Metribuzin metabolism by tomato cultivars with low, medium, and high levels of tolerance to metribuzin

Metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazine-5(4H)one] metabolism by the tomato (Lycopersicon esculentum Mill.) cultivars UGA-1113MT, tolerant to metribuzin, H-7492 (Heinz-7492), susceptible to metribuzin treatments, and the F1 cross of the two cultivars was determined. The radioactivity found in the polar fraction of leaf tissue extract from the tolerant cultivar, UGA-1113MT, was above 90% for plants treated with 14C ring-labeled metribuzin at concentrations of 1 × 10−7, 1 × 10−5, and 1 × 10−4 M. However, the radioactivity in the polar fraction of the leaf tissue of the sensitive cultivar, H-7492, and the F1 cross decreased from 94 to 58% and 97 to 65%, respectively, as the metribuzin concentration was increased from 1 × 10−7 to 1 × 10−4 M. The major metabolites found in the three cultivars were glucose conjugates of metribuzin. Differential tolerance is attributed to the rate of conjugate formation. The N-glucoside conjugate of metribuzin is restricted in the symplast near the vascular system at low metribuzin concentrations and increasing treatment concentration results in movement of radioactivity into the interveinal regions of the leaves leading to leaf damage. The F1 cross was intermediate in rate of metribuzin metabolism compared to the paternal parent, UGA-1113MT, and the maternal parent, H-7492.