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 of14C from14C-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 β-glucosidase. However, 63% of absorbed14C from14C-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.