Variation in parasitic potential of Heterodera glycines populations

Fifty-eight populations of H. glycines were collected from 10 major soyabean producing states. These populations were compared for infraspecific variation in parasitic potential on soyabean genotypes 'Peking', 'Pickett', Plant Introduction (PI) 88788, PI 90763, and 'Lee 68'. Race 3 was present in 45% of locations; it was the most widespread population. Race 6 was present in 19% of the locations. Frequency of occurrence of other races (Races 1, 2, 5, 9, and 14) ranged between 3 and 9%. On the basis of reproduction on genotypes, 83% of the populations tested had genes to parasitize Pickett. All populations from Arkansas, Florida, Georgia, Iowa, North Carolina and South Carolina produced cysts on this genotype. Average level of parasitism was greatest on Pickett and lowest on PI 90763; 91% of SCN populations tested had