USVL531-MDR: Watermelon Germplasm Line with Broad Resistance to Powdery Mildew and Phytophthora Fruit Rot

USVL531-MDR is a multiple disease -resistant (MDR) watermelon (Citrullus mu-cosospermus; Syn: Citrullus lanatus var. lanatus) germplasm line that exhibits high levels of resistance to a broad range of iso-lates of cucurbit powdery mildew (Podos-phaera xanthii) and Phytophthora capsica that cause Phytophthora fruit rot. In compar-ison, the watermelon cultivar Mickey Lee and watermelon germplasm line USVL677-PMS are highly susceptible to P. xanthii and P. cap-sici. The hypocotyls, cotyledons, and true leaves of USVL531-MDR are highly resistant to powdery mildew compared with those of USVL677-PMS and Mickey Lee, on which se-vere powdery mildew and abundant develop-ment of conidia can be observed. Resistance to Phytophthora fruit rot is expressed as signifi- cantly reduced or very small (#0.7 mm) to no lesion development, rot, or pathogen sporula-tion on the fruit compared with large lesions, severe rot, and heavy sporulation on fruit of susceptible watermelon cultivars such as Mickey Lee and Sugar Baby. USVL531-MDR has uniform growth characteristics, fruit size, shape, and color. Commercial watermelon cul-tivar with resistance to both powdery mildew and Phytophthora fruit rot are not currently available; therefore, USVL531-MDR can be a useful source for incorporating resistance in commercially acceptable cultivars. USVL531-MDR can be easily crossed with commercial watermelon cultivars to develop breeding populations.