Submitted to: Phytopathology
Publication Type: Abstract Only
Publication Acceptance Date: May 17, 2011
Publication Date: July 30, 2011
Citation: Kousik, C.S. 2011. Sources of Resistance to Phytophthora Fruit Rot in Watermelon Plant Introductions. Phytopathology. 101:S94. Technical Abstract: Phytophthora fruit rot caused by P. capsici is an emerging disease in most watermelon producing regions of Southeast U.S. Plants belonging to the core collection of U.S. watermelon plant introductions (PI) were grown in a field on raised plastic beds to evaluate for fruit rot resistance in 2009. Five fruits from each PI were harvested and inoculated with a 7-mm plug from an actively growing colony of P. capsici on V8 juice agar. The inoculated fruit were maintained in a room with high relative humidity (>95% RH) for four days. 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 varying levels of resistance to fruit rot. Variability in resistance reaction to fruit rot among plants of the same PI was also observed. The most resistant PI were re-evaluated in 2010. Fruit from resistant PI had significantly lower amounts of P. capsici DNA/g of fruit tissue compared to susceptible cultivars Sugar Baby and Black Diamond. Selections from the most resistant PI will be further evaluated using isolates from different states to confirm the stability of resistance.