Canavanine utilization by Phytophthora sp.

Abstract

Three isolates of Phytophthora that are pathogens of legumes and three that are nonpathogens were tested for sensitivity to L-canavanine. Growth of only one pathogen was affected by this amino acid. Phytophthora megasperma var. sojae race 1 was inhibited by canavanine when cultured in the basal medium. When starved mycelium of this isolate was treated with canavanine, total uptake of [H3] uridine and L-[H3] leucine and incorporation of these labeled compounds into insoluble fractions of trichloroacetic acid were enhanced. This demonstrated that under these conditions, canavanine supported some synthetic processes in the fungus.Of the Phytophthora sp. tested that are nonpathogens of legumes, one was affected by canavanine. Growth of P. cactorum was enhanced to a low degree. When asparagine (1.5 × 102 M) was replaced by canavanine (1.8 × 10−4 M) in the basal medium, growth was significantly higher than that in the asparagine-deficient basal medium. Labeling experiments with P. cactorum demonstrated that canavanine enhanced incorporation of [H3]uridine and L-[H3]leucine into insoluble fractions of trichloroacetic acid. Phytophthora cactorum apparently detoxifies canavanine and utilizes it in growth-supporting activities.