A keen eye, fast action and a vast plant collection may help nip in the bud a potential widespread mite threat to watermelons.

Last July, plant pathologist Chandrasekar Kousik of the Agricultural Research Service's U.S. Vegetable Laboratory in Charleston, S.C., was conducting field studies on a watermelon disease when he discovered significant infestations of broad mites on watermelon plants.

Kousik knew that he had made a troublesome finding, as broad mites had never been reported on U.S. watermelon plants.

Broad mites, Polyphagotarsonemus latus, feed on at least 60 plant families. Cucurbits are highly susceptible to the mite, which were damaging tender leaves and growing tips.

The discovery prompted Kousik, fellow vegetable laboratory scientists Amnon Levi and Alvin Simmons, and Clemson University researchers to seek ways to use plants' natural resistance to fight off the mite.

They turned to a collection of wild watermelon—plants from different regions of the world—maintained by the ARS Plant Genetic Resources Conservation Unit in Griffin, Ga.

The researchers studied 219 plant accessions and ultimately chose six that had the best resistance potential against broad mites. Kousik led greenhouse studies that confirmed this resistance in the six by artificially infesting the candidate plants with broad mites.


These wild watermelon varieties may be useful as sources of natural genetic resistance during the development of commercial watermelon varieties that resist the mites, Kousik says.