ROOTWORM FEEDING TOLERANCE IN SINGLE-CROSS MAIZE HYBRIDS FROM DIFFERENT ERAS

Insect-tolerant plants provide farmers with alternatives to insecticid e use for limiting crop losses. This study was conducted to evaluate w estern corn rootworm (Diabrotica virgifera virgifera LeConte) larval f eeding tolerance of single-cross maize (Zea mays L.) hybrids represent ing three successive 10-yr eras. A 2-yr study was conducted as a split -split plot with plant density (37, 50, or 74 thousand kernels ha-1) a s main plot treatments, rootworm infestation level (0, 2200, or 6600 e ggs m-1 of row) as subplot treatments, and plant genotype (11 genotype s from the 1980, 1970, and 1960 eras) as sub-subplot treatments. There was no significant interaction between genotype and infestation level for root damage ratings, suggesting that genotypes used in our study did not exhibit antibiosis to rootworm larvae. Vertical root pull resi stance values for 1980- and 1970-era genotypes were significantly grea ter than those seen for 1960-era genotypes. At the low plant density, the lodging percentage of all genotypes gradually became greater in re sponse to increased rootworm infestation level. At higher plant densit ies, however, the 1960-era genotypes suffered significantly more lodgi ng than the 1970- and 1980-era genotypes in the presence of moderate r ootworm damage. Our results suggest that large root system size and de creased plant lodging are the rootworm-tolerance traits present in 198 0 maize genotypes. Even with this level of tolerance in 1980-era hybri ds, however, substantial grain yield loss occurred when plants sustain ed moderate to heavy rootworm larval damage when these genotypes were grown at low and moderate plant densities.