USVL531-MDR: Watermelon germplasm line with broad resistance to powdery mildew and phytophthora fruit rot

Authors: Kousik, Chandrasekar - Shaker; Ikerd, Jennifer; MANDAL, MIHIR - Orise Fellow; ADKINS, SCOTT - USDA National Plant Disease Recovery System; Turechek, William

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/23/2023
Publication Date: 3/17/2023
Citation: Kousik, C.S., Ikerd, J.L., Mandal, M., Adkins, S., Turechek, W. 2023. USVL531-MDR: Watermelon germplasm line with broad resistance to powdery mildew and phytophthora fruit rot. HortScience. 58(4):475-479. https://doi.org/10.21273/HORTSCI16907-22.
DOI: https://doi.org/10.21273/HORTSCI16907-22

Interpretive Summary: Watermelon is an important vegetable crop grown in 44 states in the U.S.A. Many diseases and pests attack watermelon seedlings and plants including fruit and reduce their yield resulting in monetary loss for growers. One such disease, known as powdery mildew can infest watermelon seedlings and can cause reduced vigor or death of seedlings and also result in yield reduction in the field. Similarly another disease known as Phytophthora fruit rot can also cause pre- or post-harvest fruit rot and result in monetary losses to the growers. Growers generally spray expensive pesticides to manage these two diseases. ARS scientists in Charleston SC, have developed a watermelon germplasm line (USVL531-MDR) with resistance to powdery mildew and Phytophthora fruit rot. This resistant germplasm lines can be used by private and public sector plant breeders to develop watermelon varieties and breeding lines with resistance to these two diseases. Development of varieties with resistance to powdery mildew and Phytophthora fruit rot will help reduce pesticide use and allow watermelon growers to produce a healthy crop. The information will be useful to growers, seed company plant breeders, University researchers, extension agents and USDA scientists.

Technical Abstract: USVL531-MDR is a multiple disease resistant (MDR) watermelon (Citrullus mucosospermus; Syn: Citrullus lanatus var. lanatus) germplasm line that exhibits high levels of resistance to a broad range of isolates of cucurbit powdery mildew (Podosphaera xanthii) and Phytophthora capsici which causes Phytophthora fruit rot. In comparison the watermelon cultivar Mickey Lee and a watermelon germplasm line USVL677-PMS are highly susceptible to P. xanthii and P. capsici. The hypocotyls, cotyledons, and true leaves of USVL531-MDR are highly resistant to powdery mildew compared to USVL677-PMS or Mickey Lee on which severe powdery mildew and abundant development of conidia can be observed. Resistance to Phytophthora fruit rot is expressed as significantly reduced to practically no lesion development, rot, or pathogen sporulation on the fruit compared to large lesions, severe rot, and heavy sporulation on fruit of watermelon cultivars such as Mickey Lee and Sugar Baby. USVL531-MDR is highly uniform for growth characteristics, fruit size, shape and color. Commercial watermelon varieties with resistance to both powdery mildew and Phytophthora fruit rot are not currently available and hence 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.