ABSTRACT THE INHERITANCE AND RELATED STUDIES OF THE PARTHENOCARPIC CHARACTER IN CUCUMBER, CUCUMIS SATIVUS L. by Leonard Maxwell Pike Parthenocarpy in the cucumber is conditioned by an incompletely dominant gene 32' Heterozygous BE plants pro- duce fruits later and generally fewer in number than the homozygous 2g genotype. Homozygous recessive pp plants do not produce parthenocarpic fruits. All plants in progenies derived from a backcross to the non-parthenocarpic parent were classified as non- parthenocarpic when fruiting was identified by means of trapping pistilate flowers to prevent pollination. The fact that six out of eighteen progenies from plants self- pollinated in this backcross generation segregated typical 23 plants that were parthenocarpic and multiple-fruiting is evidence for incomplete dominance. Cage isolation of gynoecious progenies segregating for parthenocarpy is an effective technique for identifying late fruiting heterozygous plants. The difficulty of trap- ping all pistilate flowers over the entire fruiting period resulted in incorrect classification of heterozygous plants. Leonard Maxwell Pike especially in progenies segregating for monoecious sex ex- pression with very late pistilate flower production. Homo- zygous g3 plants were identified accurately in the F by 2 selecting for early, multiple fruiting in parthenocarpic plants. Progenies from selfed F2 plants of this type pro— duced only the parental type of F3. Modifying genes may influence fruit numbers since 19 of 54 plants classified as §p_produced three or more late fruits. The smooth, non-ridged skin of Spotvrije is con- ditioned by the homozygous recessive £35, £35. Gynoecious parthenocarpic plants exhibit earlier fruiting than monoecious and are necessary for field pro- duction of seedless fruits. Parthenocarpic fruits ten inches long and 2 1/2 inches in diameter did not brine satisfactorily unless pricked. Six inch fruits, 1 1/2 inches in diameter, brined as well as seed fruits the same size. A consumers panel showed no preference between par- thenocarpic and seed-type fresh market cucumbers but pre- ferred the products processed from seedless fruits. It was demonstrated that multiple-fruiting, par- thenocarpic varieties suitable for mechanical harvesting can be developed and that seedless cucumbers and processed products will be accepted by consumers. THE INHERITANCE AND RELATED STUDIED OF THE PARTHENOCARPIC CHARACTER IN CUCUMBER, CUCUMIS SATIVUS L. BY Leonard Maxwell Pike A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Horticulture 1967 ACKNOWLEDGMENTS The author wishes to express his appreciation to Dr. C. E. Peterson for his assistance during the course of this research. Appreciation is also expressed to Dr. W. J. Hooker, Dr. E. H. Everson, Dr. M. J. Bukovac, Dr. A. A. Dehertogh, Dr. W. M. Adams and Dr. D. Markarian who served as committee members. Acknowledgment is expressed to Amos Lockwood for his assistance and encouragement during the study. My wife, Roxy Ann, not only assisted with the writing of this thesis but served an an inspiration through- out the study. To her I am sincerely grateful. ii TABLE OF CONTENTS ACKNOWLEDGMENT S O O O O O O O O O O O O 0 LI ST OF TABLES O O O C O O C O O O C O 0 LIST OF FIGURES O O O I O O O O O O O O 0 INTRODUCTION 0 I I O O O O O O O O I O 0 REVIEW OF LITERATURE O O O C O O O O O 0 Characteristics of the Cucumber . . . . I. Qualitative . . . . . . . . . . II. Plant Characteristics . . . . . III. DevelOpment of Cucumber Varieties for Mechanical Harvesting . . IV. Cultural Practices Contributing to Mechanical Harvesting . . V. Observations Concerning Concentrated Fruit Set . . . . . . . . . . . . . VI. The Parthenocarpic Fruiting Character VII. Physiological Factors Associated with the Parthenocarpic Character EXPERIMENTAL . . . . . . . . . . . . . . Inheritance and Related Studies of the Parthenocarpic Character 1965 . . Materials and Methods . . . . . . . Results and Discussion . . . . . . Inheritance of the Parthenocarpic Character . . . . . . . . . . . Relation of Sex, Fruit Type, Skin Type, and Flowering Date to Parthenocarpic Fruiting . . . . Relation of Sex Expression and Earliness . . . . . . . . . . . Inheritance of Skin Types . . . . Multiple-Fruiting on Parthenocarpic Plants . . . . . iii Page ii vi 11 15 15 15 18 18 19 19 23 23 $4.1m 1;.- Page Inheritance Studies of the Parthenocarpic Character 1966 . . . . . . . . . 28 Materials and Methods . . . . . . . . . . . . 28 Results and Discussion . . . . . . . . . . . 32 Classification of Progenies from Backcross to MSU 713-205 Selfed . . . . . 40 Observations from F3 Progenies . . . . . . 41 Commerical Acceptability of Parthenocarpy in Fresh and Processed Cucumbers . . . . . . . 43 Consumer Acceptance of the Parthenocarpic Cucumber . . . . . . . . . . 43 Materials and Methods . . . . . . . . . . 43 Results and Discussion . . . . . . . . . 44 Preliminary Brining Observation on the Parthenocarpic Cucumber . . . . . . 49 Methods and Materials . . . . . . . . . . 51 Results and Discussion . . . . . . . . . 52 SUMMARY 0 C C O O O O O C O O O O O O I C O O O O O 5 8 REFERENCES CITED 0 O O O O O O O O O O O C O O O O 60 iv LIST OF TABLES Table Page 1. Segregation for parthenocarpic fruiting in cucumber progenies in 1965. A test for a single recessive hypothesis . . . . 20 2. The relation between sex expression and earliness of female flowering as ob- served in F2 generation of the cross MSU 713-205 and Spotvrije . . . . . . . . 21 3. The relation between sex expression and earliness of female flowering as ob- served in the backcross to MSU 713-205. . 21 4. The relation between sex expression and earliness of female flowering as ob- served in the backcross to Spotvrije. . . 22 5. The inheritance of skin type in cucumber. . 25 6. The relation between sex expression and fruit numbers in parthenocarpic cucum- bers O O O O I O O O O O O O O O O O O O 27 7. Example of method to record data on par- thenocarpic fruiting in cucumbers . . . . 33 8. Segregation for parthenocarpy in the cucumber I O O O I O I I O O O O O O O O 3 5 9. Number of fruits and range of nodes at which parthenocarpic fruits were borne in cucumber . . . . . . . . . . . . . . . 39 10. Results in the F3 generation from F2 plants selected for early multiple fruiting I O O O O O O O O O I O O I O O 42 ll. Acceptance of parthenocarpic fresh cucum- ber and processed products by a consumers panel at Detroit, Michigan, 1966 . . . . 50 Figure II 10. 11. LIST OF FIGURES Page A parthenocarpic fruiting plant with rough Skin I I I I I I I I I I I I I I 24 A parthenocarpic fruiting plant with smooth Skin I I I I I I I I I I I I I 24 A 12' x 80' screen cage used for pro— tecting parthenocarpic cucumber plants from insect pollination . . . . 31 A 12'x 80' screen cage used for pro- tecting parthenocarpic cucumber plants from insect pollination . . . . 31 Parthenocarpic fruiting habit of a typical plant classified as homo- zygous dominant Pg . . . . . . . . . . 36 Parthenocarpic fruit production on a typical plant classified as hetero- zygous Pi I I I I I I I I I I I I I I 3 7 A typical non-parthenocarpic plant classified as homozygous recessive a I I I I I I I I I I I I I I I I I I 38 Cross-cut sections from parthenocarpic fruits are on left and those from Spartan Dawn are on right . . . . . . 45 Spears made from parthenocarpic fruits are shown on right and spears from Spartan Dawn on left . . . . . . . . . 46 Parthenocarpic fruits are shown at top and locally purchased seed type slicers are below . . . . . . . . . . 47 The form used by the consumers prefer- ence panel in Detroit, Michgian . . . 48 vi Figure Page 12. The pricked 10 inch parthenocarpic fruits are shown on left and non- pricked on right illustrating condition after brining . . . . . . . . 54 13. Interior condition of pricked 10 inch parthenocarpic fruits are shown on left and non-pricked on right illus- trating condition after brining . . . . 55 14. The firm condition of mature 6 inch parthenocarpic fruits after brining . . 56 15. The firm non-bloated condition of im- mature 6 inch parthenocarpic fruits after brining . . . . . . . . . . . . . 57 vii INTRODUCTION The processing cucumber industry in Michigan during 1960-1964 averaged 25,000 acres which yielded 122,000 tons with a farm value of approximately seven million dollars based on 55 dollars per ton. In 1965, 17,000 acres were grown producing 95,000 tons at a value of 93 dollars per ton. In 1966, 21,000 acres yielded 122,000 tons at a value of 91 dollars per ton. Increase in value per ton from 55 dollars to over 90 reflects added cost of labor for harvest resulting from minimum wage law and increased use of domestic labor following termination, on December 31, 1964, of Public Law 78 which provided for importing Mexican laborers. The acute shortage of labor for harvesting proces- sing cucumbers has cost growers and processors in Michigan more than three million dollars per year in labor costs alone. It has threatened the loss of at least part of the fifty million dollar pickle industry to competing areas where labor problems are not so acute or where mechanical harvesting can be more easily accomplished; Ideals for plant phenotypes of new varieties suit- able for mechanical harvesting have varied among engineers, processors and plant breeders but one fact generally accepted is the need for multiple fruiting by the cucumber plant. The work reported here was undertaken to determine the inheritance and possible utilization of parthenocarpy in developing cucumber varieties for the new mechanical harvesters. Successful genetic control of this character and its incorporation into acceptable varieties might con- tribute to achieving the concentrated fruiting and higher yields needed for mechanical harvesting. REVIEW OF LITERATURE CHARACTERISTICS OF THE CUCUMBER I. Qualitative The cucumber, Cucumis sativus, has been used by geneticiststr studying inheritance of many fruit and plant characteristics. The advantages of great variability and a relatively short life cycle led many researchers to explore and to report on its characteristics. This review is limited to literature dealing with improvement of quality, yield, or other characteristics pertinent to this study. The development of any crop variety is generally the result of some demand imposed upon it either by nature or man to alter its genetic construction. Qualitative characters, generally established by the cucumber proces- sing industry and consumer preferences, stimulated inves- tigations by researchers. Fruit shape was studied very early by Tiedjens (36) who noted that environmental influence was important in develOping well-shaped fruits. Spine color, number of Spines, wartiness, skin color, skin toughness, and flesh color have been listed as important by processors. Wellington (39) reported that black spines are dominant to white, coarse spines dominant to fine and few spines domi— nant to numerous spines. Strong (33) later reported that mottled fruit color was dominant to non—mottled, wartiness dominant to non-warty fruits, green flesh dominant to white flesh color and thick, tough skin dominant to thin, tender skin. He noted what appeared to be a linkage between the group of mottled, dull, warty, thick tough skin characters and the group of non-mottled, glossy, non-warty, thin ten- der skin characters. Younger (41) reported that three- locule fruits were dominant over five-locule fruits. Bloating, a term applied in the industry to fruits which develOp internal cavities during the fermentation process, is of great importance. Bloaters can not be used in any out product except relish. The inheritance of the bloating tendency has not been reported but is presently being investigated at Michigan State University. The in- heritance of a bitter tasting compound was found by Barham (3) to be conditioned by a single dominant gene. Later Andeweg (1) reported a single recessive gene for non-bitter and outlined methods for selecting the non-bitter genotype. Quality of the cucumber often depends upon its freedom from infection by disease producing organisms. Important contributions have been made to understanding the inheritance of disease resistance and incorporating it into useful varieties. Shifriss, Myers, and Chupp (28) reported that resistance to cucumber mosaic virus was conditioned by multiple genes. A later report by Wasuwat and Walker (38) established that the resistance was con- ditioned by a single dominant gene with possibly modifying genes. Both Walker (37) and Andeweg (1) found scab resis- tance to be controlled by a single dominant gene. Barnes and Epps (4), (5), found resistance to anthracnose varied from almost complete dominance to a highly complex type of inheritance. Busch and Walker (8) reported finding a simi- lar type of resistance. The inheritance of downy mildew resistance was reported by Jenkins (16) to be conditioned by a large number of genes. Smith (32) reported that re- sistance to powdery mildew is multigenic. II. Plant Characteristics In some of the first studies concerned with multiple- pick mechanical harvesting, Stout and Ries (34) described problems of vine entanglement and foliage damage. It was demonstrated that a great disadvantage of multiple-pick machines then available was that they could not remove fruits borne within six inches of the base of the plant. The demand for developing new varieties of cucum- bers acceptable for mechanical harvesting led several re- searchers to investigate plant characteristics. Phenotypes suggested as suitable for mechanical harvesting varied from dwarf vines to indeterminant having either many laterals or no laterals. Hutchins (14) reported in 1940 that determinant plant growth in the cucumber is dominant to indeterminant and that tall plants are dominant to dwarf. Odland and Groff (20) later reported finding what was as- sumed to be a different determinant since they demonstrated that in their material indeterminant habit was dominant to determinant. Researchers interested in adapting plants for a multiple-pick harvester investigated vine habits which would permit multiple pickings with the least damage to the vines. Bowers (6) reported a radiation-induced mu- tation for absence of tendrils. Rowe and Bowers (26) later reported that the tendrilless character is condi- tioned by a single recessive gene and suggested this character might prevent tangling in multiple harvesting of cucumbers. Burnham (7) investigated the inheritance of branching, sex reversal, and ease of stem separation from the fruit. He demonstrated the branching character was conditioned by a polygenic system, in which a thres- hold number of heterozygous loci interact with the environ- ment. He reported that five generations of inbreeding failed to fix sex-reversal in which the plant produces several nodes with male flowers and then converts to gynoecious. He observed an almost constant 1:1 segregation for sex reversal and normal monoecious types. The ease of stem separation was shown to be related to the area of stem attachment of the fruit. III. Development of Cucumber Varieties for Mechanical Harvesting The rapid change from manual to mechanical har- vesting of processing cucumbers created the need for modi- fying the cucumber plant. Greatest emphasis has been on qualitative characteristics such as fruit color, spine color, length/width ratio, and bloating of the fruit during brining. A cucumber plant acceptable for mechanical har- vesting must resist mechanical damage from multiple harvest by machines or for a single destructive harvest it must produce several marketable fruits at one time even at high plant pOpulations. Peterson (21) used gynoecious sex ex- pression from the variety Shogoin (PI 220860) in a back- crossing program to develOp MSU 713-5, a gynoecious line of pickling cucumber. This development made possible the use of hybrids in which greater uniformity of maturity could be obtained. Peterson and Anhder (22) discovered that gibberellin A3 induced staminate flowers on gynoecious plants and proposed a method for maintaining gynoecious lines. The hybrid pickling cucumber Spartan Dawn described by Peterson and deZeeuw (23) was released in 1961. It con- sistantly out yielded standard monoecious varieties and proved to be acceptable for mechanical harvesting. Many similar hybrids are now being produced with most using MSU 713-5 or derivaties of it as the female parent. The inheritance of the sex expression in cucumber was reported by Shrifriss (27), who found three groups of genes conditioned the expressions. He listed one major gene for differentiating pistillate flowers, a group of poly-genes which regulate speed of sex conversion, and a major gene (Acr) which accelerates the speed of conversion. Mitchell (18) hypothesized that sex expression was controlled by levels of endogenous auxins. However, these substances were not identified. Hayashi (15) found that monoecious cucumber seedlings contained greater quantities of gibberellin Al or A3 than gynoecious. Burnham (7) reported that the multiple fruiting habit of Rhensk Drue was expressed in F1 between MSU 713-5 and Rhensk Drue. IV. Cultural Practices Contributing to Mechanical Harvesting Besides the genetical rearrangement used to increase yields for a once-over harvest, cultural practices have been eXplored. Cucumbers previously were grown at wide spacings of forty-two to forty-eight inches between rows and one foot or more between plants within the row. The main reasons were that most farm machinery was fitted for those spacings, and irrigation was neither available nor economical. Ries (24) studied the effect of spacing and supplemental fertilizer application and found both early and total yields of pickling cucumbers could be increased by close spacing. Putnam (23) showed the number of fruits per plant was greater at one foot spacing than at six inches and dollar yields were highest using 43,560 plants per acre. Higher populations did not increase dollar yields. V. Observations Concerning Concentrated Fruit Set Probably the most limiting factor in the deve10p- ment of varieties suitable for mechanical harvesting is that multiple fruiting does not occur in standard varieties of cucumbers. McCollum (l7) and Dearborn (9) reported that a developing fruit exerts an inhibitory effect on further vegetative develOpment in cucumber plants. This has led some investigators to believe that developing embryos pro- duce a growth regulating substance which limits further vegetative growth. Tiedjens (36) noted a difference be- tween varieties in their capacity to mature a number of fruits at the same time. He felt this was due to the time of flowering since in his observations flowers pollinated at the same time develOped equally well while later polli— nated fruits did not develop once the first fruit began growing. Putnam (24) found from growth measurements of normally developing and arrested fruit that both showed similar growth for the first two days after pollination, but after the third day the arrested fruit showed no fur- ther increase in size. 10 VI. The Parthenocarpic FruitingVCharacter It is evident that manipulations of the cucumber phenotype and alterations of cultural practices have not yet solved the problem of obtaining concentrated fruiting. If earlier reports are correct in assuming seed develop- ment inhibits subsequent fruit from developing it seems logical that a fruit which produced no seeds would permit a more concentrated fruit production. Parthenocarpic varieties of cucumbers have been used for many years in EurOpean greenhouse production. These varieties have not been used in outdoor production because pollination by insects results in unmarketable seed-fruits which have a depressing effect on subsequent pollinations similar to that of early fruits borne on non- parthenocarpic varieties. Peterson (21) proposed incor- porating parthenocarpy into gynoecious lines for greenhouse production. Wellington and Hawthorn (40) studied the character while developing an intermediate length fruit for use in American greenhouses. However, with the small p0pulations used in their breeding work the genetic data was not conclusive. In crosses of White Spine with Tele- graph and White Spine with Richard Invincible no seedless fruits were develOped on F1 plants. Upon replanting Fl seed the following year one plant produced a parthenocarpic fruit. This led to the assumption that the character is 11 incompletely dominant. In a cross of Fiske White Spine and Early Russian, six Fl plants produced a single par- thenocarpic fruit, one plant produced two and twelve plants produced none. In a backcross to Richard Invin- cible a progeny of six plants had only one that produced a single parthenocarpic fruit. In a cross of Arlington White Spine x Rochford Market the F1 produced no partheno- carpic fruits but an F2 plant, selfed because of its shape and color, produced an F3 progeny in which all plants de- veloped parthenocarpic fruits. The following F4 generation also produced only plants with parthenocarpic fruiting. Wellington and Hawthorn (40) also noted a difference in the capacity of the EurOpean varieties to produce high numbers of fruits. In a genetic study on the inheritance of the par- thenocarpic character in diploid bananas, Dodds and Simmond (10) found the character to be controlled by a dominant gene with additional modifier genes being responsible for the varying degrees of parthenocarpic fruit set. VII. Physiological Factors Associated with the Parthenocarpic Character Parthenocarpic fruit develoPment has been studied in several species of plants. Fitting (ll) noticed ovary development in orchids occurred in some cases if either foreign or dead pollen was applied to the stigma. He also 12 demonstrated that water and absolute alcohol extracts of pollen induced ovary development. Thimann (35) then demon- strated that pollen extracts caused a curvature of 52233 coleoptiles. Gustafson (12) studied ovary enlargement after observing that seedless fruit sometimes developed following attempted crosses between species or genera of plants. Seed never developed following these wide crosses but parthenocarpic fruit development occasionally occurred. Chloroform extracts of pollen from Curcurbita maxima were found to produce ovary deve10pment if applied to cucumbers. Usually the ovaries only doubled in size. In a later study Gustafson (13) demonstrated that ovaries from parthenocar- pic varieties of oranges, lemons, and grapes contained much higher auxin levels at the bloom state than did ovaries from seed-developing types. Two to four weeks after polli- nation the seed types attained auxin levels as high or higher than the parthenocarpic types. He suggested that this relationship should hold true for other species of plants producing parthenocarpic fruits. He also concluded that pollination and developing seeds produced auxin. Gustafson stated that auxin in parthenocarpic varieties was produced either in the ovaries themselves or was trans- ferred into the ovary from the leaves. Sinnott (29), (30), (31), analyzed the relation between cell development and ovary development in the cu- cumber and found that cell division occurs up until anthesis. 13 Further ovary develOpment then proceeds by cell enlarge— ment without appreciable cell division. He also noted that ovary development proceeded at a constant exponential rate, slowing down only as the fruit approached maturity. Nitsch (19) performed an extensive study of plant hormones in the development of fruits of several species. He observed and reported the following: 1I Previous assumptions that the fruit nourished the ovules were found to be false. It is apparent that chemical stimuli for ovary de— velopment comes from: a. vegetative parts of the plant; b. the pollen and/or pollen tubes; c. the ovules. Auxins influence the transformation from a vegata- tive to reproductive phase. In gherkin ovaries growth proceeded so smoothly and quickly that no differences could be detected in ovary growth before and after pollination, but in slower developing ovaries of orchids two growth peaks were observed, one following pollination and a second as ovules began to develOp. Since such low levels of auxin are present in pol- len, possibly a hormone in pollen converts trypto- phane to auxin in the ovary. Both pollen and ovary tissue produced auxin when incubated in the presence of tryptophane. 14 The developing seeds promoted growth of ovaries as evidenced by the observation that growth stOpped if the ovules were removed or destroyed before a certain stage of development had been reached. Plants which produced parthenocarpic fruits prob- ably have genes for increased auxin production. Indole-3-acetic acid was ineffective in producing parthenocarpic fruits. Possible reasons are that it was rapidly destroyed during application, or by plant enzymes, or that IAA is not the fruit setting hormone. EXPERIMENTAL INHERITANCE AND RELATED STUDIES OF THE PARTHENOCARPIC CHARACTER 1965 Materials and Methods During the summer of 1964, an inbred gynoecious pickling cucumber MSU 713-205 was crossed to the EurOpean, parthenocarpic variety, Spotvrije. Twelve F1 plants, grown in the greenhouse during the fall of 1964 were vigor- ous, predominantly female, and did not produce partheno- carpic fruits by the time they had grown to the height of approximately four feet. From this observation it was con- cluded that parthenocarpic is not dominant to non-partheno- carpic fruiting or that the inheritance of parthenocarpy in varieties used by Wellington and Hawthorn (40) differed genetically from that of the variety Spotvrije. A genetic study was outlined to determine the in- heritance of the parthenocarpic character. Crosses were made between MSU 713-205 and Spotvrije and the F1 was selfed and backcrossed to both parents. Spotvrije was also crossed to gynoecious lines MSU 713-5, MSU 153, MSU C-29-63 and MSU C-l4-64 to be observed in the summer of 1965. 15 16 Seed was planted in peat pots in the spring of 1965 and transplanted to the field in the first true leaf stage. A spacing of four feet between rows and two feet between plants within the row was used. The pOpulation for observation included 24 plants of each parent, MSU 713-205 and Spotvrije, 48 F1 plants, 104 of the F 89 of the backcross to MSU 713-205, and 91 2! of the backcross to Spotvrije. Twenty-four plants of each F in which Spotvrije was crossed with MSU 713-5, MSU 153, l MSU C-29-63, and MSU C-l4-64 were observed for partheno- carpic fruiting. In order to test the plants for the parthenocarpic fruiting character, all female flowers were trapped the day previous to blooming using TOp Clip No. 2 paper clips to prevent pollination. It soon became evident that trapping all pistilate flowers in these large pOpulations would be very difficult so a goal of ten trapped flowers per plant was established. Data were recorded when as many plants as possible had ten female flowers trapped. Because of extreme male- ness some plants did not produce ten pistilate flowers during the period of trapping. In these cases all pistil- ate flowers on the plant were trapped through July 21. Trapping was discontinued at this time because of excessive vine growth. 17 Records were taken on sex expression, fruit type, number of parthenocarpic fruits, date of flowering, and skin type. Sex expressions were classified as monoecious, predominantly female, and gynoecious. Fruit types were divided into three classes: short, medium and long. Parthenocarpy was classified on the basis of development of one or more fruits without pollination. Date ing was recorded when the first pistilate flower anthesis. Skin type was classified as smooth or The phenotypic expressions of sex, fruit skin type were evaluated as follows: 1. Sex types a. Gynoecious (G) - plants producing no flowers. of flower- reached rough. type and staminate b. Predominantly female (PF) - plants producing staminate flowers in the first to fifth nodes and producing only pistilate flowers thereafter. c. Monoecious (M) - plants producing predominantly staminate flowers with only occasional pistil- ate flowers. 2. Fruit types a. Short - an approximate classification of pickle type fruits resembling MSU 713-205. b. Medium - an approximate classification given to fruits with lengths generally intermediate between those of MSU 713-205 and Spotvrije. c. Long - an approximate classification given to fruits which were of the general length of Spotvrije. 3. Skin types a. Rough skin - fruits with rough or ridged skin typical of MSU 713-205 and American processing varieties. 18 b. Smooth skin - fruits with the non-rigid skin of Spotvrije. Sex expressions, fruit types, date of flowering, and skin types were recorded to detect any linkage with parthenocarpic fruiting. Results and Discussion Inheritance of the Parthenocarpic Character Observations made in 1965 indicated that partheno- carpy was not conditioned by a single dominant gene. None of the F1 plants produced any parthenocarpic fruits during the period of trapping. In the F2 pOpulation only 23 plants produced parthenocarpic fruits where 78 plants were expected if expression is due to a single dominant gene. Only five plants were classified as parthenocarpic in the backcross to MSU 713-205 while 44 were expected and 49 were classified as parthenocarpic in the backcross to Spotvrije where 91 were expected. The data in Table 1 show that genetic ratios were a good fit for a single recessive gene controlling the parthenocarpic character except for the backcross to MSU 713-205. The five out of 89 plants in the backcross to MSU 713-205, which produced at least one parthenocarpic fruit, disproved the single recessive gene theory since homozygous recessives for parthenocarpy could not occur in the backcross to non-parthenocarpic. The ratios 19 observed in 1965 will be discussed in more detail along with the data secured in 1966. However, these data sug- gested something other than single gene action with com- plete dominance. The results could only be explained on the basis of incomplete dominance and the failure to pr0per1y identify the phenotype of heterozygotes in the F1' F2, and backcross pOpulations. Relation of Sex, Fruit Type, Skin Type, and Flowering Date to Parthenocarpic Fruiting It was not possible to observe a relation between fruit length and parthenocarpy in the F2 population since only three plants out of 104 were classified as having short fruit and none were recorded as short in the back- cross to Spotvrije. No relationships were observed in the backcross to MSU 713-205 since all fruits had the rough skin and only five plants were classified as par- thenocarpic. Sex expression and skin types segregated as ex- pected in both the parthenocarpic and non-parthenocarpic portions of the populations indicating that no linkages existed between these characteristics and parthenocarpy. Relation of Sex Expression and Earliness The relation of sex expression and earliness of flowering is shown in Tables 2, 3, and 4. 20 em. as. m.ms m.m¢ me as am .uomm 1.60mm x mono a I- mm o «m m mm A.uomm x momv mom as. as. ma om Hm mm voa mm A.uomm x memo oo.o .. as o m4 o me am A.uomm x moms u- I- o em o «N am 1.5uummv mflflu>uomm .. I- «N o em o an x.suummuaocv momumas cm: x m .nunmm .nuumm .nuumm .nuumm umflmflmmmao N IGOZ IGOZ HODESZ pmuommxm pm>nwmno omnmflpmm uwnmm mcwuflsnm .mflmwzuommn m>fimmmomu mamcfim m How ummu d .mwma CH moacmmoum umnEsoso cw mcwufloum owmumoocmnuumm How coflummmummm .H magma 21 Table 2. The relationship between sex expression and earliness of female flowering as observed in F2 generation of the cross MSU 713-205 and Spotvrige. Anthesis of First Pistilate Flowers in the F2 POpulation Range of Average Total Sex Expression Flowering Date Plants Gynoecious 6-30 + 7-13 7-5 29 Predominantly Female 6-30 + 7-14 7-6 33 Monoecious 7-1 + 7—21 7-11 42 Table 3. The relation between sex expression and earli- ness of female flowering as observed in the backcross to MSU 713-205. Anthesis of First Pistilate Flowers in the BC to MSU 713—205 1 Range of Average Total Sex Expression Flowering Date Plants Gynoecious 6-30 + 7-10 7—2 58 Predominantly Female 7-1 + 7-15 7-4 31 Monoecious _a - 0 aThere were no monoecious segregates in the back- cross to MSU 713-205. 22 Table 4. The relation between sex expression and earli- ness of female flowering as observed in the backcross to Spotvrije. Anthesis of First Pistilate Flowers in the BC1 to Spotvrije. Range of Average Total Sex Expression Flowering Date Plants . a GynoeCious - - 0 Predominantly Female 7-1 + 7-8 7-5 12 Monoecious 7—10 + 7-21b -C 79 aThere were no gynoecious segregates in the back- cross to Spotvrije. bJuly 21 was the latest date recorded for anthesis of the first pistilate flower due to excessive vine growth and labor required for trapping in the study. cNo average can be shown since a few plants were so extremely male that female flowers were not produced until some time after July 21. The observations of sex expression and earliness of the first pistilate flower established the following points: 1. Gynoecious or predominantly female cucumber plants have the potential for developing fruit earlier than monoecious plants. 2. The earliness associated with the gynoecious and predominantly female plants indicated that an earlier crOp of greenhouse grown parthenocarpic fruits could be obtained in a gynoecious variety. There is a potential increased number of fruit because of the greater number of pistilate flowers. 23 3. In addition to earliness in gynoecious plants, cucumber greenhouses would not have to be screened if the parthenocarpic variety was also gynoecious. If insect pollinations occur the resulting seed- fruits are deformed in the area of seed develOp- ment and are unmarketable. Another fact of great importance is that gynoecious parthenocarpic varieties could be produced under isolated field conditions since, without a source of pollen, there would be no production of seed fruits. Inheritance of Skin Types The two distinctly different skin types of MSU 713- 205 and Spotvrije were studied in addition to the partheno- carpic character and are shown in Figures 1 and 2. It was observed that the ridged skin associated with MSU 713-205, was independent of spine color, fruit length or shape. It was also independent of uniform green and mottled fruit. The skin of Spotvrije was smooth with no ridges or warts. Table 5 illustrates the inheritance of this character. The data illustrates a good fit if the skin type of the EurOpean variety, Spotvrije is assumed to be con- trolled by a single homozygous recessive gene gar, s35 (smooth non-ridged). Multiple Fruiting on Parthenocarpic Plants It was observed that some plants in the segregating p0pu1ations deve10ped several large parthenocarpic fruit while others develOped only one fruit. Data summarized in 24 .cwxm nuoofim suds unmam mcwufldum ofimnmoocwzuumm m .N mudmfim .cfixm swoon suds panda wcfluflsnm owmnmuocwauumm m .H ousmflm 25 a mm. mo. Hm m.v¢ ms m.¢¢ we om .uomm A.podm x momv .. oo. mm o 0 am am Hum A.uomm x moms mom mm. «a. «OH mm om ms ms mm A.uomm x memo I: oo. me o o «m «N am A.uomm x memo -u I- «N «N am o o wflflu>uomm .. I- sm o o am an momumas am: A x mucmam .mxm .Hmmno .mxm .Hmmno N Hmuoa mmuvflpmm cflxm spoosm qflxm nmsom Imuofios mamcflm o How umop m .mcmm m>ammmomu msom .HwnEsoso CH waxy cwxm nDOOEm mo mocmuwumscw one .m wanna 26 Table 6 show that no direct relationship exists between the sex expression and number of parthenocarpic fruits. The gynoecious parthenocarpic segregates, in the F of 2 MSU 713-205 x Spotvrije, developed one to six fruits per plant. These fruits developed from approximately ten trapped pistilate flowers. The average of two fruits per plant is not considered significant since only six plants segregated as parthenocarpic, gynoecious types. Predominantly female plants also deve10ped from one to six fruits per plant with an average of 3.1. Monoecious plants develOped one to five fruits per plant with an average of 2.6. The backcross to Spotvrije produced no gynoecious segregates. Predominantly female plants developed one to eight fruits per plant averaging 4.2. Monoecious segre- gates ranged from one to four and averaged 2.3 fruits per plant. This indicates that there is no direct relation between sex expression and the number of fruits develOped at one time. Fruit number appears to be controlled by a gene or group of genes. Predominantly female plants in the backcross to Spotvrije averaged higher fruit numbers than gynoecious or predominantly female plants in the F2 pOpu- lation. Presumably, Spotvrije has been selected for high total numbers of fruit borne over a long season but 27 .mucmHm mama wamfimuuxm map so mEHu mco um mcflmon>mo mnm3 muflsnw moms» ou mco haco umnu mum3 mc0flum>nmmno Hmumcmm pun pmouoomu no: mnmz monsoon .mucmam pcmummmap so vocab Iona muwsum mo Honesc ummsmfin cam “mmBOH cwm3umn coflumaum> wnu mmumoflpcw mmcmmm . u n u u u u u u . om cm H u m m.~ and mm «.4 mua NH . u u .uomm l.uomm x memo m.~ mud n H.m GIH OH o.m wua o as x.uomm x memo M mmcmm madman AM mmcmm mucmHm M momcmm mucmam Hmnasz Hmnaaz HmQEsz mooflomocoz meEmm haucmcfifiopmum m50fiomocmw mmumflpmm mucmam Oflmnmoocmnuumm so muwdum mo HmQEdz .mumnesoso oamumoocmsuumm cw mumnfisc uflsum can coflmmmumxm xwm cmw3umn coaumawu msa .o magma 28 concentrated fruiting is not characteristic of this variety because of extreme maleness. This could also be the reason for low fruit numbers on monoecious plants from the back- cross to Spotvrije, some of which were extremely male. Data from the 1966 study will further verify this observa— tion. INHERITANCE STUDIES OF THE PARTHENOCARPIC CHARACTER 1966 Materials and Methods In 1965 it was found that in this material partheno- carpic fruiting is not conditioned by either a single domi- nant or a single recessive gene. Several problems had develOped which made a detailed study very difficult. They may be listed as: 1. High labor requirements made it difficult to trap all the large populations grown in 1965. 2. The attempt to trap ten pistilate flowers on each plant failed in cases where extremely male plants produced only a few pistilate flowers during the period of trapping. 3. The develOpment of parthenocarpic fruit on the three predominantly female and two gynoecious plants in the backcross to MSU 713-205 indicated that the fruit might have developed on other plants if trapping of all pistilate flowers had been achieved. A need for revisions in techniques for identifying parthenocarpic segregates was evident. Extremes in sex expressions introduced a variable which made detailed 29 studies difficult because of wide range in numbers and rate of pistilate flower develOpment. From several parthenocarpic lines in the breeding program at Michigan State University, a homozygous par- thenocarpic F3 line segregating for gynoecious sex expres- sion was selected for further study. Gynoecious segregates were propagated by cuttings so that all crosses would have an identical genetic constitution on the side of the par- thenocarpic parent. One of three vegetatively-propagated gynoecious plants (no. 3182-1) produced three well-develOped partheno- carpic fruits on the main stem early in the development of the plant. It was selected for genetic study and increased by additional cuttings. A cross was made between MSU 713-205 and 3182-1 and the F1 was selfed and backcrossed to MSU 713-205 and a 3182-1 plant propagated by a cutting from the one used in the original cross. In the spring of 1966, 22 F1 plants, 135 F 54 2: of the backcross to 3182-1, and 52 of the backcross to MSU 713-205 were planted in the field in rows four feet apart with two feet between plants. Plans were to hand trap pistilate flowers to identify fruiting habit since these gynoecious populations could be more easily trapped than those in previous experiments where there were many monoecious plants. 30 To investigate the possibility of using isolation from sources of pollen to identify parthenocarpic plants in gynoecious lines a second outdoor planting of the same material was protected under a 12 x 80 foot screen cage, Figures 3 and 4. An isolation or cage for gynoecious material would allow the breeder to observe and select in populations exhibiting the wide range of fruit numbers observed in 1965. Five F2 lines from F1 plants selected in 1965 as early multiple-fruiting were also observed in outdoor plantings to determine segregation for earliness and multiple-fruiting. Eighteen progenies from selfed plants of the back- cross to MSU 713-205 were planted to determine if partheno- carpic plants could be recovered in progenies of plants which had produced no parthenocarpic fruit. Pistilate flowers of F1, F2 and backcross progenies between MSU 713-205 and 3182-1 were trapped over a period of time that seemed sufficient for all plants to develOp fruits. The plants were vigorous, indeterminant, branching and all were gynoecious. Some plants exhibited early de- velopment of parthenocarpic fruit while others were diffi- cult to classify because ovaries of the latest flowers trapped were beginning to grow slowly. It was impossible to make a definite classification of parthenocarpic or non-parthenocarpic since it was not known if those ovaries 31 .coflumcflaaom uomwcfl Eonm mucmHm Hmnfisoso Damumoocm launmm meuomuoum Hem poms mono swmuom .om x .NH ¢ ¢ wusuflm m wusmflm _ 32 would develOp completely or if still later ovaries might develop. The excessive growth of the plants made it dif- ficult to continue trapping all pistilate flowers, so attention was directed toward the same progenies being grown under screen isolation. It was found that the same behavior was occurring in the cage and in the outside plots. Since all plants were gynoecious and were protected from insects carrying cucumber pollen, a decision was made to wait for several weeks until the plants had time enough to more completely deve10p before recording data. Detailed observations were made in September, after the plants had attained most of their vegetative growth with large fruits which in some cases were turning to a color associated with normal maturity. Each plant was pulled and stripped of its leaves and laid out for observation with fruits remaining attached. The nodes at which fruit were borne were re- corded for both the main stem and laterals in order to establish precise classes. An example illustrating the recording procedures is shown in Table 7. Results and Discussion The data were first divided into parthenocarpic and non-parthenocarpic classes then analyzed for node num- ber at which the first fruit develOped and for total number 33 Table 7. Example of method used to record data on partheno- carpic fruiting in cucumbers. Number of Fruit Plant Number Sex Fruiting Node(s) Large Small Total 6633-3 G L1, 2 = 0a 2b 0C 2 L3 - 4 = 1 L4 - 3 = 1 aLl, 2 = 0 signified that laterals at nodes 1 and 2 produced no fruit. L3 - 4 = l signified that the lateral at node 3 produced a fruit on node 4 of that lateral. L4 - 3 = l signified that the lateral at node 4 produced a fruit on node 3 of that lateral. L5, 6, 7 = 0 signified that there were laterals at nodes 5, 6, and 7 but that no fruit was produced on them. M = 0 signified that no fruits were produced on the main stem. bFruits which were fully develOped were classified as large fruit. CFruits which were small but definitely growing were classified as small fruit. of normal fruits. This procedure provided a way for the data to be analyzed to distinguish between early fruiting, late fruiting, and non-parthenocarpic fruit development. Plants in the F2 and backcross to 3182-1 were classified as homozygous PP if they produced three or more 34 parthenocarpic fruits with the first developing within five nodes. Plants which produced no fruits by September 15 were classified homozygous recessive pp and those yielding less than three fruits or later than at node five were classified as heterozygous Pp. Data on inheritance of parthenocarpy from the cross MSU 713-205 x 3182-1 are sum- marized in Table 8. Diagrams representing typical plants of the three genotypes are illustrated in Figures 5, 6 and 7. The analysis demonstrated that parthenocarpy in the cucumber material used is conditioned by an incompletely dominant gene P:, with early fruiting on homozygous PP plants, late fruiting on the heterozygous Pp and non- parthenocarpic fruiting on the homozygous recessive pp. It seems, however, that a gene or group of genes associ- ated with the parthenocarpic character modifies earliness and fruiting numbers. Table 9 shows plants in the back- cross to non-parthenocarpic had the widest range and highest average for the first fruiting nodes in the Pp. The modifying mechanism is demonstrated further by five plants in F2 and three in backcross to parthenocarpic which produced three or more fruits with the first fruit at node six to eight. These plant types classified as Pp were borderline cases and partially account for the one to six range of fruit numbers in the table. To ac- curately determine the genotypes of such plants an F3 test 35 .muflnum oamumoocmnuumm 0c pmospoum £0fln3 mucwam ou cm>flw GOADMOHMHmmmao mo Eonm mopoc m>Hm cmnu “mama mufisum ocfi05poum mucmam ou cm>flm coflumowMHmmmao d muflsum mHoE no mounp mo umuflm .mmmn unmam n .mme panda Eoum mono: w>Hm casufl3 on» mcwospoum mucmam 0D cm>wm sowumoflmwmmmao «m mm. ea. c 0 on am on ma mm x mm AHINmHm x momv Hummam pm. we. m.mH ha m.mH ma 0 o mm x mm AHINmHm x momv mom Hm. vm.m m~.m m m.mH ma mm.m ma mm x mm mm Aalmmam x momv . o o o a v o o mm x mm as Aaummam x memo m «x .mxm .Hmmno .mxm .Hmmno .mxm .Hmmno mmwuocmw mm mm mm mmumflpmm o.£uummlcoz n .fiumm mung mfiuumm 38m IEOOGH mamcam o How ummu 4 .wcmm unmaHEOU hamvmam .HmQEdoso may ca maumoocmnuumm How coflummmummm .m canoe 36 / \ / \ [A Figure 5. Parthenocarpic fruiting habit of a typical plant classified as homozygous dominant 23 showing fruit production within five nodes. 37 ’ A Figure 6. Parthenocarpic fruit production on a typical plant classified as heterozygous Pp showing fruit production later than five nodes. 38 Figure 7. A typical non-parthenocarpic plant classified as homozygous recessive pp. 39 o.m I mIH I NH I mNIm I AHINmHm x momv mom w.m m.v oIH hIm m w wanv mIN AHINmHm x momv HINmHm o.m H.m mIH mum m w HHIm mIm mm AHINmHm x momImah szv o.~ I «Ia I m I «HIm I as AHINmHm x momImHs smzv mm mm mm mm mm mm mm mm muflsum .oz uflsum mpoz uma mpoz mcfluflsum .oz mmmum>¢ mo mmcmm mmmnm>< uma mo mmcmm .nmnesoso CH mauon mumz muflsum Uflmumoocwnunmm 30H£3 um mmpo: mo mmcmu paw muflsum mo Hmnfisz .m magma 40 is needed. Nineteen of 54 plants classified as Pp, but not considered borderline cases, finally produced three or more late fruits. This indicates that possibly after a stimulus for ovary growth occurs modifiers may influence fruit numbers. Classification of Progenies from Backcross to MSU 713—205 Selfed Plants from the backcross, 205 (205 x 3182-1), selected for selfing in 1965 were predominantly female. These progenies segregated gynoecious, predominantly fe- male, and monoecious plants in the 1966 plants. Trapping of all pistilate flowers was again not possible. However, it was found that six of the 18 lines tested segregated plants which produced early parthenocarpic fruits. This demonstrated that early parthenocarpic fruiting plants could be obtained from at least one-third and probably one-half of the progenies from plants in the backcross to a non-parthenocarpic parent. The data from the 1966 study explained why par- thenocarpic segregates were recovered in progenies of six out of 18 of these backcross plants, all of which had been classified as non-parthenocarpic in 1965. One-half of these plants in the backcross to MSU 713-205, incorrectly classified by the trapping technique, were heterozygous Pp_and one-half homozygous recessive pp. The homozygous PP segregates from selfed Pp were identified by their 41 early fruiting even though trapping had to be discontinued long before the plant completely develOped. An even better fit might have been achieved if the plants had been under screen and observed for a longer period of time. Observations from F3 Progenies Five F3 lines from F plants selected as early, 2 multiple-fruiting, parthenocarpic were classified and are shown in Table 10. Line 6601 was obtained by selfing a gibberellin- induced gynoecious F2 plant. The resulting twelve F3 plants were gynoecious and all were early and multiple- fruiting. Line 6602, 6603, 6604 and 6605 were from selfed predominantly female F2 plants also selected as early and multiple-fruiting. Those four lines segregated monoecious, predominantly female, and gynoecious plants in the F3. Four plants in line 6602 and two plants in 6603 were ex- tremely male and were not classified as either partheno- carpic or non-parthenocarpic. However, since a total of 30 gynoecious, 12 predominantly female, and 9 monoecious plants were observed and classified as early, multiple- fruiting, the F3 lines were considered homozygous for the parthenocarpic character. The early, multiple-fruiting, parthenocarpic plants produced progenies which were all early, multiple-fruiting except where late fruiting and .pw>oEmH on on me pCm pommmug HOC mnoz COsz 03» Ho mCo aHCo pmoCCOCm no modum mo ooHqu on» mCHHCp muwonm mDMHHumHm 0C pmosponm mmmCmHmE wfimnuxm HmpCC pmumHH muCMHm me mCBn .mHmEmm mHuCMCHEOUmHm mm UCm muCMHm mCoHomOCmm mOHMCmHmmp 0m 42 I CC .mmm moms Cm mmIoamm NH .mmm some mm HmIoamm m .mmm moms mm soanaom m .mmm moms mm mmIoamm NH 6 Home 6 omIoamm mmemHmz mamuuxm .CuummICoz .Cuumm .mxm .oz mCHH m.mxm pCCHm n xmm xwm quHmm .oCHuHCHm mHmHuHCE mHnmm Com pmuomHmm muCMHm mm Bonn COHumumCmv mm map CH muHCmmm .OH mHQMB 43 low fruit numbers were associated with extreme male sex expression. COMMERCIAL ACCEPTABILITY OF PARTHENOCARPY IN FRESH AND PROCESSED CUCUMBERS Parthenocarpic cucumbers have been grown and ac- cepted in European countries for many years. All produc- tion of such varieties is under glass where screening and other precautions are taken to prevent pollination by insects. Obviously the production of parthenocarpic varie- ties in the Open was impossible because of insect pollin- ation and the resulting development of seed-bearing fruits. This problem was partially solved by the develOpment of a large number of true gynoecious lines beginning with MSU 713-5 (21). A combination of gynoecious sex expression and parthenocarpic fruiting should make it possible to produce such varieties out-of-doors by providing adequate isolation from sources of cucumber pollen. Once it was demonstrated that this combination could be achieved, it was necessary to learn if they might be acceptable for fresh market or for processed products. Consumer Acceptance of the Parthenocarpic Cucumber Materials and Methods During the summer of 1966 fruits of Spartan Dawn, and parthenocarpic fruits from experimental lines were 44 processed at the Michigan State food science laboratories. Three types of cucumber products were processed. A 1/4 inch cross-cut slice known as bread and butter, a 1/8 inch slice known as hamburger slices and longitudinal spears were processed in clear glass jars. The fresh fruits used in the test consisted of parthenocarpic fruits from breeding lines at Michigan State and seed type slicers purchased locally. During the fall of 1966 both the processed cucum- bers and fresh fruits were rated by a consumers preference panel at Wayne State University in Detroit, Michigan. The participants, in the standard panel used regularly by the Department of Agriculture Economics at Michigan State Uni- versity, had been selected to simulate a uniform sample of consumers in the Detroit area (17). The samples used were marked only by code and par- ticipants were asked to check their preference and to in- dicate if samples were either acceptable or not acceptable. Two sessions of the consumers panel were held comprising a total of 160 participants. Figure 8, 9, and 10 show the products as exhibited at the consumers preference panel and Figure 11 illustrates the form used in the test. Results and Discussion The afternoon session of 70 consumers preferred the products processed from parthenocarpic fruits over 45 Figure 8. Cross-cut sections from parthenocarpic fruits are on left and those from Spartan Dawn are on right. 46 Figure 9. Spears made from parthenocarpic fruits are shown on right and spears from Spartan Dawn on left. 47 Figure 10. Parthenocarpic fruits are shown at top and locally purchased seed type slicers are below. 48 PICKLES MICHIGAN STATE UNIVERSITY Preference Acceptable Not Acceptable I. % () II. & * III. # % IV. () & Name: Comments: Figure 11. The form used by the consumers preference panel in Detroit, Michigan. 49 those from normal seed fruits in a ratio of more than two to one. In the fresh market samples no preference was shown for either type. The evening session preferred the processed seed— less cucumbers three to one over the normal seed type cu- cumber products and again accepted equally the fresh fruits. Table 11 summarizes the data and provides important information for both breeders and processors. It was domonstrated that the public would accept a parthenocarpic fresh market variety and if given a choice, actually pre- ferred the products processed from seedless fruits. Preliminary Brining Observations on the Parthenocagpic Cucumber Many questions have evolved from the study on the parthenocarpic cucumber. There is no field production of such cucumbers and no previous investigations have been made on related problems such as brining and processing. The fruits are practically solid wall tissue in most cases with very small areas representing the normal seed bearing tissues. The fruit structure suggests that possibly bloat- ing and carpel separation would not occur to the same ex- tent as in typical seed types. It also led to the question of salt penetration through the thick wall tissue. 50 .mumoHHm 0mm» comm pommnounm mHHmoon a .mwOHHm mHmum Hmuusn pCm pmmHn mmumoHpCH .m H .mm III H mmH mm mumoHHm mm a comm H u H MH S¢H up HmOHHm UHQHMOOCmCuHmm III mH mvH vv mROHum HHHQ sza Cmuummw H u mm.m m mmH HHH mx0Hum HHHQ UHQHMUOCmCuHmm III ms HHH mm mmoHHm .musnsmm C3mo Cmuummm H ” mm.~ ma ASH OCH mmoHHm .ousnsmm OHQMMUOCmCuumm III om omH mv mmOHHm .m w .m sza Cmuummm H u «v.m «H mvH mOH ammoHHm .m w .m UHQHMUOCOCHHMC wOCOCmmmHm mHnmummoodlCoz mHnmummUUC pmuummmum .mme .CmmHCoHE .uHouumo um HmCmm OUCmHmmmum mHmECm ICoo m ma muospoum pmmmmooum pCm HmnECoCo Cmmum UHQHMOOCGCHHMQ mo m0Cmummoom .HH mHQMB 51 Methods and Materials Preliminary tests were made to determine brining quality of parthenocarpic fruits. A replicated study was not possible because only early generation parthenocarpic lines were available in 1966. However, plants were selected which exhibited multiple-fruiting and as many fruits as could be obtained from single plants were brined in com- mercial tanks. Fruits were harvested from individual plants ex- hibiting the following characteristics: 1. Twelve fruits 10 to 12 inches long and 2 1/2 inches in diameter from similar F3 plants were divided into two classes with one group being pricked and the other group being brined without pricking. 2. Fruits 6 inches long with a diameter of l l/2 inches representing pickle size cucumbers, were harvested at two stages of development. One stage was mature fruit with skins beginning to turn yel- low. The other group consisted of young fruits not turning yellow but of generally the same size. One-half of the 10 inch fruits tested were pricked to the center 10 times from each of four sides with small diameter needles. The remaining 10 inch fruits were brined without being pricked. The 6 inch fruits were divided into old fruits which were turning yellow and young green fruits. Mature parthenocarpic fruits were brined because they remained firm for approximately two weeks on the vine after reach- ing full size and seemed to remain useable as fresh cucumbers 52 longer than seed type fruits. The black rather than white spined fruits were used in order to more precisely select for advanced maturity. The fruits were placed into the brine at Dailey Pickle Company at Saginaw, Michigan, in late August and removed in December. The large fruits were observed be- fore and after cutting. Results and Discussion It was found that the 10 inch fruits which were not pricked had become soft inside and the skin was de- teriorating on some of the fruits. The softness seemed to be due to decay or tissue breakdown resulting from respiration which had not stopped early in the brining process. Either of these may result from slow penetration of the brine through the skin or thick wall or a combina- tion of both. The pickled fruits were firm and generally free of cavities after fermentation, suggesting that pricking might hasten penetration of brine and prevent the defects observed in unpricked samples. Despite the small number of fruits brined these preliminary observations suggest that pricking may be essential for successful brining of the typical thick-walled parthenocarpic varieites. The sample of less mature 6 inch fruits remained firm and did not bloat. Mature, 6 inch fruits remained firm but exhibited some bloating. 53 The observations of brined fruits indicated that fruits of the sizes normally used for processing should brine in an immature stage equally as well as seed type fruits of the same size. Figures 12, 13, 14, and 15 show the brined parthenocarpic fruits. More work on processing quality both for fresh pack and fermentation is needed. Parthenocarpic cucumber fruits are unique and little is known about the problems which might arise in processing if they should become generally available. 54 5/0110 Figure 12. The pricked 10 inch parthenocarpic fruits are shown on left and non-pricked on right illus- trating condition after brining. 55 Figure 13. Interior condition of pricked 10 inch parth- enocarpic fruits are shown on left and non- pricked on right illustrating condition after brining. 56 Figure 14. The firm condition of mature 6 inch partheno- carpic fruits after brining. 57 Figure 15. The firm non-bloated condition of immature 6 inch parthenocarpic fruits after brining. SUMMARY Parthenocarpy in the cucumber is conditioned by an incompletely dominant gene 32' Heterozygous Pp plants pro- duce fruits later and generally fewer in number than the homozygous PP genotype. Homozygous recessive pp plants do not produce parthenocarpic fruits. All plants in progenies derived from a backcross to the non-parthenocarpic parent were classified as non- parthenocarpic when fruiting was identified by means of trapping pistilate flowers to prevent pollination. The fact that six out of eighteen progenies from plants self- pollinated in this backcross generation segregated typical PP plants that were parthenocarpic and multiple-fruiting is evidence for incomplete dominance. Cage isolation of gynoecious progenies segregating for parthenocarpy is an effective technique for identifying late fruiting heterozygous plants. The difficulty of trap- ping all pistilate flowers over the entire fruiting period resulted in incorrect classification of heterozygous plants, especially in progenies segregating for monoecious sex ex- pression with very late pistilate flower production. Homo- zygous PP plants were identified accurately in the F2 by 58 59 selecting for early, multiple fruiting in parthenocarpic plants. Progenies from selfed F2 plants of this type pro- duced only the parental type of F3. Modifying genes may influence fruit numbers since 19 of 54 plants classified as Pp produced three or more late fruits. The smooth, non-ridged skin of Spotvrije is con- ditioned by the homozygous recessive gap, gap. Gynoecious parthenocarpic plants exhibit earlier fruiting than monoecious and are necessary for field pro- duction of seedless fruits. Parthenocarpic fruits ten inches long and 2 1/2 inches in diameter did not brine satisfactorily unless pricked. Six inch fruits, 1 1/2 inches in diameter, brined as well as seed fruits the same size. A consumers panel showed no preference between parthenocarpic and seed-type fresh market cucumbers but preferred the products processed from seedless fruits. 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