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  • Author or Editor: T.C. Todd x
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Abstract

A wide-base pickling cucumber (Cucumis sativus L.) population was formed by intercrossing all available cucumber lines (1063) and selecting for short fruit length. After intercrossing twice, 112 S0 plants and their half-sib progeny were evaluated for Rhizoctonia fruit rot resistance using a detached-fruit test. Parent-offspring regression indicated a narrow-sense heritability of 0.24, considered low to moderate. Gain from selection was calculated for 2 recurrent selection systems. Based on the heritability estimate, selection using replicated progeny rows was recommended for improving resistance to this trait.

Open Access

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.

Free access

Spring dead spot (SDS), caused by three root-infecting species of Ophiosphaerella, is a destructive disease of bermudagrass (Cynodon spp.L.C. Rich). We tested the effects of incubation temperature and duration, and exposure to decreasing freezing temperatures on bermudagrass shoot survival following inoculation with SDS pathogens. Inoculated plants exposed to freezing temperatures as high as -2 °C following a two month incubation exhibited extensive shoot mortality and had SDS symptoms consistent with those observed in the field. Lowering the freezing temperature from -2 to -8 °C increased disease severity and shoot mortality on noninoculated bermudagrass. Inoculated bermudagrass incubated for 1 month in the greenhouse, then for an additional month at 4 °C had greater shoot mortality following freezing than plants incubated at 25 °C. Although cold acclimation and freezing intensified SDS symptoms, the technique did not reliably distinguish between resistant and susceptible cultivars.

Free access