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  • Author or Editor: Todd C. Wehner x
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The inheritance of resistance to M. arenaria races 1 and 2 in Cucumis sativus var. hardwickii (R.) Alef. line LJ 90430 was studied in several crosses with cultivated cucumber (C. sativus L.). Initially, parents, F1, F2, and BC1 to both parents of `Sumter' x LJ 90430 tested in a split-root experiment showed that resistance was quantitative. In addition, it appeared that the same genes were controlling resistance to race 1 and race 2 of M. arenaria (genetic correlation of 0.97 and 0.99 for gall index and egg mass data, respectively). In later greenhouse experiments, two other families were evaluated (`Addis' x LJ 90403 and `Poinsett 87' x LJ 90430) for inheritance of resistance to M. arenaria race 1. In all crosses using gall index data, additive variance was the largest component of genetic variance, and estimates of narrow-sense heritability ranged from 0.50 to 0.85 (0.57 to 0.81 for broad-sense heritability). Estimates of the minimum number of genes (effective factors) using gall index data ranged from 1.1 to 2.7 (0.2 to 0.3 for egg mass data).

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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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Abstract

Growth analyses were conducted in the greenhouse on two commercial lines, ‘Calypso’ and M 21 [of cultivated cucumber (Cucumis sativus L. var. sativus] differing in growth habit and one line, LJ 90430, of the wild cucumber Cucumis sativus L. var. Hardwickii (R.) Alef., to determine relationships between morphological characteristics and fruit yield. Multiple fruiting in LJ 90430 was associated with high leaf area and multiple branching. The standard commercial pickling cultivar, Calypso, which usually produces one to two fruit per plant per harvest, had less leaf area and fewer branches per plant than LJ 90430. Competition between early fruit development and vegetative growth was possible in ‘Calypso’ and M 21, but not in LJ 90430, which did not begin fruit development until vegetative growth was completed. Dry weight percentage in the fruit of LJ 90430 was low initially and increased steadily until the final harvest. Dry weight percentages in the fruit of ‘Calypso’ and M 21 were high initially and decreased generally thereafter. Relative growth rates of the whole plant followed similar trends in LJ 90430, ‘Calypso’, and M 21.

Open Access

Information on the mode of inheritance of powdery mildew resistance in watermelon is important for designing a breeding strategy for the development of new cultivars. Resistance in the watermelon accession PI 270545 was investigated by generation means analysis by crossing it with susceptible PI 267677. The analyses showed involvement of two genes, a recessive resistance gene, pmr-1, and a dominant gene for moderate resistance, Pmr-2. Resistance to powdery mildew in the leaf had a large dominance effect and a heritability of 71%. The additive-dominance model was inadequate in explaining variation in leaf resistance as revealed by the joint scaling test. However, nonallelic interactions could not be detected by the nonweighted six-parameter scaling test. For stem resistance, the additive-dominance model was adequate, and inheritance was controlled mainly by additive effects. A high narrow-sense heritability of 79% suggested that selection for stem resistance in early generations would be effective.

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Seeds of cucumber (Cucumis sativus L.) cultigens were mixed and compared for fruit yield (Mg·ha-1) and crop value ($/ha). Three cultigen pairs (Gy 14A + M 21, Gy 4 + WI 2757, and `Regal' + `Carolina') and five component ratios of each cultigen pair (0:100, 25:75, 50:50,75:25, and 100:0) were evaluated in five plantings over a 3-year period. Fruits were harvested six to eight times for each planting date. Early and total fruit yields and crop values were greatest when either Gy 14A or Gy 4 were planted as pure stands. As the ratio of Gy 14A or Gy 4 increased in the seed mixture, the yield and crop value increased. However, when the two predominantly gynoecious hybrids, `Regal' and `Carolina', were mixed, the yield and crop value were greater than those of pure stands of either hybrid. The combination of 75% `Regal' and 25% `Carolina' resulted in higher early and total fruit yields and crop value than the other ratios of the same cultigen pair. The `Regal' + `Carolina' pair produced significantly higher early yield and early crop value (first two harvests) than did the other cultigen pairs tested. However, total yield and total value for `Regal' + `Carolina' did not differ from the Gy 14A + M 21 pair. The practice of mixing two cultivars in arbitrary combinations does not offer an advantage over single cultivars in a multiple-harvest system. In some cases, predominantly gynoecious-predominantly gynoecious mixtures may have advantages over monoecious-predominantly gynoecious cultigen mixtures if pollination is not limiting. Seed mixtures need to be evaluated to determine whether specific combinations offer advantages, as this study indicated that superior mixtures may exist.

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Gummy stem blight (GSB), caused by three related species of Stagonosporopsis [Stagonosporopsis cucurbitacearum (syn. Didymella bryoniae), Stagonosporopsis citrulli, and Stagonosporopsis caricae], is a major disease of watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] in most production areas of the United States. We studied the inheritance of resistance to GSB using three PI accessions of watermelon. Four families of six progenies (Pr, Ps, F1, F2, BC1Pr, and BC1Ps) were developed from four crosses of resistant PI accessions by susceptible cultivars. Each family was tested in 2002 and 2003 in North Carolina under field and greenhouse conditions for resistance to GSB. Artificial inoculation was used to induce uniform and strong epidemics. The effect of the Mendelian gene for resistance, db, was tested. Partial failure of the data to fit the single-gene inheritance suggested that resistance to GSB of PI 482283 and PI 526233 may be under the control of a more complex genetic system.

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Citrulline, arginine, and lycopene are naturally occurring compounds found in watermelon, Citrullus lanatus (Thumb) Matsum & Nakai, with beneficial effects on plant growth and human health. This study evaluated seven commercial cultivars and one breeding line for citrulline, arginine, and lycopene content in mature fruit grown at two locations in North Carolina. Correlations among these compounds and fruit quality traits (percent soluble solids and flesh pH) were evaluated. Watermelon cultigens evaluated were chosen for their fruit trait diversity. ‘Yellow Doll’ and NC-517 possessed the highest citrulline and combined concentration of citrulline and arginine of all cultigens evaluated. Lycopene content was highest in ‘Dixielee’, followed by ‘Sugar Baby’, and ‘Allsweet’, each of which have different shades of red flesh color. Location and its interaction with genotype had no significant effect on arginine or lycopene concentration. Broad-sense heritability was estimated for each trait. Arginine content (89%) and lycopene content (99%) had very high heritability. Citrulline content (41%), percent soluble solids (46%), and flesh pH (61%) had moderate heritability. Lycopene was positively correlated with flesh pH (r = 0.517) and negatively correlated with percent soluble solids (r = −0.344). Arginine content had a weak negative correlation with flesh pH (r = −0.343) and was not correlated with percent soluble solids.

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Sources of resistance to the Zucchini yellow mosaic virus-Florida strain (ZYMV-FL) have been identified within the Citrullus genus. Inheritance of resistance to ZYMV-FL was studied in PI 595203 (Citrullus mucosospermus), a resistant watermelon accession. The F1, F2, and BC1 progenies derived from the cross ‘Calhoun Gray’ (CHG) × PI 595203 and ‘New Hampshire Midget’ (NHM) × PI 595203 were used to study the inheritance of resistance to ZYMV-FL. Seedlings were inoculated with a severe isolate of ZYMV-FL at the first true leaf stage and rated weekly for at least 6 weeks on a scale of 1 to 9 on the basis of severity of viral symptoms. A single recessive gene (zym-FL) was found to control the high level of resistance to ZYMV-FL in PI 595203.

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Cucumber (Cucumis sativus L.) is one of the most popular vegetable crops grown in U.S. home and urban gardens. The objectives of this study were to identify cultivars and planting densities for high yield of container-grown cucumbers. Additional objectives were to determine the value of field trials for predicting cucumber performance in containers and to evaluate different plant types (dwarf-determinate vs. tall-indeterminate, gynoecious vs. monoecious, pickling vs. slicing) for container use and disease severity across cultivars. Fourteen cultivars and breeding lines were tested at three planting densities in two seasons for yield, quality, and disease resistance in field and patio trials. Significant differences were detected for seasons, cultivars, and densities. Yields were highest in the spring season compared with the summer season, and the best performance was obtained using three plants per 12 L container. There was a high correlation between patio and field trials, allowing extension specialists to recommend cucumber cultivars with high yield, high quality, and disease resistance based on field trial data. Home gardeners who want space-saving, high-yielding cucumbers with tender skin should consider a dwarf-determinate, pickling type that is monoecious. With monoecious type, no pollenizer is needed, and the harvest will be spread over more weeks than would be for gynoecious types.

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Cucurbit plants usually are sensitive to chilling and easily damaged. Although bottle gourds, which are members of the Cucurbitaceae family, are considered as fresh vegetables in some Asian countries, their main use in recent years is to be used as rootstocks in grafted watermelon cultivation. We tested 163 bottle gourd accessions of the U.S. Department of Agriculture (USDA) genebank for cold tolerance in the early seedling stage. The experiment was conducted using controlled environment chambers with 3 chilling durations (36, 48, and 60 hours) at 4 °C. Chilling damage was rated 0 to 9 (0 = no damage, 1 to 2 = trace of damage, 3 to 4 = slight damage, 5 to 6 = moderate damage, 7 to 8 = advanced damage, 9 = plant totally dead). We rated damage separately for the cotyledons, true leaf, and growing point. Cold damage was higher at a chilling duration of 60 hours, and decreased at 48 and 36 hours. Most tolerant cultigens were PI 491272, PI 491280, PI 491281, PI 491286, and PI 491326. Most susceptible were PI 381845, PI 381846, PI 534556, PI 636137, and PI 668365.

Open Access