DISTRIBUTION, DENSITY, AND DIVERSITY OF HETERODERA-GLYCINES IN MISSOURI

Between May, 1988, and July, 1992, the University of Missouri Plant Ne matode Diagnostic Laboratory collected data on Heterodera glycines pop ulations in Missouri by offering diagnostic services to soybean farmer s. A greenhouse bioassay (free), egg count ($10/sample), and race dete rmination test ($25) were conducted by request on soil samples submitt ed to the lab. Each test was offered for a specific purpose: the bioas say for fields not known to be infested; the egg count for population monitoring in fields with known infestations; and the race test for fi elds with a history of resistant cultivars. Of 818 samples submitted f or bioassay on a H. glycines-susceptible soybean cultivar, 13 (1.6%) c ontained brown cysts but no white females, and 364 (45%) contained whi te females after 35 days in the greenhouse. Of 6,193 egg counts, 39% w ere either free of H. glycines or contained fewer than 500 eggs/250 cm (3) soil, the action threshold for Missouri. The remaining 61% ranged from 500-400,000 eggs/250 cm(3) soil (mean = 10,617). Eleven races wer e detected, with races 3 (45%) and 1 (23%) the most common. The data s how that H. glycines is widespread in Missouri (with confirmed infesta tions in 80 of 114 counties), that most infested fields have populatio n densities above the action threshold, and that there is considerable genetic diversity among H. glycines field populations.