Insect Resistance in Vegetable and Tofu Soybeans¹

Ten tofu and 14 green-vegetable soybean, Glycine max (L.) Merrill, genotypes were evaluated over 3 yrs for resistance to defoliation by the corn earworm, Helicoverpa zea (Boddie), and seed damage by a hemipteran complex. Petri-dish assays were used to determine foliar antibiosis to corn earworm. Larvae were weighed after feeding for 10 d on excised soybean leaves. Hemipteran damage was determined at harvest by individually rating 300 randomly sampled seeds from each subplot for severity of damage and calculating a weighted damage index. The specialty soybeans most resistant to corn earworm defoliation were Tousan 122, Guanyun da hei dun, and Enrei; whereas, those with the least seed damage were Barc-8 and Houjaku. There was no significant (F = 1.193; df = 1,300; P < 0.276) correlation of larval weight with seed damage index. It is likely that different mechanisms are responsible for seed and foliage resistance. There was a small but significant correlation (F = 40; df = 1,300); P < 0.001, R² = 0.12) of seed damage index with maturity group that may be related to the phenology of soybean seed development and insect populations.