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  • Author or Editor: Nischit V. Shetty x
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Yield was evaluated in 817 plant introduction accessions of cucumber (Cucumis sativus L.) along with 19 check cultivars. The study was conducted in spring and summer seasons of 1997 and 1998 with three replications using recommended horticultural practices and optimized field plot trials. In order to get fruit from each cultigen regardless of sex expression, plants were sprayed with ethrel (2-chloroethyl phosphonic acid) to make them gynoecious. Plots were harvested once-over when 10% of the fruit in a plot were oversize. Data were collected on fruit weight (total, marketable, early and cull), fruit number (total, marketable, early and cull), fruit type, fruit quality, and days to harvest. Total fruit weight for all cultigens ranged from 4 to 214 Mg/ha, with 1 to 40 fruit per plot. Based on statistical analysis, fruit number was the most useful trait for yield evaluation. Stand corrections for yield were not found to be useful. The cultigens with the highest fruit numbers for pickling type were PI 215589, PI 179678, PI 249561, PI 356809, and PI 370643. Highest fruit number for slicing type were PI 344440, PI 422199, and PI 342951. Highest fruit number for middle-eastern type were PI 525150, PI 525153, PI 181910, and PI 534540. Highest fruit number for Oriental trellis type were PI 432849, PI 432866, PI 508455, PI 372893, and PI 532520. Several cultigens produced more than the check cultivars. High-yielding cultigens could be used in breeding programs to improve the yield of cucumber.

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In many cases, measurement of cucumber fruit weight in small research plots involves more labor and resources than just counting the number of fruit per plot. Therefore, plant breeders are interested in an efficient method for estimating fruit weight per grade (early, marketable, and cull) based on fruit number and total fruit weight. We evaluated the cucumber germplasm collection of 810 plant introduction accessions (supplied by the U.S. Dept. of Agriculture, Regional Plant Introduction Station at Ames, Iowa) along with seven check cultivars for yield. Correlations were calculated for all pairs of fruit number and fruit weight combinations for each grade. In general, the lowest correlations were observed between the fruit weight of each grade (early, marketable, and cull) and total fruit weight or number per plot. High correlations were observed for fruit weight and fruit number within each grade (early, marketable, and cull). An efficient method for estimating fruit weight per hectare of early, marketable, and cull grades is to count total, early, and cull fruit, then measure total fruit weight. Our results showed that the fruit weight of each grade (early, marketable, and cull) was best estimated using the fruit number of that grade (early, marketable, and cull) along with the total fruit weight and total fruit number.

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Suitability of commercial production of oriental trellis type cucumber (Cucumis sativus L.) was evaluated using 18 cultivars and breeding lines (referred to as cultigens hereafter). The cultigens (15 oriental trellis and three American slicers) were tested using two systems (trellis and flat bed production) in two seasons (spring and summer) in 1995 at Clinton, N.C. Traits evaluated included total yield, early yield, percentage culls, vine length, leaf area, gynoecious rating, fruit shape, fruit color, fruit length, seed cell size, anthracnose resistance, powdery mildew resistance, and fruit keeping ability. Highest yielding cultigens were `Summer Top', `Tasty Bright', and `Sprint 440'. Those with best fruit quality were `Sprint 440', `Tasty Bright', `Poinsett 76', and `Summer Top'. Most disease resistant was `Poinsett 76'. The best cultigens considering all traits measured were `Sprint 440', `Tasty Bright', and `Summer Top'. Production of cultigens on trellis rather than flat bed resulted in an average increase in total, marketable, and fancy yield of 130%, 160%, and 140%, respectively. Oriental trellis cucumbers can be produced as a less expensive alternative to European greenhouse cucumbers, and to supply consumer demand for this particular product type.

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Gummy stem blight (Didymella blight), caused by Didymella bryoniae (Auersw.) Rehm and its anamorph Phoma cucurbitacearum (Fr.:Fr.) Sacc., is the second most important disease of cucumber (Cucumis sativus L.) in North Carolina after root knot nematodes Meloidogyne sp. Both Didymella blight and Phoma blight, caused by Phoma exigua Desm., have similar symptoms and control practices, and are generally referred to as gummy stem blight. In order to determine whether resistance existed to North Carolina isolates of D. bryoniae, 851 cultigens [cultivars, breeding lines, and plant introduction (PI) lines] were evaluated in the field. Plants were inoculated with one selected isolate (highly pathogenic in preliminary greenhouse tests) at the vine tip-over stage. They were rated for foliage lesion size and number on a 0 to 9 visual scale (0 = no disease, 9 = plant killed) and average ratings for 10 plants per plot were analyzed. The ratings ranged from 2.0 (highly resistant) to 8.5 (highly susceptible) with a mean of 6.2. The most resistant breeding lines and PI accessions were PI 200815, PI 390243, `LJ 90430', PI 279469, and PI 432855. The most resistant cultivars were `Homegreen #2', `Little John', `Transamerica', and `Poinsett 76'. The most susceptible cultigens in the study were PI 288238, PI 357843, PI 357865, and PI 167134. Two popular cultivars in North Carolina, `Calypso' and `Dasher II', were moderately resistant.

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Eighteen cucumber (Cucumis sativus L.) cultivars (15 oriental trellis and three standard American slicers) were grown on trellis and flat-bed production systems during the spring and summer seasons of 1995. Vine, flower, fruit quality, keeping ability, and yield traits were measured. Vine length, incidence of powdery mildew, fruit shape, fruit quality, fruit firmness, yield of Fancy plus No. 1 grade slicer fruits, marketable yield, and percentage of culled fruits were all higher when cultivars were grown on trellis support. Anthracnose damage, fruit length, fruit diameter, average fruit mass, fruit color, overall impression, fruit shriveling, seedcell size, branch number, percentage of staminate nodes, and total yield were not significantly affected by production system. The best cultivars for marketable yield (mass of Fancy, No. 1 and 2 grade slicers) were `Summer Top', `Tasty Bright', and `Sprint 440' on trellis support and `Sprint 440' and `Poinsett 76' on flat bed. The cultivars with the best fruit quality were `Tasty Bright', `Summer Top', and `Sprint 440' on trellis and `Poinsett 76', `Sprint 440', and `Tasty Bright' on flat bed. The best cultivars overall on the trellis production system were `Sprint 440', `Summer Top', `Tasty Bright', and `89-211', and the worst were `Sky Horse', `Hongzhou Green 55', and `Fengyan'. The best cultivars overall on the flat bed were `Poinsett 76', `Sprint 440', and `89-211', while the worst cultivars were `Sky Horse' and `Hongzhou Green 55'.

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Downy mildew [Pseudoperonospora cubensis (Berk. & Curt.) Rostov] is an important disease in most cucumber (Cucumis sativus L.) production areas of the world. Resistant cultivars are available, but higher levels are needed if yield losses are to be avoided. The objective of this experiment was to test all available plant introduction accessions, cultivars, and breeding lines (collectively referred to as cultigens) of cucumber for downy mildew resistance under field conditions in North Carolina. Cultigens were tested in 2 years and two replications under natural field epidemics of the disease. Mean ratings for downy mildew leaf damage ranged from 1.3 to 9.0 on a 0 to 9 scale. The most resistant nine cultigens originated from the U.S., and were primarily adapted cultivars or breeding lines. The most-resistant cultigens, for which multiple-year data were available, were Gy 4, `Clinton', PI 234517, `Poinsett 76', Gy 5, `Addis', M 21, M 27, and `Galaxy'. The most-susceptible cultigens for which multiple year data were available, were PI 288995, PI 176952, PI 178886, and PI 211985. We classified 17 cultigens as highly resistant (1.3 to 3.0), 87 as moderately resistant (3.3 to 5.0), 311 as moderately susceptible (5.3 to 7.0), and 248 as highly susceptible (7.3 to 9.0) for the 663 cultigens with multiple-year data. No plant introduction accessions were found to be more resistant than the most-resistant elite cultivars and breeding lines tested.

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Eighteen cucumber (Cucumis sativus L.) cultivars (15 oriental trellis and three standard American slicers) were grown on trellis and flat-bed production systems during the spring and summer seasons of 1995. Vine, flower, fruit quality, keeping ability, and yield traits were measured. Vine length, incidence of powdery mildew, fruit shape, fruit quality, fruit firmness, yield of Fancy plus No. 1 grade slicer fruits, marketable yield, and percentage of culled fruits were all higher when cultivars were grown on trellis support. Anthracnose damage, fruit length, fruit diameter, average fruit mass, fruit color, overall impression, fruit shriveling, seedcell size, branch number, percentage of staminate nodes, and total yield were not significantly affected by production system. The best cultivars for marketable yield (mass of Fancy, No. 1 and 2 grade slicers) were `Summer Top', `Tasty Bright', and `Sprint 440' on trellis support and `Sprint 440' and `Poinsett 76' on flat bed. The cultivars with the best fruit quality were `Tasty Bright', `Summer Top', and `Sprint 440' on trellis and `Poinsett 76', `Sprint 440', and `Tasty Bright' on flat bed. The best cultivars overall on the trellis production system were `Sprint 440', `Summer Top', `Tasty Bright', and `89-211', and the worst were `Sky Horse', `Hongzhou Green 55', and `Fengyan'. The best cultivars overall on the flat bed were `Poinsett 76', `Sprint 440', and `89-211', while the worst cultivars were `Sky Horse' and `Hongzhou Green 55'.

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Gene linkage was investigated in 11 families using 18 genes in cucumber (Cucumis sativus L.). The genes studied were B (black spine), B-3 (Black spine-3), B-4 (Black spine-4), bi (bitterfree cotyledons), Bt (bitter fruit), Bt-2 (bitter fruit-2), D (dull fruit skin), df (delayed flowering), de (determinate habit), F (female sex expression), gl (glabrous foliage), lh (long hypocotyl), ns (numerous spines), pm-h [powdery mildew (Sphaerotheca fuliginea Schlecht.:Fr.) resistance expressed on the hypocotyl], ss (small spines), Tu (tuberculate fruit), u (uniform immature fruit color), and w (white immature fruit color). A major objective of this study was to measure linkages of genes for fruit bitterness (Bt and Bt-2), and spine color (B-3 and B-4) relative to previously studied loci: B, bi, D, de, df, F, gl, lh, ns, pm-h, ss, Tu, u, and w. The F2 progeny of LJ 90430 × PI 173889 segregated 13 bitter fruit: 3 nonbitter fruit, indicating that different genes are controlling fruit bitterness in these lines. Bt-2 is proposed as the gene controlling bitterness of fruit in LJ 90430. It is a separate locus from Bt, that causes bitter fruit in PI 173889. Several new gene linkages were found: biBt, (Bt-2)—de, D—(Bt-2), Dns, glF, ss—(Bt-2), Tu—(Bt-2), and u—(Bt-2). The Bt gene appears to be linked to bi and may be located on linkage group I. Bt-2 appears to be linked with several genes that could connect linkage groups I and IV. Bt-2 was linked to u, Tu, D, and ss, that are all on linkage group IV. Bt-2 was also found to be linked loosely to de, that is on linkage group I. No linkages were found between B-3 and B-4 and the genes evaluated in this study. Weak linkages (>25 cM) between several gene combinations [(Bt-2)-de, dens, dess, deTu, deu, nsF, and ssF] provided more evidence that linkage group I and IV may be linked. Due to the weak linkages, more information needs to be obtained using larger populations and more markers to confirm these findings.

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Field and detached-fruit screening tests were developed for evaluating cucumber (Cucumis sativus L.) plant introduction accessions, breeding lines, and cultivars (hereafter collectively referred to as cultigens) for resistance to fruit rot caused by Rhizoctonia solani Kuhn. The factors that were examined for developing a detached-fruit test were five inoculum levels of R. solani AG-4 and two cover treatments. The major influence on disease reaction was inoculum level. The best method used 50-mm-diameter fruit placed on sterile soil inoculated with 6400 oat grains/m2 colonized with R. solani and watered initially, then misted every 3 days for 1 minute, left uncovered, and rated after 10 days for the percentage of the fruit surface covered with lesions. Field and detached-fruit tests were conducted using two different inoculum levels of R. solani (3200 and 4800 oat grains/m2). The four most resistant cultigens, based on the results of field and detached-fruit tests, were PI 163216, PI 197088, PI 357852, and PI 280096. One field and detached-fruit test pair was not significantly correlated (detached-fruit screening test one vs. field screening test one), but the other (detached-fruit test two vs. field screening test two) was correlated (r = 0.50). The detached-fruit test could be used for general classification of resistance or susceptibility. Resistant cultigens could be identified with either method, but the field test had slightly lower coefficients of variation.

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Cucumber (Cucumis sativus L.) plant introduction (PI) accessions from the regional PI station at Ames, Iowa were evaluated in open-field production for single-harvest yield at Clinton, N.C. and Ames, Iowa. Check cultivars and experimental inbreds were also tested for comparison with the PI accessions (the three groups hereafter collectively referred to as cultigens). In order to make the evaluation more uniform for all cultigens regardless of sex expression and fruit size, all were crossed with Gy 14, a gynoecious pickling cucumber inbred used commonly in the production of commercial hybrids. The resulting 761 gynoecious hybrids were tested for early, total, and marketable yield using recommended cultural practices. Results were obtained for 725 cultigens at both locations. Significant differences were observed among cultigens for all traits evaluated. Differences between the two locations were also significant for total yield, corrected total yield, and percentage of early fruit. The interaction of cultigen and location was significant for standardized total yield and standardized corrected total yield. The highest yielding hybrids at both locations were produced using the following cultigens as male (paternal) parents: PI 422185, PI 390253, PI 175120, PI 173889, PI 267087, PI 175686, PI 178888, PI 385967, PI 458851, and PI 171601. The highest and lowest yielding paternal parents from the germplasm screening study were retested, along with check cultigens in a multiple-harvest trial at Clinton, N.C. Cultigens were evaluated directly, rather than as hybrids with Gy 14, and fruit number, fruit weight, and sex expression were recorded. Most cultigens performed as expected for the yield traits in the retest study. The exceptions were `Wautoma' and PI 339250, which were among the low and high yielders in the first test, but were ranked as medium and low, respectively, in the retest study.

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