Infra-species Variation in Reactions to Hosts in Heterodera glycines Population.

Eighteen hosts were inoculated with each of four races of Heterodera glycines. A discriminant function analysis of the reactions of these races to these hosts demonstrated that these races could be separated but not consistently. Then 33 H. glycines populations collected from 13 states and five obtained from Japan were tested on differential hosts. The number of variants discriminated within these 38 populations depended on the number of differentials and the rating system used. When five differentials were used with a (+) or (-) rating system there were six "races," but when 13 differentials were used with a (+) or (-) system there were 25 physiological groups. If an index rating system was used there were 36 groups. Apparently H. glycines is a very variable species and delineation of races varies with criteria chosen.