FIELD RESPONSE OF SOYBEAN IN MATURITY GROUPS III-V TO HETERODERA-GLYCINES IN KANSAS

Soybean cultivars from maturity groups III-V were grown in Heterodera glycines-infested locations in northeastern and southeastern Kansas fr om 1991 through 1994. Yield performance and nematode reproduction were significantly (P < 0.01) affected by host response to H. glycines and year, whereas effects of cultivars within host response categories an d cultivar x year interactions were generally negligible. In northeast ern Kansas, H. glycines-susceptible cultivars from maturity groups III -IV yielded 8% less than resistant cultivars across years, whereas in southeastern Kansas, susceptible cultivars from maturity groups IV-V y ielded 38% less than resistant cultivars across years. Analyses of yie ld components suggested that number of pods per plant accounted for mo st of the differences in seed yields. Heterodera glycines reproduction rates (final population density/initial population density) averaged 0.7 and 1.3 for resistant cultivars and 8.7 and 15.9 for susceptible c ultivars in northeastern and southeastern locations, respectively. Res ults indicated that the relative performance of resistant and suscepti ble cultivars can be reliably predicted based on preplant egg densitie s across most environments in eastern Kansas.