.‘Aa - .- _ LIP?‘P Y1? Michigan State University n gum; ”12“wa Lw l l 1! W um 85 THEQ'F This is to certify that the thesis entitled INHERITANCE OF PARTHENOCARPIC YIELD IN GYNOECIOUS PICKLING CUCUMBER (CUCUMIS SATIVUS L.) presented by Ibrahim Ibrahim Soliman El-Shawaf has been accepted towards fulfillment of the requirements for Ph.D. Horticulture Jegree in Majo rofessor Date LIL M%//7 77 0-7 639 OVERDUE FINES ARE 25¢ DER DAY PER ITEM Return to book drop to remove this checkout from your record. INHERITANCE 0F PARTHENOCARPIC YIELD IN GYNOECOUS PICKLING CUCUMBER (CUCUMIS SATIVUS L.) By Ibrahim Ibrahim Soliman El-Shawaf A DISSERTATION Submitted to Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Horticulture 1979 ABSTRACT INHERITANCE 0F PARTHENOCARPIC YIELD IN GYNOECIOUS PICKLING CUCUMBER (CUCUMIS SATIVUS L.) By Ibrahim Ibrahim Soliman El-Shawaf The advent of a mechanical harvest technology for pickling cucumber during the last decade has stimulated research efforts for high yields to enhance the feasibility of this once-over destructive harvest system. The advantages of superior quality and high yield potential of parthenocarpic over seeded cucumbers encouraged cucumber breeders to research the development of parthenocarpic cvs. However, little is known about the genic system which controls the parthenocarpic yield in pickling cucumbers for open-field production. The present research was undertaken to elucidate the genetic system which conditions parthenocarpy in gynoecious pickling cucumber grown out-of—doors. Relatively high GCA and SCA effects for parthenocarpic yield indicated that both additive and non-additive gene effects were important. Dominance was partial for low parthenocarpic yield with K = l to 2. Many recessive genes were controlling Ibrahim I.S. El-Shawaf high yields as measured by fruit numbers. However, the heritability estimates for yield were relatively low (0 to 32%) depending on the measurement. High phenotypic and genotypic correlations were detected between flowering time and nodal position of first-pistillate flower and between the latter and yield (fruit number). Accordingly, selection for early flowering and lower nodal positions for the first-pistillate flower could be used as criteria to select for high yields. Complete dominance was found for flowering time with a moderately high heritability (64%); whereas, the degree of dominance was partial for nodal position 0f the first-pistillate flower with a high heritability (63%). Heterosis, heterobeltiosis, and in- breeding depression were all detected for parthenocarpic yield which suggested that hybrid vigor could be utilized to increase the yield of parthenocarpic cvs. Gynaecious expression is a prerequisite for parthenocarpy to preclude pollination. The heritability for gynoecious expression was relatively high (73%) for an array of T7 topcrosses derived from gynoecious by hermaphroditic crosses. The degree of dominance was expressed as over-dominance for gynoecious expression. Thus, gynoecious inbred lines might be improved for partheno- carpic yields by recurrent selection in a breeding program because of the quantitative inheritance of yield. Moreover, transgressive segregation might occur for parthenocarpy yield by selfing highest Ibrahim I.S. El-Shawaf yielding individual plants and selecting in subsequent segregating populations. The parthenocarpic hermaphroditic lines (pollen parents) could be developed by using the backcross method to transfer the single gene, 9, for hermaphroditic expression into gynoecious parthenocarpic recurrent parents with high yield. Thus, high yielding parthenocarpic cvs. with necessary gynoecious expression could be produced from the cross of unrelated gynoecious partheno- carpic with hermaphroditic parthenocarpic parent lines. DEDICATION I dedicate all of these efforts with unlimited affection and gratitude to: l. My parents who raised me with affection and love, while instilling in me self-independence during the early years of my life. 2. My wife, Salwa, and my son, Hytham, who were patient and tolerant during this period of study. 3. My beloved country, EGYPT, and the EGYPTIAN People who provided all of the financial support for my graduate study. 4. I dedicate this work also to the Egyptian-American friendship that is based on mutual interests and a progressive relationship for the good of mankind. ACKNOWLEDGMENTS I wish to express my deep gratitude to my major advisor, Dr. Larry R. Baker, for his continual guidance, patience, and encouragement that made this study possible. I am also indebted to him for his critical review of this manuscript. My sincere appreciation is also extended to the members of my guidance committee: Dr. w. Adams, Dr. J. Gill, Dr. S. Honma, and Dr. R. Herner for their valuable criticism and suggestions during the course of this research and for review of this manuscript. Special thanks go to my colleagues: Messrs. M. Tasdighi, M. Dessert, J. Parrot, L. Yarger, and G. Lester for their willing assistance with the many research plots. Thanks also goes to Mr. Amos Lockwood and Marshall Pollok of the Horticultural Research Center for their help with cultural practices. And my thanks go to all of the undergraduate students who helped to harvest all the research plots. ii Guidance Committee: This thesis has been condensed into the format suited and intended for publication in the Journal of the American Societygfor Horticultural Science. iii TABLE OF CONTENTS DEDICATION ........................ ACKNOWLEDGMENT ...................... GUIDANCE COMMITTEE .................... LIST OF TABLES . ' ..................... LIST OF FIGURES ..................... PART I. PERFORMANCE OF HERMAPHRODITIC POLLEN PARENTS IN TOP CROSSES WITH GYNOECIOUS LINES Abstract ................... Introduction ................. Materials and Methods ............ Results ................... Discussion .................. Literature Cited ............... PART II. DIALLEL ANALYSIS AMONG SIX GYNOECIOUS LINES Abstract ................... Introduction ................. Materials and Methods ............ Results ................... Discussion .................. Literature Cited ............... IV 2l 25 28 29 3l 35 S3 57 PART III. COMBINING ABILITY AND GENETIC VARIANCE OF G x H F-I HYBRIDS Abstract .................. Introduction ................ Materials and Methods ........... Results .................. Discussion ................. Literature Cited .............. Page 60 6O 63 66 79 83 Table PART I PART II 1 LIST OF TABLES Page Description of the parental lines used to study the heritability and combining ability for parthenocarpic yield and associated characters in gynoecious hybrids under out-of-door conditions ............... 5 ANOVA for yield components and parthenocarpic yield of cucumber from top crosses involving 17 hermaphroditic pollen parents ...................... Performance of the progenies from 17 top crosses and the gynoecious parental blend (check) for yield com- 8 ponents and yield in parthenocarpic cucumber ....... 9 Combining ability of hermaphroditic cucumber lines for parthenocarpic yield components in top crosses and a gynoecious parent blend (check) in a 1977 field exper- iment .......................... Combining ability for parthenocarpic yield from 17 top crosses and a gynoecious parental blend (check). Hermaphroditic parents are ranked by their partheno- carpic yield ...................... Heritability of yield components and yield from half- sib family means of parthenocarpic cucumber based on 17 hermaphroditic top crosses in outdoor production . . Correlations among yield components and parthenocarpic yield of cucumber from l7 hermaphroditic top crosses in outdoor conditions .................... Parthenocarpic yield evaluation from 6-parent diallel of gynoecious pickling cucumbers grown in the field during the summer of 1977 ................ ANOVA for GCA, SCA and reciprocal effects of partheno- carpic yield estimates from a complete diallel (6x6) of ll l3 . T4 16 36 pickling cucumber .................... 38 VI Page 3 Combining ability for parthenocarpic yield in pickling cucumber from a complete F diallel (6x6) of gynoecious hybrids grown in the lummer of 1977. . . 39 4 The ANOVA for Hr-Vr values involving parthenocarpic yields of gynoecious pickling cucumber in out-of-doors production ...................... 42 5 (Vr,wr) regression coefficients ............ 43 6 Genetic variance components for parthenocarpic yield of gynoecious pickling cucumbers in outdoor culture. . 45 7 Heritability parameters for parthenocarpic yield in gynoecious pickling cucumber of outdoor culture. . . . 47 PART III 1 ANOVA for yield and certain components of yield for 20 gynoecious by hermaphrodite crosses of partheno- carpic gynoecious pickling cucumbers grown in the summer of l978 ..................... 67 2 Means of gynoecious F (GxH) parthenocarpic hybrids in pickling cucumber witA one parent in common and the mean of the common gynoecious seed parent ....... 68 3 Estimates of combining ability effects for flowering time and node position of the first-pistillate flower from 20 F (GxH) hybrids of parthenocarpic gynoecious pickling lucumher in the summer of 1978 ........ 7o 4 Estimates of relative GCA and SCA effects for har- vesting-time and gynoecious expression based on 20 F (GxH) parthenocarpic hybrids of pickling cucumbers glown in the summer of l978 .............. 71 5 Estimates of relative GCA and SCA effects for yield (first harvest) based on 20 F parthenocarpic hybrids of pickling cucumbers grown 1A the summer of l978 . . . 72 6 Estimates of the relative GCA and SCA effects for yield (second harvest) based on 20 F hybrids of parthenocarpic pickling cucumbers grAwn in the summer of 1978 .................... 73 VII Page Estimates of combining ability and heritability of parthenocarpic yield from gynoecious x hermaphroditic crosses of cucumber from 1978 trials .......... 76 Phenotypic and genotypic correlations for yield and associated characters from 20 F (GxH) )parthenocarpic hybrids of pickling cucumbers gIow n in the summer of 1978 ......................... 77 VIII LIST OF FIGURES Figure PART I 1 Relationship between flowering-time and first- pistillate flower in parthenocarpic pickling cucumber ....................... 2 Relationship of first-pistillate flower to partheno- carpic yield (fruit no.) in gynoecious cucumber . . . 3 Effects of gynoecious expression on parthenocarpic yield and selection of the four outstanding hermaphro- ditic cucumber lines ................ PART II 1 Hr, Vr regression for fruit no. on main stems of F1 parental arrays ................. 2 Hr, Vr regression for fruit no. on laterals of F1 parental arrays ................... 3 Hr, Vr regression for yield weight (g)/p1ant of F1 parental arrays ................. IX PART I Performance of Hermaphroditic Pollen Parents in Top Crosses With Gynoecious Lines Abstract. The top crosses method was used to judge the performance of 17 hermaphroditic lines (pollen parents) for yield and associated characters. Hybrid yields of partheno- carpic fruit averaged from 2.9 to 5.8 fruits/plant with 67.7 to 99.5 percent of desired gynoecious expression. Seven hermaphroditic lines were judged outstanding based on their hybrid performance for both high yields and gynoecious expression. Significant correlations were detected between days-to-flower and nodal position of first-pistillate flower; and between the latter and yield. Heritabilities were 64%, 63%, and 73% for days-to- flower, nodal position of the first-pistillate flower, and gynoecious expression, respectively. The heritability for yield (no. of fruit/plant) of parthenocarpic fruits was 20%. Accordingly, plant breeders might exercise selection gains for associated char- acters, but realize somewhat less success for yield (fruit no.). INTRODUCTION Inbred lines may be evaluated for yield and other economic characters by testing them in a series of hybrid crosses for com- bining ability. The line-variety (top cross) method was long ago used to test the general combining ability (GCA) of parental lines (3). Since then, the top cross method has been used in many crops, e.g., muskmelon, watermelon, corn and sweet corn (2,6,11,12,13,17,20,30,31,32). Moreover, the type and number of tester(s), the use of tester female parents, and the use of hand pollinations to derive top crosses were also ascertained and elucidated (ll,l3,l7,30,32). Obviously, the merit of the tested lines can be determined most accurately in single-cross hybrid combinations. However, because of the limited number that can be tested in single crosses (6), the top cross method is more practical. Then, the selected outstanding 1ine(s) can be care- fully evaluated in single-cross hybrid combinations. The advent of mechanical harvesting in pickling cucumber production necessitated the development of a technology to con- centrate yields for a destructive once-over harvest system (1,4, 18,35). The average yield under this system ranges from 1 to 2 fruits/plant (18). The breeding of parthenocarpic gynoecious hybrid cultivars capable of producing high numbers of fruits per plant has been suggested as a means to increase yields for once- over harvest regimes (1,4,22,23,24). Accordingly, the utilization of high yielding parthenocarpic lines as gynoecious seed parents crossed with comparable hermaphroditic male parents to produce hybrids which are both parthenocarpic and gynoecious is a breeding research strategy to increase yields for once-over harvest. Fruit no. has been used to judge cucumber cultivar produc- tivity (10.24.28.29). There is a correlation between fruit no. and fruit weight (9,35) and between yield (no. fruits/acre) and dollars/acre (28). Genotypic and phenotypic correlations for fruit no. and dollar values were high which suggested selection pressure for high fruit numbers would be effective in increasing crop value. However, the heritabilities of full-sib families for dollar value and number of fruit were 19 and 17%, respectively, which is sufficient for selection (29). A highly female hybrid (100% gynoecious) is a prerequisite for parthenocarpic fruiting (22,24). The genetics of femaleness has been reported (14,15,25,26) and gynoecious lines have been developed (14,21). Gynoecious hybrids (100% pistillate flowers) were produced from crosses of gynoecious by hermaphroditic lines (1,14,22). However, the phenotypic stability of gynoecious expres- sion in cucumber is subjected to environmental influences which may enhance or suppress female expression (1,5,25,26,34). Importantly, flowering time is a Simply inherited Character (19,27) which is highly correlated with maturity (9,19), but affected by various environmental factors (16,19,25,27). The nodal position of the first-pistillate flower is also a good measure of both female tendency and maturity (25), but it is strongly influenced by environ- ment (19,25). The objective of our research was to select among an array of hermaphroditic male parents for parthenocarpic yield and associated components based on GCA. The top cross method was used to judge the performance of the hermaphroditic lines for parthenocarpic yield and associated components (gynoecious expression, days to flowering, and nodal position of the first-pistillate flower). MATERIALS AND METHODS An array of 17 hermaphroditic pollen parents was evaluated for combining ability by the use of a "controlled" top cross. Crosses were made in the fall of 1976, in the greenhouse, between the hermaphroditic pollen parents and gynoecious seed parents (Table 1). Each of the 17 hermaphroditic pollen parents was represented by 12 plants grown in 20 cm clay pots. The seed parents were spaced 30 cm apart on raised soil benches with routine cultural practices to maximize seed yields. Each of the 6 gynoecious seed parents was represented by 136 plants; 8 of which were crossed with each pollen parent. The gynoecious seed parents were rogued for predominantly female (PF) plants. At flowering time, the bisexual flowers from each hermaphroditic line were collected daily; and then randomly used to cross-pollinate by-hand to the 6 gynoecious seed parents. Plants of the seed parents developed 2 or 3 fruits which were harvested at maturity. Several hundred seeds of each cross (6 gynoecious x 17 hermaphrodites) were obtained. A total of 17 "controlled" top crosses representing each hermaphroditic pollen parent were obtained by randomly mixing 70 seeds from each of the 6 hybrids together for each pollen parent. Table 1. Description of parental cucumber lines used to study herit- ability and combining ability for parthenocarpic yield and associated characters in gynoecious hybrids under out-of—door conditions. MSU No. Pedigree description Hermaphroditic pollen parents (9’). 661M 662M 663M 664M 665H 666M 667M 668H 669H 319H 530M 581M 532H 591H 4108M 7152H HP-61 Sib increase from (SC4OA x MSU 7154H) F10 Gynoecious seed parents Gy3 Gyl4 926 364G 402G 921G (g). (SC4OA x MSU 7154H) F1] (MSU 844G x MSU 4108H) F9 (MSU 8446 x MSU 4108H) F8 (SC4OA x MSU 7154H) F12 (SC4OA x MSU 7154H) F12 (MSU 8446 x MSU 4108H) F9 (MSU 8446 x MSU 4108H) F9 (MSU 8446 x MSU 4108H) F10 (SC4OA x MSU 7172H) F8 (MSU 3646 x 4108H) F2 x (MSU 3646)BC2 S3 (MSU 3946 x 4108H) F2 x (MSU 394)BC2 S3 (MSU 394G x 4108H) F5 (SC4OA x MSU 7152H) F9 USSR Accession (P.I. 351140) S7 USSR Accession '1031' S7 USSR Accession 'HP-6l' S2 Mass increase from breeders stock; Clemson Univ. release. Mass increase from breeders stock; Clemson Univ. release. Sib increase from cross (MSU 713-5, MSU 356, Spotvrige) F9 Mass increase from cross (MSU 356, MSU C-l4, MSU 5711, MSU 5612, and Spotvrige)F6 Sib increase from Poland Accession 'Skieriewicki' 54. Mass increase from cross (6y3, MSU 713-5, MSU 356, and Spotvrige) F7. This created a population with 420 seeds equally represented by each hybrid. A "controlled" S1 population (check) was likewise derived by blending an equal number of seeds from the 6 gynoecious seed parents. The assumption was made that, on the average, all of the individuals of the top cross had an equal female parentage; i.e., an equal and random sample of female gametes (an equal basis). So, progenies of each top cross consisted of both full-Sib and half-Sib families but averaging half-Sib family in their relation- ships; and consequently, all the crosses were composed of half-Sib families. Accordingly, the genetic variation among the top crosses is due to the genetic differences among the hermaphroditic pollen parents. Such genetic differences can be computed as a ratio (heritability estimate) of the total phenotypic variation as 2 follows: h of half-Sib family means = 626/ (626+ 62E) where 62G additive genetic variance, 62E = error variance, and 6ZG+62E=62p = Total phenotypic variance; (33). These variances can be estimated from the expected mean squares (EMS) as follows: Source of variation d,f, EMS Replications (R) 5 62E + 17 62R Top crosses (T) 16 62E + 6 62G RxT (error) 80 62E Total 101 The 17 top crosses were evaluated in a field experiment during the summer of 1977. The seeds of each controlled top cross population were divided equally into 7 lots of 60 seeds. Six lots of each controlled top cross were planted and one lot was saved for remnant. The experimental design was a randomized complete block with 6 blocks and single plots to represent each population. The seeds were planted on June 22 at the Horticultural Research Center of Michigan State University near East Lansing. Data were collected on an individual plant basis for days-to-flowering, node of the first-opened flower and sex expression. The data for yield (mean number of fruits/plant) were obtained by dividing the total number of fruits/plot by the number of plants/plot. Individual plots were harvested when 10-20% of the fruits were observed to be oversized (>5 cm diam.). Routine cultural practices were used. Data were statistically analyzed for variance components, multiple comparisons, correlation coefficients and regression coefficients (8) for yield and associated characters. RESULTS The ANOVA for the 17 top crosses (Table 2) produced highly Significant differences (1% level) for all characters. Therefore, genetic differences among the hermaphroditic parents were probable. Days-to-flowering. The analysis of variance for days-to- flowering (Table 2) was highly significant (P<0.01). The mean days-to-flowering (Table 3) for the 17 top crosses (38.7 days) Table 2. ANOVA for yield components and parthenocarpic yield of cucumber from top crosses involving 17 hermaphroditic pollen parents.5/ Mean Squares Source Of variation d'f' Days Nodes % Gynoecious No. fruits Replication 5 13.17** 0.32 9.24"5 4.46ns Top crosses 16 29.99** 1.11** 335.10** 3.21** ' Error 80 2.53 0.10 19.10 1.27 Total 101 7.41 0.27 68.84 1.74 E/"'*indicates highly significant differences at 1% level; *Significant at 5% level, and ns not significant at 5% level. Table 3. Performance of the progenies from 17 top crosses and the gynoecious parental blend (check) for yield components and yield in parthenocarpic cucumber.§/ Hermaphroditic Days to flower Node first flower Gynoecious Yield MSU line No. (No.) (No.) (%) (No. fruit) 661H 37.1 i 0.4 3.2 i 0.1 99.2 t 0.5 4.3 i 0.5 662H 36.9 t 0.3 2.2 i 0.1 94.0 i 1.3 5.7 1 0.7 663H 37.9 i 0.5 2.1 t 0.1 95.8 t 1.4 4.5 i 0.4 664H 40.1 i 0.8 2.5 t 0.1 98.4 t 1.6 3.8 i 0.7 665H 38.0 i 1.0 2.2 i 0 1 97.6 i 2.0 3.9 i 0.4 666H 36.2 i 0.9 2.2 t 0.1 96.4 2 1.6 5.2 i 0.3 667H 41.0 t 1.1 2.2 i 0 1 93.5 t 2.8 4.4 i 0.5 668M 39.2 i 0.7 2.2 i 0.1 98.4 i 0.7 4.6 t 0.6 669H 36.7 i 0.8 2.2 i 0.2 99.5 i 0.5 4.2 i 0.6 319H 38.9 t 0.6 3.4 t 0.2 98 1 t 0.9 5.3 t 0.6 530M 45.0 i 0.6 3.1 i 0.1 92.6 t 2.7 4.3 t 0.5 581H 39.5 i 0.5 2.8 t 0.2 98.7 i 0.8 5.8 i 0.4 532H 38.4 t 0.4 2.2 i 0.1 99.5 t 0.5 4.4 i 0.6 591H 35.0 i 0.6 2.2 i 0.1 98.0 t 1.0 3.9 i 0.1 4108H 39.7 i 1.0 3.3 i 0 1 99.4 t 0 6 4.7 i 0.3 7152H 38.9 i 0.4 3.0 i 0.3 97.8 i 0.8 2.9 t 0.4 HP-61 39.2 i 1.0 2.7 i 0.2 67.7 t 4.4 4.2 s 0.5 Check 38.6 i 1.0 3.1 i 0.2 90.2 i 7.2 4.5 t 0 Mean 38.7 i 0 5 2 5 i 0 1 95.6 i 2 8 4 5 i 0 zlEach value is the mean and standard error of the mean. 10 was equal to the check mean (38.6 days). The mean days-to-flower (Table 4) for the hermaphroditic parents ranged from 35 (591H) to 45 (530H) days. Two hermaphroditic lines were significantly different from the check. These were the early line (35 days), 591H, and the late line (45 days), 530H. Moreover, significant differences occurred among the hermaphroditic lines (Table 3) for flowering time which could be classified into 5 subsets (Table 4). These subsets contain the early, intermediate, and late lines. The relatively high heritability for the hermaphroditic lines was 64.4% (Table 6) for this trait. ‘ Node of first-female flower. Highly significant differences among the progenies of the 17 top crosses suggested genetic dif- ferences among the hermaphroditic lines for this trait (Table 2). A range of 1.1 nodes was detected among the means. Ten hermaphroditic lines (663H, 669H, 668H, 662H, 591H, 666H, 532H, 667H, 665H, and 661H) opened first-pistillate flowers on lower nodes than the check (Table 4). The lines were divided into 4 sub- groups. The first group included 13 of the 17 lines. A relatively high heritability of 62.9% was found (Table 6) for this trait. Gynoecious. A parthenocarpic hybrid with a high gynoecious frequency (99 to 100%) is desirable in order to avoid pollination and permit parthenocarpic fruit set. Highly significant differences were found among the top crosses (Table 2) which suggested genetic differences among the male parents. The hermaphroditic lines crossed with gynoecious seed parents produced F1 hybrids which ranged from 68 to 99% gynoecious expression 11 Table 4. Combining ability of hermaphroditic cucumber lines for partheno- carpic yield components in top crosses and a gynoecious parent blend (check) in a 1977 field experiment.§/ a ’Flowering ESeX expression Hermaphroditic Number Node first Nomber Gynoecious :30 line plants Days flower plants (%) 661H 156 37.1abc 2.3a 213 99.2a 662H 154 36.9abc 2.2a 191 94.0a 663H 155 37.9abc 2.2a 203 95.8a 664M 151 40.1cd 2.5ab 218 98.4a 665H 155 38.0abcd 2.2a 240 97.6a 666H 147 36.2ab 2.2a 162 96.4a 667H 132 41.0d 2.2a 159 93.5a 668M 152 39.2de 2.2a 179 98.4a 669H 150 36.7ab 2.2a 203 99.5a 319M 145 38.9bcd 3.4d 170 98.1a 530M 136 45.0e 3.1bcd 195 92.6a 581H 154 39.5bcd 2.8abcd 171 98.7a 532M 142 38.4abcd 2.2a 188 99.5a 591M 152 35.0a 2.2a 169 98.0a 4108H 127 39.7de 3.3cd 151 99.4a 7152H 156 38.9bcd 3.0bcd 230 97.83 HP-61 143 39.2de 2.7abc 174 67.7b Check 138 38.6 3.1 156 90.2 f/Separation between means by Tukey's multiple range test, 5% level. 12 (Table 3). The check averaged 90.2% gynoecious plants with a high standard deviation (17.6). However, most of the crosses with hermaphroditic lines ranged from 92.6 (530H) to 99.5% (532H) gynoecious plants with relatively small standard deviations in relation to those of the check and HP-61. Only one line (HP-61) was significantly different from the check; as well as, from the 16 hermaphroditic lines (Table 4). The heritability was high (73.4%; Table 6). Yield (average number fruits/plant). The analysis of variance for yield revealed a highly significant difference among the pro- genies of the 17 top crosses (Table 2). Yields ranged from 2.9 (7152H) to 5.8 (581H) fruits/plant (Table 3). The mean number of fruits/plant was 4.5 for both the 17 top crosses and the check. Four hermaphroditic lines were found to exceed 5 fruits/plant (581H, 662H, 319H, 666H). The remaining 13 lines yielded from 2.9 to 5.0 fruits/plant (Table 5). Two lines (581H and 662H) were Significantly higher for yield than the other lines which indicated high GCA. The heritable variation among the hermaphroditic lines as estimated by the heritability was 20% (Table 6). Relationships between characters. Correlation and regression coefficients were calculated to characterize the relationships among the four characters to better select hermaphroditic parents for yield and gynoecious expression. A highly significant positive correlation (0.37**) was found between days-to-flower and the node of the first- pistillate flower (Table 7). However, a significant negative cor- relation (-0.21*) was found between node of first-pistillate flower 13 Table 5. Combining ability for parthenocarpic yield from 17 top crosses and a gynoecious parental blend (check). Hermaphroditic parents are ranked by their parthenocarpic yields. Hermaphrodite Parents Number of progenies No. of fruitsa/ 581H 171 5.8 a 662H 191 5.7 a 319H 170 5.3 ab 666H 162 5.2 ab 4108H 151 4.7 ab 668M 179 4.6 ab 663H 203 4.5 ab 532H 188 4.4 ab 667H 159 4.4 ab 530M 195 4.3 ab 661H 213 4.3 ab HP-61 174 4,2 ab 669H 203 4.2 ab 591H 196 3.9 ab 665H 240 3.9 ab 664M 218 3.8 ab 7152H 230 2.9 b Check 156 4.5 ElSeparation between mean no. of fruits/plant of the hermaphrodite parents by Tukey's mu1t1ple range test; 5% level. 14 Table 6. Heritability of yield components and yield from half-Sib family means of parthenocarpic cucumber based on 17 hermaphroditic top crosses in outdoor production.§/ Character GeneticZVariance PhenotyBic Variance h2 (6 e) (6 ',1 (%) Days to first flower 4.58 7.11 64.4 Node first flower 0.17 0.27 62.9 No. fruits/plant 0.32 1.59 20.2 % Gynoecious 52.8 71.9 73.4 3/ All values were computed from the ANOVA described in Materials and Methods section. 15 and yield. All other relations between characters were not significant. Three regression analyses were done to identify dependency of a certain variable and its significant relationship with another variable. Since the node of the first-pistillate flower was highly correlated with days-to-flower and, yield was Significantly cor- related with node of the first-pistillate flower; regression analysis was done for both cases. Regression analysis for yield and % gynoecious was also done because of its importance for parthenocarpic pickling cucumbers. Regression analyses were displayed graphically (Fig. 1, 2 and 3). The regression coefficient for days-to-flowering and node of the first-pistillate flower was highly Significant (b 0.07 i 0.02). A significant regression coefficient was shown (b -0.52 t 0.23) for yield and the position of the first-pistillate flower (Fig. 2). The regression coefficient was not significant for yield and % gynoecious plants (Fig. 3). The gynoecious expression accounted for only 2% of the variability in yield. Selection for outstanding hermaphroditic parents. Because of the importance of both high % gynoecious expression and high yields for parthenocarpic cucumbers, a weighted scheme was used to select better hermaphroditic lines that produced hybrid combinations with 4.5 or more fruits per plant with 98 to 100% gynoecious expres- sion (Fig. 3). Only 4 hermaphroditic lines fit these selection criteria; vis., 4108H, 581H, 668H, and 319H. However, when yield 16 Table 7. Correlations amongst yield components and yield of parthenocarpic cucumbers from 17 hermaphroditic top crosses in outdoor conditions. Coefficienrt_s_2/ Characteristic (17' (2) (3) (4) Days to ‘first ns ns flower (1) 1.00 2 0.37** 2-0.13 0.08 r = 0.13 r =0.02 r2=0.01 Node first flower (2) 1.00 -0.16"5 -0.21* r2=0.03 r2=0.04 % Gynoecious (3) 1.00 0.15"5 r2=0.02 No. fruits/plant (4) 1.00 5/**indicates highly significant at 1% level; *Significant at 5% level, and ns not significant at 5% level. .ammzzuau wz_4xu_¢ u_¢m c oo.m BBMDWJ 3181111918 191 JD BOON YIELDINO. OF FRUIT PER PLRNT) 18 2 0.045: 5.30 - 0.52x , x Y 29- x x LEQEEP l l l I l I x Yo I .‘500 2 .000 2 .500 3 .050 3 .800 4 .600 4 .500 NODE OF IST PISTILLRTE FLOWER FIG. 2. RELATIONSHIP OF FIRST-PISTILLATE FLOWER T0 PARTHENOCARPIC YIELD (FRUIT No.) IN GYNOECIOUS CUCUMBER. 19 was arbitrarily decreased to 4.2, 7 hermaphroditic lines were over the limit of 98% gynoecious plants (Tables 4 and 5; Fig. 3). YIELD (FRUIT NO./ PLANT] 50 5.5 5.0 4.5 4.0 3.5 3.0 2.5 . 2.25 20 662 o 319 one ’ O 4108 668 ' O *5 :51: DE \ o 0532 667 y: 4.2 0661 / 639 665 T59} . 664 Q 0 II I r93 94 95 9o 97 98 99 100 % GYNOECIOUS Fig.3: Effects of gynoecious expression on parthenocarpic yield and selection for out - standing hermaphroditic cucumber lines. DISCUSSION The top cross method has been used extensively in corn and other crops to evaluate and select inbred lines according to their GCA for yield and other economic characteristics (2,3,6,1l,12,20, 30,32). Both the efficiency of the top cross method and type of tester(s), as well as number of testers, have been established for several different crop species (6,11,12,13,17,30,3l). In the present study, a modification of the top cross method was made by controlling the crosses and then creating so-called "controlled" top crosses. This reduced the time and cost from a practical standpoint for the evaluation of a relatively large array of parent lines in a hybrid cucumber program. The analysis of variance revealed highly significant differences among the herma- phroditic pollen parents for the number of days to first-pistillate flower, node no. of the first-pistillate flower, yield, and % gynoecious plants. Days-to-flowering. Flowering time (days to first-pistillate flower) had a moderately high heritability estimate of 64% which approximated a previous report (19). Moreover, this yield characteristic was previously found controlled by one dominant gene (26) or else relatively few partially dominant genes (19). 21 22 Estimation of maturity via days to first-pistillate flower was the best prediction criterion with a high correlation (r=.84, 9; r=.82,l9). According to the relatively high heritability (64%; Table 6) for flowering time among the hermaphroditic pollen parents and the dominance of this character, selection could be effectively used to develop parthenocarpic hybrids with different maturities. Node of first-pistillate flower. The hermaphroditic pollen parents demonstrated differences for the nodal position of the first-pistillate flower on the main stem, which suggested genetic control of this trait as reported earlier (9,19,25). The nodal position for the first-pistillate flower occurred with a moderately high heritability ratio of 0.63 which was higher than previously reported (19). These researchers estimated a ratio of 0.11 to 0.26; however, they reported that the character was simply inherited and the minimum no. of effective factors was 1 to 3 genes. As with time of flowering, no. of nodes to first-pistillate flower was a reasonably good measure of maturity (25). Accordingly, selection among the hermaphroditic pollen parents for early, intermediate, and late maturity "combiners" could be accomplished through selection for flowering on appropriate nodes. Gynoecious expression. Hybrids with 99.5% pistillate flowers (gynoecious) were obtained from crosses between gynoecious seed parents and hermaphroditic pollen parents (Table 4). This is considered advantageous for hybrid cultivar development based on the use of hermaphroditic parents (14,22,24). All of the herma- phroditic lines, except HP-6l, combined well for gynoecious 23 expression (93 to 99% gynoecious, Table 4). Selection among the hermaphroditic lines for those which combine well for gynoecious expression when crossed with gynoecious lines could be quite effective. The relatively high heritability of 73% suggested that the environment played a minor role in the expression of gynoecious expression. The expected gain in gynoecious expression was from 1.8 to 2.9% more than the mean of the top crosses when selection was exercised on the hermaphroditic lines that produced crosses with 98 and 99.5% gynoecious progenies, respectively. For the same hermaphroditic lines, the expected increase ranged from 5.7 to 6.8% over the mean for the gynoecious parents (check). Yield (average number fruits/plant). Fruit number was used to judge the productivity and to evaluate the yield performance of the hermaphroditic male parents in the top crosses. Fruit number was used instead of weight Since time-of-harvest influenced fruit weight. Fruit number was also used by other investigators to estimate cucumber yields (9,24). Moreover, the use of fruit no. was highly correlated with dollar/acre values on a once-over harvest basis (r=.84; 28). Furthermore, the genetic and phenotypic correlation between fruits no. and dollar/acre value was also high (29). Genetic variation for yield among the hermaphroditic parents, due to additive genetic effects, was about 20% of the phenotypic variance. Hence, the no. of parthenocarpic fruit/plant was inherited as a quantitative trait which agrees with a recent report for seeded 24 fruit yields (29). They indicated the genetic variance for fruit no. was additive with a heritability of 17% based on full-Sib families. However, they reported a high genotype by environment interaction variance. Other data (24) demonstrated differences in fruit counts for F1 hybrid plants derived from crosses of two hermaphroditic with two gynoecious lines. The present study found a wide range for yield of almost 3 fruit/plant among the progenies of the hermaphroditic lines. This variation for parthenocarpic yield suggests the development of high yielding parthenocarpic hybrids. These hybrids could be produced by crossing hermaphro- ditic pollen parents with high GCA for yield by gynoecious seed parents with high yields. Relationships between characters. The linear relationship between days-to-flowering and node of the first-pistillate flower indicated that the early pollen parent lines bear the first— pistillate flowers on lower nodes in comparison to intermediate and late lines (Table 3; Fig. 1). These data could be used to predict and select parent lines to produce hybrid cultivars with different maturities in a breeding program as suggested pre- viously (25). Days to flowering was not associated with femaleness (Table 7). Therefore, selection for differing maturities could be practiced while maintaining the desired sex expression. Recent workers also found that flowering time and femaleness were not associated (19). 10. 11. 12. LITERATURE CITED Baker, L.R., J.W. Scott, and J.E. Wilson. 1973. Seedless pickles - A new concept. Mich. State Univ. Res. Rpt. 227. Chadha, M.L. and K.S. Nandpuri. 1977. Estimation of top cross performance in some muskmelon (Cucumis melo L.) varieties. Indian J. Hortic. 34:40-43. Davis, R.L. 1927. Report of the plant breeding department. Puerto Rico Agr. Exp. Sta. 1927. pp. 14-15. Denna, 0.W. 1973. Effects of genetic parthenocarpy and gynoecious flowering habit on fruit production and growth of cucumber, Cucumis sativus L. J. Amer.Soc. Hort. Sci. 98:602-604. Edmond, S.B. 1930. Seasonal variations in sex expression of certain cucumber varieties. Proc. Amer. Soc. Hort. Sci. 27:329-332. .‘ Federer, M.T. and G.F. Sprague. 1947. A comparison of variance components in corn yield trials: I-Error, Tester x Line and Line components in top cross experiments. J. Amer. Soc. Agron. 39:453-463. Frandsen, K.J. 1952. Theoretical aspects of cross-breeding system for forage plants. Proc. Sixth Inter. Grasslands Congr. 1, 306-314. 6i11,333 a 3331.4. n .mfimwxmov x .8“ 263% a 232.8118; u 3.3-233: x .8” 2:. e seesnoa.=e anesnno.e= u Aze~-mwd\mm.v x .88. 37 Combining ability. The ANOVA for the 3 yield characters was conducted on the mean performance of the complete diallel (6x6) based on Griffing's (1956) Method 1 with Model 1 (Table 2). Signifi- cant differences were found for all yield characters as regards GCA and SCA effects, but not for reciprocal effects. The mean squares for GCA were greater than SCA for all yield characters. The ratios' of 62 GCA: 62 SCA were estimated at 15:1, 45 1, and 8:1, for fruits on the main stem, fruits on the laterals, and fruit weight/ plant, respectively. The estimation of GCA effects (Table 3) from the diallel showed that 3646 had the higher value (+0.39) for fruit number on main stem; whereas 9216 was a poor combiner for that trait. The GCA effects for fruits on main stems were not significant for the other parents. For parthenocarpic fruits on the laterals, 4 lines displayed positive and significant values for GCA effects. The line, 9216, had the greatest GCA (1.96) f01lowed by 3646 (1.50), Gyl4 (0.65) and Gy3 (0.59). The poorest combiner was 4026 (-3.85) followed by 926 (-O.86). The highest GCA values for fruit weight/plant were exhibited by 3646 (30.5) and 4026 (29.1); whereas, Gy3 and 926 were considered poor combiners with significant negative values. The SCA effects for parthenocarpic yield were also estimated from the 6-parent diallel (Table 3). However, only one of the F1 crosses displayed significant positive effects for fruit number on the main stem, Gy3 x 9216 (0.80). There were two F] crosses 38 Table 2. ANOVA for GCA, SCA and reciprocal effects of parthenocarpic yield estimates from a complete diallel (6x6) of pickling cucumber. Mean squaresz/ Source d'f‘ Main stem Laterals Weight GCA 5 0.5 * 53.7** 10722.5* SCA 15 0.2 * 7.4** 8583.0* Reciprocals 15 0.07 1.5 2832.1 Error¥/ 2124 0.07 0.8 1453.7 626CA:6ZSCA 15:1 45.1 1 7.7 1 5/* and ** are significant at the 0.05 and 0.01 level of probability, respectively. X/The error term was estimated from the variance within plots divided by 60 (number of replications x number of plants per plot). 39 .1115- exaomnsocm :«es.am coat: .3 9:» messes om dew». noao.=.=m no...n< «as unsnrmaonasu.n w.m.a .: csnrd.=n nencauns «was a naae_mnm a.o._o. Amxmv ea ma: mqqmnnmmxi m\ssm afic:.«.nm=n.< asqmmsmzn axes Nose on «so c.cm .o 0. Mean estimates of genetic variances (D,F,H1,and Hz) were cal- culated for both F1 and F2 generations (Table 6). The value of F was positive for number of fruit on the main stem in both generations which indicated a preponderance of dominant alleles. Conversely, F was negative for fruit number on laterals and for fruit wt/plant which indicated a majority of recessive alleles for these 2 yield traits. The value of D-H1 for fruit number on the main stem indicated that additive gene effects were more important than dominance effects. The average degree of dominance (111/0)15 was 0.62 and 0.83 for fruit no. on the main stem in the F1 and F2 generations, respectively (Table 7). The crude estimate for frequency of negative (v ) versus positive (u) alleles (Hz/4H1) at loci which exhibit dominance in the parents (Crumpacker & Allard, 1962) is expected to be 0.25 if equally distributed among the parents. For this study, the number of fruits 45 Table 6. Genetic variance components for parthenocarpic yield of gynoecious pickling cucumber in outdoor culture. Yieldx/ Genetic Fruit number on ( 2/ Main stem __ Lateral§__ _9 Weight g) parameter- F F F F F F l 2 l 2 l 2 D 0.71** O.75** -0.27 -1.20 -5573 -2667 H1 -O.27 -O.51 1.69 68.66* 8206 7599 H2 -0.26 -1.15* 2.14 75.50** 11914 25563** F 0.32 1.78** -l7.47** -23.40** -12232 -15792** D-H1 0.98** l.26** -1.96 -68.85** 13778* -10267* E l.Ol** O.97** 12.71** 13.63** 15145** 12240** zID = additive effects of genes; H1 = dominance effects of genes; H2 = dominance indicated asymmetry of positive and negative effects of genes; F = covariance of dominance and additive effects; E = error. ¥/**indicates highly significant at 1% level; *Significant at 5% level. 46 on the main stem exhibited a ratio of 0.24 indicative of a symmetrical distribution of positive and negative alleles at the "non-additive" loci of the parental lines (Table 7). Asymmetric distributions of positive and negative alleles were noted among the parental lines for fruit no. on laterals and fruit weight/plant. The ratios for H2/4H1 were 0.31 and 0.36 for both characters, respectively. The ratio of KD/KR for the F1 generation indicated that more dominant than recessive alleles were present for fruit no. on the main stem (KD/KR>1). Conversely, the ratio of KD/KR was <1 for fruit number on laterals and fruit weight. This indicated an equal distribution of dominant and recessive alleles that control these 2 characters. The number of groups of genes that exhibit dominance were estimated as K (Table 7). Values of 1.4, 1.3, and 2.5 were obtained for fruit no. on the main stem, on the laterals, and fruit weight/plant, respectively. The narrow sense heritability ratios were .17 and .32 for fruit number on the main stem in the F1 and F2 (Table 7), respectively. The heritability ratios for fruit no. on laterals and fruit weight were negative and very small for both characters. They were not significantly different from O; and were therefore set to zero (Table 7). 47 Table 7. Heritability parameters for parthenocarpic yield in gynoecious pickling cucumber for outdoor culture. Yield 2/ Fruit Number Genetic- Main stem Laterals Weight (g) components F1 ’Fé F} F2 F1 F2 (.H1/D)” 0.52 0.82 2.52 7.59 1.20 1.58 H2/4H1 0.24 0.56 0.31 0.27 0.36 0.84 KD/KR 2.13 -5.52 -0.86 -0.13 0.05 -0.27 Heritability 0.17 0.32 0.00 0.00 0.00 0.00 K 1.43 -0.19 1.36 0.15 2.5 0.61 3/(H1/D)% = Average degree of dominance, H2/4HI = average 35 frequency of negative vs positive alleles, KD/KR = (4DH1) I F (4DH1)% - F is the ratio of dominant to recessive alleles. Heritability is kD/(kD - %F + 5H1 + E); K = h2/H2, an estimate of number of groups of genes exhibiting dominance, where h2 = 4(MLl-MLo)2-4(n-l)E/n2, and (MLl-MLo) is the difference between the mean of the parents and the mean of their 112 progeny. 48 The Wr/Vr graphs (Fig. 1-3) are the regressions of Wr (parent-offspring covariances) on Vr (parental array variances) and their limiting parabola in the 6-parent diallel for partheno- carpic yield. The (Wr,Vr) graph provides tests of significance for the presence of dominance (b # o) and the average degree of dominance (the Sign of a); where b is the slope of the regression line and a is the intercept of b on Wr axis. According to the diallel theory (12,16), the regression of Wr on Vr is a straight line of unit slope (b is not significantly different from unity, but signi- ficantly different from zero). As indicated by Jinks (1954) and Hayman (1954), the position of the array points along the regression line depends on the relative proportion of dominant and recessive alleles present in the common parent of each array. Accordingly, the more recessive parents will be located farther from the origin because of a large array variance and covariance; whereas, parents with a preponderance of dominant alleles will have a low array variance and covariance which locates them nearer the origin. The regression of Wr on Vr for fruit number on the main stem (Fig. 1) revealed that the slope (b = 0.74 f 0.84) was not signi- ficantly different from either 1 or zero (t = 1.17 and 0.39, respectively). Hence, the assumption of no genic interaction was not valid. The gynoecious lines Gy3 and 9216 could be responsible for the slope not being different from zero. However, the array point for 3646 indicated a preponderance of recessive genes for this yield trait; whereas, gynoecious lines Gyl4, 4026, and 926 contain high frequencies of dominant genes. 49 WT 0.5 0.4 0.3 0.2 o = 0.00 ‘ 4026 b = 0.78 t. 0.84 0.1 ’ . 9216 O VT 0.! 0.2 0.3 0.4 0.5 ‘01 O Gy3 Figure 1. WT, Vr regression for Fruit no. on main stem of F1 poreniol orroys. 50 The Wr/Vr regression coefficient for yield as fruit number on laterals was neither significant from unity nor from zero (Fig. 2). The regression line intercept is below the origin (a = -2.9) which indicated over-dominance. However, the inter- mediate slope value is indicative of genic interaction which could obscure simpler genic effects. Line 6yl4 appeared to cause a deviation in the regression line. However, the position of the array point for 3646 lies near the far right end of the regression line which suggested that 3646 contains a preponderance of re- cessive genes. Conversely, Gy3 contains a preponderance of dominant genes. The remaining 2 lines (9216 and 4026) contained slightly more dominant alleles than recessive; while, 926 contains a balanced proportion of dominant and recessive genes. The regression of Wr on Vr for fruit weight per plant (b = 0.43 i 0.55) was not significantly different from either zero or unity which again indicated possible genic interaction (Fig. 3). The array points were scattered on the graph. The negative large value of "D" (-5573) in Table 5, upsets the Wr/Vr graph. However, the two lines 6y3 and Gyl4 appeared to possess recessive genes responsible for relatively low yields (weight per plant). 14.0 12.0 10.0 ' 80 60 4.0 2.0 '20 ‘40 51 4026 03’237 ' b-o.98.t.o.7o Gy3 Vr 2. ' 4.0 5.0 8.0 10.0 12.0 14.0 Gyl4 C Figure 2. Wr, Vr regression for Fruit no. on Laterals of F1 poreniol arrays. 52 Wr 12000 10 000 8000 6000 Gy3 Gyl4 4000 0= ”00 O 2000 . 9216 b = 0.43 t 0.55 3646 %?G . Vr 2000 4000 6000 8000 10000 12000 ‘2000 402 -4000 ’ Figure 3. Wr, Vr regression for yield weight (01/ plant of F1 parental arrays. DISCUSSION Ample genetic variation among the gynoecious lines for parthenocarpic yield was evident. The mean squares for GCA and SCA were significant for all three yield determinants. This suggested both additive and non-additive genetic effects were responsible for the variability among the gynoecious lines. However, a comparison of the relative magnitudes of 6266A vs 6250A effects revealed that GCA was more important than SCA for all the parthenocarpic yield characters (Table 2). The mag- nitudes and directions of GCA and SCA effects were used to further elucidate the genetic system for parthenocarpic yield in the parents. Based on desirable horticultural characteristics and a high yield performance as parent lines and hybrid crosses (Tables 1 and 3), 4 lines were selected; namely, Gyl4, 3646, 4026, and 921 6 for further evaluation in crosses with hermaphro- ditic lines. Diallel analysis (12,15,16) provided further information about the nature of the genetic system conditioning partheno- carpic yield in gynoecious cucumber. However, partial ful- fillment of the assumptions for analysis dictated caution in imposing interpretations. 53 54 For parthenocarpic fruiting on the main stem, genes with additive effects were important since 0 and D-H were significantly different from zero (P>0.0l) in both the F1 and F2 generations (Table 6). Dominance was also involved (K = l to 2; number of groups of genes exhibiting dominance). However, the degree of dominance was partial and the magnitude and direction of dominance was -0.32. Moreover, the parental line 3646 produced higher yields than the other 5 lines on the main stem. This high yield was controlled by a preponderance of recessive genes as shown from its position on the Wr/Vr regression lines (Figs. 1,2). Further- more, the correlations between the parental order of dominance (Wr+Vr) and parental measurements (main diagonal) were high (0.49 and 0.82) for the F1 and F2 generations, respectively, which suggested that most of the recessive alleles in the parents were conditioning high yield. This agrees with Russian research (18) which showed that parthenocarpy was controlled by many recessive genes. The remaining two yield characters; viz., fruit number on laterals and fruit weight per plant, were Strongly influenced by genic interactions which likely obscured the additive and dominance gene effects. Therefore, the interpretation of the diallel analysis for these characters (Table 6 and 7, Fig. 2 and 3) must be cautiously extrapolated to other cucumbers and will not be discussed in detail. Based on the information obtained from combining ability analysis (Griffing, 1956) and diallel cross analysis (Jinks, 1954; 55 and Hayman, 1954), the inheritance of parthenocarpic yield is quantitative with a heritability ratio somewhere between 0 and .32 depending on the yield trait in question. Parthenocarpic yield was controlled by both additive and non-additive gene effects. The same conclusion was drawn recently from an investigation of glasshouse cucumbers in The Netherlands (25). However, an earlier study (23), which proposed that one gene with incomplete dominance conditioned parthenocarpy, should not be confused with parthenocarpic yield, but demonstrated genetic control for partheno- carpic or non-parthenocarpic fruitation. The presence of high levels of heterosis for the partheno- carpic yield characters together with an inbreeding depression for fruit number on the main stem were not surprising. Heterosis for yield was reported long ago (11) for seeded cucumber. Heterosis were also reported for various other cucumber characters (4,11,14, 26,27). Recently, Ghaderi and Lower (9) reported heterosis and an in- breeding depression were found for fruit number and weight and a fruit-bearing index in seeded fruitation of cucumber. Based on the present study and previous reports, hybrid vigor can be utilized to improve the yield of parthenocarpic pickling cucumber. Therefore, gynoecious lines could be improved for parthenocarpy by using a recurrent selection breeding program followed by testing of inbred lines in hybrid combinations. 56 Superior parent lines and hybrid combinations with high partheno- carpic yields could be identified. If gynoecious-hermaphroditic crosses are used for hybrid cultivars, then a backcross program could be used to improve the parthenocarpic yield of the her- maphroditic (pollen) parent as a single gene is responsible for the difference in gynoecious and hermaphroditic expression (17). LITERATURE CITED Allard, R.H. 1956. The analysis of genetic environmental interaction by means of diallel crosses. Genetics 41: 305-318. Baker, L.R., R.J.W. Scott and J.E. Wilson. 1973. Seedless pickles - A new concept. Mich. State Univ. Res. Rpt. 227. Barnes, W.C. 1966. Development of multiple disease resistant hybrid cucumbers. Proc. Amer. Soc. Hort. Sci. 89:390-393. Cochran, F.D. 1937. Breeding cucumbers for resistance to downy mildew. Proc. Amer. Soc. Hort. Sci. 35:541-543. Crumpaker, D.W. and R.W. Allard. 1952. A diallel cross analysis of heading date in wheat. Hilgardia 32:375-381. Deakin, J.R., G.W. Bohn and T.W. Whitaker. 1971. Interspecific hybridization in Cucumis. Econ. Bot. 25:195-211. Denna, D.W. 1973. Effects of genetic parthenocarpy and gynoecious flowering habit on fruit production and growth of cucumber, Cucumis sativus L. J. Amer. Soc. Hort. Sci. 98:602-604. El-Shawaf, I.I.S. and L.R. Baker. 1979. Inheritance of partheno- carpic yield in gynoecious pickling cucumber (Cucumis sativus L.). I. Performance of hermaphroditic pollen parents in top crosses with gynoecious lines (In press). Ghaderi, A. and R.L. Lower. 1979. Heterosis and inbreeding depression for yield and populations derived from six crosses of cucumber. J. Amer. Soc. Hort. Sci. (In press). Griffing, B. 1956. Concept of general and specific combining ability in relation to diallel crossing systems. Aust. J. Biol. Sci. 9:463-493. Hayes, H.K. and D.R. Jones. 1917. First generation crosses in cucumbers. Conn. Storrs Agric. Expt. Sta. Res. Rpt. 40:319-322. Hayman, 8.1. 1954. The theory and analysis of diallel crosses. Genetics 39:789-809. 57 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 58 Hawthorn, L.R. and R. Wellington. 1930. Geneva, a green- house cucumber that develops fruit without pollination. Bull. N.Y. Sta. Agric. Exp. Sta. 580:1-11. Hutchins, A.E. 1938. Some examples of heterosis in cucumber, Cucumis sativus L. Proc. Amer. Soc. Hort. Sci. 36:660-664. Jinks, J.L. and 8.1. Hayman. 1953. The analysis of diallel crosses. Maize Genetics Coop. Newsl. 27:48-54. Jinks, J.L. 1954. The analysis of continuous variation in diallel cross of Nicotiana rustica varieties. Genetics 39:767-788. Kubicki, B. 1969. Investigation on sex determination in cucumber (Cucumis sativus L.). VII. Andromonoecious.and hermaphroditism. Genetica Polonica 10:101-121. Kvasnikov, B.V., N.T. Rogova, S.I. Tarakonova and 5.1. Ignatova. 1970. Methods of breeding vegetable crops under the covered ground (Russian, English summary). Trudy Prikl. Bot. Genet. Sel. 42:45-57. Lee, J. and P.J. Kaltsikes. 1971. Letters to the Editor. Crop Sci. 11:314. Mather, K. and J.L. Jinks. 1971. Biometrical genetics. Cornell Univ. Press. Ithaca, N.Y. Meshcherov, L.T. and L.W. Juldasheva. 1974. Parthenocarpy in cucumber. Proc. Appl. Bot. Pl. Breed. 51:204-213. Mates, J.E. 1976. Pickling cucumbers. Production - harvesting. Mich. State Univ. Extension Bul. E-837. Pike, L.M. and C.E. Peterson. 1969. Inheritance of partheno- carpy in the cucumber (Cucumis sativus L.). Euphytica 18: 101-105. Ponti, 0.M.B. de. 1976. Breeding parthenocarpic pickling cucumbers (Cucumis sativus L.): Necessity, genetical possibilities, environmental influences and selection criteria. Euphytica 25:29-40. 25. 26. 27. 59 Ponti, 0.M.B. de and F. Garretsen. 1976. Inheritance of parthenocarpy in pickling cucumbers (Cucumis sativus L.) and linkage with other characters. Euphytica 25:633-642. Porter, R.H. 1931. The reaction of cucumber to types of mosaic. Iowa State J. Sci. 6:95-130. Robinson, R.W. and T. W. Whitaker. 1974. Cucumis. In: Handbook of genetics, Chapter 7. Auther, King, R76. Plenum Press, N.Y. 1974. PART III Combining Ability and Genetic Variances of G x H F1 Hybrids 60 Abstract. The yield performance of 20 gynoecious partheno- carpic hybrids of pickling cucumber, obtained by crossing 4 gynoecious (6) lines (seed parents) with 5 hermaphroditic (H) lines (pollen parents) was determined in the field. Additive genetic variance was greater than non-additive genetic variance for all yield and associated characters, except gynoecious expression where non-additive was more important. The GCA for harvesting-time, gynoecious expression, and yield of the female parents was greater than that of the male parents in this population. The converse was true for flowering time. The dominance estimates indicated complete dominance for early flowering and over-dominance for gynoecious expression. The remaining characters appeared to be under the control of genes with additive effects and partial dominance. Narrow sense heritability ratios of half-sibs (males or females) differed con- siderably and were moderately high for some traits. Genetic and phenotypic correlations for flowering time and nodal position of first-pistillate flower and between the latter and yield of first harvest could be due to linkage and/or pleiotropic effects of genes that control these characters. INTRODUCTION The breeding and development of parthenocarpic cultivars of pickling cucumber with gynoecious expression for out-of—doors production has received increasing attention from cucumber breeders (1,6,17,25,26). The advantages of higher yield potentials and better quality of parthenocarpic over seeded cultivars seem apparent (1,6,17, 25.26.31). 61 Environmental conditions such as low light, short daylength, low night temperature and late season enhance parthenocarpic fruit set in pickling cucumber especially on well developed vines (11,24, 26,31,36). This phenomenon was confirmed experimentally by growing cucumber under controlled conditions (31). It was reported that genetically parthenocarpic and non-parthenocarpic lines produced more parthenocarpic fruit under short day and low night temperatures. This agreed with a previous report (26). In the latter study, the number of parthenocarpic fruits was dramatically increased in the last two weeks of the harvest when daylengths became short (12 hr). Plant growth regulators, auxins, and auxin transport inhibitors, can also increase parthenocarpic fruit set in cucumbers (2,3,11,24). The expression of parthenocarpic fruiting as a trait was 509- gested to be under monogenic control with incomplete dominance (25) for parthenocarpy. This was in agreement with an early report (13). Conversely, Juldasheva (15) suggested one recessive gene might be responsible for the expression of parthenocarpy. Moreover, Kvasnikov gt__al:(l9) suggested that parthenocarpy was controlled by many re- cessive genes. Currently, Ponti and Garretsen (27) have assigned 3 independent, isomeric major genes with additive action together with non-allelic interaction as being responsible for this same trait. However, their model was based on data from glasshouse experiments with multiple harvests. 62 The heritability and genetic variances (nature and magnitude) for yield in parthenocarpic gynoecious pickling cucumbers for once- over mechanical harvest under field conditions are not reported. Such knowledge would be valuable to cucumber breeders to make breed- ing programs more efficient towards the development of parthenocarpic cultivars. The purpose of this investigation was to estimate genetic variance components and combining ability for yield and related char- acters in parthenocarpic gynoecious pickling cucumberfrom gynoecious- hermaphroditic crosses. MATERIALS AND METHODS Five hermaphroditic (H) parental lines from the MSU breeding program (661H, 669H, 319H, 581H and 532H) were crossed with four gynoecious (G) inbred lines (Gyl4, 9216, 3646, and 4026) to make 20 F1 (GxH) hybrids. These parental lines were described earlier (7,8). The 20 F1 hybrids and 4 gynoecious lines were seeded in a randomized complete block design with five replications on June 22, 1978 at the Horticultural Research Center of Michigan State University near East Lansing. Each experimental plot was 7.6 M in length by 1.8 M in width. Plants were thinned to spacing of 25 cm in the row with a minimum no. of 20 plants/plot. Standard cultural practices were used (23) with sprinkler irrigation. The field was isolated from other cucumbers by at least 3 miles. Before flowering, 10 plants were chosen at random to obtain data on flowering time, sex expression and nodal position of the first- pistillate flower. All plants were rogued daily for staminate floral buds. Plants which produced one or more staminate flowers were con- sidered predominantly female (PF). Plots were hand-harvested when 10% of the fruits in a plot were judged over-sized (>5 cm diam) as sug- gested for once-over harvest (20) for two consecutive harvests. Data on both harvest-time and yield (avg no. and wt (9) fruit/plant) were obtained from plot yields. 63 64 Data from the G x H hybrids were analyzed using a two-way classification model with interaction to obtain general combining ability (GCA) and specific combining ability (SCA) estimates. The sums of squares for the interactions, rep x male and rep x female, were pooled with the error term since these interactions were not significant. So, the formula for the statistical model was: Yhijk = u + oi + Bj + (08)1j + Rh + Ehijk Where, Yhijk = the observation for the k-th full-Sib progeny in a plot of the h-th replication of the i-th hermaphroditic pollen parent and the j-th gynoecious seed parent. And, u = the constant which is common to all observations; and ai and aj are the random effect of the i-th male parent and the j-th female parent, respectively; (aB)ij = random effect of the interaction of male and female parents; Rh = fixed effect of the h-th replication; and Ehijk = environmental effect and the re- mainder of the genetic effect between full sibs on the same plot and the following analysis of variance was used to estimate the genetic and phenotypic variances: Source of Variation d_.__f_._ MS EH5. Replications R-l MSR Males M-l Msm 52e+ r62mf+rf62m Females F-l MSf 62e+r62mf+rm62f Males x Females (M-l) (F-l) MSmf 52e+r5sz Error (R-l) (Mf-l) MS 52 E e 65 where; 62e = environmental variance, 62m = variance of male effects, 62f = variance of female effects, and 62mf = variance due to inter- action of male and female effects. The model description and the assumptions involved were reported previously (4,5,12). The GCA'S effects for the hermaphroditic male lines and the gynoecious female lines were estimated by subtracting the mean of all hybrids from the mean of each male line and female line in the hybrid combinations. The SCA's effects were obtained by summing the mean for a particular hybrid with the grand mean of all hybrids; then, sub- tracting the grand means for both the male and female line for that particular hybrid. The 6CA:SCA ratios were estimated by (62m+62f )/62mf. The degree of dominance,5, was estimated by the square root of 2 6sz/6zm; and the maternal effects as (62f-62m)/2. Narrow-sense heritability ratios were computed by multiplying 62 2 2 2 m or 6 f by 4, then dividing by 52 which equals (52m+5 f+5 mf+52e). Genetic and p phenotypic associations between characters were estimated from both variance and covariance components (16,35). Genetic (rGij) and phenotypic (rPij) associations for character pairs, i and j, were estimated from: .= 2. 2 r513 (611110 + 500') / (5 "11+ 5 k 2 2 k f, ) (6 mj + 6 fj)’ and .. _ 2 . 2 ”’13 " (6P(rs)1'j) /(6 P(fs)l 5 P (ism)15 ’ respectively. The numerators were estimated by covariance analysis and denominators from the analysis of variance. RESULTS The analysis of variance for the F1 (GxH) hybrids revealed significant differences among the genotypes for most characters measured except yield from the second harvest (Table 1). Data were further analyzed using a two-way classification model with interaction. Since there were no significant interactions between replications with either male or female parent, the genotypic varia- tion was partitioned into the variance due to the additive effects (GCA) of male and female parents and non-additive effects (SCA) by the interaction of male x female (Table 1). The GCA'S for the males (hermaphroditic parents) were signi- ficant for all characters except yield in the second harvest. The same was observed for the GCA'S of the females (gynoecious lines) with the additional exception that flowering time was not significant. The SCA'S were only Significant for gynoecious expression. By observation, the mean performance of GCA of the female lines in the hybrids was generally superior to that of the respective female parent (Table 2). Heterosis was expressed for earlier flowering (8 days) on earlier nodes (0.7 nodes) with earlier harvesting (7 days) and a higher gynoecious expression (10%), with more yield in the second harvest (no. fruit/plant or wt/plant) in contrast to the female parents. 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