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  • Author or Editor: William W. Turechek x
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Phytophthora capsici is an aggressive pathogen that is distributed worldwide with a broad host range infecting solanaceous, fabaceous, and cucurbitaceous crops. Over the past two decades, increased incidence of Phytophthora blight, particularly in eastern states, has threatened production of many vegetable crops. Cucumis melo L. (honeydew and muskmelon), although especially susceptible to fruit rot, is also highly susceptible to crown rot. Currently, little is known about host resistance to P. capsici in C. melo. To assess crown rot resistance in C. melo seedlings, 308 U.S. PIs, and two commercial cultivars (Athena and Dinero) were grown under greenhouse conditions. Seedlings with three to four true leaves were inoculated with a five-isolate zoospore suspension (1 × 104 zoospores per seedling) at the crown and monitored for 6 weeks. All the susceptible control plants of Athena died within 7 days post-inoculation. The majority of the PIs (281 of 308) were highly susceptible to crown rot and succumbed to the disease rapidly and had less than 20% of the plants survive. Several PIs (PI 181748, PI 182964, and PI 273438) succumbed to crown rot earlier than the susceptible melon cultivars. Eighty-seven PIs selected on the basis of the first screen were re-evaluated and of these PIs, 44 were less susceptible than cultivars Athena and Dinero. Twenty-five of the 87 PIs were evaluated again and of these six PI, greater than 80% of the plants survived in the two evaluations. Disease development was significantly slower on these PIs compared with the susceptible checks. High levels of resistance in S1 plants of PI 420180, PI 176936, and PI 176940 were observed, which suggests that development of resistant germplasm for use in breeding programs can be accomplished. Further screening and careful selection within each of these PIs can provide a framework for the development of resistant germplasm for use in breeding programs.

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Watermelon vine decline (WVD) is a new and emerging disease caused by the whitefly-transmitted squash vein yellowing virus (SqVYV). The disease has become a major limiting factor in watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] production in southwest and west–central Florida and is estimated to have caused more than $60 million in losses. Symptoms of WVD typically occur at or just before harvest and are manifested as sudden decline of the vines, often with a reduction in fruit quality. In this study, we present results of greenhouse and field evaluations of U.S. plant introductions (PIs) for resistance to SqVYV. Of the 218 PIs we evaluated for resistance to SqVYV, none were completely immune, but several showed varying levels of resistance and these were further evaluated in two greenhouse and field trials. Disease progress was significantly slower on the selected PIs compared with disease progress on susceptible watermelon cultivars Mickey Lee and Crimson Sweet. Moderate resistance was observed in two C. colocynthis (PI 386015 and PI 386024), a Praecitrullus fistulosus (PI 381749), and two C. lanatus var. lanatus PIs (PI 482266 and PI 392291). Variability in the resistant reaction to SqVYV within most PIs was observed. The identification of potential sources of partial resistance to SqVYV suggests that watermelon germplasm with moderate resistance can be developed by careful screening and selection of individual resistant plants within these PIs for use in breeding programs.

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