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Christopher S. Cramer and Joe N. Corgan

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Christopher S. Cramer and Joe N. Corgan

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Christopher S. Cramer and Joe N. Corgan

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Christopher S. Cramer and Todd C. Wehner

Progress was measured in four populations of cucumber (Cucumis sativus L.) improved by recurrent selection. The populations were the North Carolina wide base pickle (NCWBP), medium base pickle (NCMBP), elite pickle 1 (NCEP1), and hardwickii 1 (NCH1). Families from each of three cycles (early, intermediate, and late) from each population were randomly chosen and crossed with Gy 14 to produce gynoecious hybrids. Gy 14 is a gynoecious inbred used commonly as a female parent in the production of pickling cucumber hybrids. Once the plants had 10% oversized (>51 mm in diameter) fruit, plots were sprayed with paraquat to simulate once-over harvest. Selection cycles were evaluated for total, early, and marketable yield, and fruit shape. Testcross performance for fruit shape rating increased over cycles for the NCWBP and NCMBP populations when tested in either season. Testcross performance for total and early yield of the NCEP1 population tested in the spring decreased with selection, but remained constant over cycles in the summer season. The majority of yield traits in each population remained unchanged across selection cycles. Of the four populations studied, the NCMBP population had the greatest gain (7%) in testcross performance over cycles and averaged over all traits. In addition, testcross performance for fruit shape rating had the greatest gain (11%) with selection and averaged over populations. Years and seasons greatly influenced testcross performance for fruit yield and shape rating. In most instances, the fruit yield and shape of Gy 14 was higher than the testcross performance of population-cycle combinations. The performance of several families exceeded that of Gy 14 when testcross combinations were made. Those families could be selected for use in the development of elite cultivars. Chemical name used: 1,1'-dimethyl-4,4'-bipyridinium ion (paraquat).

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Christopher S. Cramer and Joe N. Corgan

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Christopher S. Cramer and Joe N. Corgan

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Christopher S. Cramer and Joe N. Corgan

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Christopher S. Cramer and Michael J. Havey

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Christopher S. Cramer and Todd C. Wehner

Plant breeders often measure selection progress for yield by measuring the hybrid performance (combining ability) of a breeding line. This information is used to develop breeding lines with higher combining ability. The objectives of this study were to measure the specific combining ability for yield traits over three selection cycles from four slicing cucumber populations with `Poinsett 76', a popular slicing cucumber cultivar; and to determine the change in specific combining ability for yield traits in four populations improved through recurrent selection. Four slicing cucumber populations, North Carolina wide base slicer (NCWBS), medium base slicer (NCMBS), elite slicer 1 (NCES 1), and Beit Alpha 1 (NCBA1), were developed and improved through modified half-sib selection from 1983 to 1992 to improve yield per se and fruit quality in each population. Eleven families were randomly selected from each of three selection cycles (early, intermediate, advanced) from each population and were hybridized to `Poinsett 76'. Twenty-three seeds from each cross were planted in 1.2-m plots in Spring and Summer 1995. When 10% of fruit were oversized (>50 mm in diameter), plants were sprayed with paraquat to defoliate them and to simulate once-over harvest. The experimental design was a randomized complete block with 22 replications per population arranged in a split plot with the four populations as whole plots and the three cycles as subplots. The combining ability for early and marketable yield of NCWBS and NCBA1 increased as the number of selection cycles increased. Conversely, selection for higher yield per se decreased the combining ability of the NCES 1 population for early and marketable yield. The NCBA1 population exhibited the largest gain (131.2%) from cycle 0 to 8 averaged over all traits. Early yield exhibited the largest gain (60.8%) averaged over all populations.

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Christopher S. Cramer and Todd C. Wehner

Increased fruit yield in slicing cucumber (Cucumis sativus L.) has been difficult to achieve since yield is quantitatively inherited with low heritability. From 1981 to 1993, four slicing cucumber populations differing in their genetic diversity (wide, medium, elite, and `Beit Alpha') were advanced through six to ten cycles of modified half-sib recurrent selection. The objectives of this research were to determine 1) the fruit yield and yield component means; 2) the correlations between yield components, between yield traits, and between components and yield; and 3) the change in means and correlations with selection for improved yield of four slicing cucumber populations. In 1994 and 1995, four families were randomly selected from three cycles (early, intermediate, and late) from each population and self-pollinated. Thirty plants from each S1 family were evaluated in 3.1-m plots in Spring and Summer 1995 and 1996 at the Horticultural Crops Research Station in Clinton, N.C. Plants were harvested and data were collected on number of branches per plant and nodes per branch, proportion of pistillate nodes, fruit set and shape, and total, early, and marketable yield. When averaged over all populations, seasons, and years, fruit yield and quality increased with selection while yield components remained unchanged with selection. Fruit yield and components differed between populations, seasons, and years. Most correlations between yield components and between yield components and fruit yield were weak, and strong correlations varied between populations, seasons, and yield components. Indirect selection of proportion of pistillate nodes has potential for improving yield for certain population-season combinations. Selection weakened many strong correlations between yield components and between yield and components. Changes in correlations often did not correspond with changes in trait means. Based on this research, selection for yield components would not be advantageous for improving fruit yield in all slicing cucumber populations. Additional yield components, yield component heritability, and better component selection methods need to be determined before component selection can be used to improve fruit yield.