Variation in sensitivity of Western Australian isolates of Phytophthora cinnamomi to phosphite in vitro


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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 EC50 values ranging from 4 to 148 µg 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.