Pyrus pyrifolia rootstock than on P. com­ munis roots0 -28Diseases Fireblightl Pyrus pyrifolia has been used with the hope that it was resistant to pear blight and pear root aphid. Ac­ cording to Davis and Tufts (1941/ this species is at least 50 per cent more resistant to blight than r. com­ munis . They hold that this stock suckers negligibly and hence is less easily infected than the French pear0 Day (1947/, however, holds that this species is not more resistant to blight than the French stocks. Where blight cankers are present the trees are girdled as rea­ dily as the French pear seedlings. Reimer1s inoculation experiments (1925) reveal that this species exhibits a great variation, i.e., while some seedlings are highly blight-resistant, others are highly susceptible. The trunk and roots are especially more susceptible to this malady than those of Pyrus calleryana and r. ussuriensis. However, its roots are slightly more resistant to blight than those of P. betulaefolla. Fortunately, it suckers negligibl:/ and hence does not expose itself much to the blight attacks. lerkes (1929> mentions that P. pyrifolia is more blight-resistant than French roots but not en­ tirely immune. Chandler (1925) writes that sprouts of Japanese stock are as susceptible to pear blight as the French stocks. Reporting about the hybrids iP. communis A P. pyrifolia Drain (1943; writes that these have little -29- more than survival resistance to the attack of pear blight, xhey do blight off and on but continue to survive and produce some fruit. Chandler ^1942^ observes that when trees on r. pyrifolia ,roots, which produce black-end fruits, are inarched with several r. communis seedlings and after a few years, the ori­ ginal root being severed, the trees then no longer produce black-end pears. Mushroom Root H o t: Pyrus pyrifolia is not as resistant to this di­ sease as French pear seedlings. Special precautions must be taken to avoid the use of soil which is in­ fected with this disease, necause it is susceptible to this disease and not tolerant of wet soils, iteimer (1925) considers that this species may be eliminated from the orchards on the pacific Coast. ether diseases. The pear varieties on this stock develop black-end or hard-end fruits although it does not seem to be as serious as on Pyrus ussuriensis and P. betulaefolia rootstocks. Davis and Tufts il9bl> report that pear varieties on P. pyrifolia rootstock produce the grea­ test number of black-end fruits; kieffer seedlings come next and P. ussuriensis produces the least black- end fruits. They also state that the first black-end fruits appear on the trees which had the largest number of affected fruits the previous season. Day (1947j reveals that nardy is resistant to the blackend disease on P. pyrifolia rootstock. Chandler (1925; says that pyrifolia is less resistant to oak root fungus yarmillaria mellea; than the French roots. insects: The Japanese seedlings are more highly resistant to pear root aphid than the French pear (Pyrus communis; . Sometimes, however, some nursery trees are seen to be infested by it but such cases are very rare. In other words this insect is not a serious pest of Japanese seedlings. This species is supposed to be resistant to other insect pests of pears. Value as a rootstock; Reimer ^1925j, Yerkes (1929;, Johnston ^1930j, and Tukey and Brase (1934; hold that most of the pear varie­ ties make strong unions and vigorous growth with Pyrus pyrifolia understock, amos et al (1936; , with Dr. Jules Guyot on different clonal selections of this spe­ cies, report that six year old trees made satisfactory growth, aowever, Chandler (1928;, Johnston (1930;, and Day (1947; reveal that different pear varieties on this -31stock develop black-end pears, xt is also more resis­ tant to blight and pear root aphid in comparison to the French roots (P. communis). In California this root- stock came into use in 1912 and was rather preferred over the other pear stocks between 1918 and 1926. During this period nearly 40 to 50 percent of the pear orchards were on this stock according to Day (1947)0 Howard v1918) states that about 63 percent of the pear trees were on P. pyrifolia roots. Chandler (1925) writes that in 1923 about 45 percent of the pear trees were on French roots while only 41 percent were on Japanese roots. Tufts and Jtiansen (1931; hold that in California, possibly more that 30 percent pear trees were on this stock. However, the black-end trouble started about 1920 and has made this rootstock value­ less. During the last 15 years or so about one third of the pear acreage on this stock has been discarded from the orchards of California. Davis and Tufts (1941) state that by 1940 it was hard to find pear varieties on this stock in California nurseries, uver- holser et al (1944) reveal that this black-end disease is particularly common with Bartlett pear and has caused considerable loss to fruit growers, aansen and Eggers (1936, write that P. pyrifolia is an unsatisfactory rootstock because, like most of the other Oriental -32species, it develops black-end disease, ‘ i'ukey and Brase (1934; mention that this species exhibits marked susceptibility to winter injury and the scion variety develops black-end trouble on the pacific Coast. How­ ever, these workers have not reported the existence of this disease in the Northeastern states. Childs and Brown ^1931; indicate that Anjou, Bose, and Bartlett show more winter injury to the trunk when grown on P. pyrifolia rootstock than on the French roots P. communis. Scion varieties on this stock demon­ strate weakness, black-end, irregular fruit ripening, and so on. Chandler (1925; records that the French roots are much more resistant to wet soils and alkali than the P. pyrifolia. Tukey and Brase (1933 and 1934; with four pear varieties on P. pyrifolia, report that Kieffer (P. pyrifolia X P. communis; grows satisfactorily on this stock but Bartlett and Seckel produce weak and short-lived trees. Reimer (1925; states that Bart­ lett, Anjou, Bose, Winter Nelis, Howell, and Comice propagate easily on this stock on the Pacific Coast, and make strong and compatible unions. There the scion does not overgrow the stock when the union is set at or below the soil surface. Old Home and Variolosa also make vigorous growth with this stock but not as vigorous as on P. calleryana. Reimer goes on to say that almost all the other species of pear make strong and congenial unions with P. pyrifolia except in New York state where failure, in some cases, may be the result of winter injury. Day i1947; cites a worker, Allen, who holds that shortage of moisture causes the fruit on this stock to be firm, high in soluble solids and color at ripening time in contrast to the fruit on French roots. Davis and Tufts (1941j hold that this species pro­ pagates easily and make satisfactory growth for 10 to 12 years under favorable environment but then the growth slows down and ultimately the trees become dwarf and unprofitable0 -34Pyrus ussuriensis. Historical; Hedrick \,1921; says "The habitat of this species is northern and Northeastern China and Eastern Siberia. Manchuria, Korea, Amurland, and ussurri are named as re­ gions in which it is most commonly found." Reimer (1925; writes "Pyrus ussuriensis is a native of extreme northern China, Manchuria, northern Korea and southeastern Siberia. There it is abundant on the rich valley soils. The trees are moderately vigorous, long-lived, and very old speci­ mens attain great size," The history of this pear in the United States is un ­ known. Reimer (1925) reports that its history in this country cannot be traced beyond 1880. At that time it was designated as Pyrus sinensis (Chinese sand pear) and was used a good deal in breeding work. it was identified as P . ussuriensis. However, in 1916, In 1907, a repre­ sentative of the United States Department of Agriculture collected seeds of P. ussuriensis from the Orient. The department further distributed the seedlings to various research stations f'or their trial as an understock. Reimer, in 1917, collected scion wood and seeds of this species from northern China and tested them for blight-resistance in Oregon. His inoculation experiments proved it to be highly blight-resistant. Again in 1919, Reimer visited China and collected seeds and scion wood from the wild and cultivated types of this species and tested them for blight-resistance in Southern Oregon. Botany* The trees are vigorous and long-lived. The wild type tested in United States is however, a slow grower. The leaves are glossy and glabrous, orbicular to ovate, medium to large with broad or subcordate base; in wild types the leaves are broadly ovate and produce a ro­ sette of leaves at the end of the shoots, the leaves are setose-serrate, reddish pink. margins of xhe blossom buds are The flowers are white to pink depending upon the variety, have short pedicels, and are larger than any other pear species, retals are large and obovate, sometimes slightly clawed; stamens, 18 to 20 with red an­ thers; pistils 5. The fruits are greenish yellow with persistent calyx; flesh usually soft, juicy, and sub-acid but in wild types, usually hard and with acid flavor. Soil adaptation: it prefers deep, rich, and well drained silty loam soils, xn the Orient such soils have enough moisture during the summer but are dry during the rest of the year. x t is possible that this species may not be suc­ cessful where winters are quite wet. -36The trees of this species are deep rooted. For this reason shallow soils with hard pans are con­ sidered unsuitable. Reimer (1925/ states that young trees on this stock have made satisfactory growth on heavy adobe soils but may not be as long-lived as on deep mellow soils. The trees cannot tolerate excess of alkali in the soil, it has been noted that an ex­ cess of lime readily causes a chlorotic condition. Climatic requirements: This species is a native of cold northern re­ gions of the urient. There the summer is short and wet while the rest of the year is dry. are very cold and dry. from -10 to -40° F. The winters The temperature goes down Obviously, it is winter hardy, xiowever, when the winters are wet, winter injury may show up even at -20° F, In America the wild type has been able to endure a temperature as low as -40° F. in northern Iowa and South Dakota. This species is, therefore, best suited for those regions of united States which have short, wet, and cool summers and dry winters. Reimer (1925, states that this species is unsuited for Southern Oregon because there the summers are hot and dry. The trees need irrigation, and even then, the intense heat causes sunburn of the leaves. -37Re imer further notes that uuar Li, a cultivated variety of ryrus ussuriensis has adapted itself to the soil and climatic conditions prevailing in the neighbourhood of Washington, I). C. Diseases and insects: Pyrus ussuriensis is highly resistant to fireblight especially the seedlings of the wild type. Reimer (1925/) says it is more resistant to blight than any other spe­ cies of pear. The seedlings of the cultivated varieties, however, come second to P. calleryana in this respect, Reimer states that the seedlings of one variety are even more blight-resistanc than P. calleryana. The seedlings of P„ ussuriensis are planted directly in the orchard and Bartlett is top worked on them. Day (1947/ mentions that it makes a nice blight-resistant framework. Mushroom root rot is quite troublesome to these seedlings on ahe racific Coast. The soil to be used for its cultivation should, therefore, be free from the fun­ gus infection in order to insure long life and producti­ vity. Pyrus ussuriensis is resistant to pear root aphid bit the pear varieties on this stock develop black-end di­ sease although less in intensity than on P. pyrifolia. P. ussuriensis is not resistant to oak root fungus. -38nappily, the pear woolly aphis, which is a serious pest of pears on French roots, has not proved serious on P. ussuriensis. The black-end trouble on this stock, however, makes it an undesirable stock for pears. Value as a rootstock: Because of its resistance to blight and winter injury this species has been extensively tested as a stock for pears. Reimer (1925; reports that wild type and also a cultivated variety known as oa Li Hsiang are highly resistant to pear blight. The wild types make very slow growth and pear varieties on wild type stock have a tendency to overgrow the stock and ulti­ mately break at the point of the union. For this rea­ son, the wild type should never be used as a stock. The cultivated varieties are, however, usually more vigorous and productive than the wild type. Johnston (1950; indicates that it is hard to dis­ tinguish the seeds of the cultivated and the wild types. For this reason, the Chinese seed collectors have been misleading American nurserymen for a long time, xhe collection of the right type of seed is evidently of great importance in production of pears on this stock. Reimer (1925/ mentions that seedlings of Ba Li Hsiang are as vigorous as French pear seedlings but he cautions concerning the possibility of obtaining some - 69 - slow growing seedlings inheriting this quality from their wild ancestors, Hsiang is the best, uf all these varieties ca Li it is not only immune to blight but produces a greater percentage of vigorous seed­ lings. This variety is quite productive and begins to bear fruit at an early age. it produces abundant seed and hence can serve as a very good seed parent, unfortunately, the quality of the fruit is not good, xt is not very commonly grown in China and hence America needs to meet her own seed requirements. Yerkes (1929/ thinks Pyrus ussuriensis to be a promising pear stock. anjou, Bartlett, this stock. Keimer (1925/ points out that and dosc make excellent unions with Unions with Winter Nelis and nowell are satisfactory but the top slightly overgrows the stock. xukey and Brase v 1933 j mention that Kieffer makes vigorous and large trees; Anjou makes poor growth; and Beckel and eartlett make less vigorous trees on ryrus ussuriensis than on the French pear or P. betulaefolia rootstocks. At present it is not considered to be a satisfactory pear rootstock because pear varieties on this stock de­ velop black-end disease, which eliminates this rootstock from any further consideration, nowever, its resistance to cold and blight makes it desirable for breeding work. -40- Uverholser et al (1944; state; "The Manchurian pear (Pyrus ussuriensis, Maxim; is another oriental pear that seems to be resistant to cold but the seed­ ling understock lacks uniformity, grows slowly and has not proved satisfactory." Johnston (1948; in his letter to the writer expressed the same opinion,, -41Fyrus betulaefolla Historical; This species is said, to be a native of northern and central China. It is also called "birch-leaf pear". Reimer (1925/ found, it widely distributed from the ureat Wall in northeastern China to the Yangtze river and from the sea coast to about one thousand miles inland, ne holds that this species has never been reported from Japan and Koreac It was first introduced into United States in 1882. The seed was imported from reking, China, and grown at the -arnold Arboretum. Later, in 1896, Professor Hansen of South Dakota imported some nursery trees of this spe­ cies from (iermany. Mr. Meyer of the united States Depart­ ment of Agriculture collected the seeds of this species from different places in Northern China and sent them to this country. Reimer visited China in 1917 and 1919 and collected a large quantity of seed. He grew thousands cf seedlings at the Oregon Experiment Station in order to test their blight resistance. botany: The trees are medium to very large, vigorous, uprightspreading, and quite hardy. or otherwise. The seedlings may be thorny The branches are thick, brownish red and covered with light gray pubescence. The leaves are of -42medium size, ovate-acuminate, with long tapering apex and. wedge-shaped base, and are grayish green. white, small, and in dense clusters. The flowers are The stamens are 18 to 20 and there are 2 to 3 pistils. The fruit is small, brown, and borne in clusters of 5 to 10. cells. xhe greenish flesh is usually free of grit The seeds are small, and of dark brown or grayish black color. Propagation: it is propagated just like other Oriental species. The desired pear varieties are budded or grafted onto Pyrus betulaefolia seedlings grown from seed imported from the Orient. other species. This species hybridizes readily with For this reason, the seeds obtained from a single tree sometimes show great variation, aowever, normally, the seedlings are uniform and can be readily distinguished from other species by their characteristic light gray color. Reimer (1925j reports that Pyrus betulaefolia can be more easily propagated by root cuttings than any other species. j.t produces abundant seed. The seedlings are vigorous and can be budded over a long season. Reimer further notes that some seedlings are blight resistant and may prove valuable as parents of rootstocks. This -43species is widely grown in China and reliable seeds can be secured easily, uardner, Bradford, and Hooker ^1922j think it to be a satisfactory stock for light soils but mention that scarcity of seed has prevented its trials. Soil adaptation; Reimer ^1925j states that in the Orient this species is successful on soils varying from coarse sands to heavy clays, swampy places. it is drought-resistant yet it grows in This species does very well under adverse soil and moisture conditions. It endures alkali very well and is called an alkali-resistant pear stock, m sandy and alkaline regions of Honan Province, China, this spe­ cies is commonly grown as a wind or sand break. Day 11947; states that on alkali soils Pyrus betulaefolla seedlings, do better than P . communis, P. ussuriensis, or P. pyrifolia seedlings. However, in less alkaline areas nartlett produced "black-end" pears on P. pyrifolia, P. betulaefolla, and P. calleryana. disease on French roots was noticed. Ho evidence of this Further, Day notes that one-year-old P. calleryana and P. betulaefolla seed­ lings were more sensitive when transplanted to alkali soil than the old ones. The seedlings of this species show a great variation in development of their root systems; some form a well -44branched deep root system while others develop deep, and unbranched tap roots. The tap roots of one-year-old seedlings are, therefore, trimmed at the time of trans­ planting into the nursery in order to secure well bran­ ched root systems. Climatic requirements: It is widely grown under a wide range of climatic conditions in China ranging from dry and very cold win­ ters to mild ones, Brookings, South xt is quite hardy at Mies, Iowa and Dakota.. It grows equally well inSouth Oregon where the summers are dry and hot. it shows this species can be grown in a wider areain North America than any other species of pears. that Diseases and insects; Reimer (1925; states that some of these seedlings are quite blight resistant and "may become valuable as the parents of rootstocks.11 However, Tukey and Brase (1943; report the com­ plete destruction in New York State of trees of B, betulaefolla which had been propagated especially for the production of a seed supply for rootstocks, xn a letter to these authors in 1936, Hansen of South Dakota mentions that seedlings of this species obtained from several sources blighted severely and within 20 years were dead. Tukey and Brase (1943; cite another worker, -45Rilderbrand, who reports that all types of P. betulaefolla tested by him have proved blight susceptible, ne recom­ mends strongly that these should be eliminated in lections where blight resistance is desired. Reimer, however, reports finding 18 seedlings of P. betulaefolia which are blight resistant and hence of some value in Oregon. P. betulaefolla has proved resis­ tant to leaf blight near Washington, D. G. where this di­ sease is quite common with P. pyrifolia and French pear seedlings. Day (1947/ mentions that Pyrus betulaefolia roots are fairly resistant to pear root aphid in California. He further suggests that no observations have been re­ corded on its resistance to oak root fungus. Since most other Oriental pears are susceptible to this disease this species may also behave similarly and hence it should be regarded with suspicion. Reimer in his letter to Day (1947/ mentions that Anjou pear on Byrus betulaefolia rootstock has developed a slight percentage of black-end fruits. Day reports that in the less alkaline orchard area of Stanislaus County some Bartlett trees on P. betulaefolia have pro­ duced black-end pears. Davis and Tufts (1941/ mention that Bartlett on p. betulaefolla produces black-end pears. They stress that this fact should eliminate this stock from further consideration. Overholser et al (1944/ -46write that P. betulaefolla is susceptible to blight and that several pear scion varieties develop black-end pears on this stock. Value as a rootstock: The fruit of this species is so small that it has absolutely no economic value, it is extensively grown for pear rootstock production in China. Reimer (1925,, with six commercial pear varieties on Pyrus betulaefolia rootstock, mentions that all have made more vigorous growth than the same varieties on French roots by the time they were six years old. cartiett, Anjou, and part of the winter Nells made per­ fect unions; hose, Howell, and part of Winter Nelis showed slight enlargement below the union. however, tends to overgrow this stock. Comice, Reimer recom­ mends the grafting of these varieties at or below the ground surface to overcome this defect, he further notes that uld Home grows faster on P. betulaefolia stock than on French roots. Tukey and brase (1934> report that Bartlett, Aieffer, and deckel make vigorous growth and fruit earlier on this stock while anjou is uncongenial. The trees of this latter variety are weak, unsatisfactory, and exhibit some mortality. The authors further write -47"while one of the Oriental stocks iP. betulaefolia; gives promise as a vigorous, early fruiting stock for certain varieties its striking uncongeniality with Anjou sounds a warning for its use until it has been more thoroughly tried". Davis and Tufts (1941) hold that Pyrus betulaefolia is a blight-resistant stock in California, but produces black-end fruits. Overholser et al (1944) hold the same view. Overholser et al (1943) report: "Unions between com­ mercial varieties of pear and the Tu Li or Doo Li (P. betulaefolia, Bunge), another Oriental pear, tend to over grow the understock at point of union, even in the nursery". Day (1947) suggests that since some commercial pear varieties are uncongenial on this stock, Old Home should be used as an intermediate stock. Reimer in 1938 mentions that Anjou and Bartlett _ make perfect union with this stock while Winter Nelis, Howell, Bose, and Comice tend to overgrow the stock. Some Anjou trees on this root also developed black-end pears, Day (1947)c Reimer (1925) reports that the root system of Pyrus betulaefolia is sometimes unsatisfactory or poorly branched. He recommends trimming of the tap roots before transplanting them to the nursery in order to obtain a well branched root system. Summarizing, this stock is alkali-resistant, rea­ sonably blight-resistant in some sections but susceptible in others, vigorous, early fruiting, produces an abun­ dance of seed, and is resistant to leaf spot and woolly aphis. However, like other Oriental stocks, it may pro­ duce black-end pears. -49 Pyrus calleryana; Historical; This species is a native of central China and. is widely distributed in the Yangtze Valley. Reimer (1925) writes that "It is widely distributed from near sea level in Eastern China to more than a thousand miles inland and to an elevation of at least five thousand feet. The most northern limits of the species in China are not known. In 1919 the writer found large trees growing vigorously in southern Shangtung province, considerably further north than any point from which it had formerly been reported and this is probably near its northern limit. Its southern limit has not been determined." It was introduced to America in 1908 by E. H. Wilson who collected the seeds of this species from Hupeh Pro­ vince of China at an elevation of 4000 to 5000 feet. This species is hardy even in the vicinity of Boston. Reimbr (1925) and Meyer of the United States Depart­ ment of Agriculture collected in 1917 a large quantity of seed from Hupeh Province and the mountains west of Ichang (China). Reimer again visited China in 1919, collected seed, and studied some pear species. Thousands of seed­ lings have been obtained from these seeds and tests made to check their blight resistance and value as a rootstock. -50Botany; The trees of Pyrus calleryana are vigorous, and medium to large in size. The bark on the young wood is smooth and glossy whereas the older wood is some­ what furrowed. The leaves are ovate, crenate, and medium to large with glossy surface. very early and profusely. The trees bloom The flowers are short, white, stamens 18 to 20 with red anthers, and styles 2 to 5. The petals are roundish and white. The fruit borne in clusters, is extremely small with slightly gritty, greenish flesh and poor flavor. deciduous. The calyx is The seeds are dark brown to black. Propagation; The seeds of this species are imported from China and the desired varieties are budded or grafted onto the seedlings obtained from the imported seed. It is very hard to distinguish the seeds of this species from those of Pyrus betulaefolia but Reimer (1925) mentions that the College of Agriculture, Nanking, China, has been collecting reliable seeds of this species for American nurserymen. The seed of this species germinates quickly and do not require more than one months stratifi­ cation. Drain (1940) mentions that the seeds of this species germinates very well if handled properly and the seedlings show thrifty growth. Further, they are easy -51to bud and succeed well with most pear varieties. Drain alsosuggests that local production ofthe seed of P. calleryana can be highly profitable. Reimer (1925) points out that if once a vigorous and blight-resistant seedling of Pyrus calleryana is obtained it can be increased by budding or grafting. Day (1947) thinks that some good parent trees of this species should be grown to meet seed requirements in this country. Experiments at Davis, California, indi­ cate the possibility of growing nursery trees of this species by root cuttings. 85 percent In one season a stand of was obtained but in another season the re­ sults were not as good. Soil adaptation; It can be grown on a variety of soils and under a wide range of moisture conditions. In this respect, it can be compared with French pear seedlings. Reimer (1925) observed it growing on dry mountain sides, streams, and poorly drained soils. However, like other pear species, the trees grow most vigorously on a rich, deep, and well drained loamy soil with adequate moisture supply. Reimer planted the trees of this species on a variety of soils in Southern Oregon and observed them growing satisfactorily in valley soils ranging from clay loams to heavy adobes. This worker further mentions -52that the trees of this species do very well on a dry hill in contrast to Pyrus ussuriensis which suffers under simi­ lar conditions. The trees do not, however, tolerate ex­ cess of lime and readily show a chlorotic condition. Climatic requirements: This species hails from Central China where summers are hot and humid and the winters mild. Evidently it is not as winter hardy as other pear species. Reimer (1925), however, mentions that some hardy types of Pyrus calleryana grown from seed collected from high altitudes in the Orient are successful near Boston, Mass. All the forms of this species have proved hardy in Southern Oregon even when the temperature went below the freezing point. But Reimer suggests that it should not be grown in very cold regions where temperatures go to -10° P. until considerable evi­ dence is available to prove it winter-hardy. Johnston (1950) reports that seedlings of this species are subject to winter injury at South Haven, Michigan, and that a high percentage of the pear trees on this stock have to be replanted. Tukey and Brase (1953) write: “it has been suspected of tenderness to winter cold because it is not found outside the more favored sections of its home." This species is particularly suited to the mild pear growing regions on the Pacific Coast. It should also do well in the Southern States especially near the Gulf Coast -55 where summers are identical with those in Central China* The trees of this species have shown excellent growth in Florida, and Mississippi. It can endure drought very well and the leaves never show sunhurn even when the trees are located on dry sandy soils. Reimer suggests that seeds used in different sections of this country should be collected from regions of China with identical climatic conditions. This species may prove useful for a wide range of climatic conditions and serve as a promising rootstock all over the country. Diseases and insects: Reimer's inoculation experiments (1925) indicate that a higher percentage of roots and trunks of Pyrus calleryana are resistant to fireblight than any other species. Yerkes (1929) states that a high degree of resistance to fireblight is one of the mos t valuable characteristics of P. calleryana. He further mentions that it is negligibly affected by leaf diseases in the nursery and hence exhibits strong growth throughout the season. For this reason, it can be budded any time during the summer. Overholser et al (1944) consider this species blight resistant and think that it may prove a good pear stock. Hansen and Eggers (1936) hold that pear orchards on this stock develop only a slight amount of black-end disease and suggest that the affected trees may not be on true P. calleryana root­ stocks . -54Davis and Tufts (1941) state that this species is far more blight resistant than any other species of pear and develops the least black-end disease. Day (1947) con­ siders this species to be resistant to pear root aphid but more susceptible to oak root fungus than the Pyrus communis. He mentions that Bartlett on P. calleryana roots exhibits a highly chlorotic condition if grown on a land with limy subsoil. Reimer (1925) reports that Pyrus calleryana is highly resistant to pear woolly aphis and considers it the best of all the pear species in this respect. Value as a rootstock: This species promises to be a valuable stock for pear. It is blight resistant, develops little black- end trouble, and is resistant to pear root aphid. Tukey (1928) states that Pyrus calleryana has proved to be a valuable pear stock in Southern Oregon because it is highly blight resistant and makes vigor­ ous growth. j.erkes (1929, reports that most pear varieties make more vigorous growth on P. calleryana than on P . communis. He cautions against the use of this stock in cold climates since it has shown evidence of winter injur:/ when the temperature falls below the freezing point. Reimer (1925, states that most of the -55standard pear varieties make splendid growth on this stock at six years of age. He notes that Bartlett and Anjou make perfect unions with this stock; Bose, Howell, and Winter Nelis also make strong unions and splendid growth but the scion very slightly overgrows the stock; the Comice behaves likewise but the overgrowth is grea­ ter. The latter shows this characteristic especially when it is budded or grafted above the ground level but when it is budded at or below the ground this condition is absento At East Mailing, England, Amos et al (193b) worked with Dr. Jules Guyot on different clonal selections of Pyrus calleryana and found them to be compatible and vigorous at six years of age. Johnston (1930)reports that different pear varieties exhibit a great variation in growth in Michigan; while some make vigorous growth others are weak and hence worthless. He also considers this stock to be susceptible to winter injury. He pre­ fers P. communis (French roots) over any of the Oriental stocks. Tukey and Brase (1933 and 1934), with Bartlett, Anjou, Seckel and Kieffer on P. calleryana, report that all four varieties produce weak and tender trees which show some mortality. The authors have not, however, attributed this failure to stock-scion disagreement but to some other causes. Magness (1937) considers this -56stock to be valuable for regions only where winters are mild since they are thus far of questionable hardiness in cold regions. Ghang (1933) reports that Bartlett pear exhibits partial incompatibility with this stock. Hansen and Eggers (1936) hold that this species does not have a clear record regarding the black-end trouble and should be avoided even though it is more blight resistant than French pear or quince roots. Overholser et al (1943) report that although this stock makes a good union with the standard commercial pear varieties and is drought resistant such trees exhibit variable growth. For this reason, they consider the stock to be unsatisfactory. In Southern Oregon and California Pyrus calleryana has been employed as rootstock with Old Home as the intermediate trunk and scaffolding. is then topworked on Old Home framework. Bartlett Day (1947) writes that this combination has been bearing very satis­ factorily for the last 12 to 15 years. He states that little trouble with black-end has been noticed on them. However, since other Oriental species develop this disease seriously, research workers in general are very reluctant to unreservedly recommend this species as a rootstock. Gourley and Howlett (1941) report that Old Home is susceptible to bacterial canker which is active during the dormant season in California but is not troublesome in the -57Last. They mention that the variety Lemon is commonly used in California. Although it is resistant to bac­ terial canker, it is less resistant to firebllght than the Old Home. The 1927 experiments at Davis, California indicate that Old Home makes the more vigorous growth on this stock than on Pyrus betulaefolia or French stocks. In another experiment elsewhere in California, Bartlett and Winter Nelis made equal growth on P. calleryana, P. ussuriensis and French rootstocks. Johnston in his letter to the writer mentions that Old Home makes un­ certain unions, some are good, others are poor, Figs. (1 and 2). He encountered the same trouble with P. ussuriensis understocks. French and Japanese roots gave good results, but the latter generally developed black-end trouble. Day (1947) states that the root system of Pyrus calleryana is poor in a large proportion of the seed­ lings and hence yields on this stock may be unsatis­ factory. Heimer (1925) reports that both P. calleryana and P. betulaefolia develop poor root systems. By cut­ ting the tap roots of one-year-old nursery trees and replanting them in the nursery it may be possible to develop a well branched and satisfactory root system. Pig. 2, Pig. 1. Old Home on Pyrus calleryana rootstock. Poor union. Old Home on Pyrus calleryana rootstock. Good union. f e 1.: .MVtijfc’ -58Day (1947) states that pear trees on Pyrus calleryana bear more heavily and at a younger age than on French pear rootstocks (P. communis)• However, when Old Home is used as an intermediate stock the Bartlett variety be­ haves more like the trees directly on P. communis normally. It is also noted that Old Home makes more vigorous growth on P. calleryana than the Bartlett. Drain (1940) considers Pyrus calleryana a favorite rootstock for pears in the southeastern states since most of the pear varieties grow rapidly and make good unions with it. If this stock proves to be winter-hardy and re­ sistant to the black-end disease it can be a valuable pear stock in America. -59Pyrus serrulata Historical: This species grows widely in central China and is commonly called "Chinese-Saw-leafed pear". hardy. It is very This species is intermediate between Pyrus calleryana and P. pyrifolia. Reimer (1925) considers it to be a hybrid between these two species and states that it hybridizes readily with P. calleryana and P. pyrifolia. Mr. B. H. Wilson of Arnold Arboretum in 1907 first found this species in the province of Hupeh, Central China, at an elevation of 4,000 to 5,000 feet. Reimer (1925) observed this species in Ichang, China, at an elevation of 3,000 to 3,700 feet. Botany: The trees are small. The leaves are slightly longer but otherwise similar to those of Pyrus calleryana. P. serrulata has smaller leaves than P. pyrifolia and the setose serratures are absent. The flowers are smaller than those of P. pyrifolia with three or four styles. The fruit is brown and intermediate in size between P. calleryana and p. pyrifolia. sistent. The calyx is usually per­ Soil adaptation and Climatic requirements: Pyrus serrulata prefers the deep, fertile, well drained, and silty clay loam soils in Southern Oregon. Reimer (1925) states that this species is seen on a variety of well-drained sandy and clay loam soils in China. The species is a native of central China where the summers are hot and humid and the winters, com­ paratively dry. The temperature seldom goes below freezing point. Reimer (1925) mentions that 2-year old seedlings of this species can tolerate a tempera­ ture of -10° P. He further notes that this species is hardy near Boston, Massachusetts. Value as a rootstock: The seed of this species is imported from Central China. able. The seedlings obtained are, however, very vari­ Some resemble Pyrus calleryana, some others are similar to P. pyrifolia, while the rest are interme­ diate in type. They show a similar variation in their resistance to pear blight. Reimer (1925) reports that 40 percent of the inoculated seedlings proved suscep­ tible to blight. The writer also states that this species is more susceptible to blight than P. calleryana. Obviously, P. serrulata should not be recommended as a blight-resistant stock. However, if some immune seed- -61lings are propagated vegetatively (by root cuttings) "they may prove of some value. Reimer is of the opinion that some of the trees of this species may form a good trunk or framework stock. Hedrick (1921) mentions that '*it is affected but slightly by leaf-blight, holds its foliage well in hot summers, and has a long budding season." He suggests that these qualities justify further trials of this species as a rootstock. .None of the commercial pear varieties has been grafted onto this stock in uregon. However, Amos et al 13-956; , at East Mailing, England, report that six-yearold trees of Dr. Jules u-uyot made as vigorous growth on this stock as on ryrus communis and appeared entirely compatible.. -62ihe Quince Historical: The quince, Cydonia vulgaris, Lindl, formerly (Gydonia oblonga, Mill.) , is said to be a native of Persia and Turkestan and was called the "golden apple of the Hesperides", Hedrick (1948). Prom there it came to western countries through Greece. It was in­ troduced into England during the Roman occupation. Pliny writes that quinces were commonly grown in Italy during his time. After 1629, it became quite common in England and America and was as freely grown as apples and pears. Chandler (1928), however, holds that the quince originated in Eastern Europe in prehistoric times. Sanders (1926) also thinks it to be a native of Europe. In America the quince is commonly grown on the Paci­ fic Coast from Central California north to British Columbia. Today, it is not an important fruit in the commercial orchards in other areas. Botany; Quince is a small, low, slow-growing tree or bush with crooked branches. It has a shallow root system. leaves are ovate to oblong. The The flowers are white or pink and are solitary at the end of leafy shoots of the current season. The fruit is either pear or apple-shaped. A p p l e - s h a p e d quince; The fruit is large and roundish with golden yellow color. It ripens early and the flavor is excellent. The trees are very productive. Pear-shaped quince: The fruit i3 large, pyriform in shape and yellow in color when ripe. It ripens late and the fruit has a moderately good flavor. The flesh is rather dry. Portugal quince: The fruit is large, pyriform and golden yellow in color when ripe. It ripens late and the flavor is good. It is commonly used as a pear stock. Propagation: The quince is usually propagated by mound or trench layering and by cuttings. propagate clonal lines, It Is, therefore, easy to .angers quince, one of these clones, is usually employed to dwarf pears. Previously the clonal quince stocks were imported from angers, Prance. However, due to the quarantine restric­ tions imposed on imported stock in 1950, the rootstock in­ dustry has been stimulated a good deal in the northwest sections of the country and in Texas. The various pear and quince varieties are usually budded or grafted on Angers stock. Tukey and Brase (1955) found that mound -64layering is better than trench layering for propagating quince. Using a clay loam soil, they recommend the use of granulated peat moss to facilitate aeration and water penetration at the surface. scattered in the rows. The wet peat moss is usually Frequent cultivations help to in­ corporate the material with the soil. Before the buds begin to start growth in the spring the layered plants, previously mounded with soil to pro­ tect them against the winter cold are partly uncovered leaving only about 1 to 1-g- inches of soil over the buds. As the new shoots grow up, they are regularly mounded throughout the growing season. During November or early next spring the mounds are turned down and the rooted shoots are separated from the parent plants. This pro­ cedure is followed year after year. The propagation of the quince by mound layering can be a profitable commercial enterprise. Tukey and Brase (1955) report that one acre of a mature plantation may yield from 50,000 to 40,000 saleable quince stocks. One can expect even higher yields in case hardwood cuttings are also taken from the stools. Tukey and Brase (1935) state that hardwood cuttings collected during the fall have given better results than those collected during the spring and that heel cuttings have given significantly better results than straight cuttings. -65Climatic requirements: Quince culture is usually confined to the regions having cool summers and mild winters. Under hot and humid conditions the ravages caused hy fire blight are considerable. The trees and also the fruits are quite resistant to summer heat. Chandler (1925) states that in Asia Minor the fruit shows best development under hot summer temperatures. For this reason, it does very well in the hot valleys of California. The dry hot winds prevent the spread of fire blight. Quince wood is a little more winter-hardy than peach wood. be seriously injured at a temperature of -15 It may to -20° F„ Small and even large bushes are sometimes killed at this temperature. The quince is a late blooming tree and usually escapes injury by spring freezes. The tender shoots which bear fruit terminally are, however, killed occasionally by spring freezes. This is particularly true under Hew York conditions. Quince buds do not require as long chilling require­ ments as most apple and pear varieties. They open quite early in regions where the winters are warm. Quince culture is, therefore, mainly confined to the fruit regions of California, Pennsylvania, New York and Ontario. Quince roots are very tender to cold in comparison to pear roots (Pyrus communis). It is interesting to note that when the temperature goes 24° below the freezing -66polnt the quince roots are killed, while the stem portions are not injured at all, Carrick (1920) „ Diseases and Insects: F ire-blight: The quince, like the pear, has numerous diseases and insect pests. Fire-blight and leaf-blight also attack the quince seriously. The former can be reduced by avoiding over stimulation of the trees and by trimming the di­ seased portions. of mercury. The wounds are disinfected with cyanide Care should be taken to remove the wild trees like hawthorn from the neighborhood since they often carry this disease. Black spot: (Fabroea maculata) . It is a fungus disease which causes black spots on leaves and fruits. Infected leaves fall prematurely. Sprayings with Bordeaux mixture before the blossoms open and as soon as they fall is recommended as a control measure. Oriental fruit moth, curculio, and codling moths are three serious insect pests of quinces. often troublesome in quince culture. dig them out. Borers are The remedy is to The quince root is fairly resistant to root aphis and is, therefore, used as a stock in the fruit regions of California where this insect is common. -67Value as a rootstock: Dwarf pear trees are produced by budding or graf­ ting the desired varieties on quince rootstocks. The size of the tree is reduced without affecting appre­ ciably the size or the quality of the fruit produced* Dwarfing the pear on quince rootstock has been prac­ ticed in Europe for the last three centuries and in America for a century or so. Many horticulturists who have been associated with dwarf pear culture hold that Angers quince when true to type, is the best and most suitable rootstock for dwarfing pears. It dwarfs the pear moderately and, as mentioned before, is easily propagated by stooling. But, in the past, the dif­ ferent quince strains were seriously intermixed and the results obtained from such impure strains were u n ­ certain. The East Mailing Research station in England has classified the quince into seven strains. These strains are placed in two groups depending upon their congenia­ lity with different pear varieties. consisted of quinces a , B, and C. The first group Most pear varieties are successful on them and so this group is called "safe". Quinces D to S formed the second group. They exhibited incompatibility with most of the varieties and are called "unsafe". -68The Angers quince (Quince a ) is commonly used for dwarfing pears in North America. Quince G is less vi­ gorous than quince a . Trees on Quince G also bear earlier and this stock seems best for shy-bearing varie­ ties. There is an opinion, however, that Bartlett is more congenial on Quince C than on Quince A. Upshall (1946) writes that 10-year old trees of four pear varie­ ties on Quince C rootstock are half the size of those on Quince A. fruit yield was also nearly one-half. The The tree survival record was better on Quince G than on Quince A. It may serve as a satisfactory stock for varie­ ties like Vermont Beauty which grow vigorously on Quince A and have to be trained on trellises. CJpshall thinks that Bartlett and Howell on this stock require more feeding to maintain the desired vigour. Quince B is generally con­ sidered slightly more vigorous than Quince A and somewhat more productive. There is a widespread feeling among fruit growers that standard pear varieties become too large in size, especially in height, for profitable management. For this reason, among others, an interest has developed in dwarf, pears. a.s compared with standard trees the dwarf trees provide high quality fruits, bear at a younger age, are less susceptible to blight, crop regularly, are more economically pruned, sprayed, thinned, and harvested, mature their fruits earlier in the season, and are better -69adapted as filler trees. They are also best suited for shallow soils and can be trained to the cordon system, or against walls where they receive maximum sunshine and produce fruit of exceptionally high quality. The variety Duchess, for example, produces poor quality fruit on standard rootstocks, when dwarfed on quince, the quality of fruit is excellent. Some other pear varieties, such as, Beurre Diel, Glou Morceau, Duchesse d» Angouleme, and Louise Bonne produce decidedly better quality fruit on quince than on pear root-stock. It is generally noted that the fruit is more highly colored, of better size, and has higher sugar content on the quince stock than on the pear stock. Perkins (1847) writes that, "Quince stock will pro­ duce fine melting fruit with certainty, if taken care of, while all the care of the gardener and proprietor united, will not prevent some kinds of pears from canker, cracks, and blight, if produced on pear stocks". There are, however, certain limitations to dwarf pears from the commercial standpoint. They are short­ lived, more trees must be planted per acre, the cost of double-working and supporting is high, they sucker badly, and require greater care in pruning, training and culti­ vation. As dwarf trees are shallow-rooted they are easily blown over by winds unless strong supports are provided. On the whole, the cost of producing dvmrf -70- pears may be greater than for standards and the fruit does not command an appreciable premium on the market. Thomas River (1849) states that a serious objection often put against the quince stock is that it is short­ lived. He points out that he has seen dwarf pears in France which were more than 50 years old. With proper care and management, abundant crops of high quality fruit can be expected. Parson (1857) mentions that dwarf pear trees give good yields for a couple of years and then become less thrifty than the standards. He further writes his opinfon about the dwarf pear trees that, "They are nice toys, and like a beautiful picture, may give great pleasure. They are admirably fitted for a small garden where they can be nursed, spaded, trowelled, and fed with special manure. No one should be without them, if it were only for the pleasure they give. I have no hope what ever that they will be found profitable in orchards for growing on a large scale for the demands of our large cities," It is well known that certain standard pear varie­ ties do not agree well with Quince a. Therefore, double­ working is practiced to "bridge" the incompatibility. In such cases, an interstock, which is congenial to both stock and scion is substituted mid-way. If double-working is not practiced in such varieties, the plants may break cleanly at the time of strong windstorms. If the union -71is burried deeply In the ground the trees throw out roots from the scion and eventually become standards. Upshall (1946) mentions that Kieffer, Bartlett, and Clapp make poor unions witn quince 'while nardy, Anjou, Howell, and Vermont Beauty make strong unions. The variety Beurre Hardy is compatible with most of the quinces and is employed as an intermediate stock in North America. In California, Hardy is usually used as an interme­ diate stock, between a Bartlett top and quince root. This combination makes long-lived ahd comparatively dwarf trees. Day (1947) mentions that some 55-year old orchards (dwarfs) are quite productive. The fruits from these double-worked trees are known to be of larger size and better color. Heavy production for a period of time, however, tends to nullify these advantages. In the Santa Clara Valley 5 to 5 year old Hardy pear on quince roots are grafted to the desired variety at an approximate distance of 10 inches along the scaffold branches. In fact, this practice is preferred over that of double budding in the nursery, according to Day the substitution of a 2 to 3-inch piece of Hardy between the desired scion and the quince root tends to dwarf the trees too much. At Davis, California, 10 to 12 year old Bartlett trees with a short Hardy in­ terpiece have made satisfactory growth. In addition to - 72 - Bartlett, Bose, Winter Wells, Anjou, and Comice also exhibit good performance when doubleworked on a scaffold of Hardy on Quince A. Day (1947) reports that Anjou, Howell, Vermont Beauty, Clapp, and Kieffer make good unions with Quince A under California conditions. He suggests, however, that for orchard purposes these varieties should be double worked with Hardy as an intermediate stock. Comice on Quince A produces heavily for a period of time and then declines in growth. Day lists many other pear varieties which do not make compatible unions with Quince A, namely, Bartlett, Bose, Nelis, Easter, Seckel, Comice, and Guyot. Hansen and Eggers (1936) mention that Old Home on Quince A has made very satisfactory growth for 12 years and suggest that quince roots with blight-resistant Old Home framework and Bartlett top may be used without em­ ploying Hardy as the intermediate stock. In fact, the quince rootstock is budded with Old Home in order to get a blight resistant framework. When the graft-union between Quince and Old Home is burried 10 to 12 inches deep in the soil, the scion roots originate, and there­ fore, besides a blight-resistant framework, a blight resistant root is also established. Davis and Tufts (1941) mention that Old Home pol­ linates Bartlett successfully because both of these varieties bloom at the same time. In fact, if a few -75flowers are permitted, to hang from the Old Home frame­ work the pollination problem can be easily solved. The Old Home fruits can be identified from the Bartlett easily at the time of harvest. According to Johnston (1936) Old Home also pollinates Bose, Seckel, Clapp, Howell, Kieffer, and Flemish Beauty successfully. -74Some other rootstocks for Pears Apple (Pyrus malus): Bailey (1919) writes that the apple is sometimes used as a rootstock for pears hut that the resultant trees are short-lived. Pear scions set in the top of old apple trees, however, bear large fruits for a few years. In case pear stock is not available the apple may be substituted, the graft-union being buried under­ ground in order to encourage scion-rooting. After a time, the stock roots die and own-rooted trees are ob­ tained. Bradford and Sitton (1929) consider pear on apple an incompatible combination. Hawthorn or white thorn (Crataegus oxyacantha): The seedlings of this species are occasionally used as a pear stock in France, Argles (1937) and dwarf pear trees have also been obtained on thorn in the United States, Bailey (1919). Amos et al (1936) wor­ king with Fertility pear on this root stock found it exceptionally vigorous up to nine years of age. Mountain ash, (Pyrus aucuparia); This stock is suitable for sandy soils. Bailey (1919) thinks it to be of little "consequence". Fer­ tility pear grafted on this stock showed stunted growth at Hast Mailing, Amos et al (1936). Korshunov -75(1941) considers mountain ash a very superior dwarfing stock for pears. He says it is very resistant to cold and that scion varieties usually bear good quality fruit. White beam (Pyrus aria) and wild service (P. torminalis) have been occasionally employed as pear stocks but are of little importance. Fertility pear on these two stocks shows stunted growth at East Mailing as reported by Amos et al (1956). -75SUMMARY AMD CONCLUSIONS Domestic pear seedlings are commonly employed as pear rootstock in North America. These seedlings are usually raised from Bartlett seeds. susceptible to fireblight. They are quite For this reason, Old Home is, sometimes, employed as a blight-resistant inter­ mediate stock between the Domestic pear root and the scion top. Many Oriental species, supposedly more resistant to fire-blight and to pear root aphis, have been tried. But some of the pear varieties produce black-end fruits on most of these stocks. They also exhibit variable growth and congeniality with the same scion varieties. Therefore, at present, the Domestic pear is the best standard pear rootstock in North America. The Angers quince is commonly used to dwarf pears. However, some pear varieties do not make congenial unions with Angers quince and, therefore, Hardy or Old Home is employed as an intermediate stock. In Califor­ nia, the graft-union between Old Home and quince is set 10 to 12 inches below the ground level In order to en­ courage scion rooting. In this way the tree is fur­ nished with blight resistant roots, trunk, and scaffold branches. The history, botany, adaptation to various soil and climatic conditions, resistance to diseases and in­ sect pests and value as a stock of the different rootstock species are discussed. PART II EFFECT OF SCION ROOTING ON GROWTH a ND CROPPING OF 14-YE a R DWARF PEAR TREES -77I INTRODUCTION Standard pear trees are often relatively slow in coming into bearing. It has been suggested that earlier bearing might result from planting dwarf trees (on quince, Cydonia vulgaris) deeply, with the idea of eventually getting scion rooting and a tree of standard size, mainly or wholly on its own roots. To give this idea a practi­ cal test, trees of four varieties (Anjou, Bartlett, Clapp Favorite and Vermont Beauty) on Quince A and French pear seedlings (Pyrus communis) were planted at the Ontario Horticultural Experiment Station in the fall of 1932. This material was placed at the disposal of the author for measuring the effect of scion rooting on growth and cropping of these trees in Fall, 1946. It was hoped that such studies might be of value to the grower who wishes to regulate the size and cropping of his trees. Further it is often necessary to identify rootstocks in connection with nursery and orchard prac­ tices. It was proposed therefore also to undertake the identification of Pear and Quince rootstocks from rootpieces. -78REVIEW OF LITERATURE If the bud-union of a dwarf pear is located below the surface of the soil, rooting takes place from the scion and sooner or later the tree becomes a semi­ dwarf or standard. Gardner (1922), Tukey (1928), Hatton (1934), Gould (1959), Upshall (1940), Gourley and Howiett (1941) and Lucas (1948) have sounded a warning against the danger of scion rooting in dwarf fruit tree culture. Tukey (1928) recommended pruning as a partial measure in keeping a tree dwarf. Gourley and fiowlett (1941) des­ cribed scion rooting as a hazard and suggested shallow planting to maintain the dwarfing effect. Lucas (1946) held that there was less danger of scion rooting in pears than in apples. He further recommended that the graft union should be placed considerably above ground level since normal cultivation would, after a period, raise some soil to cover the union. Upshall (1940) and Gardner (1922) also recommended shallow planting in dwarf fruit culture. Hatton (1934), in his bulletin to the fruit growers of Europe, showed the danger of scion rooting with many illustrations. He described scion- rooted trees as "passenger" trees because they were shy croppers. He advised growers to abandon the practice of placing the union below ground. -79Shaw (1919), Moore (1919), Hatton (1935), and De Haas (1937), who worked with pears and apples, claimed that scion rooting was definitely a varietal characteristic. Hatton (1935), using seven pear varieties on Quinces A to E, reported that two of them, namely, Hardy and Conference, did not form any scion roots. Hatton also observed that the trees with less compatible unions (Quinces D to G) produced scion roots more readily than those on Quinces a to C. In all cases the scion roots exhibited upright vigorous growth, and affected cropping adversely. Shaw (1919), with apples, noted that "some varieties rooted readily, others only in niggardly fashion". Moore (1919) found that in apples, scion roots were readily formed in a moist soil. He further observed that deeply planted grafts formed scion roots more readily than did shallow planted ones. Recent findings at the Iowa Experiment! Station revealed that winding the point of grafting tightly with a copper wire accelerated scion rooting, Gardner et al (1922), Lucas (1946) observed that certain soil conditions were less favorable than others for scion rooting. He recom­ mended deep planting of the tardy ones to protect the plants from winter injury and from quince borer. This would also reduce the risk of breakage at the point of union. De Haas (1957), using seven varieties of pear on Quince A, considered scion rooting a varietal characteris- -80- tic, and scion rooting and incompatibility as entirely unconnected. He noted that scion rooting exerted a strong effect in increasing wood growth. He did not however, note the effect of scion rooting on cropping and held that it needed systematic investigation through, trials laid out for that purpose. It is thought, as mentioned before, that deeply planted dwarf trees may give early crops and yet be as long-lived as standard trees. Hatton (1935) hinted at the possibility of such success. He observed '’there is some slight evidence that if the tree has been growing normally on a compatible quince stock, and has begun to crop to any extent before scion rooting, the results on fruit are less detrimental than when the variety gets away on its own roots, quite early in its career or after a period of extreme dwarfingness on an incom­ patible rootstock". Prom the above literature it is evident that little or no systematic work has been done on the phenomenon of scion rooting and its relation to growth and cropping. The identification of tree rootstock is an important problem in horticulture. Many horticulturists, such as Heppner (1925), Tukey (1930) Upshall (1931), Nebel (1931), and Day (1942), have worked on it, but their work per­ tains mostly to cherry rootstocks and evidently bears little relation to pear. -81EXPBKIMEHTAL MATERIAL AND LAYOUT The present investigations were undertaken as a continuation of Project 331 of the Horticultural Experi­ ment Station, Vineland, Ontario. by the Station in 1932. This project was started The history of the material is given below. A total of fifteen trees of each of the following four pear varieties, Bartlett, a.njou, Vermont Beauty, and Clapp Favorite on French pear seedlings and quince A root­ stocks, respectively, were examined. The trees were plan­ ted when two years old, in the fall of 1932. Of each variety there were five standard trees, five dwarf trees with the union about 6 inches below ground level (dwarf deep), and five dwarf trees with the union about one inch above ground level (dwarf shallow). The trees were planted in this order in single-tree compari­ sons. At the same time three dwarf Bose trees were plan­ ted with the union at the 6-inch depth and three with the union about one inch above ground level. One dwarf deep Bose tree died from blight infection in 1943. The soil in this orchard is classed as Vineland clay loam -poorly drained, high in organic matter, slightly to me ­ dium acid. Trunk circumferences, fruit yields, and size of fruit were taken annually for each tree until the fall of 1946 when the trees were dug for the purpose of making observations on scion rooting. -82After the necessary measurements were taken on capa­ city of scion rooting in the different varieties, these pear and quince roots were employed for identification studies, ihe roots of young plants employed in the studies of stock-scion compatibility in Part III of this paper, were also used for this purpose. -83METHODS The different methods employed for recording the data during these investigations are given below. 1. Observations on tree growth. Before the trees were dug, observations on growth habits, whether upright or spreading, were made on the standard, dwarf deep and dwarf shallow trees and photo­ graphs were taken. 2. Technique of excavation. Before excavation, the trunks of the trees were cut off with a pruning saw and the trees were labelled on the remaining portion of the trunk for later identifi­ cation. The root system of all the trees employed in this study were excavated by the"skeleton” method as des­ cribed by Rogers and Vyvyan (1928). This method was modified, however, to suit the requirements. Instead of digging the trench near the "drip” of the branches, it was dug around the tree at a distance of 3 feet. All the roots that extended beyond the trench were severed. The soil was then removed gently, bit by bit, across the inner ground occupied by the roots. Since scion roots were close to the ground level, every precaution was taken not to damage any of them. Each scion root was carefully uncovered by hand to obtain it in an undamaged condition. -843. Observations on root growth. During the excavations, and immediately thereafter, records on root distribution and growth were made for the three types of trees. 4. Washing the roots. Before recording the number or measurements of scion and stock roots, they were thoroughly washed to facili­ tate their identification and so that accurate measure­ ments could be recorded. 5. Number of roots. The number of both scion roots and stock roots of standard, dwarf deep and dwarf shallow trees of the different varieties were counted for the purpose of ma­ king comparisons. 6. Measurements of roots and determination of age of the scion roots. All roots were measured with caliper or tape as near as possible to their origin from the main axis and from these figures the total cross sectional area was computed. The percentage that the scion roots bore to the total root system was considered as a measure of scion rooting. The age of the scion roots was determined from a count of the annual rings at the point of origin. 7. Identification of Pear and Quince rootstocks from rootpieces. a . Macroscopic tests. 1. Color of the bark. During the excavations of 14-year-old pear trees, the surface color of the scion roots, i.e., roots that originated above the union and that of the stock roots, was observed and recorded. Similarly, in young standard and dwarf pear root systems the color differences were noted. 2. Color of inner bark. The color of the inner bark was observed by giving the pear and quince roots a smooth tangential cut with a knife. b. Chemical tests. The cut made to observe the color of inner bark above was treated with a few drops of different chemi­ cals, and the change in color, if any, was recorded. Chemicals belonging to each of the following groups were used: Ammonium, sodium, calcium, barium, and iron. -86PRESENTATION OF DATA 1. Observations on tree growth. From the general observations which were made on the growth of the trees in the field and examination of the scion roots, it was concluded that the scionrooted trees produced upright, vigorous growth, stan­ dard trees, as well as non-scion rooted dwarf deep and dwarf shallow trees were more spreading in growth. Standard trees, however, showed the most spreading growth habit of all the types. 2. Observations on root growth. The standard trees of all the varieties were essen­ tially without taproots but many vertically descending strong roots were noticed. On the whole, the root system was quite coarse and deep. In the dwarf deep trees, however, the stock roots were in the main, shallow, where­ as the scion roots were semi-vertical. In the dwarf deep trees of certain varieties the quince roots were com­ pletely dead and therefore the trees were on their own roots. In others, the tree was partly supported by both stock roots and scion rootse In the dwarf shallow non-scion rooted trees, the quince roots were finer, numerous, and chiefly shallow. The quince roots penetrated the soil horizontally. -87Table 1. Type of trees Number of trees Variety Bartlett Anj ou Vermont Beauty Clapp Favorite Bose Scion Hooting in .Different Varieties. NonScion-Rooted Quince roots Quince" roots Scicn rooted dead alive b 2 Dwarf deep 5 Dwarf shallow 5 Dwarf deep 5 Dwarf shallow 5 3 2 Dwarf deep 5 2 3 Dwarf shallow 5 2 3 Dwarf deep 5 Dwarf shallow 5 2 Dwarf deep 2 2 Dwarf shallow 5 3 2 3 2 1 3 4 3 The Bartlett variety formed scion roots readily; in the five dwarf deep trees, three were on their own roots, and two were partly supported by stock roots and partly by scion roots. Furthermore, in the five dwarf shallow trees, three had developed scion roots. gree of scion rooting. Anjou followed Bartlett in de­ In the five dwarf deep trees of this variety, two were on their own roots and three were partly supported by scion roots and partly by stock roots. In the dwarf shallow trees, three of the five had made scion roots. Next in turn was Clapp Favorite; one dwarf deep tree was -68observed. to be on its own roots and four were supported partly by stock roots and partly by scion roots. In the dwarf shallow trees, two showed scion roots and three were completely on stock roots. All the trees of Bose, whether dwarf deep or dwarf shallow formed scion roots but they were supported both by stock roots and scion roots. Vermont Beauty proved to be a shy scion rooter; two dwarf deep and two dwarf shal­ low trees formed scion roots to some degree and the rest were completely on stock roots. 3. Number of scion roots. In the standard trees, Bartlett produced the most roots, and Clapp Favorite, Vermont Beauty, and Anjou followed in this order (Table 2). Among the dwarf deep trees of Bartlett, Bose, and Anjou the number of scion roots was considerably greater than the Quince roots; in Vermont Beauty and Clapp Favorite it was quite the reverse. In the dwarf shallow trees, Bose formed the most roots followed by anjou, Vermont Beauty, Bartlett, and Clapp Favorite in this order. -89- Table 2. Number of Live Roots in Three Types of Trees of Different Pear Varieties. Total Number of Roots Variety Standard Scion Roots <4ulnce Roots Total Bartlett 80.6 Dwarf Deep 15.2 2.6 17.8 .8 16.6 17.4 Dwarf Deep 8.4 5.6 14.0 Dwarf Shallow 2.6 17.2 19.8 Dwarf Deep 1.2 16.6 17.8 Dwarf Shallow 1.6 16.4 18.0 Dwarf Deep 5.8 10.8 14.6 Dwarf Shallow 0.2 16.0 16.2 10.0 20.5 50. 5 7.0 14.7 21.7 Dwarf Shallow Anjou Vermont Beauty Clapp Favorite Bose Dwarf Deep Dwarf Shallow 17.8 21.8 29.0 - -904. Capacity of scion rooting. Bartlett showed the roots (Table 3). In the the live root system was greatest capacity to develop scion dwarf deep trees, 9o percent of contributed by the scion. Anjou was next with 82.7 percent; Clapp Favorite ranked third with 63.9 percent; Bose was lowest with only 38.4 percent of the root system as scion roots. In the “dwarf shallow" trees, the capacity to form scion roots in the different varieties was as follows, in order of decreasing proportions; Anjou, 46.8%; Bose, 24.1%; Bartlett, 21.7%; Vermont Beauty, 18.7%; and Clapp Favorite, .3%„ Table 5. Capacity to Form Scion Roots in Different Pear Varieties. (Cross-sectional area in sq.cm. of the root systems. )*Variety Standard Total crosssectional area Total crosssectional area Percent scion roots Percent quince roots Bartlett 192.0 Dwarf Deep Dwarf Shallow 87.0 45.1 93.0 21.7 7.0 78.3 An jou 357.4 Dwarf Deep Dwarf Shallow 143.0 70.3 82.7 46.8 17.3 53.2 Vermont Beauty 395.0 Dwarf Deep Dwarf Shallow 125.4 89.1 38.4 18.7 61. 6 81.3 Clapp Favorite 431.4 Dwarf Deep Dwarf Shallow 106.4 68.1 63,9 •*5 36.1 99.7 Bose Dwarf Deep Dwarf Shallow 143.9 117.1 61.2 24.1 38.8 75.9 * The cross sectional area of the root systems of the standard trees of the different varieties is given for convenience in comparison. -91Ref erring to the studies presented later in part III, Bartlett and Glapp Favorite were relatively incompatible on quince A. Bose was in the same category, other hand, made a good union with quince A. Anjou, on the It is ob­ vious therefore, that incompatibility and scion rooting were entirely unrelated. 5. Age w h e n s c i o n roots o r i g i n a t e d . In the dwarf deep trees, Clapp Favorite developed scion roots earlier than did the rest of the varieties, i.e., in 1939 (Table 4), or at an age of seven years in the orchard. Bartlett, Anjou, and Bose produced scion roots a year later, or in 1940. In the dwarf shallow trees, Bose and Clapp Favorite formed scion roots in 1942, whereas Vermont Beauty did so in 1943. In Bartlett, however, the scion roots originated in 1944. It was con­ cluded therefore, that these pear varieties when dwarfed on quince a rootstock developed scion roots after being seven to ten years in the orchard. -92Table 4. Age at which First Scion Roots Originated in Different Varieties. (Trees planted in fall, 1932) Variety Scion roots originated Dwarf Shallow Dwarf Deep Bartlett 1940 (8th year) 1944 (12th year) Anjou 1940 (8th year) 1943 (11th year) Vermont Beaiity 1942 (10th year) 1943 (11th year) Clapp Favorite 1939 (7th year) 1942 (10th year) Bose 1940 (8th year) 1942 (10th year) 6. Effect of scion rooting on growth, a. Bartlett. The standard trees made more growth than did the dwarf deep and dwarf shallow trees (Pig. 3, and Table 1 in Appen­ dix) , The growth in the dwarf deep and the dwarf shallow trees was almost equal from 1932 to 1940. The dwarf deep trees then produced scion roots, with the result that the growth increased moderately up to 1942 but. then became rapid and approximately the same as that of the standards. This indicates that scion roots showed their effect two years after they originated. The growth in the dwarf shallow trees was moderate up to 1944, when they produced some scion roots; subsequently, the scion root 3 accelerated Fig. Fig. 4 Mean cross-sectional area of trunk of Bartlett on French oear seedling and. quince a rootstocks in relation to the time of origin of scion roots. Mean accumulated yield per tree of Bartlett on French pear seedling and • Quince A rootstocks in relation to the time of origin of scion roots. 60. 55. • 50 AR£A Of CROSS seCTION OF TRUNK (S q.C *s.) 45* STANDARDTR6€ DWARF D f f P 45. DWARF SHALLOW 35 * V6ARIN WHICH SCION ROOTS 0 RUINATED 30 . 25 - 2015* 10* . 5 VEftR YIELD I N LBS. _ Pig* 3 i0‘ - t Dw x — y e a r in w h ic h 50 * 30* . 20 Pig. 4 arf s h allo w » f . x * J w arf Deep •--------- •--------- • s t a n d a r d t r e e s S c io n R o o t s o r i g i n a t e d the growth rapidly. However, they made considerably less growth than the dwarf deep trees because they had developed scion roots later in their life and because a smaller pro­ portion of their root system was of scion origin. b. An jou The growth in all three types of trees was practically equal from 1952 to 1955 (Table 1 in the .appendix.). Then the standard trees began to outgrow the dwarf trees. The two dwarf groups produced equal growth until 1956 but then the dwarf deep trees began to outgrow the dwarf shallow trees and finally (fall of 1946) there was a difference of about 16 square centimeters in the cross-sectional area of their trunks. In the dwarf deep trees where scion roots originated in 1940, growth was moderate until 1942 and then became rapid. The dwarf shallow trees developed scion roots in 1945 and growth soon became rapid. ■ c. Vermont Beauty. The standard trees made significantly more growth than did the other two groups (Table 1 in the Appendix.). The dwarf deep and the dwarf shallow trees made almost equal growth throughout in spite of the fact that they had rooted moderately from the scion, the former in 1942 and the latter in 1945. After these dates however, the effect of scion roots was appreciable, both groups showing a quick increase in growth. -94Vermont Beauty was the only variety in which some of the dwarf deep trees remained wholly on quince roots. The scion rooted trees were more vigorous than the non-scion rooted trees. The effect from scion roots was small in this variety. d. Clapp Favorite. The standard trees made appreciably more growth through­ out their life than did the other two groups (Table 2 in the Appendix). The growth in the dwarf deep and the dwarf shal­ low trees was almost equal until 1957; after this date, the dwarf deep trees began to outgrow the dwarf shallow trees. The dwarf deep trees formed scion roots in 1959; growth was moderate until 1941 and then it became quite rapid. Simi­ larly, the growth in the dwarf shallow trees was moderate until 1942 when they produced scion roots and then the growth in­ creased. Therefore, scion roots exerted an invigorating effect on growth,, e. Bose. The first scion roots were produced on the dwarf deep trees in 1940, i.e., when they were 8 years old. In the dwarf shallow trees the scion roots were produced in 1942, i.e., when they were 10 years old. The growth in the dwarf deep and the dwarf shallow trees was almost equal until 1955 but after that date the dwarf deep trees outgrew the dwarf shallow trees (Table 2 in the .appendix) . Mention is, how­ ever, made here that number of trees in this variety was small, i.e., 2 dwarf deep, and 5 dwarf shallow. -95It seems clear that scion roots markedly affected the growth of Bartlett, Anjou, Clapp Favorite, and Bose. In the case of Vermont Beauty, however, this effect was small because scion-rooting was meager. 7. Effect of scion-rooting on cropping. a. Bartlett. The development of scion roots in the dwarf deep trees of Bartlett reduced the yield in the year following their origin, but recovery occurred soon afterwards (Fig, 4 and Table 6 in the Appendix). The yield from the dwarf deep trees was slightly less than that from the dwarf shallow trees. The latter, however, produced a moderate yield throughout until 1941 when they produced even more fruit than the standard trees but subsequently, the latter sur­ passed them. The dwarf shallow trees produced scion roots in 1944, i.e., when they were 12 years old, and the yield then declined. But, mention should be made here that the season of 1945 and 1946 were unfavorable for pollination and this reduction in yield was not necessarily because of the effect of scion roots, b. Anjou The standard trees of Anjou produced the highest yield from the start (Table 5 in the appendix). The yield from the dwarf deep and the dwarf shallow trees was almost equal up to 1940, i.e., when they were 6 years old. Then, -96the former commenced to develop scion roots. Their yield then increased and was maintained until 1945 at which time the dwarf shallow trees produced some scion roots and there, after surpassed the dwarf deep trees in yield. However, the total difference in yield between the two groups was negligible. c. Vermont Beauty. The dwarf shallow trees of Vermont Beauty produced more fruit throughout than did the standard or dwarf deep trees, and the difference was quite high (Table 5 in the Appendix). They formed scion roots in 1945, i.e., when they were 11 years old, but still the yield increased steadily. The stan­ dard trees gave the lowest yield until 1941 but after that they out-yielded the dwarf deep trees. The latter, in turn, produced scion roots in 1942, i.e., when 10 years old but the yield steadily increased, though finally dwarf shallow trees gave 60 pounds more accumulated yield per tree than did the dwarf deep trees. d. Clapp Favorite. The standard trees of Clapp Favorite produced more fruit throughout than did the other two groups (Table 4 in the appendix). The dwarf deep trees formed scion roots in 1959, i.e., when they were 7 years old, but the yield after this date showed a steady increase. The dwarf shallow trees produced scion roots in 1942 i.e., when they were 10 years old, but their yield too, steadily increased until -971944. In this variety, the dwarf deep trees produced about 21 pounds more crop per tree than did the dwarf shallow trees, e . Bose. The dwarf shallow trees of Bose produced a greater yield up to 1943, but after that they were surpassed by the dwarf deep trees (Table 4 in the appendix). The scion roots in dwarf deep trees originated in 1940, i.e., when the trees were 8 years old; then the yield increased slightly in 1941, but after that there was a rapid in­ crease until finally the dwarf deep trees yielded 38 pounds more than the dwarf shallow trees. The scion roots in the latter trees originated in 1942, i.e., when the trees were 10 years old, and yield increased soon there­ after. These studies indicate that the formation of scion roots does not adversely affect the yield of Bartlett. In case of Anjou, the scion roots increased the yield of both the dwarf deep and the dwarf shallow trees. In Vermont Beauty, the scion roots caused a detrimental effect on the yield. Scion roots improved the yield of Clapp Favorite and Bose. 8. Effect of scion rooting on weight per fruit. To ascertain the effect of scion roots on weight per fruit, Bartlett was selected as a representative variety. -98To begin with (Table 5 in the Appendix), dwarf deep trees formed scion roots in 1940, and the weight per fruit de­ creased in 19e2 owing to the effect of scion roots. After 1942, the weight per fruit increased again but not beyond that of the dwarf shallow trees. The latter trees produced scion roots in 1944; the weight per fruit increased in 1945 but declined in 1946. Although the standard trees gave re­ latively small fruits for about 10 years they then began to produce larger fruits. In Bartlett, the dwarf shallow trees produced the heaviest fruits. In general, the standard pear varieties, when dwarfed on quince A rootstock, produce heavier fruit. But, when they develop scion roots this effect is nullified and the fruit becomes in size more like that from a standard tree. 9. Identification of Pear and Quince rootstocks from rootpieces. a. Identification through macroscopic characters, i. Color of bark. Young pear roots were noted to be reddish brown in color, whereas young quince roots were dull dark brown. In old quince roots, however, this color was further deepened to a prominent blackish tinge. These colors were so distinct that during ex­ cavations of old pear trees the Pear and Quince roots could be identified at a glance. -99ii. General growth characters. Quince roots were fine and penetrated the soil horizon­ tally; Pear roots were strong and tended to penetrate the soil vertically. iii„ Color of inner bark. The color of inner bark proved to be a definite means of identification. Pear roots were creamy white; Quince roots were pearly white, sometimes with pink streaks, i v . Color of bark on exposure to air. The old Pear and Quince roots were washed after the excavation and slight slices were given with a knife. Pear roots turned yellowish brown, whereas the quince roots turned dark pinkish brown, b. Identification by the use of chemicals. More than 50 chemicals were tried in the identifica­ tion studies on pear and quince roots. The chemicals which proved helpful are given in Table 5, along with the reaction on pear and quince roots0 -100- Table 5. Reaction of Different Chemicals on the Inner Bark of Fear and Quince roots. Chemical Reaction on inner bark Pear Quince Ammonium hydroxide, 5% Deeper white Deep creamy Ammonium hydroxide, (concentrated) Creamy Light yellow Ferric chloride, 60;* Dark greenish brown Darkens slightly Sodium hydroxide lc on o n f ' pd ' Ochraceous-Salmon,^ Lemon Yellow, @ turns turns Vinaceous-Tawny Xanthine Orange after some time after some time. @ Colors from Ridgway's Color Standards and Nomenclature. -101- DISC USSION Information o n the effect of scion roots on the vigor and. cropping of pear trees is of great value to By utilizing certain the commercial d w a r f pear grower. facts it is possible to obtain a type of tree which will not only produce at a younger age but will probably be as long lived as a standard tree. Prom general observation on the growth of trees in the field and examination of the scion roots after dig­ ging the trees it was noticed that scion-rooted trees produced upright, vigorous growth. Standard and non­ scion rooted d w a r f deep and dwarf shallow trees were more spreading in growth. The standard trees showed the most spreading growth habit of all the types. In sup­ port of these observations, Hatton (1935) has stated that a scion-rooted tree can be detected by its excep­ tionally upright vigorous growth and large greenish foliage. The standard trees of all the varieties proved to be essentially w it hout taproots but there were many vertically descending strong roots. was quite coarse and deep. On the whole, the root system In the dwarf deep trees, how­ ever, the stock roots were chiefly shallow, whereas the scion roots were semi-vertical. of some varieties and, therefore, In the dwarf deep trees the quince roots were completely dead the trees were on their own roots. In -102the remainder, the tree was partly supported by both stock roots and scion roots. Bartlett showed the greatest capacity to develop scion roots. In the dwarf deep trees of this variety, 95 percent of the root system was contributed by the scion roots. Anjou was next with 82.7 percent. Clapp Favorite was third with 65.9 percent; Bose closely followed with 61.2 percent; and Vermont Beauty was lowest with only 58.4 percent of the root system as scion roots. In the dwarf shallow trees, the capacity to root from the scion in different varieties was as follows, in order of decreasing percentage: Anjou, Bose, Bartlett, Vermont Beauty, and Clapp Favorite. It was concluded from these studies that there were wide differences in the ability of different varieties to produce scion roots. In other words, scion rooting was a varietal characteristic. Hatton (1955), De Haas (1957), Shaw (1919), and Moore (1919) , who worked with pears and apples, claimed that scion rooting was definitely a varietal characteristic. Hatton (1955), with pears, re­ marked that two varieties, namely Hardy and Conference, did not form any scion roots at all. He also observed that trees on Quinces D to G made scion roots more readily than on Quinces A to C. Shaw (1919), with apples, noted that some varieties rooted readily from the scion, others did so only occasionally. -105In Part III of this study it was found that Bart­ lett and Clapp Favorite were relatively incompatible on Quince A rootstock. Bose was in the same category. Anjou, on the other hand, made a good union with the Quince A. Upshall (1946) and Overholser (1944) believed that Vermont Beauty made a vigorous tree on quince A rootstock. Therefore, it was contended from the present studies, that incompatibility and scion rooting were entirely unconnected. De Haas (1957), who used seven varieties of pear on Quince a rootstock, considered that incompatibility and scion rooting were not related, Moore (1919), with apples, found that deeply planted grafts formed scion roots more readily than did shallow planted ones. The present findings, therefore, supported his deduction; it was noted that the dwarf deep trees pro­ duced scion roots more readily than did the dwarf shallow trees. These studies also indicated that different pear varieties when dwarfed on quince a rootstock formed scion roots after the trees had grown 7 to 10 years in the or­ chard. In the dwarf deep trees, Glapp Favorite developed scion roots earlier than did rest of the varieties, i.e., in 1959, Bartlett, Anjou, and Bose produced scion roots in 1940. Among the dwarf shallow trees, Bose and Glapp Favorite formed scion roots in 1942, Vermont Beauty did so in 1945. Bartlett formed scion roots in 1944, i.e., after 12 years in the orchard. -104It appears that scion rooting in deeply planted dwarf pears was much slower in developing under the conditions prevailing in this orchard than in experiments reported by Hatton (1935) in England and Day (1947) in California. In England the trees were not deeply planted, but in Cali­ fornia the union was submerged 12 inches, and in fact that is the depth recommended by Day. The relation between scion rooting and growth proved to be very strong. The scion rooting markedly increased the growth of Bartlett, Anjou, Clapp Favorite, and Bose. In the case of Vermont Beauty, the effect was moderate, probably because this variety was a shy scion rooter. It was assumed that dwarf deep trees were likely to overshadow the standard trees in growth after a period of time. Hatton (1935), and De Haas (1937), working with pears, found that the effect of scion rooting on the wood growth was very strong. The present investigations, therefore, support the views of these authors. Hatton (1935) also believed that scion rooting had a great detrimental effect on the yield of•pear trees. His findings came true from the theoretical point of view. The reasoning was that vegetative growth was inimical to fruit formation and required quite different physiological conditions as compared to conditions conducive to fruit for­ mation. a vigorously growing tree, would, naturally pro­ duce less fruit. -lUDScion roots did not generally adversely affect the yield of the pear varieties under the present study. Scion roots did not reduce the yield of Bartlett. In the case of Anjou, the scion rooting increased the yield of both dwarf deep and dwarf shallow trees. In Vermont Beauty, scion roots reduced the yield slightly. The scion roots, on the other hand, improved the yield of the Glapp Favorite and Bose varieties. The above results might be explained by the reason put by Hatton (1955). He remarked '*there is some slight evidence that if the tree has begun to crop to any extent before scion rooting, the results on fruit are less detri­ mental than when the variety gets away on its own roots quite early in its career or after a period of extreme dwarfingness on an incompatible rootstock.'* The different pear varieties used in the present in­ vestigations cropped after four to seven years in the or­ chard. In the case of Clapp Favorite, the standard trees bore fruit after seven years, whereas the dwarf trees bore fruit after 5 years. These studies revealed that this variety formed scion roots when 7 years old. fore Hatton*s explanation held in this case. There­ Similarly, Bartlett bore fruit after the fourth year in the orchard and it formed scion roots when it was 8 to 10 years old. and so, naturally there was no detrimental effect on the yield of these pear varieties. -106It was further observed that scion rooting did not materially affect the weight per fruit in these pear varieties. To begin with, non-scion rooted dwarf trees produced heavier fruit but when they had developed scion roots that effect was nullified and fruit became like that from a standard tree. While it is true that the deeply planted dwarf trees usually come into bearing a year or two earlier than the standard trees, it was only a few years before the stan­ dard trees surpassed the dwarfs in yield. The only justi­ fication therefore, under Vineland conditions, for using dwarf trees planted deeply in preference to standards would be th...t they might be planted more closely, thus compensating for the lower yield per tree. However, not knowing how large the trees of each variety might eventu­ ally become on their own roots, a closer spacing of trees would be in the nature of a gamble. If dwarf pear trees are to be retained indefinitely on the quince root they must be planted very shallow, with the union at least five inches above the ground level. This makes it desirable that nurserymen bud pear higher on the stem of the quince rootstock than is the common practice for standard rootstocks. If, at all, the union is covered with soil incidental to cultivation the growers should re­ move the soil around the upper roots of their trees, identi­ fy the scion roots by the methods suggested in the previous chapter and prune the "undesirables". -107SITMMARY Under conditions at Vineland dwarf pear trees planted with the union 6 inches below ground level did not begin to grow scion roots until the seventh to tenth year. Then, scion roots developed rapidly, the quince root became less a and less important, and in some instances was dead at the end of the fourteenth year. In this orchard scion roots did not exert a repressive influence on fruiting. Varie­ ties varied considerably in their capacity to develop scion roots. Scion rooting and incompatibility were found entirely unrelated. The pear and quince roots can be readily identified by treating the inner bark with a drop of concentrated sodium hydroxide; pear roots turn Ochraceous-salmon whereas quince root turns lemon-yellow. Fourte-:*n-year Bartlett on quince jx rootstock "dwarf shallow" scion rooted. Note upright growth. *T:•<■••“ i.t.-^Jt’^ ^ W ft •?■-11« £ & . vJrt1 .?jff\ Pig. 5 Pig. 6. Fourteen-year Bartlett on quince a rootstock "dwarf shallow" not scion rooted. . J&i am* l. 1 A vs**.-V *rvr ' -_ . : / i w bA*?7 r-W * !.<*?"<>1(;■»>V .r S .- 'i ^ ■tV'.^vT, itA Z&ZM'-A}. Mips mi*82£" EpSf?- ' c z i y i & r ? * }..■,A;.,:pi.•, -l "',~-;^4l'*>';<"*■ ' ■VV'<’ 4' -- ®te;« iff•/"■'•.' . v '- (1r ;>t«v 5.v ! v .’.' J . v*r- ' k.*--’ . I Pig. 6 Figo 7. Fig, 8, hoot system of 14-year pear on Quince a. rootstock. Scion-rooted, stock roots are dead. Hoot system of 14-year pear on French pear seedling rootstock. Fig. 8 Fig. 9. Fig. 10. Hoot system of 14-year pear on Quince a rootstock, scion-rooted. Live stock roots (6), are marked with white pieces of p a v e r . Root system of 14-year pear on Quince rootstock. Rot scion rooted. "Dwarf shallow” . PART III STUDIES IN INCOMPATIBILITY BETWEEN STOCK a ND SCION OP DWARF PEAR TREES - 108 - I INTRODUCTION That some varieties do not produce a congenial union with quince a cannot be denied. Nurserymen, neverthe­ less, propagate such varieties on this rootstock and sell them to the fruit growers. These plants make good growth for a year or two, but subsequently the growth declines, if they survive longer or at all, the trees, especially when mature, may break cleanly at the point of union. The growers then suffer a great loss. In view of these circumstances the problem of stock scion incompatibility in dwarf pears was taken in hand. The aim in this phase of the work has been to provide in­ formation which would be of value to the nurseryman and the grower who might then refrain from selling or pur­ chasing incompatible combinations. s -109REVIBW OF LITERATURE It is a familiar fact that tree fruits do not re­ produce true to variety from seed. Therefore, fruit varieties are normally propagated by means of budding or grafting. The history of the art of graftage gives a glimpse into the romance surrounding fruit tree cul­ ture from the early days of civilization to the present time. Pliny, before the birth of Christ, wrote that graftage was a horticultural practice and that it was practiced even before his time. Chang (1938) cited a Chinese author who as early as 500 a .D. mentioned that the pear was best suited on Pyrus phaeocarpa, Rehd and that the bark of the scion should be in close contact with that of the stock. Chang also cited an English author, Thomas Andrew Knight, who in 1812 mentioned that plum stocks were best suited for peach, and. apricot stocks for Moorpark apricot. The failure of a scion to make a harmonious union with its stock is termed incompatibility. The choice of a suitable stock is influenced by many factors, such as soil, locality, climate and environmental conditions, and it plays a significant part in obtaining dwarf, disease resistant, hardy, and fruitful trees. Because of the necessity of selecting different rootstocks for dif­ ferent localities or environments the problem of incom­ patibility has become of increased importance in fruit production. -110Botanlcal Relationship flot a Reliable Quide Chandler (1925) stated "It is known from experience that only botanically related species can be successfully budded or grafted onto each other. On the other hand, nearness of relationship does not alone determine the degree of compatibility of stock and scion - something more of that kinship is required for a good union". He further stressed that some plants which belong to unre­ lated species or even genera could be united by budding or grafting. Hatton (1928) observed that different quince strains (Cydonia vulgaris, Lindl) were not equally compatible with different standard pear varieties. Brad­ ford and Sitton (1929), with pear and apple grafts, found that these two kinds when intergrafted failed to form a congenial union. Chang (1958) mentioned that plants of certain different species or genera, such as citrus on Poncirus trifollata, Lindl were successfully worked in China. Percentage of Bud-take Mot a Reliable Guide to Compatibility. Chang (1938) claimed that climate, weather, and environ­ ments along with other factors such as variety, method or technic of propagation, age and size of stock, position of the top bud of the graft, etc. influence the bud take. Even in incompatible combinations favorable climatic and environmental conditions delay failure. It can be assumed -111that symptoms of incompatibility readily appear in such combinations growing under adverse conditions. Moreover, the various varieties which are suitable in one region may not necessarily be best in another region since the success of the grafts depends upon many factors such as climate, weather, soil, and so forth. Toxopeus (1956) mentioned that whereas sweet orange (Citrus sinensis, Osbeck) was successful on sour orange understock (Citrus Slurantium, Linn) in most citrus growing areas, it was incompatible in Java and South Africa, Growth Behavior in the Nursery Mot a Reliable Guide to Compatibility. Incompatible combinations, sometimes, make more growth the first year in the nursery than do the compa­ tible combinations. However, in the second or third year the root-shoot growth declines, more or less, in propor­ tion to the degree of incompatibility. Climatic and weather factors also affect the growth of plants from year to year, and so, observations must necessarily be made over a period of time before the final verdict can be given. From the practical point of view, a slight incompatibility may supress the vegetative growth and promote early or prolific bearing. Certain manifesta­ tion of incompatibility may also appear in such com­ binations but they cannot be taken as a reliable guide of incompatibility unless they are serious,, -112Stock scion disagreement or otherwise usually exists in four degrees. 1). Absolute incompatibility. There is a complete failure between stock and scion and no union is formed. apple on oak, and cherry onpoplar. 2). Incompatibility. The scion and stock unites readily but the plants are short-lived. apple or apple on 6)c For example, For example, pear on pear, and peach on American plum. Partial incompatibility. The stock-scion combinations are more lasting than those in group 2 but the union is not as good as a normal one. For example, pear on quince, and sweet cherry on Mahaleb. 4). Compatibility. Stock, scion combinations which form harmonious bud or graft union, the resulting plants being long-lived and productive. For example, peach on peach, and apple on apple. Causes and Symptoms of Incompatibility. Many horticulturists, with different fruits, all over the World, have made appreciable efforts to explain incom­ patibility. Hoopes (1875), Daniel (1894), Waugh (1904), Gleisberg (1927), Heppner and McCallum (1928), Proebsting (1928), Bradford and Sitton (1929), Shippy (1950), Harvey (1951), Sass (1955), Crafts (1954), Halma (1954) and Mendel (1956), working with different fruits, mostly de­ ciduous, showed that incompatibility is due to structural weakness, deposits at the union, or a difference in.an- -115atomy of stock and scion. Daniel (1894), Gabion (1903), Laurant (1906), Green (1926), Jensen et al (1927) Hofmann (1927), Proebsting and Begger (1927), Haas and Halma (1929), Roach (1931), Kobel (1931), Eaton and Blair (1935), and Toxopeus (1936) claimed that the cause of incompatibility is of physiological or biochemical origin, Kostoff (1928) working on Solanaceae found that a toxin produced by antibodies from antigens is respon­ sible for incompatibility. But, none of these findings have been finally accepted. Proebsting (1926) pointed out that the weakness of incompatible unions was due to the accumulation of paren­ chymatous tissue at the point of union. This layer of tissue might form a continuous sheet between stock and scion. After some years, owing to windstorms or greater weight of the top, the trees break off smooth at the line of union where this tissue accumulation exists. Bradford and Sitton (1929) reported that uncongenial grafts such as pear on apple, or some pears on quince stocks, fail to maintain cambial activity. When the stock and scion expand they leave a sheet of suberized parenchymatous tissue between them and the conduction channels along the phloem become discontinuous. This discontinuity, they believed, responsible for dwarfing the plants and that dwarfing itself was a sign of in­ compatibility. -114Argles (1957) suggested that the combination in which a high percentage of trees die within the first few years or break off smooth at the point of union can only be explained by the phenomenon of incompati­ bility. Amos et al (1936), Argles (1937), and Quinn (1935) thought that decline in growth or death of trees in the orchard after a few years, when their initial growth was normal, can only be explained by stock-scion incompatibility which makes such combina­ tions short-lived. Amos et al (1956) further explained that dwarfness was of two types; healthy, which was responsible for precocity and heavy cropping, and un­ healthy, which was associated with stock-scion disagree­ ment and evidently short life. Haas and Halma (1929), working on citrus, wrote as follows: "in general the degree of so called congenia­ lity or compatibility implies a comparison of the rela­ tive rate of growth of scion and stock; the more nearly equal the rate of growth of scion and stock, the greater the congeniality or compatibility." Kostoff (1929) found that for satisfactory growth in intergeneric grafts, the scion should maintain an equality of growth with the stock. If the scion predominates, root growth is serious­ ly hampered. Kostoff (1928) also found that in inter­ specific and intergeneric graft combinations large de­ posits of starch occur above the union. Bradford and -115Sit ton (1929), and Amos et al (195b) showed that a swelling at the union was not an indication of incom­ patibility. The latter mentioned that the presence of a prominent buldge was absent in some incompatible combina­ tions whereas it was present in certain compatible com­ binations. Kobel (1951) explained that this swelling at the union was mainly due to the obstruction of carbohy­ drates but was also caused by proliferation which results from the union of stock-scion tissues. Hafekost (1955), referring to different pear scions on four vigorous clonal quince stocks at hast Mailing, .England, observed th^t the concentration of cell-sap of the stock increases to such an extent during the growth periods that pear scions can no longer exchange their materials with'their stocks. The recent work of Chang (19ob) revealed a number of symptoms of incompatibility. He found that in in­ compatible combinations there were: 1, low' bud take, premature autumn leaf coloration, early defoliation, dying back of shoots, etc.; 2, gradual decline in year­ ly root-shoot growth; 5, mechanically weaker union and smooth break at the union; 4, bark and wood discontinuity, and accumulation of parenchymatous tissue at union; and 5, obstruction at union, especially of water or dyes and accumulation of starch above union. -116Argles (1937) gave these two symptoms as certain indications of incompatibility: 1, presence of a layer of parenchymatous cells at the line of union; 2, smooth breaking of trees at the union, especially after some years. -117EXP EHIMEWTAL MATERIALS AND METHODS To study scion-stock incompatibility in dwarf pear trees, twenty-four, 1-year, 2-year, and 5-year combina­ tions of standard pear varieties on quince A and domes­ tic pear rootstocks, were obtained from various nurseries for critical examination. The purpose of including the s standard pear combinations was to compare them with dwarf pear combinations. Two distinct methods were employed to test stockscion incompatibility in dwarf and standard pear trees, namely, field and laboratory. Field methods. a. General observations The various dwarf and standard pear combinations were examined in the field and notes were taken regarding their growth behavior, color of the foliage, time of de­ foliation, and so forth. b. Swelling at the union. The diameter of the stock and scion was recorded at a distance of 2 centimetres both ways from the union. The diameter at the point of union was also recorded. The average of stock and scion deducted from the average at the bud-union gave a measure of the swelling at the union. Laboratory methods. a • W ater-conductivity tests . The type of apparatus devised by Chang (1958) to -118- perform the water—conductivity tests in grafts of dif­ ferent deciduous fruits, was used in the present investi­ gations . b . Starch-accumulation tests. A simple test was made to determine the deposit of starch above or below the union. Slanting cuts were made in the stock and scion at 2 centimetres length either way from the bud-union. solution. These cuts were treated with iodine The color difference was noted through a hand lens . c. Bark and wood continuity. The bud-unions of the different dwarf and standard pear combinations were examined both externally and after slicing at the union. The bark and wood continuity or otherwise in various combinations were observed and recorded. Photos were taken to illustrate the condition in different combinations. d . Strength-at-union tests. The apparatus used to test the strength of the bud unions of various combinations was based on the same simple principle as the apparatus devised by Chang (1958). His apparatus was unnecessarily complicated, and so a sim­ pler one was devised. The diagram of this apparatus and its description is given under the heading "Strength-atunion tests" in the section on Results. -119e. Mature of fracture at the union. After the strength-at-union tests, the fracture at the union was observed in all the various dwarf and stan­ dard pear combinations. moderate, or smooth. These were expressed as tearing, Photos to illustrate the nature of fractures in different combinations were taken. Similarly, in all the dwarf or standard pear combina­ tions that showed premature autumn leaf coloration or early defoliation symptoms, the above tests were made and are recorded under the heading "Premature autumn leaf coloration or early defoliation in different standard and dwarf pear combinations" in the next section. -120RESULTS 1. General growth behavior In the nursery. The general observations of dwarf pear trees In different nurseries revealed that, in a comparative way, Bose shows poor bud take, some trees die soon after starting to grow, and a high percentage of the remainder exhibit stunted growth, (Figs. 11 and 12). Kieffer on quince a rootstock is short-lived; trees of this variety make good growth at first but after a few years they die. Bartlett and Clapp Favorite make ap­ parently good growth but are subject to breakage at the union. Seckel shows good growth and is less sus­ ceptible to breakage at the union. Other varieties like Beurre Hardy, Old Home, and Anjou make long-lived trees of moderate vigor. 2. Swelling at the union. Swelling at the union was greater in dwarf pear trees than in the standard ones (Table 1). Among dwarf pear combinations, however, Bartlett, Clapp Favorite, and Kieffer produced significantly greater swelling at the union than did the other varieties. In all the stock-scion combinations, the diameter of the stock was more than that of the scion, except in the case of Kieffer on Quince stock.. a where the scion was larger than the Fig. 11. Growth behaviour of Anjou and Bose on quince a rootstock in the nursery one year -fter budding. Note poor stand and growth of Bose on Quince a. Fig. 12. Right Bartlett/Hardy/Quince a . Left Bose on Quince A. Growth behaviour of Bose and Bartlett on Quince A rootstock in the nursery two years after budding. Note poor growth of Bose on Quince a . aziizj ' m -, ...u ,( ,t.... \ ■,<( i.' ;liin Fig. 11 l\ III Fig. 12. -121Table 1. Measurement of Swelling at the Union. Combinations (6 trees of each) Diameter of stock and scion 2 cm. both ways from union.(cm) Scion Stock Average (A) Diameter of union (cm) . Swelling at union. B minus A. (B) One-year tops Bartlett on Quince A 1.18 1.47 1.55 2.07 .74 Bartlett on domestic pear 1.21 1.62 1.42 1.86 .44 Clapp Favorite on Quince A 1.25 1.56 1.41 2.16 .75 Clapp Favorite on domestic pear 1.55 1.88 1.61 1.94 .55 Orange Quince on Quince A. 1.16 1. 58 l.o7 1.71 •04 Old Home on Quince A 1.40 1.47 1.44 2.12 .68 Beurre Hardy on Quince A 1.57 1.55 1.46 1.98 .52 Kieffer on Quince A 1.50 1.25 1.28 2.04 .76 Old Home on Quince A 1.70 1.80 1.75 2.29 .54 Bartlett/Hardy/ Quince A* 1.40 1.50 1.45 1.95 .50 Beurre Hardy on Quince A 1.40 1.50 1.45 1.82 .57 Bartlett/Anjou/ Quince a -s:- 1.00 1.56 1.18 1.57 .39 Two-year tops -* Bud-union on quince A was used -1225 0 Obstruction to the passage of water and elaDorated foods In" the region of the union. a. Water conductivity tests. The different dwarf and standard pear trees studied were freshly dug. The plant was cut at 4 centimetres above and 4 centimetres below the union in order to obtain a piece 8 centimetres long to fit in the apparatus, nega­ a tive pressure of 700 nun. of mercury through the vacuum pro­ duced by a water tap was maintained throughout the test. Ten minutes after the vacuum was produced readings were taken and these were repeated at one-hour intervals. The total water that passed through the union was calculated in cubic centimetres per square centimetre of the crosssectional area by taking the average of the stock and scion diameters which were recorded 2 centimetres above and below the union. Considerably less water passed the bud-unions of dwarf Bartlett, Clapp Favorite, and Kieffer, than the bud-unions of dwarf Beurre Hardy, Old Home, and Anjou com­ binations (Table 2). In this respect, the latter combina­ tions proved to be equal to the standard pear combinations. Thus, the dwarf Bartlett, Clapp Favorite, and Kieffer com­ binations exhibited a strong obstruction to the flow of water at the union, whereas the other dwarf pear combina­ tions did not offer as much resistance. There was, how­ ever, one exception, viz., Orange Quince on Quince A rootstock. This combination showed a greater obstruction to the flow of water than did the other combinations. Possibly -123the Orange Quince wood offers more resistance to water flow than does pear wood. Table 2. Water Conductivity Tests Through the Bud-unlon. Combinations (6 trees of each) Mean total Mean cross water pas­ sectional area (sq. cm.) sed in 1 hour (c.c.) Mean c.c. of water pas­ sed per hour per sq.cm. 1-year plants Bartlett on Quince A 1.40 24.1 17.2 Bartlett on domestic pear 1.63 69.7 42.8 Clapp Favorite on Quince A 1.40 16.2 10.5 Clapp Favorite on domestic pear 2.01 83.5 41.8 Orange quince on Quince A 1.48 30.8 20.8 Old Home on Quince A 1.54 86.2 55.9 Beurre Hardy on Quince A 1.67 102.1 61.1 Kieffer on Quince A 1.33 17.4 13.1 Old Home on Quince A 2.54 108.5 44.7 Bartlett/Beurre Hardy/ Quince A# 1.67 84.4 50.5 Beurre Hardy on Quince A 1.67 98.5 58.9 Bartlett/Anjou/Quince A*- 1.15 46.1 40.7 2-year plants •;:-Bud-union on Quince A was used. b . Starch-accumulation tests. Bartlett, Clapp Favorite, and Kieffer on Quince A -124showed heavy deposits of starch above the union (Table 3). In Orange Quince on quince A, a deposit of starch occurred below the union. In Old Horne, Beurre Hardy, and Anjou on quince A there was no accumulation of starch either above or below the union. Similarly, In standard pear combina­ tions no accumulation of starch was observed. Table 3. Accumulation of Starch Above or Below the Bud-union. Combinations (6 trees of each.) No accumulation of starch Accumulation of starch Above union Below union 1-year plants Bartlett on Quince A X Bartlett on domestic pear X Clapp Favorite on domestic pear X Clapp Favorite on Quince A X Orange quince on Quince A X Old Home on Quince A X Beurre Hardy on Quince A X 2-year plants Kieffer on Quince A X Old Home on Quince A X Bartlett/Hardy/Quince A* X Hardy on Quince A X Bartlett/Anjou/Quince A-sc- X ■K-Bud-union on Quince A was used. -1254 . Bark and wood continuity. The bud-unions of different dwarf and standard pear combinations were examined, both externally and after slicing the union, to observe the continuity or otherwise of the bark and wood. All the combinations examined were then classified into these four groups: 1. Bark and wood continuous. 2. Bark continuous but wood discontinuous 5. Wood continuous but bark discontinuous. 4. Bark and wood discontinuous. In Old Home, Beurre Hardy, and Anjou on Quince A and all the standard pear combinations both the bark and the wood were continuous (Table 4). In Bartlett and Clapp Favorite on Quince A the bark was continuous but the wood was discontinuous. However, in some plants of these two combinations a discontinuity of both wood and bark was ob­ served but since most of the plants belonged to group 2 they were given a place there. Kieffer on quince A showed complete discontinuity of bark and wood. Some dead plants of Kieffer on quince A were collected from the Horticultural Experiment Station, Vineland, and their bud-unions were examined. A deep prominent brown streak was noted at the point of union. Similarly, in live trees of Bartlett, Clapp Favorite and Kieffer on Quince a the.brov/n streak was noted to be very prominent, (Figs. 15, 14, and 15)„ The external examination of the Fig. lo. Bark and wood continuity in different standard and dwarf pe-r combinations„ Fig. 14. Bark and wood continuity in different standard and dwarf pear combinations. 5 e c / i f i Q.A- J e c / r F t on P p a r C L a p r 0 ,, P fA R Fig. 13 Fig. 14 C L a p p Fig. 15. Fig. 16, Bark and wood continuity in different standard and dwarf pear combinations. Nature of fracture at the union in dif­ ferent standard and dwarf pear combina­ tions . O rA N G £ Q vtryet to, Q . A . OrANG£ Qutfvct un Q.A. H t£F F £R Q.A. H l £ £ F £ f t on Q.A. O t t Ho« it on Q. A . Otfi Ho*i£ on Q. A . Fig. 16 H a RVY HaRD)' QA on Q . A -126bud—unions revealed that in combinations showing this brown streak, the unions were rough and. irregular, where­ as in the other combinations they were smooth. Table 4. Continuity of Bark and hood, of the Bud-union. Combinations (6 trees of each) Bark and Bark con­ wood con­ tinuous wood dis­ tinuous continuous Bartlett on domestic pear X Clapp Favorite on domestic pear X Orange quince on Quince A X Old Home on Quince A X Hardy on Quince A X Anjou on Quince A X Bartlett on Quince A X Clapp Favorite on Quince A X Wood con­ Bark and wood dis­ tinuous , bark dis­ continuous continuous Kieffer on Quince A 5 • & trength-at-union X nature of fracture tests. The apparatus used to determine the strength of the budunions is shown in Fig. (17). In this figure, a is a fixed point, the distance from point a to point B is 4 inches, and the distance from point B to point C is 40 inches. Thus, Fig. 17* Diagram of breaking apparatus for- strengthat-unlon testa„ 'I A Fig. 17 -127there is a ten-fold leverage. the union firmly. V is the vise which holds Pressure is applied to point G. A push of one pound with the fruit pressure tester means a force of 10 pounds at the hud-union. It was expressed in pounds required to break one square centimetre of cross-sectional area at the bud-union. The bud-unions of Bartlett, Clapp Favorite, and Kieffer on Quince A were weaker than the bud-unions of Old Home, Beurre Hardy, and Anjou on Quince A (Table 5), In all stan­ dard pear combinations the bud-unions were considerably stronger than comparable dwarf pear combinations. Old Home, Hardy, and Anjou on Quince A had stronger unions, and they broke at the stock during these tests. The fractures at the union between Bartlett, Clapp Favorite, Kieffer and Quince A were smooth and occurred right at the prominent brown streak present at the budunions of these combinations. In the other combinations the nature of the fracture was a tearing one. In some com­ binations, as mentioned before, the bud-unions were so strong that they did not break during these tests. The fracture in such strong combinations probably would be tearing, (Figs. 16, 18, and 19). -128Tab le 5. Stre.ngth-at-unlon and Nature-of-Fracture Tests. Mean pounds Mean pounds Uature Mean diaCombinations required to to break pe r of (4 trees of each) meter at fractur< break sq. cm. of (cm.) union crosssectional area 1-year Bartlett on Quince A 2.07 83.8 26.9 Smooth Bartlett on domestic pear 1.86 207.0 82.8 Tearing Clapp Favorite on domestic pear 1.93 236 .0 84.3 Tearing Clapp Favorite on Quince A 2.16 95.0 2o.O Smooth Orange Quince on Quince A 1.71 208.0 90.4 Tearing Old Home on Quince A 2.12 Beurre Hardy on Quince a 1.98 ii Kieffer on Quince A 2.04 82.0 Old Home on Quince A 2.29 Bartlett/Hardy/ Quince Ac- 1.95 ii it it ii ii Hardy on Quince A 1.82 it it ii ii ti Bartlett/Anjou/ Quince Ac- ii ii it ii n Broken at stock. it ii Union strong. ii ii 2-year Broken at stock. 1.57 c-Bud-union on Quince a 26.1 was used. Smooth Union strong. Fig, 18. Nature of fracture at the union in different standard and dwarf pear combinations„ Fig. 19. Nature of fracture at the union in different standard and dwarf pear combinations, Pe/ nf ? Q.A. Cl/jr/j Pe a r CLapp B artlett on Pear . Ba r t l e t t on Q.A Fig, 19 -129b„ Premature autumn leaf coloration and early defoliation In different standard and dwarf pear combinations. Premature autumn leaf coloration and. early defoliation symptoms are associated with incompatibility; moreover, the standard pear combinations with such symptoms are known to bear under-size fruit. In view of this, the different standard and dwarf pear combinations showing such symptoms were studied and the results tabulated under this heading. a, Swelling at the union. In the dwarf Seckel that showed premature autumn leaf coloration the swelling was comparatively greater than in normal standard Seckel. In all Vineland selections that showed such symptoms the swelling at the bud-union was greater than the same selections showing no such symptoms, Beurre Hardy on Quince A showed premature autumn leaf colora­ tion and when it was compared with the same combination showing no such symptom it was noted that swelling in the former case was greater than in the latter. -130Table 6. Measurement of Swelling at the Union, Combinations. No. of Diameter of stock and Diameter trees scion 2 cm. both ways 0f Union from union, (cm.). (cm). Swelling at Union B minus A Scion Stock Average ____________________________________ ( A h _______[ B A _____________ Seckel on Quince A. (red-leaf) 1.69 2.14 1.92 2.72 .80 Seckel on do­ mestic pear (green-leaf) 5 1.57 1.79 1.68 2.28 .60 Beurre Hardy on Quince A. (Red-leaf) 1 2.25 1.80 2.01 2.95 .94 Beurre Hardy on Quince A (Green-leaf) 1 2.30 2.75 2.52 3.20 .68 Vineland Selec­ tion 29015 (Green-leaf, late defoliation 1 2.90 5.90 5.40 4.30 .90 Vineland Selec­ tion 29015.(Redleaf, early de­ foliation) . 1 2.65 o.90 5.28 4.40 1.12 Vineland Selec­ tion 29011 (green-leaf) 1 2.60 4.00 3.30 4.05 ,75 Vineland Selec­ tion 29011 (redleaf) 1 2.30 5.40 2.85 5.80 .95 Vineland Selection 29015 (green leaf) 1 2.40 3.00 2.70 5.30 .60 5.21 . .69 Vineland Selec­ tion 29013 (red-leaf 1 2.50 2.75 2.52 Predominant leaf color in (Sept.- Oct.)- -131Table 7. Water-Conductivity Tests Through the Bud-union. Combinations No. unions Seckel on Quince A (Red leaf) Mean cross­ sectional area (s q . cm.) Mean total water passed in 1 hour (c.c.) Mean c.c. of water passed per hour per sq. cm. 2.83 41.5 14.7 5 2.21 119.8 54.2 Beurre Hardy on Quince A (Red leaf) 1 2.00 122.0 38.5 Beurre Hardy on Quince A (Green leaf) 1 1.70 156.8 68.1 Vineland Selection 29015 (Green leaf, late defoliation) 1 3.40 289.3 31.4 Vineland Selection 29015 (Red leaf, early defoliation 1 3.3 247.4 29.1 Vineland Selection 29011 (Green leaf) 1 3.3 285.6 35.5 Vineland Selection 29011 (Red leaf) 1 2.8 142.8 23.4 Vineland Selection 29013 (Green leaf) 1 2.7 241.8 42.4 Vineland Selection 29013 (Red leaf) 1 2.5 148.8 30.3 Seckel on domestic pear (Green leaf) -132b . O b s t r u c t i o n to t h e passage of water and elaborated f o o d in the r e g i o n of the unlonT 1 „ W a t e r c o n d u c t i v i t y tests. The d w a r f Seckel coloration u n i o n as no rm al t h a t showed premature autumn leaf exhibited an obstruction to water passage at the c o m p a r e d to t h e standard Seckel combination with a c o l o r of f o l i a g e . In autumn all the V i n e l a n d selections that showed premature leaf co loration o r early defoliation and Beurre Hardy on Q u i n c e A struction to w a t e r p a s s a g e than did the same combinations without It whether above (red-leaf) t h e bud-unions offered greater ob­ s u c h symptoms. is concluded, (Table 7). therefore, s t a n d a r d or d w a r f , symptoms, that all combinations, showing either or both of the o b s t r u c t e d the passage of water at the bud- union. 2. S t a r c h - a c c u m u l a t i o n tests. I n S e c k e l and B e u r r e Hardy on Quince A and in the Vineland selections a deposit union. of abnormal color or early defoliation, o r a c c u m u l a t i o n of starch was found above the bud- T h i s was not t h e d e f o l i a t i o n was normal. These rized b y tion s h o w results case when the leaf color or time of (Table 8) „ i n d i c a t e that all combinations characte­ e a r l y d e f o l i a t i o n and premature autumn leaf colora­ so me i n t e r f e r e n c e to water passage and accumulate starch a b o v e the union. -135) Table 8. Accumulation of Starch Above or Below the Bud-union. Combinations ho. plants No accurnulation of starch Seckel on Quince (Red leaf) a 5 Seckel on domestic pear (Green leaf) 5 X Beurre Hardy on Quince A (Green leaf) 1 X X Beurre Hardy on Quince A (Red leaf) 1 Vineland Selection 29015 (Green leaf, late defoliation) 1 Vineland Selection 29015 (Red leaf, early defoliation) 1 Vineland Selection 29011 (Green leaf) 1 Vineland Selection 29011 (Red leaf) 1 Vineland Selection 29013 (Green leaf) 1 Vineland Selection 29013 (Red leaf) 1 accumulation of starch Above union Below union X X X X X X X c. Bark and wood csontinuity. The bud-unions of all the dwarf or standard pear combinations were examined both externally and after slicing the union to observe the continuity or otherwise of the bark and. wood. All the combinations were then classified -134Into fo\ir groups as mentioned, before. Seckel on Quince a the bark was continuous. showed discontinuity of wood but In the standard Seckel pear both the wood and the bark were continuous. In the former com­ binations, however, the brown streak was quite prominent, (Fig. 13). In most of the Vineland selections the combinations that showed premature autumn leaf coloration exhibited some discontinuity in bark, but the wood invariably was continuous. The unions of such combinations were somewhat rough and irregular. In the selections which lacked the above symptoms, both the bark and the wood were continuous and the union, in turn, was smooth. d. Strength-at-union and nature of fracture tests. The union of Seckel on Quince A was weak. The union was broken right at the brown streak and the nature of the fracture was smooth. The bud-unions of Vineland selections were twisted at 300 pounds pull and were considered fairly strong. Table 9. Strength-at-union and Nature of Fracture at Budunion. Combinations No. of unions Seckel on (Quince A (Red leaf) Mean dia- Mean total meter at pounds re­ union (cm) quired to break Mean Nature pounds of to break fracture per sq. cm. of cross-sec­ tional area 2.72 200.0 54.4 Smooth 2.28 254.0 56.4 Tearing Beurre Hardy on Quince A (Red leaf) 2.9 250.0 55.8 Smooth Beurre Hardy on Quince A (Green leaf) 2.25 290.0 72.5 Tearing Seckel on domestic pear (Green leaf) 5 DISCUSSION From general observations made on the growth behavior of different dwarf pear combinations the incompatibility in dwarf pears is considered to be of these three types: 1. The bud unites with the stock and growth starts in a normal manner. After a few weeks the growth declines and some of the trees soon die. Example: Bose on Quince A. 2. The bud unites with the stock and normal growth starts but after one or two years the plants die. Example: Kieffer on Quince A. 3. The bud unites with the stock, growth starts nor­ mally, but after some time in the nursery or later in the orchard the trees break clearly at the point of union. Example: Bartlett, Clapp Favorite, and Seckel on Quince A. The literature discloses that the strength of union, smooth fracture at the union, or accumulation of parenchyma­ tous tissue at the union, are the only reliable indications of incompatibility. Therefore, tests were made to determine the influence of these factors; however, other tests, such as to determine the obstruction to the flow of water through the union or deposit of starch above the union, were also performed as supporting evidence. Bradford and Sitton (1929), and Amos et al (1936), observed that a swelling at the union was not necessarily an indication of incompatibility. In the present studies it was found that swelling .in the dwarf pear combinations -137was greater than in the standard ones. In the dwarf pear combinations, Bartlett, Clapp Favorite, Kieffer, and Seckel showed significantly greater swelling at the union than did the other combinations. In the dwarf and standard pear combinations that showed premature autumn leaf coloration or early defoliation the swelling at the union was greater than in the same combinations without those symptoms. Chang (1938) observed that in all incompatible com­ binations there was some form of obstruction at the union. Such combinations exhibited a higher resistance to the flow of water and dyes through the union. These combina­ tions also showed a deposit of starch above the union. Sablon (1903) discovered that the scion of a dwarf pear tree possessed a higher carbohydrate content than that of a standard pear tree. Iiostoff (1928) contended that although some of the scion products were changed into ac­ ceptable form for the stock, other products were not so changed, were unacceptable, and accumulated above the union. Haas and Halrna (1929) pointed out that accumula­ tion of starch above the union could be an effect rather than a cause, because the scion overgrowths accompanying these accumulations could be regarded as having produced an effect comparable to girdling. In the present studies it was observed that the dwarf Bartlett, Clapp Favorite, and deckel pear combina- -158tions showed a much higher resistance to the flow of water through the union than did the standard and other dwarf pear combinations. In all these four dwarf pear combinations there was observed an accumulation of starch above the union. This was not the case in the standard or the rest of the dwarf pear combinations ex­ cept in one case. Orange Quince on Quince A showed a deposit of starch below the union. Chang (1958) observed that in incompatible combina­ tion the bark or wood, or both of these, were discontin­ uous. In compatible combinations, however, both the bark and wood were continuous. In these studies it was found that in standard and dwarf Old Home, Hardy, and in Anjou combinations, both the bark and wood were continuous. In dwarf Bartlett, Clapp Favorite and Seckel the bark was continuous but the wood was discontinuous. A few plants of these combinations also exhibited a discontinuity of both bark and wood. Kieffer on Quince discontinuity of bark and wood. m. showed a complete It is the reason why such Kieffer trees die after one or two years in the nursery. In the dwarf Bartlett, Clapp Favorite, Kieffer, and Seckel pear combinations a brown streak was observed at the point of union. This brown streak, as described by Chang (1958), was an accumulation of dead parenchmatous tissue which could be observed in incompatible combina­ tions up to 12 weeks after budding. The unions of all -169these combinations were found to be rough, whereas in nor­ mal combinations they were quite smooth. Proebsting (1928) noted that if there was any great difference in regeneration capacity of stock and scion, there might be variation in the period of cell differentiation, and meristematic cells pro­ duced by stock might not find similar scion cells and ab­ normal tissue formation at the union. were said to be incompatible. Such combinations So there was good reason to believe that any combination showing such an accumulation at the union should be discarded from the nursery as incom­ patible . It is to the growers advantage that suspicious pear combinations be examined in the nursery. The union should be sliced with a knife and the brown streak representing the dead parenchymatous tissue observed macroscopically. Chang (1958) observed that in all incompatible com­ binations the unions were weak. Argles (1957) believed that this was a sure indication of inherent incompatibility. In the present studies, weaker unions occurred in the dwarf Bartlett, Clapp Favorite, Kieffer and Seckel pear combina­ tions than in the dwarf Beurre Hardy, Old Home, and Anjou pear combinations. In the former four combinations, Seckel formed the strongest union and it also showed good growth in its second year in the nursery, and so it was assumed that dwarf Seckel was a case of delayed incompatibility -140and good crops could be expected for a period of time. However, the other three combinations showed signs of inherited incompatibility and good performance cannot be attained from them. Overholser et al (1944) held that Clapp Favorite formed a strong union with Quince. Waugh (1912) mentioned that in Europe Clapp Favorite and also Seckel were directly budded or grafted onto quince. (Jpshall (1940), however, observed that some plants of Clapp Favorite were subjected to breakage at the union <;hile in the nursery. The present inves­ tigations confirmed his findings; it was concluded that Clapp Favorite formed as weak a union with quince A as did Bartlett. The unions of standard pear combinations were con­ siderably stronger than the dwarf pear combinations of the same variety. Some standard combinations were so strong that the stock was twisted and the union did not break. It was further observed that the dwarf Bartlett, Clapp Favorite, Kieffer and Seckel pear combinations exhibited a smooth fracture at the point of union, all such combinations broke right at the brown streak of the union. In the other combinations, whether dwarf or standard, the fracture was tearing. Chang (1958) gave premature autumn leaf coloration and early defoliation as two symptoms of incompatibility. -141All the incompatible combinations showed red foliage because of the low moisture content and low nutrient supply from the soil due to obstruction at the union. In the present investigations all the dwarf pear com­ binations with these two symptoms invariably showed all the manifestations of incompatibility. For example: Beurre Hardy formed a good union with quince A but any plant of this variety with the above symptoms on examina­ tion showed all the signs of an incompatible combination. Even in the standard pear combinations which showed the above symptoms, an accumulation of starch above the union, obstruction to the flow of water through the union, and swelling at the union, were observed. However, plants of the same combinations but without these symptoms showed absolutely no such signs of incompatibility. Scion wood of the dwarf Bartlett, Clapp Favorite, Kieffer and Seckel pear combinations was purplish, whereas in the dwarf Old Home, Beurre Hardy, Anjou, and other standard combinations without these two symptoms, it was greenish. It would seem that the dwarf Bartlett, Clapp Favorite, Seckel, and Kieffer pear combinations were incompatible and all these varieties must be double worked with some good interstock. Beurre Hardy is a good interstock but in localities where the danger of pear blight is great, Old Home can be employed. But, if any of the above -142incompatible combinations are growing in orchard their unions should be "bridged over". Garner (1944) thinks that by inserting one end of a long scion stick just below the union, and the other end above the union, a direct connection between stock and scion could be es­ tablished and thus the incompatibility could be "bridged over". -14bSHmMARY AND COHCLUSIOHS The following pear varieties were found to pro­ duce poor unions when worked directly on quince A: Bartlett, Kieffer, Clapp Favorite, and Seckel. There­ fore, for orchard purposes, these varieties should he double-worked with Beurre Hardy or Old Home as the intermediate stocks. The following varieties make strong unions with Quince a : Hardy, Old Home, and Anj ou. All the stock-scion combinations, whether dwarf or standard, which showed premature autumn leaf coloration or early defoliation, were found uncongenial. PART IV RELATIONSHIP BETWEEN THE GR a FT-UNION. AUTUMNAL LEAF COLORS, AND GROVvTH AND FRUITING OF STANDARD KIEFFER PEa R TREES -144INTRODUCTION During the past twenty years the Kieffer pear has assumed considerable importance in Eastern United States and Canada, where it is mainly used for commercial canning purposes. In most of the Kieffer pear orchards a propor­ tion of the trees show premature autumnal leaf coloration (September and October) poor quality. and bear under-sized fruits of Observations in Ontario nurseries show that from 5 to 10 percent of the Kieffer trees exhibit a similar early autumn leaf coloration. The trees which have shown early autumn leaf coloration in nursery and orchard are usually dwarfish and show higher than normal mortality in the orchard. The fruit is, sometimes, so small that its sale is almost impossible since the canners do not accept fruit below a specified caliper. In this case the grower suffers a heavy loss. These abnormal trees occur at random throughout an orchard. Where an entire orchard, or one or more portions of it, is bearing small fruit the trouble is probably due to poor physical condition of the soil or to unfavorable nutrient level. The observations and experiments in this paper are presented as possible factors which bring about small-size fruit, and as aids to avoidance and correction. F i g . j 20. Variation in Kieffer fruit size in relation to foliage color. Upper -- large pears from green-leaved trees; lower -- small pears from red-leaved trees. -145EXPERIMENTAL MATERIALS M D METHODS The experimental material employed in these investi­ gations was obtained from several nurseries and orchards of Michigan and Ontario. The methods employed in recording the data are given below. Physical Measurements: Tree size - The cross-sectional area of the trunk com­ puted from the girth measurement of the tree, was used as an Index of tree size. 2. Fruit size - Fruit size was determined by weighing a number of fruits and recording the average, o. Study of the graft-union - The methods employed for determining swelling at the union, obstruction to passage of water and starch at the union, and strength-at-union have already been described in part III of this write-up. Chemical Measurements: Total acidity - To 100 grams of fruit 100 ml. of water was added. It was thoroughly macerated in a Waring Blendor. 10 ml. of this extract was titrated against N/10 sodium hydroxide using phenolphthalein as indicator. Ml. of N/10 sodium hydroxide used for 10 ml. of the extract was con­ sidered as measure of acidity. -14b2. Total solids - The refractometer was used to measure the total solids in the pear juice. 3, .ascorbic acid. - ascorbic acid content was measured by the method advocated by Lucas (1944) „ 4 0 Pear-tissue analysis - The material was air dried and ground. It was analysed for nitrogen, potassium, calcium, protein, phosphorus, and total ash by Official Methods, (1940). 5. Soil analysis - Spurway's methods were employed for determining the nutritional status of the soil. - 147 - RE S'JLTS . A. Orchard Trees. Relationship between leaf coloration, tree size, fruit "size and quality"! In general, there is a correlation between autumnal leaf coloration, size of tree, fruit size, and quality (Tables la. and IB) . Green leaves are associated with large trees, large fruits, good quality; whereas red leaves are associated with small trees, small fruits, poor quality. In comparison to the "reds", the "greens" bear fruits with an appreciably higher content of total solids and ascorbic acid. Total acidity, however, ap­ pears to have no relationship to the colour of the foliage, (Table 1). It was observed that fruits from the red-leaved trees were more gritty, (i. e., contained more stone cells) were more astringent, and had a thicker hypodermal layer than fruits from the green-leaved trees. -1*8Table 1A. Tree Relationship between -autumnal Leaf Coloration. Tree Size, Fruit Size and Quality (Vineland Urchards). Foliage Tree size Colour, X-sec.area Oc t . 5 cm.above 1948 union, (sq.cm.) Total Fruit Size. solids Wt. per fruit 1° (gra.) Total acid 177.3 135.0 7.2 4.5 7.2 87.2 84.5 6.4 5.5 5.0 Ascorbiacid.mg, 100 gm. fruit Troup Orchard. R1 T19 green R1 T18 red R2 T14 green 207.8 116 .0 7.1 2.7 5.7 R2 T13 red 114.3 63.4 6.2 5.5 4.9 R5 T17 green 193.4 104.5 8.2 4.7 8.6 R5 T16 red 96.9 57.4 7.7 4.1 6.6 Culp Orchard. R3 T17 green 221.9 94.2 8.7 4.1 5.4 R3 T16 red 122.3 48.6 o.O 2.1 1.0 R- row T- tree no. -149Table I B. Relationship between .autumnal Leaf Coloration, Fruit'Size, and Quality. (Michigan Orchards) Orchard N o . of Foliage Fruit Size Color (w t ./fruit) No. trees in sam­- Oct. gm. ple . I II III IV. > Total Total Solids Acid­ ity ascorbic acid mg/lOOgm fruit 3 Green S o .2 10.8 o •u 3.8 3 Red 77.8 9.4 4.0 5.2 2 Green 63.6 10.4 2.4 3.7 2 Red 51.6 8*6 2.1 2.4 1 Green loo.3 10.4 2.4 6.6 1 Red 62.7 8.4 1.9 5.8 2 Green 85.7 11.6 2.3 3 08 2 Red 61.6 9.2 2.0 3.7 Chemical analysis of leaves. (i) Ontario orchards: In both Ontario orchards the nitrogen, protein, and calcium contents were appreciably higher in green leaves than in red ones. In the Troup orchard, the green leaves also contained more potassium, phosphorus, and total ash than the red leaves. However, in the Culp orchard the case was quite the reverse (Table 2A), -150Table 2A. Chemical Analysis of Pear Leaves. orchards). (Vineland Percentages expressed on dry weight basis. Foliage colour Nitrogen Protein Potas­ Phosph­ Calcium Total sium orus . Oct.1948 ash Tree Troup Orchard. R1 T19 green 1.52 9.52 1.01 0.11 1.49 5.48 HI T18 red 1.31 8.19 0.66 0.09 1.53 4.35 R2 T14 green 1.50 9.38 0.56 0.12 1.53 5.01 h2 T13 red 1.15 7.19 0.20 0.08 1.39 4,64 R5 T17 green 1.64 10.25 0.87 0.10 1.67 6.39 R5 T16 red 1.33 8 031 0.81 0.09 1.35 5. 50 Culo Orchard. R3 T17 green 1.73 10.81 0.88 0.09 2.19 5.18 R3 T16 red 1.43 8.94 1.07 0.11 1.50 6.71 (ii) Michigan Orchards. The green leaves contained appreciably higher percen­ tage of nitrogen, protein, and calcium than the red leaves. The percentage total ash. had a similar trend except that in orchard 4 the red leaves had a higher ash content in contrast to the green leaves, potassium and phosphorus seems to bear no relationship to the color of the foliage, (Table 2.B.) Apparently, the deficiency of nitrogen, protein, and calcium seems to encourage anthocyanin formation in the pear leaves, which accounts for the early autumn leaf coloration. -151Table 2 B. Orchard Ho. I II III IV Chemical Analysis of Pear Leaves (Michigan Orchards Y~» Percentage expressed on dry wt . basis No. trees Foliage in Color Nitro­ Pro­ Pot­ Phoso . Cal­ Total October gen s ample teins ash . cium Ash 5 Green 1.14 7.15 .88 .08 1 .55 7.55 5 Red 1.11 6.94 1.07 .09 .89 5.25 2 Green .98 6.15 .98 .10 1.59 6.75 2 Red .65 4.06 .94 .06 1.52 6.27 1 Green 1.26 7.88 .78 .08 1.55 6.07 1 Red .82 5.15 .72 .08 1.25 5.66 2 Green 1.54 9.65 .44 .12 1.45 5.48 2 Red 1.02 6 .38 .76 .10 1.30 5.92 Soil analysis. There seems to be no difference in the nutrition status of the soils upon which the two types of trees stand. It is obvious that the premature autumn leaf coloration is not due to lack of soil fertility in the cases under study (Table 5). i Table 3• Determination of the Soil Nutrient Status under paired trees (Vineland Orchards) T r e e N o . E o l i a g e & A c t i v e __________________ C o l o r p H P h o s . K C a p o u n d s / a c r e T r o u p P h o s . ____________ K p . p . m C a p o u n d s / a c r e N O -g p . p . m . O r c h a r d . R 1 T 1 9 ( g r e e n ) 5 . 4 5 1 5 0 4 0 3 4 3 9 6 1 0 0 6 R 1 T 1 8 ( r e d ) 5 . 1 0 1 6 9 5 0 5 3 3 9 2 1 7 5 6 R 2 T 1 4 ( g r e e n ) 5 . 2 0 4 4 1 5 0 2 7 6 9 0 1 5 0 1 0 R 2 T 1 3 ( r e d ) 5 . 4 0 4 3 2 4 0 2 8 7 1 2 2 1 5 0 8 R 5 T 1 7 ( g r e e n ) 5 . 4 3 2 6 9 7 5 2 5 6 6 9 2 0 0 6 R 5 T ( r e d ) 5 . 5 5 4 7 8 5 0 2 5 6 1 2 2 1 5 0 5 2 5 1 3 6 3 O hf\ i— 1 1 c\i ir\ H 1 _________________________ R e s e r v e __________________ N O ^ 8 5 2 2 9 6 1 7 5 8 C u l p 16 O r c h a r d ’ . . R 3 T 1 7 ( g r e e n ) 5 . 8 5 5 1 7 6 7 5 R 3 T 1 6 ( r e d ) 5 . 9 8 1 0 1 8 2 7 5 o -15bB. Nursery Trees. Behaviour of red-leaved nursery trees after planting In the orchard. The standard Kieffer pear tre^s with green foliage are usually larger in size in the nursery row than those with red foliage (Table 4 a .). It is noticed that this differ­ ence often widens year by year wh-n these trees are trans­ planted to the orchard (Tables 4B and 4C). The size dif­ ference in the nursery may not seem to be very striking but the presence of these dwarf trees in the orchard may have an appreciaole bearing on the total yield. There is a suggestion, however, that not all of the trees which show red leaves in the nursery develop into dwarf trees in the orchard. Tree b in Table 4B and Tree 4 in Table 4 G illustrate this point. It may be significant that these were the largest of the red-leaved trees in each lot at planting time. Trees 2 and 4 of Table 4B, on French pear seedlings, originally red-leaved in the nursery are now very dwarf trees but seldom show early leaf coloration or small fruit size. In other words, uncongeniality with the rootstock is now being demonstrated in a different way. In a standard commercial orchard, however, these abnorxnal trees are still quite undesirable. -104Table 4A. Number of trees measured. 70 8 Relationship between Foliage Colour and Size of one-year Kieffer Pear Trees in the Nursery R o w . (Kieffer on Domestic Pear Seedlings), Oct. 1948, Vineland Station. Foliage colour mean crosssectional area of trunk. 2 cm. above union. (s q . cm.) green 1.88 red 1.58 Table 4B. Relationship between autumnal Leaf Coloration, Size of Two-year Nursery Tree and Orchard Tree. (Kieffer on French pear seedlings), Planted in fall, 19 o9 (Vineland Station). Tree NO . Foliage Colour in nursery row, Fall 1939 Cross-aectional Area of Trunk (sq.cm.) Nursery Orchard 19o9 1940 1944 1948 1948 1 green 2.5 5.8 15.9 20.9 28.7 2 red 1.3 1.3 2.4 4.2 8.1 3 green 2.0 2.5 17.0 2 o .7 57.8 4 red 1.8 2.5 4.7 7.0 12.2 5 green 2.5 o.l 20.8 55.1 47 .4 6 red 2.3 2.8 15.8 51.2 45.8 -154Table 4A. Number of trees measured. 70 8 Relationship between Foliage Colour and Size of one-year Kieffer Pear Trees in the Nursery Row. (Kieffer on Domestic Pear Seedlings), Oct. 1948, Vineland Station. Foliage colour mean crosssectional area of trunk. 2 cm. above union. (s q . cm.) green 1 o86 red 1.38 Table 4B. Relationship between Autumnal Leaf Coloration, Size of Two-year Nursery Tree and Orchard Tree. (Kieffer on French Pear seedlings), Planted in fall, 1959 (Vineland Station). Tree No. Foliage Colour in nursery row, Fall 1939 Cross-sectional Area of Trunk (s q.cm.) Orchard Nursery 19o9 1940 1944 1946 1948 1 green 2.5 5.8 15.9 20.9 28.7 2 red 1.3 1.3 2.4 4.2 8.1 3 green 2.0 2 .5 17.0 2o .7 57.8 4 red 1.8 8.5 4.7 7.0 12.2 5 green 2.6 o.l 20.6 35.1 47 .4 6 red 2.3 2.8 15.6 51.2 45.8 -155Table 4C. Tree No. Relationship between .autumnal Leaf Coloration, size of Three-year Nursery Tree and. Orchard Tree (Kieffer on Kieffer Seedlings) Planted i n Fall, 1945, Vineland Station. Foliage Colour in Nursery 1941-1943 Cross- sectional area of trunk (sq. cm.) Nursery 1943 1944 Orchard 1945 1946 1947 1948 1 green 1.3 3.1 12.4 18.4 30.0 58.9 2 red 0.8 1.9 7.5 9.6 15.4 18.6 5 green 5.3 9.1 8.6 17.4 21.4 24.4 4 red 1.3 2.5 5.0 14.1 25.2 39.2 5 red 0.8 1.5 4.6 9.6 17.0 23.5 Chemical analysis of tops (including leave s) . The woody tops and leaves of the green-leaved Kieffer trees bad an appreciable higher content of nitrogen, pro­ tein, and calcium than those of the red-leaved trees. This is the same relationship as found in orchard trees. Regarding potassium, the woody tops of the red-leaved trees had a higher content than the green-leaved, trees but no such trend was found in the leaves. The woody tops of the green-leaved trees had less ash and phosphorus than the tops of red-leaved Kieffer trees, but in the leaves, phos­ phorus and ash were higher in the green leaves than in the red ones. It is interesting that the leaves had a-much higher percentage of total ash than the tops in both types of trees (Table 5). -IbdTable 5. Chemical Analysis of Woody Tops and Leaves of Kieffer Pear Trees in the jflursery Row. Wo. of Foliage colour trees Oct.1948 Portion Witro - Pro­ Potas­ Phos­ Cal­ of phor­ cium gen tree tein sium us Total Ash Lot 1. green 2 red 2 Tops 1.52 9.52 0.72 0.08 0. o7 2.04 Leaves 1.64 10.25 1.85 0.15 1.48 7 .47 Tops 1.15 7.19 0.79 0.11 0.55 o Leaves 1.51 8.19 1.55 0.10 0.70 4.80 Tops 1.50 9.58 0.47 0.08 0.52 2.17 Leaves 1.75 10.81 1.05 0.14 1.55 7.15 Tops 1.55 8.51 0.80 0.11 0.57 5 ,05 Leaves 1.45 8.94 l.o9 0.12 0.76 5,24 .05 Lot 2. 2 2 green red Swelling at the graft-union. The Kieffer trees with red-foliage had greater swel­ ling at the union than those with normal green foliage (Table 5). In red-leaved trees the graft-unions were rough in outer appearance while in green-leaved trees they were smooth and symmetrical. Bradford and Sitton (1929) and Amos et al (1956) found that there was no direct correlation be­ tween degree of swelling at the union and congeniality. Other writers on stock-scion compatibility, however, report an association^ between swelling at the union and lack of congeniality, angles (19o7) . Proebsting (1928) noted inter- A -157ference with translocation across certain graft-unions and found it related to swelling at the union,, In the present studies a similar relationship has been found. Table 6. Measurement of Swelling at the Graft-Union between Kieffer and Domestic Pear Seedlings, Combination Wo. of Diameters of stock trees and scion 2 cm. both ways from union, (cm). Scion Diameter of Union. (B) Swelling at union B minus A Stock Aver­ age , (A) 1.10 1.50 1.30 1.72 ,42 1.25 1.07 1.40 2.15 67 Kieffer (green leaf) 1.63 1.98 1.81 2.26 ,45 Kieffer (red leaf) 1.44 1.78 1.61 2.18 57 .95 1.20 1.08 1.70 ,62 1.00 1.37 1.19 1.95 ,7o Lot 1 . (Pall, 194d) Two-year tops Kieffer (green leaf) Kieffer (red leaf) 3 Lot 2. (Fall, 1947) Two-year tops Lot 5. (Fall, 1947) One-year tops Kieffer (green leaf) Kieffer (red. leaf) -158Obstruction to the passage of water and carbohydrates In the region of the union. 1. Water conductivity test. Less water passed through uhe red-leaved Kieffer graft unions than through the green-leaved graft-unions (Table 7). Evidently, there is more resistance to the passage of water at the point of union in the red-leaved trees. Since most of the mineral elements and other food materials are transported from root to scion as solutes, a deficiency of water to the top would also affect them. Table 7. Water-Conductivity Tests Through the Graft-Union. Combinations No. of Mean crossMean total Water pasgrafts sectional area water pas- sed per (sq.cm.) sed in one hour per hour. sq.cm. (cc.) x-sec. _________________________________________________________ (cc.) Lot 1 (Fall, 1946) Two-year tops. Kieffer (green leaf) Kieffer (red leaf) 5 3 1 033 1.69 56.5 35.9 42.5 21.5 4 4 2.57 2.03 125.1 79.8 48.7 39.3 1 1 0.95 1.00 o5.2 28.7 o7.0 28.7 Lot 2 . (Fall, 1947) Two-year tops Kieffer (green leaf) Kieffer (red leaf) Lot 3 . (Fall, 1947) One-year tops Kieffer (green leaf) Kieffer (red leaf) -1592. St arch-accumulation tests. Red-leaved Kieffer trees (nursery) showed a deposit of starch above the union while green-leaved trees showed no such deposit (Table 8). This indicates that in the case of red-leaved trees there is some hindrance at the union to the translocation of elaborated foods from the scion to the stock, as a result, there is an accumula­ tion of products of photosynthesis(mostly carbohydrates) above the union. This condition is known to favour an- thocyanin formation, Meyer and Anderson (19b9)0 The partial check to the passage of elaborated foods from scion to stock "starves" the stock which in turn dwarfs the scion. Table 8. This effect is, therefore, reciprocal. A ccumulation of starch above the Graft-Union K ieffer on Domestic Pear Seedlings). No. of plants l\!o accumulation accumulation of of starch. .starch above the Graft-Union. Lot 1. (Fall,19461 Two-year tops Kieffer (green leaf) 3 3 Kieffer (red leaf) X X Lot 2. (Pall, 1947) Two-year tops. 4 4 X Kieffer (green leaf) 1 1 Kieffer (red leaf) X Kieffer (green) Kieffer (red leaf) X Lot 3. (Pall, 1947) One-year tops. X ~loU~ strength-at-union and nature of fracture at the graft-union. The graft-union of nursery trees having red foliage was weaker than that of trees with green foliage. The nature of the fracture at the union was moderate in the for­ mer case, and tearing in the l a t e r (Table 9). Incompatible graft-unions are known to be weaker than compatible unions, Chang 1(3-5 . It is very important that trees in commercial orchards have strong unions. If graft- unions are weak, heavy windstorms may cause breakage at this point. Table 9, Strength-at-union and Nature of Fracture at the Graft-Union. (Two-year Kieffer on Domestic Fear). No. of unions Diameter at union (cm.) Total pressure to Nature req'd to break per of break sq.cm. x-sec.fracture (lh.) area. _________________ L_____________________ dh.)__________ Kieffer (green leaf 5 1.72 16b.0 70.8 Tearing Kieffer (red leaf) b 2.13 137.0 36.5 'moderate -161DISCUSSION. These studies indicate that the relationship between premature autumnal leaf coloration and fruit size is due to nutritional difficulties brought about by a poor graftunion. The graft-unions of red-leaved Kieffer trees show a partial check to the passage of water, and elaborated foods at the point of union. In contrast to the green­ leaved Kieffer graft-unions they are weaker and show greater swelling. In a successful graft, the water, mineral nutrients, and elaborated foods are freely ex­ changed between stock and scion. However, in uncongenial grafts there is a partial check to the passage of these materials in the region of the union, which adversely affects the growth, cropping, and longevity of the trees. Experiments at Vineland Station show that these "off type" pears are not due to differences in strain, Dickson (1945). Poor soil may result in early leaf coloration and under-size fruits but in tne present investigations the soil analysis figures did not furnish an explanation of the differences in tree behaviour found in the abnormal trees. The deficj.ency of nitrogen, protein, and calcium en­ couraged anthocyanin formation in the leaves. Blank (194-10 reports that a decrease in nitrogen increased anthocyanin formation in barley kernels. Meyer and Anderson (1959) state that a deficiency of nitrogen favours anthocyanin formation. The present investigations agree with the findings of these authors. It is interesting to note that calcium has a close relation to nitrogen in pear leaves, as with nitrogen, a deficiency of calcium seems to encourage anthocyanin formation. Blank (1947) says that Lundegardh found calcium deficiency in the tomato to he the cause of an increase in formation of anthocy­ anin pigment. Two conditions tend to cause an accumulation of car­ bohydrates in the tops of the abnormal trees - (1) ob­ struction to downward flow at the union and (2) resistance to the upward flow of nitrogen at the union, which may limit the synthesis of amino acids from nitrogen and car­ bohydrates. On the other hand, the early colouration of the foliage undoubtedly reduces the total carbohydrate supply in the tree through a reduction in photosynthesis. Orchard experience suggests that Kieffer is not al­ ways congenial on French or Domestic pear (Pyrus communis, seedling rootstocks. It is interesting to note, as well, that Kieffer may not always do well on Kieffer seedlings . (Pyrus communis X P. pyrifolia) (Table 5 C). rootstock for Kieffer would be desirable. A better Unless such a rootstock becomes available it may be wise to grow Kieffer on its own roots. Tukey (1928) records the existence of -loosuch an orchard in the Hudson Valley, New York. The trees in this orchard are very healthy, productive, and uniform. The chief possibility of getting Kieffer on its ovm roots is from cuttings. Considering the popularity of Kieffer pears with the canners, the growers should think seriously about getting own-rooted Kieffer trees for future plantations. unfortunately, propagation of Kieffer from cuttings is not a commercial possibility in the north­ eastern States or in Ontario. Growers will probably have to get own-rooted Kieffer trees from Georgia or adjoining states where Kieffer can be p.opagated readily from cuttings. At present, the best plan appears to be the elimination of all small red-leaved Kieffer trees from the nursery. Very dwarf Kieffer trees in the orchard should also be re­ placed. —10 “ SUMMARY a ND CONCLUSIONS Premature autumnal coloration of the leaves of the Kieffer pear, s m a l l size and poor quality of fruit are due to nutritional difficulties brought about by a poor graft-union. A low level of nitrogen and calcium seems to favour anthocyanin formation in Kieffer leaves, and. is correlated with poor unions. ii better rootstock for Kieffer is desirable. Un­ less such a rootstock becomes available it may be wise to grow Kieffer on its own roots. At present, the best plan appears to be the elimination of all small red­ leaved Kieffer trees from the nursery. Very dwarfish Kieffer trees in the orchard should also be replaced. 4 % -105BIBLIOGRAPHY Alderman, W. H. Cited by Argles (5). July 1936. Correspondence. Allen, P. W. The texture and ripening of Bartlett pears as influenced by the rootstocks, proc. Amer. Soc. Hort. Sci. 26:325-27. 1929. Amos, J., and others. 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No. 6. 1925. ___________ , and McCallum, R. D. Compatible and non-com­ patible graft unions, proc. A m e r . Soc. Hort. Sci. 24*137-58. 1928. -170Herse, F. Reitrage zur Kenntnis der histologischen Erscheinungen bei der Veredlung der Obstbaume. Landw Jahrb. o7;71-136. 1908. Hoopes, J. Influence of the stock on the scion and vice versa. Horticulture, 28:355. 1873. Hofmann, F. M. Res. Reciprocal effects from grafting. 34:675-6. 1927. Howard, W. L. Rootstocks studies in Europe. Soc. Hort. Sci. 18:250-55. 1922. J. Agr. Proc. Amer. ____________ . Discussions of relative merits of different rootstocks. Calif. Mo. Bui. Corn. Hort. 7:20-22. 1918. ____________ . Progress report on rootstock experiment. Calif. Mo. Bull. Com. Hort. 8: 13-14. 1919. . The value of different roots as stocks. Better Fruit. 14(10): 19-20. 1920. Vegetative propagation of deciduous fruits. Proc. Amer. Soc. Hort. Sci. 28:465-69. 1931. Howe, G. H. Pear growing in Hew York. H.Y. State .w.gr0 Exp. 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Lehrbuchs des Obstbaus auf physiologischer Grundlage. Julius Springer, Berlin, 1951. Korshunov, K. N. Mountain ash as a rootstock for pears. (Russian) Sady-i-ogordy. No. 6:25-6. 1941. Kostoff, D. Studies on callus tissue. 565-76. 1928.. Amer. J. Bot. 15: Acquired immunity in plants. 37-77. 1929« Genetics. 14: . Studies in the acquired immunity in plants induced by grafting. Z. Immun-Forsch. 74:55946. 1951. Lantz, H. L. Pear breeding. An inheritance study of Pyrus communis X P. ussuriensis hybrid fruits. Proc. Amer. Soc. Hort. Sci. 26:13-19. 1929. Laurant, G. Variation de la composition et de la resis­ tance comparee de piantes greffes et non greffes. Trav. Sci. Univ. Rennes. 5:57-65. 1906. ________ Sur les variation de composition de certaines plantes alimentaires apres greffage. Trav. Sci. Sci. Univ. Rennes. 5;141-7. 1906. Lee, S. H. A taxonomic survey of the Oriental pears. Amer. Soc. Hort. Sci. 51:152-56. 1948. Proc. Lincoln, F. B. Propagation of apple and quince by layering. ■Maryland Agr. Exp. Sta. Bull. A28:53-56. 1945. Lucas, E. H. Determining ascorbic acid in large numbers of plant samples. Ind. and Eng. Ghem. 16:649-652. 1944. Lucas, I. B. Dwarf fruit trees, Inc., N. Y. 1946. a . T. De La Mare Company, Magness, J. K. Origin and improvement of pear. Year Book, pp. 615-50. 1957. S.S.D.A. -172- McClintock, J. A. Further evidence of uncongeniality in disease resistant stocks. Proc. Amer. Soc. Hort. Sci. 2 2 : 2 6 1 - 6 2 . 1926. . Some problems in the use of superior rootstocks for fruit trees. Proc. Amer. Soc. Hort. Sci. 33:529-51. 1956. — ~ ________________. The possibility of producing fruit tree stocks in the Southern United States. Proc. Amer. Soc. Hort. Sci. 24:152-54. 1927. _________________ . Importance of Leaf spot in the selection of pear varieties used as stocks for budding. Proc. Amer. Soc. Hort. Sci. 25:177. 1928. — ________________„ Some problems in the use of superior rootstocks for fruit trees. Proc. Amer. Soc. Hort. Sci. 33:529-51. 1955. Mendel, K. The anatomy and histology of the bud-union in Citrus. Palestine. J. Bot. Hort. Sci. 1, Ho. 2:15-46. 1956. Meyer, B. S., and Anderson, D, B. Plant Physiology. Van. Nostrand. Co. 19o9. D. Moore, J. G . Scion root production by apple trees in the nursery. ©roc. Amer. Soc. Hort. Sci. 16:84-88. 1919. Nebel, B. R. A chemical thumb test for distinguishing mazzard and mahaleb. Amer. Nat. .65:95. 19ol. Newman, C. V. Responses of citrus trees to different rootstocks. Calif. Citrogr. 11:375, 406-7. 1926. Overholser, E. L., and others. Nursery fruit trees, dwarf and standard understocks, their handling and planting. Washington State Agr. Exp. Sta. Popu­ lar. Bui. 170. 1940. _____________ , and others, pear growing and hanaling in Washington. Washington State Agr. Exp. Sta. Popular. Bui. 174. 1944. -175Parson, S. B. Cultivation of pears on the quince. ticulturist. (VI (1): 29-50. 1851. . Dwarf pears. 1857. Horticulturist. Hor­ Vll:125. Paulsen, T. Does the stock influence the future trees. Bien. Rpt. Oreg. St. Board of Hort. 9o-94. 1891. Perkins, S. G. Quince stocks for pears. 1 (9):412-14. 1847. 5 Horticulturist. Proebsting, E. L. Structural weaknesses in interspecific grafts of Pyrus. Bot. Gaz. 82:335-8. 1925, _________________, and Barger, E. H. The precipitin reaction as a means of determining the congeniality of grafts. Science. 55:575-74. 1927. _________________ . Further observations on structural de­ fects of the graft-union. Bot. Gaz. 86:82-92. 1928. Quinn, G. The state experiment orchard, Coromandel valley, near Blackwood, South Australia; Rootstocks for cherry trees. J. Dept. Agr. S. Aust. 58:1109-24 and 1245-62. 1955. Rehder, a.. Synopsis of the Chinese species of Pyrus. Proo. Amer. Acad, of Arts & Sciences. 1 (10):225-41. 1915. Reimer, F. C. A promising new pear stock. Com. Hort. 5:166-71. 1916. Mo. Bui. Calif. __________ . pear blight and resistant varieties and stocks. Proc. Amer. Pom. Soc. 39-45. 1916. _____________. Blight resistance in pears and characteristics of pear species and stocks. Ore. Agr. Exp. Sta. Bui. 214. 1925. Riker, A. J. Correlation of the wound overgrowth and crowngall of apple in parts of Europe and of the United States. Phytopathology. 18;128. 1928. River, T. Culture of the ..ear on the quince stock. culturist. 1V(1): 19-29. 1849, Horti­ -174Roach, W. A. The chemistry of the rootstock-scion effect. 1. The elements absorbed from the soil. E. Mailing Res. Sta. Ann. Rpt. 101-4. 1931. Roberts, /»'. P. Pear versus quince root for the Bartlett. Bull. Calif. Com. Hort. 7:415-19. 1918. Tufts, Vif. Ma P., and Hansen, C. J. Variation in shape of Bart­ lett pears. Proc. Amer. Soc. Hort. Sci. 28: 62755. 1951 ___________ , and Day, L. H. Nematode resistance of certain deciduous fruit tree seedlings. Proc. Amer. Soc. Hort. Sci. 51:75-82. 1954. Tukey, H. B. The pear and its culture. N. Y. 1928. Orange Judd Co., . The importance of stocks in Iiieffer pear growing. J. Hered. 19:115-14. 1928. __________ . A preliminary report upon the production of ~ seedling fruit stocks. Proc. Amer. Soc. Hort. Sci. 25:158-161. 1928. _________ . Seedling fruit stocks. N. Y. Agr. Exp. Sta. ("Geneva) Bull. 569. 1929. _________ . Fruit regions and varieties of eastern New York, N. Y. Agr. Exp. Sta. (Geneva) Bull. 565. 1929. ~ . Identification of mazzard and mahaleb cherry rootstocks. N. Y. Agr. Exp. Sta. Circular. 117. 1950. ___________ . Granulated peat moss in field propagation of apple and quince stocks. Proc. Amer. Soc. Hort. Sci. 27:106-8. 1950. ______ , and Erase, K. D. Experience in rooting soft and hard wood cuttings of Hardy fruits. Proc. Amer. Soc. Hort. Sci. 28:460-64. 1951. __________________________ . Correlation studies of the growth of apple and cherry trees in the nursery from the seedling to the two-year budded tree. N. Y. Agr. Exp. Sta. (Geneva) Tech. Bull. 185. 1951. -17 6Tukey, H. B. and brase, K. D. Trials with pear stocks in New York. Proc. Amer. Soc. Hort. Sci. 30:361-4. 1934. Random notes on fruit tree rootstocks and plant propagation. 1. N.Y. Agr. Exp. Sta. (Geneva) Bull. 649. 1934. _______________ . What yield of rooted shoots may be expected from mother plantations of hailing apple and opiince rootstocks. Proc. Amer. Soc. Hort. Sci. 33:336-45. 1935. ______________________________ . Random notes on fruit tree rootstocks and plant propagation. 11. N.Y". Agr. Exp. Sta. (Geneva)Bull. 657. 1935. _________________________ ' Random notes on fruit tree rootstocks and plant propagation. 111. N.Y. Agr. Exp. Sta. (Geneva) Bull. 682. 19o8. ______________________________ . An attack of fire blight upon trees of Pyrus betulaefolia. Proc. .amer. Soc. Hort. Sci. 43; 129-30. 1943. ITpshall, W. H. An easy means of distinguishing the roots of mazzard and mahaleb. Proc. Amer. Soc. Hort. Sci. 27:87. 1931. _____________ . Dwarf apple trees tested in Ontario. Herald and Weekly Star. April 5, 1939. Family ______________. Dwarf apple and pear trees. Canadian Hor­ ticulture and Home Magazine. Jan. and Feb., 1940 . ______________. Compatibility of Bechtels crab on some Mailing rootstocks. Sci. Agr. 21:11. ,1941. ______________. Project 331. Ont. 54. 1942. Ann. Rpt. H.E.S., V i n 1 and.,. . Dwarf apple and pear trees. Canadian Horticulture and Hoxrie Magazine. May and June, 194o„ Waite, M. B. Control of pear blight on pacific Coast. Amer. Pom. Soc. 75-77. 1907. Proc. -177Waugh, F. A. The graft union. Bui. 2:16. 1904. Mass. Agr. Exp. Sta. 'Tech. Dwarf fruit trees. 1912. Orange Judd Co., N. Y . , Webber, H. J. The lemon rootstock problem. 11:374, 398-401. 1926. Calif. Citrogr. . Rootstock reactions as indicating the degree of congeniality. Proc. Amer. Soc. Hort.' Sci. 23:30-6. 1927. Wheeler, W. Pear culture. 29. 1914. Trans. Mass. Hort. Soc. pp 12o- Wilder, H. J. Pennsylvania fruit soils and soil variety adaptation. Pa. Agr. Exp. Sta. Rpt. 512-677 1912. Wisker, a. L. Blight-resistant roots -- the first step towards pear-blight control. Mon. Bui. Calif. Comm. Hort. 5;48-5o. _____________ . Discussion on rootstocks. Mon. Bui. 7:22-33. 1918. Witt, a Calif. Dept. agr. . W., and Gardner, h. J. Peach stock trials. Mailing Res. Sta. Ann. Rpt. 21-31. 1951. Yerkes, G. E. Propagation of trees and shrubs. F m ’rs. Bui. 1567. 1929. E. U.S.D.a. _____________ . Experiments in the propagation of fruit tree stocks. Proc. Amer. Soc. Hort. Sci. 20:24144. 1923. i APPENDIX Table 1. _ __ ...I..7r..-~ . .rr at., . - seedlings and Quince A rootstocks. ' 3 3 ' 3 4 & ' 3 6 ' 3 7 ' 3 8 ' 3 9 • 4 0 ' 4 1 ' 4 2 ' 4 3 ' 4 4 1 . 8 1 . 8 2 . 1 2 . 9 4 . 3 6 . 2 9 . 1 1 3 . 2 1 8 . 1 2 0 . 4 2 5 . 5 3 2 . 2 • 9 . 9 1 - 4 2 . 3 3 . 8 4 . 9 6 . 2 9 . 1 1 3 . 2 1 3 . 1 2 0 . 4 Dwarf Shallow 1 . 1 1 . 3 1 . 6 2 . 4 3 . 8 4 . 9 7 . 5 1 1 . 3 1 3 . 2 1 5 . 2 Standard 1 . 7 2 . 4 2 . 5 3 . 6 7 . 5 1 3 . 2 1 8 . 9 2 7 . 3 3 7 . 4 Dwarf Deep 1 . 5 2 . 5 2 . 7 3 . 4 . 5 6 . 6 1 1 . 3 1 8 . 1 Dwarf Shallow 2 . 2 2 . 3 2 . 4 2 . 7 4 . 2 5 . 8 8 . 1 1 . 9 Type of trees Bartlett Standard Dwarf Deep 3 8 . 5 4 5 . 4 5 2 . 8 2 8 . 3 3 5 . 3 4 1 . 9 4 7 . 3 1 8 . 1 2 0 . 4 2 2 . 9 2 8 . 3 32.2 4 9 . 6 0 . 3 7 5 . 4 9 1 . 6 1 0 7 . 5 1 2 0 . 8 2 2 . 9 2 3 . 3 3 3 . 2 4 9 . 5 3 . 1 6 3 . 1 1 5 . 9 1 8 . 9 24.6 3 5 . 3 4 0 . 7 4 6 . 6 — I ' O'• i 46 ' 4 5 1 I - 4 1 9 3 2 Variety Anjou .T‘ 2 o . 4 Table 2. M e a n o n c r o s s - s e c t i o n a l F r e n c h V a r i e t y a r e a ( s g . c m s . ) o f t r u n k a n d Q u i n c e A 1 9 3 2 ' 3 3 ' 3 4 ' 3 5 ' 3 6 2 . 3 2 . 4 2 . 9 4 . 5 1 . 3 2.2 2 . 4 S h a l l o w 2 . 3 2 . 5 S t a n d a r d 2 . 9 p e a r s e e d l i n g s T y p e o f o f V e r m o n t B e a u t y , C l a p p F a v o r i t e , a n d B o s e p e a r v a r i e t i e s r o o t s t o c k s . ' 3 7 * 3 8 * 4 0 ' 4 1 ' 4 2 ' 4 3 8. 1 3 . 9 1 9 . 6 30.2 4 0 . 7 5 1 . 5 6 7 . 9 3 . 1 6.2 10.8 1 3 . 5 22.1 2 7 . 3 32.2 3 . 1 4 . 6 7 . 5 8. 1 5 . 2 2 2 . 9 2 7 . 3 3 3 . 2 2 . 9 3 . 5 4 . 5 7 . 1 13.2 2 0 . 4 2 8 . 3 3 7 . 4 4 9 . 1 . 3 1 . 5 2. 2.8 4 . 9 5 . 2 1 1 . 3 18.1 2 2 . 9 2 6 . 4 1 . 3 1.8 2. 2 . 5 4 . 5 5 . 8 1 4 . 5 1 8 . 1 ’3 9 '46 ' 4 4 ' 4 5 8 3 . 3 1 0 3 . 9 1 1 8 . 3 3 7 . 4 4 4 . 2 5 4 . 1 63.6 7 3 . 9 3 8 . 5 4 5 . 4 5 4 . 1 63.6 6 7 . 9 7 3 . 9 9 1 . 6 1 1 3 . 1 32.2 3 8 . 5 4 7 . 8 5 8 . 1 6 5 . 2 0 . 4 23.8 2 8 . 3 3 4 . 2 4 0 . 7 4 5 . 4 t r e e s V e r m o n t B e a u t y S t a n d a r d 1 3 4 . 9 D w a r f D e e p D w a r f C l a p p F a v o r i t e 5 5 . 4 1 2 8 . 7 D w a r f D e e p D w a r f S h a l l o w B o s e 8.6 D w a r f D e e p . 4 . 7 1.2 3 . 1 6.2 . 5 .6 1.1 2 . 3 4 . 9 1 3 . 2 1 8 . 1 2 5 . 5 3 5 . 3 4 1 . 9 4 9 . 60.8 7 0 . 9 8 9 . 9 1 0 0 . 3 9 . 1 1 4 . 5 2 0 . 4 2 8 . 3 3 4 . 2 4 1 . 9 52.8 6 6 . 5 7 2 . 4 8 4 . 9 D w a r f S h a l l o w Table 3. Mean accumulated yield (pounds) of Bartlett, ,An.jou, Quince A rootstocks. V a r i e t y T y p e o f p e a r v a r i e t i e s ' 4 4 o n ’4 5 F r e n c h 1 9 3 6 ' 3 7 ' 3 8 ' 3 9 ' 4 0 ' 4 1 ' 4 2 * 4 3 * 4 6 1 . 6 2 . 4 3 . 0 1 2 . 2 2 . 1 4 3 0 . 0 5 9 . 0 7 8 . 8 1 1 5 . 8 1 1 6 . 4 1 2 3 . 0 3 . 5 5 . 5 8 . 7 16.1 2 5 . 7 2 8 . 1 5 3 . 5 62.1 1 0 2 . 9 1 0 3 . 3 1 0 4 . 1 3 . 2 7 . 6 9 . 0 2 3 . 8 3 4 . 2 4 1 . 4 5 7 . 6 7 0 . 8 1 0 4 . 4 1 0 5 . 0 1 0 7 . 4 . 4 1 3 . 4 1 6 . 2 2 0 . 0 68.6 7 1 . 2 1 3 5 . 0 1 3 6 . 8 1 3 6 . 8 7.8 1 1 . 4 12.2 3 7 . 2 37.2 48.8 48.8 5 0 . 0 7 . 5 U 1 3 . 1 3 0 . 7 3 0 . 7 5 1 . 7 5 1 . 7 5 2 . 1 t r e e s B a r t l e t t S t a n d a r d D w a r f . D e e p D w a r f S h a l l o w A n j o u S t a n d a r d D w a r f D e e p . 4 1.2 D w a r f S h a l l o w .o . 9 . l p e a r s e e d l i n g s a n d Table 4. Mean accumulated yield (pounds) of Vermont Beauty, Clapp Favorite, Bose pear varieties on French pear seedlings and Quince A rootstocks. V a r i e t y T y p e o f 1 9 3 6 ’3 7 * 3 8 ' 3 9 ' 4 0 ' 4 1 ' 4 2 ' 4 3 ' 4 4 ' 4 5 ' 4 6 t r e e s V e r m o n t B e a u t y S t a n d a r d . 4 .8 1 . 8 4 . 6 5 . 4 1 1 . 0 3 3 . 4 3 6 . 0 6 3 . 0 6 9 . 4 7 3 . 4 .8 .8 1 . 4 2 . 2 5 . 0 2 0 . 6 3 0 . 6 3 9 . 4 4 1 . 8 5 0 . 4 5 9 . 6 1 . 1 4 . 9 8 . 3 1 5 . 3 3 7 . 1 5 2 . 9 6 8 . 1 9 7 . 7 1 0 6 . 3 1 1 9 . 3 . 2 . 2 2 4 . 0 2 4 . 2 1 0 6 . 4 1 5 8 . 6 1 5 8 . 6 1 6 6 . 2 .8 2 . 2 2 . 2 6.6 2 0 . 2 2 8 . 6 6 1 . 0 8 0 . 4 1 0 7 . 2 1 0 7 . 2 1 0 9 . 4 . 4 2 . 4 2 . 4 3 . 6 2 1 . 8 2 3 . 2 46.6 5 7 . 4 9 1 . 6 9 1 . 6 9 6 . 6 D w a r f D e e p D w a r f S h a l l o w .8 C l a p p F a v o r i t e S t a n d a r d 1 1 . 0 9 6 . 2 Dxirarf D e e p D w a r f S h a l l o w B o s c D w a r f D e e p 3 . 1 4 . 3 4 . 5 4 5 . 0 9 3 . 5 1 2 0 . 5 1 7 2 . 0 1 7 2 . 0 2 0 3 . 0 D w a r f S h a l l o w 1 . 7 3 . 4 2 1 . 1 3 8 . 4 5 5 . 4 8 5 . 7 1 2 6 . 4 1 3 8 . 7 1 3 8 . 7 1 6 5 . 3 Table 5. Average weight per fruit■ ■■(l/lO of_ Bartlett on French pear seedlings A rootstocks. a .... ___ _ a... -c *>— f . ,pounds) r. — - i ■ ____ — . pear r i j ,.and Quince ... — — ,w V a r i e t y T y p e o f 1 9 3 6 ' 3 7 ' 3 8 ' 3 9 ' 4 0 ' 4 1 > 4 2 ’4 3 * 4 4 • 4 5 > 4 6 . 1 9 . 1 9 .26 . 2 5 . 1 8 .16 . 2 8 <>27 . 2 5 . 4 2 . 2 2 . 2 0 . 3 6 . 3 7 . 3 8 . 2 4 . 2 7 . 2 3 . 2 8 . 3 2 . 3 3 .26 . 2 9 . 4 3 . 3 5 . 2 1 . 2 8 . 2 6 . 3 4 . 3 0 . 4 3 t r e e B a r t l e t t S t a n d a r d D w a r f D e e p D w a r f S h a l l o w . 3 2