METHODS OF MEASURING THE IMPACT OF THE XA17 GENE ON IMAZETHAPYR INJURY IN CORN (ZEA-MAYS)

Imazethapyr dose response curves were developed under laboratory and f ield conditions with the imazethapyr-resistant and -susceptible corn h ybrids Pioneer 3180IR, IR denoting a hybrid homoyzgous for the XA17 ge ne conferring resistance to imazethapyr, and normal Pioneer 3180, resp ectively, and their F-1 progeny to establish methods of measuring the presence of the XA17 gene and quantifying its impact. At two field loc ations, absorption of photosynthetically active radiation was a sensit ive index of corn injury caused by imazethapyr, Imazethapyr, at 35 g/h a (one half the labeled rate), reduced absorption of photosyntheticall y active radiation in Pioneer 3180 by 8.3% at 1 wk after treatment. Pl ant height also was a sensitive index of injury. The minimum rate al w hich imazethapyr injury was detected in the Pioneer 3180IR/Pioneer 318 0 F-1 hybrid differed with location. Pioneer 3180IR was not injured by 280 g/ha of imazethapyr. The Pioneer 3180IR/3180 F-1 hybrid was injur ed slightly by imazethapyr at 140 g/ha, but recovered within 5 wk afte r treatment, and grain yield was not reduced by 280 g/ha of imazethapy r. A seedling assay reliably detected differences between progeny of P ioneer 3180IR and Pioneer 3180IR/3180 F-1.