Variation in sensitivity of Western Australian isolates of <i>Phytophthora cinnamomi</i> to phosphite <i>in vitro</i>

Abstract

Seventy‐one Australian isolates of Phytophthora cinnamomi (68 from Western Australia) were tested for sensitivity to phosphite on Ribeiro's modified medium. Isolates formed a continuum in their response to phosphite, but could be divided into sensitive (9% of isolates), intermediate (82%) and tolerant (9%) groups. Sensitivity varied between isolates, with EC 50 values ranging from 4 to 148 µ g phosphite mL −1 . Phytophthora cinnamomi A1 mating‐type isolates were at the upper end of the range of tolerance shown by the A2 mating‐type isolates.