Studies on the in vitro variability in sensitivity to Metalaxyl, Fosetyl-AL, cuprous oxide and malachite green within and among isolates of Phytophthora palmivora, P. capsici and P. citrophthora from cacao. In: Agrotrópica v. 11 p. 9-18, 1999.

Abstract

Variability in sensitivity to metalaxyl, fosetyl-Al, cuprous oxide and malachite green was investigated for cacao isolates of Phytophthora palmivora, P capsici and P citroph/hora from Brazil. Differences in colony morphology on com mea! agar amended with differcnt concentrations ofthe fo ur fungicides was studied and phenograms were generated following the sequential. agglomerative, hierarchical and nested (SAHN) c1ustcring method using fungicide sensitivity data. The three species showed diffcrent dcgrees of variability. Phytophthora citrophJhora and P capsici were the most variable species, whereas P palmivora had a much more uniform response to the fungicides tested. Two distinct groups were found among isolates of P citrophthora; the citrus and cacao groups did not seem to be closely related to each other. Two groups emerged from the analyses of sensitivity lo fungicides among isolates of P capsici; one group originated from the Amazon region and the other from the State of Bahia. These two groups did not seem to be related to each other at alI. Although, differential sensitivity to fungicides among species of Phytophthora may not be a definitive taxonomic criterion, it could bc of considcrable benefit as an initial screening step for speciation of Phytophthora from cacao in Brazil.