New Peanut Types Could Mean Trouble for Nematodes

New peanut strains from abroad could spell relief for southern peanut farmers bedeviled by root-knot nematodes, tiny roundworms that cost $20-40 million annually in losses and chemical controls.

Geneticist Corley Holbrook of USDA’s Agricultural Research Service worked with ARS colleagues to examine hundreds of exotic peanut strains whose roots deter the nematodes from feeding or laying their eggs. About two dozen of the top picks are now being crossed with commercial cultivars to improve their pest resistance, reports Holbrook, at ARS’ Nematodes, Weeds and Crops Research Unit.

Such cultivars could be available within five years, offering peanut farmers in Georgia, South Carolina and other southeastern states a welcome respite from chemical nematicides.

Female Meloidogyne arenaria nematodes are prime targets for such chemical control. Unchecked, they establish knot-like feeding sites called root galls on plant roots. These galls choke off nutrients needed by the peanut plant, sometimes causing yield losses of more than 70 percent. Females also lay thousands of eggs on the roots, setting the stage for more losses next season.

To break the cycle, Holbrook’s group examined peanut germplasm collected from Asian, African and South American countries. They began with the National Peanut Germplasm Collection in Griffin, Ga., where 7,000 seed samples, called “accessions,” are stored.

From a core collection of 831 accessions, they narrowed the search to 36 resistant strains. Next followed a painstaking screening regimen in the greenhouse. There, scientists repeatedly exposed the plants to the nematodes to rate the severity of feeding and egg-laying.

Compared to commercial check varieties like Florunner, 21 of the peanut strains suffered 70 percent fewer root galls and egg clusters. Two Chinese peanuts showed a 90 percent reduction. Both are top picks for breeding new domestic cultivars.

A more detailed story in Agricultural Research magazine’s April issue is featured on the Web at:

http://www.ars.usda.gov/is/AR/archive/apr99/pean0499.htm

ARS is the U.S. Department of Agriculture’s chief scientific arm.

Scientific contact: Corley Holbrook, ARS Nematodes, Weeds and Crops Research Unit, Tifton, Ga., phone (912) 386-3372, fax (912) 386-3437, holbrook@tifton.cpes.peachnet.educ.