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Peanuts To Be Reckoned With

A peanut breeding project under way at Tifton, Georgia, could spell trouble for pesky root-knot nematodes.

Geneticist Corley Holbrook, Jr., and scientist colleagues have identified several dozen peanut germplasm strains resistant to this tiny roundworm that costs $20-40 million annually in yield losses and chemical controls.

Holbrook, along with Agricultural Research Service nematologist Bill Johnson and agronomist Mike Stephenson, is now cross-breeding the pest-resistant strains with higher yielding commercial cultivars. They hope to release the new material within 5 years. For farmers in Georgia and other southeastern states, it won't be a moment too soon. That's because the varieties they now grow generally can't survive severe nematode attack without protection from chemical nematicides.

The root-knot nematode, Meloidogyne arenaria, inflicts its costly mischief inside the plant's roots.

"The female penetrates the root and establishes a feeding site, which forms a gall that can disrupt the flow of nutrients," says Holbrook. He is in the ARS Nematodes, Weeds, and Crops Research Unit at Tifton. Severe infestations can cause yield losses of 70-plus percent.

Females also lay thousands of eggs on plants' roots, setting up farmers for a fresh round of losses the next season.

To break the cycle, scientists examined peanut germplasm collected from around the world for traits that inhibit nematode feeding or egg laying. They started with the National Peanut Germplasm Collection in Griffin, Georgia, a repository with 7,000 accessions, or seed samples from South American, African, and other countries.

From a core collection of 831 seed accessions, the scientists narrowed the search to 36 resistant strains. They did it by repeatedly exposing the plants to nematode attack in greenhouse studies. This enabled them to count the number of nematode galls and egg clusters deposited on plant roots.

Compared with Florunner and other commercial varieties, 21 of the resistant accessions had 70 percent fewer root galls and egg clusters. The two most resistant peanuts, both from China, showed a 90-percent reduction and are top picks for the breeding program.—By Jan Suszkiw, Agricultural Research Service Information Staff.

C. Corley Holbrook, Jr., Alva (Bill) Johnson, and Michael G. Stephenson are in the USDA-ARS Nematode, Weeds, and Crop Research Unit, P.O. Box 748, Tifton, GA 31793; phone (912) 386-3176, fax (912) 386-3437.

"Peanuts To Be Reckoned With" was published in the April 1999 issue of Agricultural Research magazine.