Metabolism of Pyrazon in Susceptible Species and Inbred Lines of Tolerant Red Beet (Beta vulgaris L.)1

Pyrazon (5-amino-4-chloro-2-phenyl-3(2H)-pyridazinone) was readily metabolized to the N-glucosyl derivative of pyrazon (N-2-chloro-4-phenyl-3(2H)-pyridazinone glucosamine) in red beet ( Beta vulgaris L. cv. Detroit Dark Red), but there was no metabolism of pyrazon in the 8 susceptible species examined. In leaf discs from 9 inbred lines of red beet, the percent conversion of pyrazon to the N-glucoside ranged from 44% to 76% after 10 hr. In 2 lines of red beet treated with 2 concentrations of pyrazon in nutrient culture, there was a direct relationship between the rate of pyrazon metabolism and plant tolerance.