Submitted to: International Phytophthora Capsici Conference
Publication Type: Proceedings
Publication Acceptance Date: 10/26/2013
Publication Date: 12/3/2013
Citation: Kousik, C.S., Ikerd, J.L. 2013. Development of Phytophthora fruit rot resistant watermelon germplasm lines: USVL489-PFR, USVL782-PFR, USVL203-PFR and USVL020-PFR. International Phytophthora Capsici Conference. pp 15.
Interpretive Summary: N/A
Technical Abstract: Phytophthora capsici, distributed worldwide, is an aggressive pathogen with a broad host range, infecting solanaceous, leguminaceous, and cucurbitaceous crops. Phytophthora fruit rot of watermelon (Citrullus lanatus) caused by Phytophthora capsici was first reported in the U.S. in 1940. Since then, the disease has occurred on a regular basis across the country. During the past several years, Phytophthora fruit rot has resulted in severe losses to watermelon growers in southeastern states especially GA, SC, and NC. Hence it is considered an important problem and a top research priority by the National Watermelon Association (NWA). In 2009, we evaluated 205 watermelon plant introductions (PI, www.ars-grin.gov) belonging to the core collection and identified 25 PI as potential sources of resistance. Variability in the resistance reaction among plants within these PI was also observed, and the lack of homogeneity for resistance indicated a need for careful screening and selection for several generations to develop homozygous resistant germplasm sources. We have developed USVL782-PFR, USVL203-PFR, and USVL020-PFR, which were essentially derived from PI 186489, PI 306782, PI 595203, and PI 560020, respectively after five generations (S5) of intensive screening and selection. These four watermelon germplasm lines exhibit high levels of resistance to Phytophthora fruit rot under conditions favorable for disease development (95% RH, Temperate 25±2º C). Resistance in these germplasm lines is expressed as significantly reduced (<1 cm diameter) to practically no lesion development, rot or pathogen sporulation on and in the fruit compared to large lesions (5-19 cm), severe rot and heavy sporulation on commercial watermelon cultivars Sugar Baby, Black Diamond, and Mickey Lee. These four USVL germplasm lines are each highly uniform for growth characteristics, fruit size, shape, and color. All four have white flesh and are not considered for consumption in the U.S. Currently commercial watermelon cultivars with resistance to Phytophthora fruit rot are not available. Though not edible, these four germplasm lines may be a useful source for incorporating resistance in commercially acceptable watermelon cultivars. Small amounts of seeds of USVL489-PFR, USVL782-PFR, USVL203-PFR, and USVL020-PFR produced by hand self pollination in a greenhouse are available for distribution to interested research personnel and plant breeders. We have made crosses of these four germplasm lines with susceptible commercial watermelon cultivars to determine the genetics of resistance and develop red fleshed watermelon breeding lines.