Battling virus disease of watermelon with bottlegourds

New help may be on the way for beleaguered growers of popular cucurbit crops like cucumbers and watermelons. Many varieties of the widely grown bottlegourd (Lagenaria siceraria) appear to have resistance to Zucchini yellow mosaic virus (ZYMV), a scourge of commercial cucurbits that includes pumpkins, squashes and other kinds of melons, including watermelons. ZYMV infects cucurbits throughout North America and in other parts of world, and is a particular concern to U.S. producers of watermelon, a crop valued at $435 million in 2006.

Two scientists with the Agricultural Research Service (ARS), which is the chief intramural scientific research agency of the U.S. Department of Agriculture (USDA), are screening bottlegourds for genetic resistance to ZYMV. Plant pathologist Kai-Shu Ling and geneticist Amnon Levi, who work at the U.S. Vegetable Laboratory in Charleston, S.C., have been searching for effective and environmentally friendly techniques to control watermelon pathogens and pests.

Ling and Levi obtained seeds for 190 bottlegourd accessions that were collected from different parts of the world and kept at the ARS Plant Genetic Resources Conservation Unit in Griffin, Ga. They raised the seeds in their Charleston greenhouses, and then inoculated the bottlegourd plants with ZYMV and evaluated how well they resisted the virus.

To their surprise, 36 accessions of the 190 screened—33 from India alone—were completely resistant to ZYMV infection, and another 64 accessions were partially resistant. They also found that ZYMV resistance is heritable in crosses between different bottlegourd accessions, enabling the development of bottlegourd varieties with enhanced virus resistance.

Popular watermelon cultivars could be grafted onto bottlegourd rootstocks with enhanced resistance to bolster the watermelons’ ability to resist ZYMV. Some watermelon growers have already been experimenting with grafting watermelon on bottlegourd rootstocks to control soilborne diseases and to enhance fruit production and quality.