MAGNITUDE OF IMAZETHAPYR RESISTANCE OF CORN (ZEA-MAYS) HYBRIDS WITH ALTERED ACETOLACTATE SYNTHASE

laboratory study was conducted to evaluate the magnitude of imazethapy r resistance of field corn hybrids with altered acetolactate synthase (ALS) by comparing the responses of ALS extracted from homozygous and heterozygous resistant corn to nicosulfuron, primisulfuron, and imazet hapyr. ALS isolated from Pioneer 3162 IR, Pioneer 3180 IR, Pioneer 337 7 IR, and Ciba 4393 RSC hybrids was much more resistant to inhibition by these herbicides than ALS from the hybrids Pioneer 3162, Pioneer 31 80, Pioneer 3377, and Ciba 4393, and the public inbred LH 74, Corn hyb rids heterozygous for the Pioneer resistance gene were intermediate in response to the herbicides, ALS from ICI 8532 IT was resistant to ima zethapyr but not to primisulfuron or nicosulfuron, The level of resist ance of ALS from ICI 8532 IT was similar to that of ALS from Pioneer 3 162 IR x Pioneer 3162 and Pioneer 3180 IR x Pioneer 3180 crosses that were also heterozygous for the resistance gene.