Sensitivity of Phytophthora megasperma f.sp. glycinea to metalaxyl
In Illinois, US, investigations were carried out to test the effects of low-level metalaxyl exposure on the virulence and metalaxyl sensitivity of Phytophthora megasperma f.sp. glycinea (EPPO A2 organism).
Cornmeal agar was amended with low concentrations of metalaxyl and subsequently inoculated with isolates of P.m. glycinea. After six successive transfers an isolate of the fungus showed a reduced sensitivity to metalaxyl and an increased virulence of metalaxyl-treated seedlings of soybean. Two isolates were more virulent on seedlings treated with metalaxyl than their parental isolates.
The authors conclude that the exposure of P.m. glycinea to metalaxyl in saprophytic growth can select for both altered virulence and decreased sensitivity to the fungicide in metalaxyl treated plants.
Sources
Lamboy, J.S.; Paxton, J.D. (1992) Metalaxyl sensitivity selection within Phytophthora megasperma f.sp. glycinea.
Plant Disease 76, 932-936.