DIFFERENTIAL PRODUCTION OF PARASITICEIN, AN ELICITOR OF NECROSIS AND RESISTANCE IN TOBACCO, BY ISOLATES OF PHYTOPHTHORA-PARASITICA

Fifteen isolates of Phytophthora parasitica, nine from tobacco (causing black shank disease) and six from other host plants, were compared by root inoculation with regard to their pathogenicity to young tobacco plants. A progressive invasion of the aerial parts over 1 week was observed only with the black shank isolates, while the non-tobacco isolates induced leaf necrosis within 2 days. Similar necrosis occurred when the roots of tobacco plants were dipped in diluted culture filtrates from non-tobacco isolates, but not in those from tobacco isolates. The necrosis-inducing filtrates were shown to contain a c. 10-kDa protein band which was not present in the other filtrates. This protein (named parasiticein) was purified by ion-exchange chromatography to homogeneity in SDS-PAGE and reverse-phase HPLC. Parasiticein was serologically related to cryptogein, a member of the elicitin family of proteinaceous elicitors previously described from other Phytophthora species. Like the other elicitins, parasiticein induced necrosis in tobacco plants and protected them against black shank. It most closely resembled capsicein in being acidic and in inducing resistance at concentrations (10-100-mu-g per plant) that caused little leaf necrosis. It is suggested that the absence of parasiticein production by the black shank isolates might be a factor involved in their specific pathogenicity to tobacco.