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  • Author or Editor: Todd C. Wehner x
  • Journal of the American Society for Horticultural Science x
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Abstract

Variance components for low-temperature germination ability in cucumber (Cucumus sativus) were estimated for 3 germination variables (actual days to germination, days to 50% germination, and percentage of germination) at 17°C using a North Carolina Design I analysis. The estimates were made using the North Carolina Medium Base Pickle (NCMBP) population, which was developed by intercrossing adapted pickling cucumber cultivars with diverse lines for 3 cycles without selection. Estimates of additive and dominance variance for the percentage of germination and days to 50% germination were equal, but additive variance was predominant for actual days to germination. Heritabilities based on half-sib families tested in 2 replications ranged from 0.44 to 0.61 for the 3 germination variables. There were large significant genetic correlations among the 3 germination variables, ranging from 0.61 to 1.03 in absolute value. Selection for either the percentage of germination or for actual days to germination at 17° should result in significant progress in improving low-temperature germination ability of cucumbers in the NCMBP population.

Open Access

Fruit yield, earliness, and quality have low to moderate heritability, but are traits of major importance in cucumber (Cucumis sativus L.). The objective of this study was to determine the changes made in those traits using recurrent selection in three slicing cucumber populations (NCMBS, NCES1, and NCBA1). During population improvement, one or two replications of 200 to 335 half-sib families were evaluated in the spring season for five traits: total, early, and marketable fruit per plot, fruit shape rating, and a simple weighted index (SWI = 0.2(total yield)/2 + 0.3(early yield) + 0.2(% marketable)/10 + 0.3(fruit shape). Families from each population were intercrossed in an isolation block during the summer season using remnant seeds of the best 10% selected using the index. Response was evaluated using a split-plot treatment arrangement in a randomized complete block design with 32 replications in each of two seasons (spring and summer). Whole plots were the three populations, and subplots were the 11 cycles (cycles 0 to 9 plus checks). We measured improvement in performance of the populations in a selected (spring) and unselected environment (summer). Significant gains were made for all traits in all populations over the 9 to 10 cycles of recurrent selection. Greatest progress was made for the NCMBS population, with an average of 37% gain from cycle 0 to 9 over all five traits. The trait where most progress was made was early yield, with an average of 63% gain from cycle 0 to 9 over the three populations.

Free access

Belly rot, caused by the fungal pathogen Rhizoctonia solani Kühn., is a severe disease in many regions that produce cucumber (Cucumis sativus L.). Annual crop loss to belly rot is commonly 5% to 10%, but losses as high as 80% can occur in individual fields. There are no resistant cultivars, so fungicides are used to provide partial control. Genetic resistance in an acceptable cultivar would be more desirable and economical. Studies were conducted in Summers 1991 and 1992 to screen promising germplasm for belly rot resistance using field and detached-fruit screening methods. In 1991, 105 cultigens (cultivars, breeding lines, and plant introduction accessions) were evaluated for belly rot resistance. The tests were repeated in 1992 with 63 cultigens, including the most resistant cultigens identified in 1991 and appropriate controls. Several cultigens were identified as potential sources of resistance genes. Pickling cucumbers showing resistance included PI 197085, PI 271328, and an F4 selection of PI 197087 × PI 280096. Slicing cucumbers with resistance included `Marketmore 76' and the F1 of Gy 14 × PI 197087. Belly rot resistance was not correlated with other horticultural traits measured, including fruit type, skin type, spine color, and firmness. The resistant cultigens identified should be useful for developing cucumber cultivars with enhanced resistance to Rhizoctonia solani.

Free access

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).

Free access

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.

Free access

Recurrent selection has been used as a breeding method to improve traits having low heritability such as fruit yield, earliness, and fruit shape. The objective of this study was to measure the progress of recurrent selection in four slicing cucumber populations in terms of hybrid performance when crossed with a common tester. The four populations, North Carolina wide-base slicer (NCWBS), medium-base slicer (NCMBS), elite slicer 1 (NCES1), and Beit Alpha 1 (NCBA1) populations, which differed in their genetic diversity and mean performance, were developed using modified intrapopulation half-sib recurrent selection to improve fruit yield and quality. Eleven S0 families were taken randomly from each of three selection cycles (early, intermediate, and advanced) from each population. Those families were self-pollinated to form S1 families, and the S1 families were crossed to `Poinsett 76', a popular slicing cucumber cultivar. The experiment was a splitplot treatment arrangement in a randomized complete-block design with 22 replications per population, with the four populations as whole plots and the three cycles as subplots. When 10% of fruit were oversized (>60 mm in diameter), plants were sprayed with paraquat to defoliate them for once-over harvest. Plots were evaluated for total, early, and marketable yield and fruit shape. Recurrent selection for improved fruit yield and shape per se resulted in improved hybrid performance of the NCWBS and NCBA1 populations for fruit yield and shape rating when tested in the selected or nonselected environment. The NCWBS population had the largest gain (21%) in hybrid performance averaged over all traits. In addition, early yield was improved an average of 18% from early to late cycles for each population. Even though the fruit yield and shape rating of `Dasher II' was greater than the hybrid performance of each population mean for the same traits, several F1 families within each population exceeded the fruit yield of `Dasher II'.

Free access

The effects of leaf age, guttation, stomata and hydathode characteristics, and wounding on the symptom development of gummy stem blight [Didymella bryoniae (Auersw.) Rehm] of cucumber (Cucumis sativus L.) were studied to develop a useful germplasm screening method. Older cucumber leaves were more susceptible than younger leaves in field, greenhouse, and detached-leaf tests. Compared to seedlings with true leaves, seedlings at the cotyledon stage were less susceptible, had a smaller variance for ratings, and were more likely to escape infection. Stomata density and hydathode counts were not correlated with field ratings; but, stomata length on older leaves was highly correlated with susceptibility y. In greenhouse and field tests, susceptibility y increased as guttation increased and actively guttating plants were more susceptible than nonguttating plants. Phylloplane moisture and/or nutrition were more important in the infection process than was stomata] opening. Although important, guttation was not necessary for infection. Dawn inoculation of field or greenhouse tests increased leaf symptoms compared with dusk inoculation. The increase was likely due to the free water and nutrients provided by guttation. Genotype ranks and ratings for detached-leaf tests were not correlated with field results. A useful method, highly correlated (r = 0.82 to 0.96) with field ratings. for screening germplasm in the greenhouse was developed.

Free access

Heritability of resistance to gummy stem blight (Didymella bryoniae (Auersw.) Rehm.) was measured in two diverse cucumber (Cucumis sativus L.) populations [North Carolina elite slicer 1 (NCES1) and North Carolina wide base pickle (NCWBP)]. Heritability was estimated using parent-offspring regression and half-sib family analysis in North Carolina field tests during 1991 and 1992. NCES1 is a slicing cucumber population with a narrow genetic base, and NCWBP is a pickling cucumber population with a wide genetic base. Heritability estimates were low to moderate ranging from 0.12 to 0.49 for the gummy stem blight leaf rating and from -0.03 to 0.12 for stem rating. Estimates of gain from selection were at least two times larger for selection based on half-sib families than for mass selection for all traits in both populations. Approximately three to five cycles of selection would be required to improve the NCES1 population mean for gummy stem blight leaf resistance by one rating scale unit, and three to four cycles of selection would be required to improve the NCWBP population mean for gummy stem blight leaf resistance by one rating scale unit, based on half-sib family selection. One rating scale unit decrease is equivalent to an 11% reduction in susceptibility. Gain would be slower if selecting for stem, or leaf and stem resistance. A moderate amount of additive genetic variation exists in both populations for gummy stem blight leaf resistance, but estimates for additive genetic variation for stem resistance indicate little to no additive genetic variation. Development of populations specifically for greater initial resistance and greater additive variance than found in these populations should aid in selection for resistance.

Free access

Leaf and stem resistance to gummy stem blight [Didymella bryoniae (Auersw.) Rehm.] in five resistant by susceptible crosses of cucumber (Cucumis sativus L.) was investigated using generation means analysis. No single gene of major effect controls either leaf or stem resistance to gummy stem blight in these five crosses. The mean number of effective factors controlling leaf resistance in the cross `Slice' × `Wis. SMR 18' was estimated to be at least five. Estimates of broad- and narrow-sense heritabilities indicated that environmental effects were larger than genetic effects. In general, additive variance was the larger component of genetic variance. Epistasis was significant in most crosses, and dominance was present in several crosses. Additive gene effects contributed more to resistance than to susceptibility in contrast with dominance gene effects. Reciprocal differences for leaf rating were detected in the crosses M 17 × `Wis. SMR 18' and `Slice' × `Wis. SMR 18'. Phenotypic correlations between leaf and stem ratings were moderate (r = 0.52 to 0.72). Estimates of genetic gain for resistance to gummy stem blight ranged from low to moderate. Breeding methods that make best use of additive variance should be used because much of the variance for resistance is additive, and dominance effects, at least in these crosses, tended to contribute to susceptibility.

Free access

Abstract

Growth patterns of cucumbers (Cucumis sativus L.) were studied by photographing developing fruit at 2- or 3-day intervals over a 30-day period beginning with pollination (day 0). Nine cultivars were studied: ‘Chinese Long Green’, ‘Sprint 440’, ‘Marketmore 76’, and ‘Minisol’ (all fresh-market types); ‘Riesenschal’ (a schälgurken type); and ‘Marbel’, ‘Kobus’, ‘Calypso’, and ‘Wisconsin SMR-18’ (all pickling types). Analysis of the photographs showed that all sections of the fruit grew in length at a constant rate during the 30-day period. The pattern of growth was fairly uniform, except that there was slightly more growth in the center section than at the ends, and slightly more growth at the blossom end than at the peduncle end of the fruit. Fresh-market and schälgurken types had the longest fruit over the 30-day period of growth, but pickling types had the highest percent change in length. Pickling types produced shorter fruit because they stopped growing earlier than the two other types (12 vs. 14 days, respectively).

Open Access