Watermelons Screened To Find Those That Resist Two Major Diseases

Watermelon lovers may someday have a lot to thank Amnon Levi for: a better melon with built-in disease resistance.

Over the last two years, the Agricultural Research Service geneticist, colleagues at the ARS U.S. Vegetable Laboratory in Charleston, S.C., and researchers at North Carolina State and Clemson universities screened watermelons to find those that are disease- and pest-resistant.

Fusarium wilt and gummy stem blight are the most destructive watermelon diseases. The researchers are evaluating plant introduction accessions stored at the U.S. Department of Agriculture Germplasm Collection Center in Griffin, Ga. They have also checked the cultivars for resistance to silverleaf whiteflies that infest watermelon fields, damage the crop and introduce plant viruses.

The value of the U.S. watermelon crop in 1999 was more than $268 million. In some wet years, Fusarium and gummy stem blight can cause up to 15 percent yield loss to this high-value fruit.

The team’s goal is to evaluate the genetic diversity of watermelon germplasm and to develop watermelons with enhanced disease and pest resistance. The scientists are constructing a genetic linkage map of watermelon genes. The map will be useful in breeding programs, locating genes that confer disease resistance and genes that affect fruit qualities like fruit shape and size, flesh color and sugar content.

Watermelons are grown on 2 percent of the world area devoted to the production of vegetables. Although many watermelon varieties have been developed worldwide during the past two centuries, there is still an ongoing need to improve watermelon fruit qualities and better meet market demands.

So far, the team has found wild watermelon accessions that are resistant to whiteflies but not to gummy stem blight. The scientists are continuing to screen the plants for resistance to Fusarium and gummy stem blight diseases.

ARS is the chief scientific research agency of USDA.

Scientific contact: Amnon Levi, ARS, U.S. Vegetable Laboratory, Charleston, S.C., phone (843) 556-0840, fax (843) 763-7013, alevi@awod.com.