Submitted to: HortScience
Publication Type: Abstract Only
Publication Acceptance Date: 2/14/2011
Publication Date: N/A
Technical Abstract: Phytophthora capsici is distributed worldwide, and is an aggressive pathogen with a broad host range infecting solanaceous, leguminaceous, and cucurbitaceous crops. Fruit rot, caused by P. capsici is an emerging disease in most watermelon producing regions of Southeast US. Resistance to fruit rot of watermelon is sorely needed to manage P. capsici. Evaluations to identify sources of resistance have not been conducted before. Plants belonging to the core collection of watermelon plant introductions (PI, www.ars-grin.gov) were grown in a field on raised plastic beds in Charleston SC in 2009. Five fruits from each PI were harvested when the tendrils next to the fruit were dry. Harvested fruit were placed on wire shelves and inoculated with a 7-mm plug from an actively growing colony of a SC isolate of P. capsici on V8 juice agar. The shelves were kept in an enclosed room where high relative humidity (>95% RH) was maintained. Four days after inoculation, data on length of disease lesion and intensity of sporulation were recorded for each fruit. Of the 205 PI evaluated, majority were highly susceptible and extensive sporulation was observed on most fruit. Overall we identified 25 PI (12%) as potential sources of resistance. Twenty two (12%) of the 159 Citrullus lanatus var. lanatus PI we evaluated from the core collection, one C. colocynthis (PI 388770) and two C. lanatus var. citroides PI (PI 189225) showed tolerance to fruit rot. We also observed variability in the resistant reaction to fruit rot within these PI, indicating the need for further screening and selections. The most tolerant PI were re-evaluated in 2010. Fruit from PI that were tolerant had significantly lower amounts of P. capsici DNA/g of fruit tissue compared to susceptible commercial cultivars Sugar Baby and Black Diamond. Selections from the most tolerant PI will be further evaluated using different isolates of P. capsici to confirm the stability of resistance.