Resistance of Phytophthora infestans to the dimethomorph fungicide

摘要

Analysis of 110 strains of P. infestans collected in 1996-97 in Russia revealed a very low concentration (0.3-0.8%) of dimethomorph tolerant isolates. No isolates with cross tolerance to metalaxyl and dimethomorph were found but polytolerant strainsappeared in metalaxyl-tolerant populations after treatment with dimethomorph and vice versa. In comparison with dimethomorph sensitive strains, tolerant isolates grew slowly on rye-A agar and lost their tolerance after several cycles. The growth rate increase correlated with the loss of tolerance to dimethomorph. The repeated treatment of potato plots with dimethomorph had a selective effect on the population, increasing the rate of tolerant clones. The low adapting capacity of tolerant strains reducedthe hazard of fungicide accumulation.