"7r" \v.“———-‘n_ A, A —v - — “w—‘wfi-.— - - *wt‘i‘ .::;~‘i:ue-:' «es-r»; -‘ CERTAEN PHYSiOLv‘CA' AND moapHomGtCAL RESPGNSES m POTATOES Ami)? ewoks INDUCED fl . MALEiC Hummus ‘ Thai: for fhc f “ I51}, 90 m. n MiCHlGAN STATE CGLLEGE Sunpanom Nagéswara Rao 1954 “JIM! This is to certify that the thesis entitled CI’IRTAIN PHYSIOLOGICAL AND MORPHOLOGICAL RESPONSES IN POTATOES AND ONIONS INDUCED BI MALEIC hYLRAZIDE presented by Surapaneni I‘Jageswara Rao has been accepted towards fulfillment of the requirements for Ph- D- degree ill—WT . UTE? Major professor ‘ 5' /7s’;( Date , .. —A.-."\. ’ _._.h - “Mun...- __ 4—“ _ - CERTAIN PHYSIOLOGICAL AND MORPHOLOGICAL RESPONSES IN POTATOES AND ONIONS INDUCED BY MALEIC HYDRAZIDE BY Surapaneni Nageswara Rao A THESIS Submitted to the Scheol 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 195u 1‘452‘ A‘ib Surapaneni Nageswara Rao Detailed morphological and physiological aspects of the nature of naleic hydrazide (NH) induced sprout inhibition favorable for the commercial long-time storage of potatoes and onions, were studied during a three-year period. A crOp of potatoes was grown in 1952 and again in 1953 including A and 10 varieties, respectively, and MB at 2500 ppm (3 pounds per acre) was applied as a foliage spray at different stages during the development of each variety. Differences in varietal response to treatment were noted. ‘ Chippewa, Sebago, andeathadin (1953 only) showed the least injury following early applications, 36 days (June u) and 50 days (June 18) from planting in 1952; and 31 days (June is) and as days (June 29) from planting in 1953. In contrast, Russet Bur- bank, Kennebec, Irish Cobbler and Triumph'were very susceptible to injury from early applications as evidenced by the increase in nnnber of deformed and small tubers, reductions in total yield, and yield of U.S. No. l tubers. Whereas varieties individually differed in response to treatments applied on the same dates from tine of seeding, applications of the chemical at comparable stages of maturity gave similar results with respect to tuber injury, yield of tubers, and inhibition of storage sprouting. Significant reductions in total yield from all spray treatments were detected in 1952 where all were applied prior to six weeks of harvest. However in 1953. no significant reductions in total yield or yield of 0.8. No. 1 tubers were noted with the ten varieties when.MH was applied either on August 13 or 25, hi days and 30 days, respectively, before harvest. Storage data for the ten potato varieties grown in 1953. indicated that satisfactory mam r, l‘ Surapaneni Nageswara Rao inhibition of sprouting resulted from a single preharvest foliar spray of 2500 ppm of NH applied on either July 13, July 31 or August 13, 1953. HE applied July 1, July 15 or August 14, in 1952 showed complete inhibition of sprouting at the apical regions of the tubers but some growth was evident on the basal parts. Tubers harvested from plants sprayed with 2500 ppm of NH applied July 1, July 15, and August 1;, in 1952 and planted January 7, 1953 in the greenhouse remained sound but completely dormant for eight weeks, whereas non-treated tubers and those treated June 1; and June 18, 1952 grew normally producing profuse roots and large vegetative taps. Although no post-harvest chemical treatment, among the many tested, was found effective in breaking the dormancy induced by ME in storage of potatoes or onions, field studies on 20 varieties of onions in 1952 showed that a preharvest application of 2,114) (0.1%) following treatment with MB (0.25%) completely nullified the usual storage growth inhibitory influence induced by ME. Externally sprout inhibition in potatoes was characterised morphologically by a loss of apical dominance and lack of growth in the apical buds because of inhibition of cell division. From detailed records of plant growth in the field, storage quality, and anatomical observations of sectioned meristems of sprout initials from potato tubers and root primordia from onion bulbs, it was found that treatment with MH resulted in depressing of differentiation of tissues in the buds and root primordia accom- panied by a retardation of cell division. '1 .l-."\"||' .l‘ Surapaneni Nageswara Rao Differences in the response of potato varieties to treatment with MH were described in light of data reported in other investi- gations for different varieties of craps treated with MH as well as possible antiauxin effects related to its growth-suppressing prepertie s. , . KW” I] 27-59’ TABLE OF CONTENTS I INTRODUCTION . . . . . . . . . . . . . . . . . . . . IIREVIEWOFLITERATURE................ A. Effect of plant growth substances other than MH on histological reSponses in plants . . . . . . B. Effect of MH on histological responses in plants. C. Effect of NE on plants in general . . . . . . . . III THE PROBLEM FOR.INVESTIGATION. . . . . . . . . . . . IV EXPERIMENTAL . . . . . . . . . . . . . . . . . . . . A. Field and storage eXperiments with potatoes . . . l. The effect of time of application of pre- harvest foliar sprays of MB on the total yield of four potato varieties (1952).. . . 2. The effect of time of application of pre- harvest foliar sprays of MH on the yield, marketability, injuries, the size and number of tubers of ten potato varieties (1953) . . . 3. The effect of time of application of MH on storage sprouting of four potato varieties (1952). e e e e e e e e e e u. The effect of time of application of MH and CDAA on storage sprouting of ten potato varieties (1953le e e e e e e e e e e e 5. Effect of post harvest application of chemicals on the sprout growth of Irish Cobbler tubers which were harvested from non-treated plants e e e e e e e e e e e e e e 6. Apical dominance studies of potato tubers to be used for seed purposes harvested from plants sprayed with 2500 ppm of MH . . . . . . B. Storage tests with onion varieties treated with a preharvest application of MH for sprout inhibition and subsequently with 2,u-D as an herbicidae e e e e e e e e e e e e e e e e e C. Storage tests concerned with breaking MH- induced dormancy in onion bulbs and potato tubers. e e e e e e e e e e e e e e e e e e e e D. Histological studies of potato tubers and onion bulbs following treatment with MH . . . . ‘I‘ “W ‘5’ L“.lfd )3 11 15 16 16 16 19 31 38 1+5 119 52 57 TABLE OF CONTENTS Continued V DISCUSSION 0 O O O O O O O O O O O 0 O 0 VI SWARYO C O O O O O O O O O 0 O O O O O VII LITERATURE CITED . . . e . . . . . . e . Table II III IV VII VIII IX XI XIII LIST OF TABLES The effects of time of application of NH on total yield of potato varieties - 1952 . . . . . The effects of time of application of MH and CDAA on total yield of potato varieties - 1953 . The effects of time of application of MH and CDAA on yield of U.S. No. l tubers - 1953. . . . The effects of time of application of MH and CDAA on tuber size - 1953e e e e e e e e e e e e The effects of time of application of NH and CDAA on yield of deformed tubers - 1953. . . . . The effects of time of application of MH and CDAA on number of deformed tubers - 1953 . . . . The effects of time of application of MH and CDAA on the production of small tubers - 1953. . The effects of time of application of MH on sprouting of potato varieties held in storage at 55 Effect of preharvest foliar Sprays of MH and CDAA on 10 otato varieties after 3 months storage at 50 F and 1 month at 60° F on weight of Sprouts - February 10, l95h. . . . . . The effects of post-harvest application of various chemicals on inhibition of Sprout growth of Irish Cobbler potatoes stored at 55° F from November 20, 1952 to February 10, 1953 O O O O O O O O O O O O O O O O O O O O O 0 Comparative heights of potato plants grown from tuber-halves of Irish Cobbler and Chippewa potatoes harvested from plants sprayed with MH . Sprouting and breakdown of 20 varieties of onions h weeks after harvest as influenced by pre- harvest foliar Sprays of MH (2500 ppm) and 2,u-D (1000 ppm) - OCtObeP 15, 1952e e e e e e e Sprouting and breakdown of 20 varieties of onions 18 weeks after harvest as influenced by pre- harvest foliar Sprays of MH (2500 ppm) and qu'D (1000 ppm) ‘ January 23, 19530 e e e e e e F fOP 21 weeks. e e e e e e e e e 24 25 27 28 29 3O 32 #3 as 48 53 54 LIST OF TABLES Continued Table Page XIV Sprouting and breakdown of 20 varieties of onions 36 weeks after harvest as influenced by reharvest foliar Sprays of MH (2500 ppm and 2,u-D (1000 ppm) - June 10, 1953. . . 55 Figure 10 11 12 LIST OF FIGURES Modification of leaf size and shape following MH treatment. e e e e e e e e e e The effect of time of application of MB on Sprout growth of Triumph potatoes6 following six weeks storage at 55 F. . . . The effect of time of application of MB on Sprout growth of Irish Cobbler potatoes, following six weeks storage at 55° F. . . . The effect of time of application of MB on Sprout growth of Chippewa potatoes, following six weeks storage at 55° F. . . . The effect of time of application of MB on sprout growth of Sebago potatoes,o following six weeks storage at 55 F. . . . The effect of time of application of MH on Sprout growth of Triumph potatoes, following 15 weeks storage at 55° F . . . . The effect of time of application of NE on Sprout growth of Irish Cobbler potatoes, following 15 weeks storage at 55° F . . . . The effect of time of application of NE on Sprout growth of Chippewa potatoes, following 15 weeks storage at 55° F . . . . The effect of time of application of MH on Sprout growth of Sebago potatoes6 following 15 weeks storage at 55 F . . . . Destruction of apical dominance of Chippewa potatoes induced by an early application or MH (July 1, 1952)e e e e e e e e e e e e Destruction of apical dominance of Chippewa potatoes induced by an early application or MH (July 1, 1952)e e e e e e e e e e e e The influence of preharvest foliar sprays of NE on the growth and develOpment of Sprouts of Irish Cobbler tubers stored at 55° F for 9 monthae e e e e e e e e e e e e e e e Page 23 3h 35 36 37 39 MO 50 51 60 LI ST OF FIGURES Continued Figure ' P889 13 Photomicrographs of the longitudinal sections of the buds of Irish Cobbler tubers (20 weeks after harVOSt). . o e o e e e e o e e o 61 1h Camera lucida drawings of longitudinal sections of buds of Irish Cobbler tubers. . . 62 15 Drawings of gross longitudinal sections of‘Y-hO onions after two months of common storage. e e e e e e e e e e e e e e e 6S 16 Photomicrographs of longitudinal sections of the bases of onion stems (15 weeks after harvest). e e e e e e e e e e e e e e e 66 ACKNOWLEDGEMENTS The author is deeply indebted to Dr. S. H. Tittwer, Professor of Horticulture, Michigan State College, for not only his guidance of the work connected with this thesis, but also his unfailing friendliness, help and courtesy. Appreciation is also given to other members of the guidance committee: Dr. R. L. Carolus, Dr. L. w. Mericle, Dr. D. P. Watson, and L. H. Turk for their 000peration and advice. Thanks are given.to W. D. Eaten of the Nichigan Agri- cultural EXperiment Station for suggestions in analysis of the data. The author is indebted to Naugatuck Chemical Company for supplying the chemical maleic hydrazide and for giving financial support which made these investigations possible. I. INTRODUCTION Millions of tons of potatoes and onions are lost every year throughout the world as a direct result of Sprout growth during storage. If storage house temperatures could be maintained under h0° F, very little, if any, Sprouting would occur. However, it is not always possible nor desirable in.the ease of potatoes to maintain such temperatures throughout the storage period. As a result, excessive Sprout growth and weight losses occur. This is of economic importance to growers, distributors, potato dehydrators, and potato chip manufacturers. Certain chemical treatments have recently made possible storage at higher temperatures, without appreciable shriveling and loss from Sprouting in both potatoes and onions held in long-term storage. It has been demonstrated that maleic hydrazide1 (MB) is an effective Sprout inhibitor on various crepe and the effects of concentrations and time of application of this chemdcal on the storage quality of potatoes and onions have been summarized (68, 69, 72). These observations have suggested a more detailed study of the physiological and morphological responses of potatoes and onions to foliar Sprays of MH. It is likely that external differences in 1. 1,2-dihydro-3,6-pyridazinedione Sprouting of potatoes and onions induced by ME are closely associated with certain cellular characteristics in.meri- stematic tissues pertaining to Sprout initiation or inhi- bition. A knowledge of the histological characteristics associated with the initiation of Sprouts, therefore, is of utmost importance and value in any fundamental study of the factors associated with Sprout inhibition in onions and potatoes. During the course of these investigations, studies having to do with morphological responses of various potato varieties to ME were suggestive of marked varietal interactions. Accordingly, data pertaining to differences in yield performance, susceptibility to tuber injury, and the induced Sprout inhibition of a number of potato varieties sprayed with.MH at various stages of plant deve10pment are presented. II. REVIEW OF LITERATURE A. Effect of Plant Growth substances Other Than NE on Histological ReSponses in Plants Among the noteworthy investigations on the effects of plant growth regulators, have been the studies of their histological effects on bean plants. Kraus, Brown and Banner (36) found the endodermis and cambium the most reSponSive to application of indoleacetic acid, the endo- dermis proliferating and differentiating into vascular strands, and the eambium.cells proliferating rapidly but ‘with delayed differentiation of derivatives. The primary phloemnwas also highly sensitive with abundant prolifer- ation and frequent radial elongation. The epidermis and pericycle were not very responsive while the pith prolifer- ated slowly but profusely. Hamner and.Kraus (26) extended their observations to indolebutyric acid and naphthalene- acetic acid and obtained Similar results. Kraus and Mitchell (37) reported the histological reSponses of the bean to naphthaleneacetamide. There was less extensive prflflferation.than with indoleacetic acid and the most evident feature was the great increment of secondary xylem, the decided thickening of the walls of cells of most of the tissues composing the stem and the partial suppression of elongation of axillary buds. The effect was similar in the African.marigold and in Mirabilis. Another'most obvious characteristic was the increased firm- ness of the treated internodes, resulting in prevention of abscission, when decapitated and treated. Among other effects were the reduction in the height and total leaf area, and reduction in size of primary leaves. Mitchell and Stewart (uh) compared the effects of naphthaleneacetic acid and naphthaleneacetamide upon the bean. They showed again the tendency of the acetamide to increase the wall material, cepecially of the xylem.and the pericyclic fibers, and not to affect the cortex. They observed that the treated leaves were lighter green in color and thicker, that the abscission of cotyledons was delayed by several days, and that treatment inhibited bud develOpment. Hamner (21;) found that a-naphthaleneacetamide when applied to the bean in nutrient solution reduced tap growth and increased root growth, and induced earlier maturity and greater extension of xylem and phloem in the roots. Palser (51) observed.that Xigig'fgbg reSponded to indole- acetic acid histologically with activity to some extent in every parenchymatcus tissue, and notable was the some- what extensive vascularisation of derived tissues. Beal (7) applied four substituted phencxy compounds to Xigig‘fgbg and found that in the second internode next to the point of application, with the exception of the epidermis, possibly the pericycle and limited portions of outer cortex, all the other tissues were active, whereas in the first inter- node and hypocotyl, farther from the point of application, only the endodermis, cambium, phloem and ray parenchyma were activated. 'Whiting and Murray (6k) reported that histological reactions of bean to phenylacetic acid consisted of marked proliferation of inner cortical parenchyma, endodermis and primary phloem parenchyma, the rays and the peripheral pith, and the cambium with slight reSponse in the pericycle and secondary phloem, with no activity in the epidermis and central pith. Mullison (N6) observed that application of tetrahydrofurfurylbutyrate induced reSponses different from those obtained from other growth substances, among which 'were the more localized reSponse, an increased activity of the xylem tissues and moderate activity of the endodermis ‘with no differentiation of vascular tissue. Swanson (58) studied the histological reSponses of the Red.Kidney bean to aqueous Sprays of 2,h-dichlor0phen- oxyacetic acid (2,h-D) and noted the activity in the endo- dermis, pericycle (if undifferentiated or embryonic), phloem parenchyma, cambium and rays (the latter two zones being very active). He found that the formation of xylary elements was greatly inhibited and when occurring, much disorganized; the cortex showed little response, and epidermis and pith no reSponse. He observed that the effect of 2,h-D was systemic in nature, even at relatively low concentrations and in this reSpect, it differed from other growth regulating substances. Murray and Whiting (47) studied the histological reSponses of been stems to low concentrations of indole- acetic acid and compared them with those described by Kraus (35) for tryptOphane. The important differences between the two substances were that with tryptOphane, the cortical parenchyma was more reactive, vascularization in proliferated endodermis greater, primary phloem less active, pith relatively inactive and the course of vascularization in other tissues different for the two substances. Borthwick, Banner and Parker (9) studied the histo- logical reSponse of the tomato stem to indoleacetic acid. The results were similar to those reported for the bean. Cortical enlargement occurred, accompanied by some division; the endodermis divided actively; the phloem and the wood parenchyma proliferated, while the epidermis and pericycle were not very reSponSive. Bausor, Reinhart and Tice (h) reported on the reSponse of tomato stems to treatment with I -naphthoxyacetic acid. In the young stem there was enlargement of the cortical cells and great activity of cambium and differentiation of secondary xylem. In older stems the cortex was also acti- vated but the greatest change occurred in the tissues from cambium to endodermis, inclusive, in.which proliferation took place rapidly. Laibach and Fishnich (38) observed the histological effects of indoleacetic acid upon ccleus,‘1igigflfggg and the tomato and noted in ccleus that new vascular bundles appeared among the three originally present on each Side. Goldberg (l9) applied.indoleacetic acid to cabbage stems and found that all tissues reSponded to some extent; most generally reSponSive were those of phloem, rays and pith. The cambium, cortex, endodermis and xylem were moderately stimulated, while epidermis and pericycle reacted weakly. Harrison (27) treated Iresine lindenii with indole- acetic acid. The endodermis and cortical parenchyma were not very reactive, while the phloem, pericycle rays and extra fascicular cambium proliferated. Thinning of the ‘walls of the collenchyma was also noted. The fascicular cambium was not very reSponSive. Rather unusual was the proliferation of cutinized epidermal cells with thickened walls. The general degree of activity of Iresine resembled more clearly that of the tomato than of the bean. Beal (6) worked on three Species onLilium with indole- acetic acid. The rate of reSponse was much slower than that reported for bean, tomato and Iresine. In Lilium philippi- ‘23233 and Lilium longiflorum, there was proliferation of the parenchyma cells centripetal to the bundles, which later became organized into roots. In these, the outer cortex and the epidermis were only slightly affected. In.Lilium harrisii, however, the epidermis and the cortex in the axil of the leaf were activated to divide and become organized as buds. Hamner (25) treated.Mirabilis jalapa with indoleacetic acid and found wide variation in histological responses of the various tissues. The pericycle, interfascicular paren- chyma just inside it and the interfascicular cambium (in the older stems) were the most reactive, while the vascular tissues were generally unreSponsive, the epidermis and cortical parenchyma showed little reSponse and the endo- dermis considerable. The pith was slow to start activity bum once activity was initiated it proliferated rapidly, differentiating as internal roots or as strands of vascular tissue. Blum (8) worked on sunflower stem and found that naphthaleneacetic acid caused marked epinasty, completely inhibited bud develOpment and differentiation of secondary xylem and marked development of activity of the horizontal cambium. Beal (5) treated the sweet pea with h-chlorOphenoxy- acetic acid and observed stem curvature, epinasty, inhi- bition of buds, swollen rootétips with most proliferation of the pericycle. Pfeiffer (5h) applied indolebutyric acid to the aerial roots of Cissus siczoides and found that the cells of the phloem and pericycle proved most reactive, enlarging and dividing with derivations of the pericycle Opposite the protoxylem forming the lateral roots. B. Effect of MH on.Histological RSSponses in Plants Naylor and Davis (50) have reported that in many instances MH-treated wheat, sunflower and Turkish tobacco plants develOped abnormal leaf shapes. In addition, Naylor and Davis (50) observed the following sequential changes in plants after treatment with NE: (a) loss of apical dominance, (b) expansion of leaves already formed, (0) an intensifi- cation of green color, (d) increase in anthocyanin pigment, and (e) some chlorosis. The degree of expression of these characters depended largely upon the concentration of MH used and the age of the plant when treated. Moore (RS) noted that MH-treated sweet corn and garden beet plants develOped narrower leaves than the controls. Darlington and Mcleish (1h) studying the action of MB on cell division in Eigi§J£gbg, noticed that high concen- trations of MH, 0.005 molar and above, did not step mitosis. However, such concentrations inhibited cell division for two days. These investigators (1h) further observed that concentrations of MH at 0.005 molar and above induced a large number of breakages in the heterochromatic portion of the chromosomes. It has not as yet been reported as to whether or not chromosome breakages are reSponsible for the male sterility which MH induces in maize, as reported by Naylor (RB). Greulach and Atchison (20) noted that MH inhibits cell 10 division at low concentrations, but not cell enlargement. They also observed that high concentrations of MH stepped both cell division and cell enlargement. Currier, Day and Crafts (12) reported that MH may cause the collapse of the phloem elements, thereby allowing certain elaborated foods to differentially accumulate in Specific parts of the plant. There are other unique aspects of the action of MH 'which distinguish it from most other plant growth regulators. Leapold and Klein (39) noted that MH stimulated the growth of lateral buds while inhibition is usually induced by other plant growth regulators.. Struckmeyer (55) noted that leaves of treated plants were thicker as a result of somewhat large cell Size, had a less compact arrangement of the Spongy parenchyma cells and larger intercellular Spaces. In addition, Struckmeyer observed that the phloem elements of the vascular bundles of both stems and leaves were commonly found in varying stages of collapse. This investigator (56) further explains that the greater diameter of the stems of treated plants is partly due to an increase in Size of the cells. ‘Hatson (63) observed the histological effects of MH upon Red Kidney beans and noted that the abscission zone of petioles was in a more advanced stage in treated plants. No abnormal cell division was observed. 11 0. Effect of MB on Plants in General Schoene and Hoffman (55) first described MH as a unique growth regulant, and subsequent workers have initiated many varied lines of investigation with this chemical. Miller (R3) reported that MH can cause abscission of young flowers or fruits. Crafts, Currier and Day (13) used it as a herbicide; Naylor (R8) stated that MH will shift the critical day length of Xanthium;'White (65) found that this chemical delayed the fruiting of raSpberries; and Naylor and Davis (R9) reported that MH produced sterile staminate flowers on 523. Accordingly, the Specific effects of this chemical on the plants used in this study (onions and potatoes) are reviewed briefly. Using MH as a herbicide on netted gem potatoes, Barnard and'Warden (3) reported a Slight increase in tuber- ization from 1000 ppm of MH applied two weeks after emergence and accompanied by a Slight reduction in Size. When 5000 ppm of MH were applied, tuber set was further increased but a amaller percentage of the tubers attained U.S. No. 1 Size. Many second growth and aerial tubers were fermed. Denison (15) noted the effects of concentrations of MH ranging from 375 ppm to 6000 ppm on the Kennebec variety when applied as a herbicide on July 6, July 20, and July 28, 1950. Yields of potatoes resulting from the early appli- cation showed.marked reductions with each increase in con- ccntration, while the second application gave a smaller 12 yield reduction and the last application resulted in no significant reduction. No influence was reported in the specific gravity of tubers treated with any of the concen- trations of MH or from.different dates of application. Marshall and Smith (h2) reported effective Sprout inhibition from 2500 ppm of MH applied to potato tubers when the material was injected into the tuber by sticking impregnated toothpicks in the tuber. TuberS immersed in a 2500 ppm solution of MH exhibited no Sprout inhibition. ‘Zukel (71) first reported that foliar applications of 3000 ppm of MH seven weeks after planting prevented Sprouting of potato tubers in storage. Kennedy and Smith (33) Showed the effects of concentration of 10, 100, and 1000 ppm of MH on the Sebago variety when applied at four dates during the growing season. A concentration of 1000 ppm of MH applied about the time of initial tuber set caused a large increase in the number of tubers fonmed, severe injury to the tubers and curling and chlorosis of foliage accompanied by stunting of growth. Foliage and tuber injury decreased with later application and with less concentrated appli- cations of MH. In general, a high concentration of MH early in the growing season caused vine and tuber injury, but applied later resulted in a reduction in amount of Sprouting of the tubers in storage. Kennedy and Smith (3h) further reported that increasing the rates of MH applied per acre to the growing crap gave a 13 reduction in Sprout growth, a reduction in total weight loss in storage, and an increase in the number of eyes showing activity in tubers stored at 50° F. They also showed that MH-treated tubers exhibiting a reduction in sprouting in storage, upon planting failed to produce as complete a stand as non-treated samples. AS the concen- tration of HR was increased, emergence of plants from treated tubers decreased. According to Wittwer and Paterson when.MH was applied at concentrations of 1000 and 2500 ppm four to six weeks before harvest, Sprouting was completely prevented in Irish Cobbler and Pontiac varieties of potatoes even.when held in storage for seven months at 55° F (67). Harris (28) reported that young wild onions, Allium canadense, when treated on November 1h, l9h9 with 1, 3, 5, 6, and 12 pounds per acre of MH as a herbicide gave 98 per cent control at the 3-pound rate and approached eradication at lZ-pound rate. A second treatment in March showed excellent control at all rates, but the onions were not completely eradicated. No onion Shoots developed on treated areas in the fall. Greulach and Atchison (20) made the interesting obser- vation that Southport Yellow Globe onions grown in a solution of 1 ppm of MH produced many more roots than comparable control bulbs indicating a possible root stimulating effect of MH. 1h Wittwer and Sharma (69) reported that MH inhibited Sprouting of Yellow Sweet Spanish onions in storage when the chemical was applied at a concentration of 2500 ppm when one-third of the t0ps were down, approximately two weeks before harvest. There was a significant reduction in Sprouting accompanied by a reduction in storage rots five months after storage when 500 ppm was applied. Bulbs from plants treated with 2500 ppm of MH Showed normal internal structure with no effect on flavor, color or odor. The onions were planted at the end of the fivedmonth storage period but remained dormant and sound for eight weeks. Thus, a preharvest foliar Spray of MH has been the first entirely successful chemical treatment devised for the control of storage Sprouting in onions. Johannessen and Oebker (32) observed that a preharvest foliar Spray of 2500 ppm of MH applied to Early Yellow Globe and Brigham Yellow Globe onions reduced Sprouting in a l6~week storage test at 320 F and h0° F and also reduced Sprouting under Simulated retail store conditions five weeks after this storage period. Wittwer and Paterson (68) have further demonstrated that MH applied at concentrations of 500 to 2500 ppm to the foliage of mature onions of Brigham Yellow Globe, Early ‘Yellow Globe, Downing'Yellow Globe and M.S.C. Sweet Spanish in the field prevented subsequent Sprouting and breakdown in storage. Losses from Sprouting of‘Y-hO, an early hybrid, were greatly reduced in bulk storage (53). 'III. THE PROBLEM FOR INVESTIGATION It has been demonstrated that maleic hydrazide (HE) is an effective inhibitor of storage Sprouting in potatoes, onions, sugar beets and vegetable root crOpS (65). The present investigations were concerned with the effects of various times of application of this chemical on yields, marketability, deformities, size, number of tubers and subsequent Sprouting behavior in storage of potato tubers of several leading commercial varieties. The use of 2,h—D as a herbicide in onion fields applied late in the season following MH but prior to harvest was also investigated. The effect of various chemicals on breaking the MH-induced dormancy in both potatoes and onions was studied. Histo- logical preparations of potato eyes and onion stem bases during storage and following treatment with‘MH were also 313410 0 IV. EXPERIMENTAL General The principal parts of these investigations, included three field eXperiments, one in the greenhouse, storage eXperiments, and a series of histological studies of potato eyes, periderm and onion stem bases. The first and the second field eXperiments were conducted in 1952 and.a third in 1953. The greenhouse test was carried on during the 'winter months of 1952-1953. The storage experiments were conducted during the fall and winter months of 1952-1953. A. Field and Storage Experiments with Potatoes 1. The effect of time of application of preharvest foliar sprays of NE on the total yield of four potato varieties (1952) . Procedure. Certified seed pieces of the Triumph, Irish Cobbler, Chippewa and Sebago varieties were planted April 29 on.a Hillsdale sandy loam soil in rows 36 inches apart ‘with seed pieces at 12-inch intervals. A 3-12-12 fertilizer ital applied broadcast before planting at 800 pounds per acre, and 10-6-h'was applied as side-dressing June 20th at the :rate of 500 pounds per acre. A solution of Nugreen (20 jpounds per 100 gallons of water) was Sprayed on the foliage three times during the early part of the season. The plants 17 were dusted with DDT, Dithane, and basic copper for pre- vention and control of insects and diseases. As outlined in Table l, a single aqueous spray of 2500 parts per million (ppm) of HR was applied to the foliage of replicated plots of all four varieties June h, June 18, July 1, July 15, and August A. Approximately 7 pounds of the diethanolamine salt (30 per cent MH) was applied per acre. The sixth treatment consisted of a control in which no chemical was applied. Three-gallon hand sprayers were utilized in applying the chemicals. "Draft" (Proctor and Gamble) was added to the spray solution at a concentration of 0.1 per cent as a wetting agent. A split-plot design was employed with varieties as main plots and spray treat- ments as subplots. Each plot consisted of two 18-foot rows. Harvesting was completed and the total yield recorded September 17, 1952. Following harvest the potatoes were held in common storage for 25 days to allow suberization of the peridenm of the tubers injured during harvest. Followa ing common storage they were placed in a thermostatically controlled storage at 55 $.20 F. Results. Data 111‘ Table 1 show that the control plots gave higher yields, significant at one per cent level, than those sprayed with MH. Sebago gave the lowest yield of the varieties tried in this experiment. Harvest records showed a reduction in yield at the five per cent level with the plants of all the four varieties treated June 18, July 1, 18 TABLE I THE EFFECTS OF TIME OF APPLICATION OF MH ON TOTAL YIELD OF POTATO VARIETIES - 1952 Treatment and Total yield (Bushels per acre) tine of application Triumph Chippewa Irish Sebago Treatment Cobbler * averages W 1- June I. 464 549 550 412 483 2- June 18 101 370 393 320 296 3- July 1 438 472 421. 326 415 1+- July 15 445 1.49 472 264 1.07 5- August 4 504 497 514 323 460 Control 606 605 595 435 560 (No chemical treatment) Variety averages 423 489 491 347 5 per cent 1 per cent LSD for testing between varieties and treatments 108 148 LSD for testing between varieties 49 90 180 for testing between treatments 51. 74 19 and July 15 with 2500 ppm of MH in comparison with the control and a reduction in yield significant at the one per cent level between the plants of Triumph, Irish Cobbler and Chippewa varieties sprayed June 18 with 2500 ppm of MB in comparison with the control (Table I). Also significant reductions in yield (one per cent level) cccurred.with Triumph and with Irish Cobbler sprayed July 1, and yield reductions significant at the five per cent level were noted with the Chippewa and Sebago sprayed July 1 with 2500 ppm of MB in comparison with the non-treated control. However, the significant yield reductions of all the varieties likely induced in part at least by soil variation rather than chemical treatment leaves doubt as to whether this experiment was an adequate test of either the effects of MB on the yield of potatoes or of the yielding ability of the four potato varieties involved. 2. The effect of time of application of preharvest foliar sprays of NE on the yield, marketability, injuries, the size and number of tubers of ten potato varieties (1953). Procedure. Certified seed pieces of the Green Mountain, Kennebec, Russet Rural, Triumph, Pontiac, Chippewa, Russet Burbank, Sebago, Irish Cobbler and.Kathadin varieties were planted May 15 on Hillsdale sandy loam in rows h8 inches apart and with seed pieces at lS-inch intervals. All the cultural practices were the same as in 1952 except that the Nugreen sprays were omitted. 20 As outlined in Table II, a single aqueous spray of 2500 ppm of ME was applied to the foliage of all ten var- ieties June 15, June 29, July 13, July 31, August 13, and August 25. 0n.July 31, an aqueous spray of 1000 ppm of CDAAZ was also applied. The eighth treatment consisted of a control inuwhich no chemical was applied. The varieties and treatments were randomized in a split-plot design with three replications. The treatments made up the subplots with varieties constituting the main plots. Each plot consisted of 12 plants. From time to time, observations were made during the growing season regarding the general appearance of foliage. Prior to harvest, the number of plants in each plot was recorded. Harvesting was completed on September 2h, 1953. The potatoes were held in common storage for 3 weeks to allow for suberization of the periderm of the tubers injured in harvest and.were then transferred to a storage in which the temperature was thermostatically controlled at h5;: 2° F. Records were taken regarding the total yield, the yield of U.S. No. 1 potatoes, the yield and number of deformed tubers, the number of small (excluding the deformed and the U.S. No. 1 potatoes) and the size of tubers. Observations and results. Injury to plants as a result of early (June h and June 18 in 1952 and June 15 and June 29 2. a -cyano-,e'-(2,h-dichlor0phenyl)acrylic acid obtained . from Ethyl Corporation, Detroit, Michigan. 21 in 1953) applications of 2500 ppm of MH has been previously reported (51). The following is an account of the nature and extent of injury resulting from the early applications of the chemical. The leaves were malformed and dwarfed. This was reflected in ultimate reduction in leaf area. Pronounced upward rolling of leaves was one of the first symptoms of injury (Figure l). Damage to flower buds and leaf buds was severe. A great number of them were killed. The udtimate result of reduced yield of tubers was, however, attributable to decrease in leaf area, damage to buds and injury to the plant as a whole. 'While injury itself was a direct result of the treatment, there were certain factors, chiefly light, temperature of the atmosphere at the time of spraying, vigor of the plant, physiological age of the plant, the concentration of the chemical and variety that seemed either to accentuate or to ameliorate the injury. A closer examination of the plants that were injured showed small necrotic areas and brown flockings on the leaves. Pronounced browning was noticeable in the pith of the stem. Daily observations showed that the Opening of flowers was delayed by several days, depending upon the variety and time of application. Delayed foliation and delaying blossoming is related to bud inhibition. Delay in the develOpment of flower buds in celery following treatment with.MH has been reported by Jackson (30). In the present experiments, the Figure l. Modification of leaf size and shape following MH treatment. TOp: Left to right -- Control (not treated) leaves of Kathadin, Triumph and Irish Cobbler varieties. Bottom: Left to right -- Leaves of’Kathadin, Triumph and Irish Cobbler from plants treated with.MH June 15, 1953. Photographed June 25, 1953. _. #.f. _.-. ,J -4 PHOTOGRAPHIC LABORATORY InformatiOn Services Michigan State College East basing, Michigan Negative NumbeL L A ‘ ' 23 delay was due to the treatment as shown by formative responses. The greater the injury, the greater was the delay in.bud growth. Harvest records showed a reduction both in yields of U.S. No. l tubers (Table III) and total yield (Table II), at the one per cent level with plants of all the ten varie- ties treated June 15, June 29, July 13 and July 31 with 2500 ppm of ME in comparison with the control, and no significant reduction in yields in comparison with controls among the ten varieties treated August 13 and August 25 ‘with 2500 ppm of MH and 1000 ppm of CDAA applied July 31. The interaction of varieties x treatments was statistically significant with respect to the production of U.S. No. 1 tubers suggesting that the time of treatment was not equally effective on all varieties, but it was not significant in the total yield. Green.Mountain, Kennebec, Russet Rural, Triumph, and Pontiac gave high yields in comparison with the other varieties. 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Reductions in tuber size were greatest with Green.Mountain, Russet Rural, Triumph, Russet Burbank and Kathadin. 0n the other hand, Pontiac, Kennebec, Kathadin and Sebago produced the highest average weights per tuber. 2500 ppm of NH applied June 15 and June 29, 1953 Save significantly higher yields of deformed and also produced :Iore defonned and small tubers compared with non-treated controls (Tables VI, VI, and VII). It is very interesting to note in both 1952 and 1953 Years that the second early application of ME applied June 18 in l952 and June 29 in 1953 had a more pronounced effect on reducing the yields of U.S. Ho. 1 tubers of some varieties (Russet Rural, Triumph, Russet Burbank, Sebago) than the earliest spray treatments June h and June 15, respectively. Sebago, Chippewa and Kathadin were less subject to injury caused by early applications of MB, than the other varieties. 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B0 N@.OH no.0H mo.HH mo.mm 00009900 hpoHns> mq.mH 00.0 mm.0H mo.® oo.o~ mH cash no.5H mo.m 0N.OH Ob.HH mm.bm _# cash mum 00wm I m: «a.HN 0N.MH om.HH mm.mH ow.o< Hoapsoo commune. neHnnoo Hanan-ens omunem nuHAH useamfino nmsuahe :OHpsOHHsz Ho esHa can vac-vuena gag HN mom 04 0mm 94 muéoam 2H 5% €98.55 0.32.00” ho czHBDommm 20 m: 03 040HH4UHHAHQ< .mo age .8 wag Mme HHH>.mnde 33 that the treatments were not equally effective on all varieties or that the varieties responded differently to the treatments. In the last three treatments there were no significant differences among varieties. The Triumph variety gave significantly higher weights of sprouts per tuber than Irish Cobbler, Chippewa and Sebago when the averages of two early spray applications (June h and June 18) were combined with the control. Figures 2 through 9 show the effect of 2500 ppm of MH on the deve10pment of sprout growth of the four varieties after 6 and 15 weeks storage. After six weeks at 550 F practically no sprouting was evident in Triumph and Irish Cobbler (Figures 2 and 3). However, severe malformations of tubers were noted resulting from June 18 application of MH, with lesser effects observed for the June h and July 1 treatments. Tubers harvested from plants sprayed July 15 and August h.were normal in all instances. In Chippewa a few sprouts one-half to one inch long are seen in controls and tubers treated June u (Figure h). 'With Sebago, however, on the same date considerable sprouting was evident in controls and those treated June h and June 18, with some showing for the July 1 treatment. After storage for 15 weeks at 550 F tubers treated on July 15 and August h showed sprout initials, whereas several sprouts 3 to h inches long had deve10ped on the tubers har- vested from plants treated June h, June 18, July 1 and on Figure 2. The effect of time of application of MB on sprout growth of TriMph potatoes, following six weeks storage at 55° P. 10 Control MB - 2500 ppm 20 June h. 30 June 18 he July 1 0 July 15 6. August 1; Photographed December h, 1952. 3h Figure 3. The effect of time of application of NE on sprout growth of Irish Cobbler potatoes, following six weeks storage at 55° F. 1. Control MH - 25009p13 20 June 30 June 1 ’4». July 1 Se July 15 6. August h Photographed December 4, 1952. 35 Figure h. The effect of time of application of MB on sprout growth of Chippewa potatoes, following six weeks storage at 550 P. 1. Control MH - 25004ppm 20 June is June 1 0 July 1 5. July 15 0 August ’4. Photographed December h, 1952. 36 Figure 5. The effect of time of application of NH on sprout growth of Sebago potatoes, following six weeks storage at 55° F. 1. Control MEI - 2500 ppm 20 June is June 1 0 July 1 Se July 15 6. August )4 Photographed December h, 1952. 38 non-treated tubers of Triumph, Chippewa and Sebago (Figures 6, 8 and 9). Irish Cobbler tubers treated July 1 showed very little sprouting (Figure 7). Tubers from plants receiving MH on either July 15 or August h were clear, bright, firm and practically free from any sprout growth, even after 15 weeks storage (Figures 6 - 9). h. The effect of time of application of MH and CDAA on storage sprouting of ten potato varieties (1953). Procedure. Fifteen-pound samples of the ten varieties were taken on October 10, 1953 from each treatment (Table II). placed in SO-pound onion.mesh bags and held at h5° F for 12 weeks and at 600 F for the succeeding four weeks. On February 10, 195R. after approximately four months of storage the samples were removed from storage and de- sprouted and the weight of sprouts for each sample deter- mined. The data were evaluated by the analysis of variance method using the original weight values for sprouts and by arc-sine transformation for per cent of original weight (56). Results. The sprout growth expressed as per cent of original weight for the various treatments applied to the ten varieties is given in Table IX. In general, the sprout growth was many times higher for the non-treated samples (controls) than for plants sprayed July 13, July 31, August 13 and August 25 with 2500 ppm of MH (Table IX). Spraying the plants on July 31 with 1000 ppm of cm; significantly reduced sprout production in some varieties and increased it in others. Figure 6. The effect of time of application of NH on sprout growth of Triumph potatoes, following 15 weeks storage at 55° F. 1. Control 20 June ‘4, a. June 18 . July 1 Se July 15 6. August h Photographed February 9, 1953. 39 Figure 7. The effect of time of application of MB on sprout growth of Irish Cobbler potatoes, following 15 weeks storage at 55°F. 1. Control MH - 2500 ppm 20 June is June 1 . August h Photographed February 9. 1953. Figure 8. The effect of time of application of MB on sprout growth of Chippewa potatoes, following 15 weeks storage at 55° F. 1. Control MH - 2590 ppm 20 June a. June 1 s July 1 50 July 15 60 August Ll. Photographed February 9, 1953. Figure 9. The effect of time of application of NH on sprout growth of Sebago potatoes, following 15 weeks storage at 55° F. 1. Control MH - 2500_ppm 20 June ’4. 3. June 18 LL. July 1 Se July 15 6e AUEHSt Ll. 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This suggests that the treatments were not equally effective on all varieties or that the varieties responded differently to the treatments. Pontiac, Chippewa and Triumph produced significantly more sprout growth than the other varieties when the averages of all the spray applications were combined with the control. Spraying the plants on July 31 with 1000 ppm of CDAA gave significantly more sprout growth in.Kennebec, Russet Rural and Pontiac, when compared with non-treated control samples. 5. Effect of post-harvest application of chemicals on the sprout growth of Irish Cobbler tubers which were har- vested from non-treated plants. In order to determine the sprout inhibitory effect of certain newer growth regulators after penetration of the tubers was insured, a number of chemicals were dusted on the tubers or injected by toothpicks into the tuber. It has been reported that CDAA inhibited the growth of tomatoes and the flowering of marigolds (hl). The following study was made to ascertain the comparative effects of various concentrations and formulations of CDAA with other reportedly effective substances on inhibiting sprout growth of potatoes in storage. Procedure. The dusts were applied by placing the tubers in.Kraft paper bags and sifting the dust on tOp of them; the bags were then closed with paper clips and shaken so the dust would become thoroughly distributed. Toothpicks were us injected into tubers as described by Marshall and Smith (hl). Ten tubers for each lot and two lots making a total of 20 tubers were used in each treatment. For comparison tubers stuck with toothpicks soaked in distilled water were included. Treatments were applied on November 20, 1952 and all treated potatoes were placed in storage at a temper- ature thermostatically controlled at 55° F. Results. Weights of sprouts in 00000 per tuber were recorded February 10, 1953 and are shown in Table X. The weight of sprouts in grams per tuber was significantly higher for the non-treated control samples than when the tubers were injected with 500 or 1000 ppm of 2,h,5-tri- chlorOphenoxyacetic acid (2,h,S-T) and 500, 1000 or 2500 ppm of ethyl ester of CDAA. Toothpicks soaked in distilled water had no significant effect on weight of sprouts com- pared with the unpierced control tubers. Treatment with Fusarex3 did not reduce the weight of sprouts produced; treatment'with.MENAu, however, resulted in significant reduction of sprout growth. 6. Apical dominance studies of potato tubers to be used for seed purposes harvested from lants sprayed with 2500 ppm of MH (From EXperiment 1?. Since approximately five per cent of the potato crOp is used for seed purposes any chemical that retards sprouting 3. 2,3,S,6-tetrachloronitrobenzene obtained from Sterwin Chemicals, Inc., New'York. h. Methyl ester of a-naphthaleneacetic acid obtained from Dow Chemical Company, Midland, Michigan. 06 TABLEX THE EFFECTS OF POST HARVEST APPLICATION OF VARIOUS CHEMICALS ON INHIBITION OF‘SPROUT GROWTH OF IRISH COBBLER POTATOES STORED AT 55° F FROM NOVBZBER 20, 1952 TO FEBRUARY 10, 1953 Rate of ‘Weight of sprouts Treatment application (grams/tuber) (ppm) T c c t CDAA (acid formulation) 1000 1.95 2500 1.65 Sodiun salt of CDAA 1000 1.90 2500 1.80 Ethyl ester of CDAA 500 0.75 1000 0.85 2500 0.80 2,4,54T 500 0.60 1000 0.30 Maleic hydrazide 1000 2.45 2500 1.35 Control (distilled water) None 1.95 W m 1 gm/bushel 0.10 mum 2 gin/bushel 2.70 Control (no treatment) None 2.55 LSD at 5 per cent 0.69 LSD at 1 per cent #7 or growth of potato sprouts poses the question as to the effect of this chemical on seed stock potatoes. The following study was made concerning the effects of MH applied at various times during the growing season on seed stock potatoes and on the apical dominance of the tubers. Procedure. Tubers of Irish Cobbler and Chippewa varieties harvested from plants, the vines of which were sprayed at various times during the 1952 growing season with 2500 ppm of ME as outlined in Table XI, were divided into halves and planted January 7, 1953 in 8-inch clay pots of sandy loam soil. Four weeks later plant heights were recorded. Results. From Table XI it can be seen that a concen- tration of 2500 ppm of MH applied on July 1, July in or August A resulted in no growth. The heights resulting from plants grown from seed pieces from the apical and basal positions of the non-treated tubers, are greater than the heights from the treated tubers (Table XI). The mean heights of plants grown from apical-halves of the tubers are signifi- cantly higher than the plants grown from basal-halves. The interaction of treatments 1 tuber-halves was statistically significant which indicates that the treatments were not equally effective on both the positions of the tuber. The June h application for Irish Cobbler resulted in greater growth of sprouts from basal than apical half in sharp con- trast to the controls of the same variety where growth was 48 TABLE II CGdPARATIVE HEIGHTS OF POTATO PLANTS GROJN FROIVI TUBER-HALVES OF IRISH COBBLER AND CHIPPENA POTATOES HARVESTED FROM PLANTS SPRAIED WITH ME Treatment and .Average plant heights (Centimeters per plant) time of application Irish Cobbler Chippewa Treatment Apical Basal Apical Basal "mug” half half half half MH - 2500 m 1- June 4 1.78 2.80 9.46 5.15 4.80 2- June 18 4.00 2.29 8.19 2.16 4.18 3- July 1 0 0 0 0 0 4- July 15 0 0 0 0 0 5- August 4 O O O 0 0 Control 9.97 1.59 17.59 6.73 8.93 Tuber—halves Irish Cobbler Chippewa Averages Of tuberhhalvos Apical half 5.25 11.75 8.50 Basal half 2.26 4.68 3.45 variety'sverages 3.76 8.22 5 per cent 1 per cent LSD for testing between tuberbhalves and varieties 2.74 3.62 LSD fer testing between treatments 2.37 3.14 LSD for testing between varieties 1.94 2.56 LSD for testing between tuber-halves 1.94 2.56 #9 six times greater from apical halves. Figures 10 and 11 show complete inhibition of sprouting by ME treatment at the apical positions of the tubers but not at the basal positions.‘ B. Storage Tests with Onion Varieties Treated with a Preharvest Application of ME for Sprout Inhibition and Subsequently with 2,h-D as a~ Herbicide The successful use of MH as a sprout inhibitor by Wittwer and Paterson (66, 67) made it desirable to study its effects if followed by a preharvest application of 2,4-D as an herbicide on several hybrid onion varieties. ‘Weeds in onion fields frequently become a serious problem follow- ing the maturity of the crop but prior to harvest. In the mechanical harvesting of onions it is desirable that fields be weed free. Procedure. Onions of 20 inbred and hybrid varieties were grown from greenhouse plants seeded.March 15 and trans- planted into a field of productive mineral soil May 3, 1952. In one treatment, an aqueous spray of 2500 ppm of HR was applied to the plants of the 20 varieties on August 7. A second treatment consisted of an aqueous spray of 1000 ppm of 2,4-D to plants of all varieties on August 23. The third treatment consisted of an aqueous spray of 2500 ppm of ME applied August 7 and followed by an aqueous spray of 1000 ppm of 2,h-D applied on August 23. The fourth treat- ment consisted of a control in which no chemical was applied. Figure 10. Destruction of apical dominance of Chippewa potatoes induced by an early application of MH (July 1, 1952). Apical ends facing down. Left - Controls Right - Treated Photographed December 23, 1952. 50 #9 six times greater from apical halves. Figures 10 and ll show complete inhibition of sprouting by ME treatment at the apical positions of the tubers but not at the basal positions.' B. Storage Tests with Onion Varieties Treated with a Preharvest Application of ME for Sprout Inhibition and Subsequently with 2,h-D as a~ Herbicide The successful use of MH as a sprout inhibitor by Wittwer and Paterson (66, 67) made it desirable to study its effects if followed by a preharvest application of 2,h~D as an herbicide on several hybrid onion varieties. 'Weeds in onion fields frequently become a serious problem follow- ing the maturity of the cr0p but prior to harvest. In the mechanical harvesting of onions it is desirable that fields be weed free. Procedure. Onions of 20 inbred and hybrid varieties were grown from greenhouse plants seeded.March 15 and trans- planted into a field of productive mineral soil May 3, 1952. In one treatment, an aqueous spray of 2500 ppm of MH was applied to the plants of the 20 varieties on August 7. A second treatment consisted of an aqueous spray of 1000 ppm of 2,h-D to plants of all varieties on August 23. The third treatment consisted of an aqueous spray of 2500 ppm of MH applied August 7 and followed by an aqueous spray of 1000 ppm of 2,h-D applied on August 23. The fourth treat- ment consisted of a control in which no chemical was applied. Figure 10. Destruction of apical dominance of Chippewa potatoes induced by an early application of MH (July 1, 1952). Apical ends facing down. Left - Controls Right - Treated Photographed December 23, 1952. 50 Figure 11 e Destruction of apical dominance of Chippewa potatoes induced by an early application of MB (July 1, 1952). Apical ends facing down. Left - Controls Right - Treated Photographed.May 7, 1953. 51 52 Three-gallon hand sprayers were utilized in applying the chemicals. The leaves were sprayed to run off. Triton B 1956 (Rohm & Haas, Philadelphia) was added at a concen- tration of 0.1 per cent as a wetting agent. Results. The sprouting and breakdown for all the varieties after one month, 4% months and 9 months in common storage for the various treatments are given in Tables XII. XIII and XIV respectively. MH applied August 7 gave fair control of sprouting (Table XIV) in all the varieties except Y-hO (Asgrow), 620 Sweet Spanish (Harris), 6-51 (Pieters Wheeler), and 5-51 (Pieters‘Wheeler). 1000 ppm of 2,h-D applied August 23 resulted in marked increases in per cent breakdown and in some instances sprouting when compared with non-treated samples and when not preceded by an appli- cation of 2500 ppm of ME. NH applied August 7 followed by 2,h~D on August 23 resulted in the least overall sprouting but breakdown comparable to 2,h-D used alone (Tables XII, XIII, XIV). The desired effect from inhibition of sprouting induced by 2500 ppm of MB is completely nullified by an increase in breakdown resulting from the addition of 1000 ppm of 2,h-D. C. Storage Tests Concerned with Breaking MH-induced Dormancy in Onion Bulbs and Potato Tubers Any method or treatment of forcing normally dormant or chemically (MH) induced dormant bulbs and tubers to sprout when desired would be of great advantage for prepagation 53 00000 300000 00000.00 u 000 3000 30000 00.30 n 000 0 0 0.00 0 0.0.0 0 0 0 8.8: 0.0.8.0 .. 00000 000 .00 0 0 0.00 0 0.00 0 0.0 0 00.2020 a 3000 300000 00.000 .00 .moym 0 0 0.00 0 0.0.0 0 0 0 0080 n 3000 300000 0000300 .00 0 0 0.00 0 0.3 0 0.0 0 02000 n 0.70 .00 0 0 0.00 0 0.00 0 0.0. 0 0000 ... .00 .0 32000 000000 00 .00 0 0 0.000 0 0.00 0 0:0 0 30.0000 u 0.0.0 .00 0 0 0.00 0 0.00 0.0 0.0 0 38000 .. 0.0 .0 .00 0 0 0.00 0 0:00 0 0.0 0 30.0030 u 0.0.0 .00 0.0 0 0.0.0 0 0.00 0 0.00 0 38000 .. 00.0 .00 0.0 0 0.000 0 0.000 0 0.0 0 00.500 .. 0000000 0830 000 .00 0 0 0.00 0 0.00 0 0.00 0 5008.00 .. 000 .00 0 0 0.00 0 0.0.0 0.0 0.0 0 000000.00 .. 000 .0 0 0 0.0 0 0.0 0 0.0 0 0000 .. 000 .0: 0000 0 0000 000 .0 0 0 0.00 0 0.00 0.0 0.00 0 0000 .. 000 3.200000 000 .0 0.0 0 0.00 0 0.0 0.0 0.0 0 0000 a :00 .020 0000 000 .0 0.0 0 0.00 0 0.00 0 0.0 0 .8080: 28000 .. 00:00 .0 0.0 0.0 0.000 0 0.00 0.0 0:0 0 0000 .. 000 00 000 0 00 0 .00 .0 0 0.0 0.00 0 0.00 0.0 0.0 0 000000.00 1.8000000: .0 0 0 0.00 0 0.00 0 0.0 0.0 0.00.0: 23000 a 00:0 .0 0 0 0.00 0 0.00 0.0 0 0 0.00.02 0000.00 .. 00:0 .0 $3 33 A00 A00 A00 33 E 30 «50300.5 mfipsoumm 050000095 000006.005 050000095 magnoam 86300.5 000.00.06.00...» 00.3000 0:0.0 Hm 00000000. 02 0:000 00% 00.0060. ps0 0.000.000» .02 0000500000 h0ymm 0000 .00 00000.00 .. 0200 00000 0.0.0 020 $000 00000 0: .00 000000 00000.0 000000500 00 0002000000 00 000.0000 00.5. 0000: .0 020020 .00 000000000 00 .00 050000000 02.0 02000000 HHN mqmda 0‘ l G . l I . . . t‘ ' - ',. . 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Accordingly the following eXperiments were designed. Procedure. In one instance'Y-hZ (Asgrow) bulbs in which sprouting had been chemically inhibited by a pre- harvest foliar application of MH were kept for us hours in air-tight containers which contained 0.1, 0.2, 0.25 and 0.30 per cent of ethylene chlorohydrin. A second method of treatment consisted of using solutions of thiourea, cou- marin, dithioxamide, benzo-thiazole-Z-oxyacetic acid, levulinic acid, dithiobiuret, potassium thiocyanate and 2,h~D at various concentrations (10, 25, 50, 100, 500, 1000, 5000, 10,000 ppm) which were placed in widedmouth, round, screw-cap bottles into which the bulbs were inserted in such a.manner that the bulb bases were slightly immersed in the solutions. Each treatment consisted of five bulbs. Treatments were initiated February IA, 1953 and the bulb bases were left immersed in the solutions for three weeks. The bottles containing the solutions with the bulbs were kept at laboratory temperature (70-750 F). For a control comparison distilled water was used. In a third procedure Irish Cobbler tubers were kept for h3 hours in air-tight containers which contained ethylene chlorohydrin, the same as for the onions. A fourth.method of treatment consisted of injecting the above chemicals at the various concentrations listed for onions into potato tubers by the toothpick method (ul). Round polished 57 toothpicks were soaked for four days in the chemical solutions. These toothpicks were then allowed to dry for a few minutes and inserted to one-half of their length into tubers. Ten toothpicks were used per tuber. Ten tubers were used in each treatment. Treatments were made December 10 and 11, 1952 and the tubers were immediately placed in storage where the temperature was thermostatically controlled at 55° F and allowed to remain until March 15, 1953. Results. No chemical treatment had any effect on breaking the artificial dormancy by MK. D. Histological Studies of Potato Tubers and’ Onion Bulbs Following Treatment with MH While some of the effects of MH on the visual external appearance of plants have been described, limited information is available as to its effect upon internal structure. Accordingly, the following study was made to correlate the internal somewhat detailed histological changes with the external evidences of sprout growth and.MH-induced sprout inhibition on potatoes and onions. Collection of material. Samples of buds at three positions (apical, basal and middle) and from MH-treated and control plots of Irish Cobbler tubers were collected beginning July 30, 1951 at intervals of three‘weeks up to October 20, 1951 and at intervals of 7 days until February 22, 1952. Samples of buds or eyes from MH-treated tubers 58 between the apical and basal ends on the tubers were collected beginning July 15, 1952 at intervals of four weeks up to November 1, 1952 and at intervals of one week until March 15, 1953 (from field experiment A-l, early samples were from plants still growing in the field, while later samples were collected during storage). Samples of buds were also collected from the tubers which were treated with sprout inhibitors in storage (from storage experiment A-h). Samples of stem bases of onion bulbs (Y-kO, Asgrow) from both treated and non-treated plots were collected at three-week intervals beginning August 5, 1951 following treatment with MH and continuing up to October 15, 1951 and then at intervals of one week during storage until, March 2h, 1952 (onions procured from a field eXperiment not described in this thesis). Fixation, sectioning and staining. The materials collected were all fixed in killing solution of the follow- ing formulation: 5 m1 Formaldehyde 5 ml Glacial acetic acid 50 ml Absolute ethanol #0 m1 Distilled water The tissues were dehydrated with ethanol and cleared with chloroform. The tissues were imbedded in paraffin, then sectioned with a rotary microtome and stained with Conant's quadruple stains (31). Measurements and drawings. Detailed drawings were made /‘ S9 with a camera lucida to one scale for the same set of com- parative materials, to give identical enlargement. Many detailed measurements became unnecessary, because of the obviously large differences resulting from treatment. In studies of this kind, the comparative rather than the absolute measurements stress the nature and extent of responses obtained by treatment. Results - Potatoes. Figure 12 shows the type of sprouts produced by both non-treated and.MH-treated tubers after approximately nine months of storage at 550 F. A study of the internal structure of the buds revealed a few important features as indicated in the photomicrographs (Figure 13) and in the camera lucida drawings (Figure 1h). A typical bud or eye from a non-treated tuber 20 weeks after harvest had two outer scales which were highly paren- chymatous. There was slight disintegration of some cells towards the tips of the bracts, possibly caused by dehy- dration either during handling in storage or during the preparation of the material. These bracts appeared to be a projection of the periderm (Figure 13). The apical meri- stem, which was very prominent in its meristematic condition, was similar to a stem meristem containing tunica and corpus initials. The cells in the apical region were mostly meri- stematic and two vascular traces diverged distally and followed through the periderm as they advanced proximally (Figure 1h). Figure 12. The influence of preharvest foliar sprays of MB on the growth and development of sprouts of Irish Cobbler tubers stored at 55° F for 9 months. Tap - Control (Not treated) Bottom - MH (2500 ppm) applied 62 days before harvest Photographed July 10, 1953. Figure 13. Photomicrographs of the longitudinal sections of the buds of Irish Cobbler tubers (20 weeks after harvest). Left - Typical bud or e e of a non- treated (control tuber showing high meristematic activity. Magnification: x120 Right - Typical bud or eye from a MH- treated tuber showing no meris stematic activity. It was evident that the apical cells which would normally be meri- stematic were enlarged resulting in a flattening of the apical region. Magnification: x120 61 I \ ‘ o \\ t i . . ._, ‘ ‘1‘ . . . ‘ . ‘ p , .... n a. . V \\ (D. N“-'_\ \‘ . .‘ .‘ I - 's‘. ‘ ." .5 - ‘ I)-‘ >.' .. IA .. . . a Figure 1h. Camera lucida drawings of longitudinal sections of buds of Irish Cobbler tubers. Tap: Left - Right - Bottom: Left - Right .- A bud from a tuber of a control plant, 15 weeks after harvest. Magnification: x75 A bud from a tuber of a HR plant, 15 weeks after harvest. Magnification: x75 A bud from a tuber of a control plant, 20 weeks after harvest. Magnification: th A bud from a tuber of a treated plant, 20 weeks after harvest. Magnification: x40 62 TREATED o I a I a o o o I o I. a s u e ‘i i O s o e s u 0 so a n s e o o o a o l I e o s n O a n i. an o 0 so. 0 V I O O a. C 1 I . .0: . . . I C .. . ... . . . s...... . . u o ... . l o. the... s c s o u“C., I I a ’0 . o .- le sun. :0 ’3‘ r O .- g.“ .7? . ‘Ie . I as... a. I .... s . s so. I I n). s so . .I C . no. a on e u. s ... I; O . 0.. e a u. . 0.. .00. a c as so. DEVELOPMENT OF BUD soumuu Tuseaosuu NORMAL AFTER I!) WEEKS AFTER 20 WEEKS 63 A typical bud or eye from a tuber of a treated plant had also a pair of outer bracts which enclosed one more pair of scales which enclosed the meristem. The maical meristem was much flattened and was without meristematic tissue. Most of the cells were differentiated and larger in size. The most typical alteration due to NH was the flattened shape of the apical meristem and the lack of meristematic cells (Figures 13 and IA). A detailed study of buds or eyes at three positions (apical, basal and intermediate) on the tubers revealed that there were no differences in the structure except in their degree of development. Apical buds on the non-treated (control) tubers were more developed than the intermediate or basal buds. But in the MH-treated tubers when inhibition of Sprouting was accomplished, the basal and middle buds were more deve10ped than the apical buds. The histological study made during the 1952 season revealed that there were no structural differences between buds from non-treated tubers and buds from tubers which were harvested from plants treated with MH early in the season (June h and June 18, 1952). The buds of the tubers harvested from plants treated with MH late in the season (July 1, July 15, and August u) were strikingly different from the controls. A study of the buds of the tubers which were directly treated (post-harvest application) with Sprout inhibitors 61+ revealed that there was a slight disintegration and tearing apart of the cells of the buds probably caused by dust appli- cations of MENA (M1) and Fusarex (17). The tubers which were injected with MH, CDAA (hO) and 2,u,5-T (#1) produced buds which were similar in their structure to the MH-treated in the field (July 1, July 15 and August a, 1952). Results - Oniong. Figure 15 shows comparative gross longitudinal sections of control and MH-treated‘Y-ho onion bulbs after approximately two months of common storage. Sections of bulbs resulting from treatment with 2500 ppm of MH revealed an internal structure that was very much similar to non-treated controls except for less bud growth. A study of the anatomy of the bases of the onion stems showing root primordia emerging through the cortex, revealed a few important features as indicated in the photomicro- graph (left in Figure 16) of the base of an onion stem of a non-treated (normal) bulb 15 weeks after harvest. Two histogens were present: (a) a well-defined plerome which gives rise to a stele, (b) and overlying it a group of initial cells two layers in thickness from which originate the cells of the root cap, epidermis, and cortex. The cells are highly meristematic, full of protOplasm and actively dividing. In sectioned stem bases from MH-treated bulbs most of the meristematic cells in the root tips were differ- entiated. Cells are larger in size than those in the control stem bases and no cell division was evident. Figure 150 Drawings of gross longitudinal sections of'Y-ho onions after two months of common storage. TOp - Treated with MH (2500 ppm). Bottom - Control (no treatment). Whit 65 Figure 16 e Photomicrographs of longitudinal sections of the bases of onion stems (15 weeks after harvest). Left - Section from a control bulb Right - showing the root primordium with its high.meristematic activity. Magnification: x266 Section from treated bulb. It is evident that the apical cells of the root primordium which would normally be meri- stematic were enlarged, resulting in a broadening of the apical region. Magnification: 1266 'lL ~ ll h".'l‘ " ... :nq awn, ’ ’0 '0 I. \.I s ‘qi‘al ‘1 ‘11 ‘ i r . ':* 66 V. DI SCUSSI ON The effects of foliage applications of MH on the growth and-deve10pment of plants and tubers of potatoes were dependent largely upon the age and the variety of the plants treated. Results from these studies showed that the age of the plant when treated is very important. Potato plants which received MH applications at an early stage of growth, showed greater injury than those which received late appli- cations of the chemical. The very earliest applications were not as injurious as the second early. Potato plants which received.MH treatments late in the growing season undoubtedly were in a physiological condition which per- mitted greater tolerance to the chemical without observ- able injury. MH inhibited growth more wherever conditions for growth were more favorable. In the case of older potato plants, a higher concen- tration of MH (2500 ppm) was applied with little apparent injury (12). ‘Thus old maturing plants are capable of toler- ating 2500 ppm of MH with less injury than young vigorously growing plants. Crafts 32 21. (12) also observed that MH inhibited vegetative plant growth temporarily if physiolog- ically tolerable concentrations were applied. Observations made during the course of these studies showed that 2500 ppm of MH seriously injured the plants which received the 68 treatments on June h and June 18 in 1952 and June 15 and June 29 in 1953. Plants treated with MB on June 18 in 1952 and June 15 and 29 in 1953. were the most severely inhibited. When.MH inhibited terminal vegetative growth, some stimulation of lateral bud growth was observed (72). In most cases where terminal buds were killed or permanently injured no later terminal growth took place. Thickening of potato stems above ground was noticed when the growth of terminal buds was stepped. Injury from early applications of 2500 ppm of MH varied according to the variety. Sebago, Chippewa and.Kathadin showed more resistance than the other varieties to ME injury. Russet Burbank, Kennebec, Irish Cobbler and Triumph seemed to be the most susceptible to both vine and tuber injury from MH. Differences in vari- etal responses to NH have been noted also for corn (59) and sweet potatoes (18). Very little "pitted scab-like" injury (h2) on potatoes was found when plants were treated at the time the largest tubers were one-half to one inch in diameter. The applications of MH at later stages of growth did not damage the buds or tuber eyes or increase the amount of "pitted scab-like" injury. It has been reported (h8) that MH exerts variable influences on the reproductive processes in various plants. Jackson (30), using 500 to 1000 ppm of MH applied to plants 20 to 22 weeks old inhibited seed stalk elongation. Results of these studies with potato plants showed that the reduced 69 number of flowers, abscission of flower buds, resulting from the application of high concentrations of MH were due pri- marily to the inhibition of growth and development of flowers subsequent to their initiation. That the MH sprayed on leaves and stems is translocated to the tubers is indicated by the fact that misshapened tubers resulted in some varieties with the early treatments and also that sprout growth was retarded in tubers harvested from sprayed plants. One of the most puzzling questions is regarding the consistent and definite change of shape of the tubers of certain varieties as a result of early foliage sprays of 2500 ppm of MH. Discussion of the change of shape of the tubers under these experiments is beyond the scepe of this paper, except to state the application of plant growth regulators might result in modification of the "field forces" in the tubers. It has been reported by Paterson (52) that early applications of high concentrations of MH affected the size and shape of the tubers. 2500 ppm of MH applied June 15, June 29 and July 13, 1953. reduced the average weight per tuber significant at the one per cent level (Table IV). MH applied June 15 and June 29, 1953, gave significantly higher yields of deformed tubers and also resulted in the production of a greater number of deformed and small tubers compared with non-treated controls (Tables V, VI and VII). It is very interesting to note in both 1952 and 1953 years that the second early application of MH had 70 a more pronounced effect on increasing the yields of deformed tubers, the number of deformed and small tubers, and also in the reduction of tuber size than the earliest spray treat- ment applied shortly following vine emergence. This might have resulted from the presence of a greater amount of foliage at the second early application of MH and also due to the possibility that tuber formation might have been greater than at the time of the earliest spray treatment. Although there is some latitude in the time during the growing season that MH can be applied with effectiveness and in the concentrations which can be used, this chemical will decrease the total yield and the yield of U.S. No. 1 potatoes if applied too early in the growing season as is shown in Tables I, II and III and as has been reported by Paterson (52). Significant reductions in yield from the spray treat- ments (June h, June 18, July 1, July 15 and to a lesser extent for August A, 1952) were detected indicating the necessity for proper timing of application of the chemical if satisfactory results are to be obtained. Sprays of MH at 2500 ppm applied June 15, June 29, July 13 and July 27, 1953. significantly depressed the total yield of most potato varieties, but 1000 ppm of CDAA applied July 27, 1953 did not affect the yields (Tables II and III). With respect to the yield of U.S. No. 1 potatoes, it is clear that with the depressing effect early (June 15 and June 29) 71 applications of ME, and that the Triumph and Irish Cobbler varieties were affected more than any others (Table II). Even though Sprays of MH applied June h and June 18, 1952 Significantly depressed the yield of potatoes, they did not Significantly decrease sprouting in storage. Almost complete inhibition of Sprouting for all varieties resulted only from single preharvest foliar Spray of MH applied July 15 and August h, 1952 (Table VIII). The Sprouts of potatoes treated earlier (June h and June 18) in the growing season were normal in appearance as contrasted with the Sprouts shown in Figure 12 (bottom) when the same concen- tration of the chemical was applied July 15, 1952. Apparently, the MH Spray should be applied after the young tubers or the buds on the young tubers have been initiated to give effective Sprout inhibition during storage. In contrast to the results of treatment of the 1952 potato crep, the data obtained for the 1953 crOp on storage Sprouting (Table IX) and yield of 10 varieties and 8 treat- ments (Tables II and III) reveal some interesting facts. With Irish Cobbler, Pontiac, Kathadin and Chippewa, Sprouting was almost completely controlled by the July 31 application with no reduction in total yield or yield of U.S. No. 1 tubers. In Sebago, Russet Rural, Russet Burbank and Triumph, Sprouting was effectively controlled by the August 13 application with no accompanying reduction in total yield or yield of U.S. No. l tubers. In Green Mountain, sprouting was effectively x) 72 controlled by the July 13 and 31 applications with no reduction in total yield or yield of U.S. No. 1 tubers. An exception was Kennebec, in which the July 13 and 31 treatments with MH gave the most effective control of Sprouting but this was accompanied in.each instance by a significant reduction in total yield and yield of U.S. No. l tubers. These data however, on control of storage Sprouting should be considered with some reservation since only a small amount of Sprouting had occurred in all treatments and varieties on February 10, 195A. The data nevertheless suggest that although the most desirable time for treatment with MH may vary with variety, storage Sprouting may be controlled without reduction in yield (3h). The toothpick technique of treatment which has been described by Marshall and Smith (hZ) was employed to insure penetration of some newer growth regulators. No significant difference was found between the sprout growth of tubers pierced with toothpicks soaked in distilled water and tubers with no toothpicks. Significant reduction of Sprouting was noticed in tubers treated with 500 ppm and 1000 ppm of 2,h,5-T, 500, 1000 and 2500 ppm of ethyl ester of CDAA and MENA at the rate of 1 gram per bushel of potatoes. Fusarex dust at a rate of one pound per five bushels of potatoes did not retard the Sprouting (Table IX). It is assumed that one of the reasons for no reduction of Sprout growth by Fusarex 73 was due to its successful use in bin storage but not in bag tests (17). The inhibition of Sprouting of tubers by post harvest treatment in storage with chemicals seems to be very temporary, because the treated tubers started to Sprout again after 5 weeks. Paterson (52) and Jackson (30) Showed that MH destroys apical dominance in potatoes and celery plants reSpectively, depending upon the concentration of the chemical and age of the plants. It can be seen from Figures 10 and 11 that there is almost a complete inhibition of Sprouting by ME treatment (July 1, 1952) at the apical regions of the tubers but not at the basal regions. It is interesting to note that tubers resulting from treatment with 2500 ppm of MH applied July 1, July 15 and August h, 1952 and planted January 7, 1953 in the greenhouse remained sound but com- pletely dormant for eight weeks, whereas non-treated tubers and those treated June a and June 18, 1952 grew normally producing profuse roots and large vegetative tOps. Any practical method of forcing normally dormant or chemdcally induced dormant tubers and bulbs to Sprout when desired would be of great advantage. The possibility of the artificial chemical stimulation of the tubers and bulbs from a dormant into an active condition was investigated. No chemicals tested had any effect on breaking the dormancy induced by MH. It seems as though the dormancy caused by MB is permanent and no artificial stimulation tested would affect it. 71L Although no chemical tested had any effect on breaking the dormancy induced by ME in storage, the field studies on onions in 1952 showed that the application of 2,h~D following treatment with.MH completely nullified the favorable storage influence induced by MH. LeOpold and'Klein (39) have demon— strated that indoleacetic acid completely overcomes MH inhibition using four different inhibitory levels. Studies by LSOpold and Klein (39) showed that auxins are necessary for apical dominance in plant growth. Work with plant growth regulators such as triiodobenzoic acid, coumarin, 2,h-chloranisole, and trans-cinnamic acid has Shown that these substances possess anti-auxin capacities capable of lessening or destroying apical dominance (39). Therefore, these plant growth regulators are classed as anti-auxins because of their inhibitory action on apical growth in plants. Histological studies other than those reported in this thesis have revealed that among the most significant reSponses following treatment with growth regulators has been the greater develOpment or influence of the vascular system. In almost all of the literature concerning histo- logical reSponses to growth regulators, activity of the vascular tissues has been recorded but it seems to the author that only a few have recorded it with the emphasis that it needs. In dealing with the relationship of plant growth regulators and the vascular system, one of the most striking effects of these substances is the tendency for vascularization 75 of derived tissues even outside the normal regions of existence of vascular strands, for example, in such unusual places as the pith, the endodermis, etc. (36, 37). Liabach and Fishnich (38) noted in Coleus that new vascular bundles appeared among the three originally present on each side. There is no doubt that the vascular system has played an important role as a conducting tissue in producing all the reSponses which we have recorded, such growth reSponses as the increased thickness of organs -- the stem and the leaf. With reSpect to other histological reSponses, they have been in consonance with the general feature of behavior of growth regulators to the effect as expressed by Kraus, Brown and Hamner (36) that none of the types of cells were fundamentally different from cells occurring in the plant grown under the usual conditions of culture and environment. Histological studies of the bases of onion stems and buds of potato tubers showed a definite inhibition of cell division by ME treatment. The most typical alteration induced by MB is the flattened shape of the apical meri- stems and the lack of meristematic cells (Figures 13 and 16). These effects of MB on the anatomical structure of onions and potatoes characterize it as a growth inhibitor. Further evidence of this comes from the work of Greulach and Atchison (20) who, working with root tips of'Yellow Globe onions, showed that MH inhibited mitosis and cell division in pro- portion to the concentration used. They also observed that 76 onion roots failed to grow again following_MH treatment. It is probable that the internal differences of the meri- stematic activities of the cells in the roots and buds or eyes are closely associated with the visually observed external differences in Sprouting. VI. SUMMARY A study of some effects of preharvest foliar Sprays of maleic hydrazide (2500 ppm) on certain physiological, morphological and histological reSponses in potatoes and onions, disclosed the following: Foliar sprays of NE at 2500 ppm applied June h and June 18.1n 1952 and June 15 and June 29 in 1953, resulted in delay of the Opening of flowers, malformed and stunted leaves, and thickened stems of all the potato varieties. A marked difference in the response of potato varieties to ME was noted. Chippewa, Sebago and Kathadin showed the greatest resistance to injury following early applications of MH. Russet Burbank, Kennebec, Irish Cobbler and Triumph were very sus- ceptible to ME injury. Early applications of MH definitely reduced the tuber size and increased the number of small and deformed tubers. Significant reductions in total yield from all Spray treatments were detected in 1952. However in 1953. no significant reductions in total yield or yield of U.S. No. 1 potatoes were noted with the 10 varieties tested when.MH was applied August 13 or 25. CDAA at 1000 ppm applied July 31 resulted in no yield reduction. 78 Satisfactory inhibition of sprouting resulted from a single preharvest foliar spray of 2500 ppm of MH applied on either’July 1, July 15 or August A, 1952. Storage data for the 10 potato varieties grown in 1953 (planted.May 15 and harvested September 2h) indicate that satisfactory inhibition of sprouting resulted from.a single preharvest foliar Spray of 2500 ppm of ME applied on either July 13, July 31 or August 13. 1953. CDAA at 1000 ppm applied July 31 resulted in no practical reduction of Sprouting in storage. Preliminary experiments conducted in storage using the toothpick technique revealed that the ethyl ester of CDAA may be prmmising as a Sprout inhibitor on potatoes. Fusarex was not as inhibitory to Sprouting as was MENA when.both were applied in the dust form to potatoes in storage as a post-harvest treatment. MB applied July 1, July 15 and August h, 1952 showed complete inhibition of sprouting at the apical regions of the tubers but some growth was evident at the basal regions. Tubers harvested from plants treated ‘with MH early in the growing season, were almost as good as non-treated ones for seed purposes. Sprouts from the basal ends of tubers harvested from plants treated early in the season with MR and those harvested from.non-treated plants grew slower than Sprouts arising from.the apical ends of non-treated tubers. 79 No chemical treatment was found effective in breaking the dormancy induced by MR in either onions or potatoes. In field studies, however the desired effect from inhibition of Sprouting induced by 2500 ppm of MH, is completely nullified by an increase in breakdown resulting from a subsequent spray application of 1000 ppm of 2,h-D. Histological studies revealed that with.MH there was some inhibition of differentiation of tissues in the buds and root primordia of tubers and bulbs, reSpectively, and there was also a retardation of cell division. The greater diameter of stems of potato plants following treatment with MH can in part be explained by an increase in cell Size. l. 2. 3. h. 5. 6. 7. 8. 9. 10. 11. VII. LITERATURE CITED Artschwager, E. 1918. Anatomy of the potato plant with Special reference to the ontogeny of the vas- cular system. Q, Agr. Res. 1hz221-252. Artschwager, E. 192h. Studies on the potato tuber. .1: Agr. Res. 27:809-836. Barnard, E. E. and Warden, R. L. 1950. The effects of various herbicides on weed control, stands and yield of netted gem potatoes. Pros. 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