ARS | Publication request: Watermelon Fruit Age and Development of Phytophthora fruit rot on resistant and susceptible lines

Submitted to: HortScience
Publication Type: Abstract Only
Publication Acceptance Date: February 15, 2012
Publication Date: N/A

Technical Abstract: Phytophthora fruit rot caused by Phytophthora capsici is an emerging disease in most watermelon producing regions of the southeast U.S. The disease has resulted in severe losses to watermelon growers, especially in GA, SC, and NC. It is considered an important problem by the National Watermelon Association (NWA). Fruits from watermelon plant introductions (PI) belonging to the core collection were evaluated for resistance to fruit rot by inoculating them with a 7-mm agar plug from an actively growing colony of P. capsici. Inoculated fruit were maintained in a room with >95% RH for four days after which data on disease development (lesion length & sporulation intensity) was recorded for each fruit. A majority of the 205 PI evaluated were highly susceptible and extensive sporulation was observed on the fruit. We identified 25 PI (12%) as potential sources of resistance. Twenty-two (12%) of the 159 Citrullus lanatus var. lanatus PI we evaluated, one C. colocynthis (PI 388770) and two C. lanatus var. citroides PI (PI 189225) showed some level of resistance to fruit rot. Variability in resistance reaction to fruit rot among plants of the same PI was also observed. Plants from the most resistant PI were self pollinated and the S1 generation was evaluated in 2010 and 2011. Fruit from PI that were resistant had significantly (P=0.05) lower amounts of disease and P. capsici DNA/g of fruit tissue compared to the susceptible cultivar Sugar Baby. Resistance to Phytophthora fruit rot was not correlated with the age (10 to 50 days after pollination) or developmental stage of the fruit. Fruit of two susceptible checks (Sugar Baby and PI 536464) were susceptible and two resistant selections (USVL-903 and 904) were resistant at all fruit developmental stages. Phytophthora fruit rot resistant germplasm developed from these PI will be useful in breeding resistant varieties.