PHYSIOLOGICAL-BASIS FOR DIFFERENTIAL BENTAZON SUSCEPTIBILITY AMONG CORN (ZEA-MAYS) INBREDS

Experiments were conducted to confirm the bentazon susceptibility of corn inbred GA209 and determine the physiological basis of this susceptibility. Bentazon (1.1 to 4.4 kg ha-1) plus crop oil concentrate (1 % by vol) did not cause visible injury or dry weight loss of corn inbred B73 but caused 66 to 89% visual injury and 62 to 70% dry weight reduction of GA209 1 wk after treatment. Bentazon (2.2 kg ha-1) inhibited variable chlorophyll fluorescence decay in GA209 and B73 8 h after treatment. Variable fluorescence decay recovered in B73, but not in GA209, 96 h after treatment. Absorption and translocation of C-14 from C-14-bentazon was greater in GA209 than B73 during a 48-h time course. Both inbreds converted bentazon to a polar metabolite which formed 6-hydroxybentazon upon hydrolysis with beta-glucosidase. However, 63% of absorbed C-14 from C-14-bentazon remained in the parent form in GA209 compared to 25% in B73 over a 72-h time course. A decreased ability of GA209 to metabolize bentazon may explain bentazon sensitivity of this inbred compared to B73.