DIFFERENTIATING SOYBEAN RESPONSES TO HETERODERA GLYCINES RACES

Physiological variation among populations of Heterodera glycines Ichinohe, the soybean cyst nematode, has been a problem for soybean [Glycine max (L.) Merr.] growers and scientists. These populations have been classified into 16 races, but the system still leaves ambiguity, especially in the characterization of resistance. Two schemes are proposed: one to classify the nematode races and the other to designate the soybean response to the nematode. The existing race system by Riggs and Schmitt still serves as a basis for differentiating populations of H. glycines, but with soybean PI 437654 added as an additional nematode response parameter. A practical system using a popular resistant cultivar as the type for resistance is proposed for advisory purposes. Soybean reactions to parasitism by the nematode are denoted by four levels of resistance: resistant, moderately resistant, moderately susceptible, and susceptible.