RESISTANCE OF RUSSIAN PHYTOPHTHORA INFESTANS STRAINS TO FUNGICIDES METALAXYL AND DIMETHOMORPH

Abstract

In total, 2000 P. infestans isolates collected during 1988—2004 in different regions of Russia were tested for resistance to metalaxyl. In the majority of field populations frequency of resistant strains decreased after 1993—1994. Possibly it was connected with changes in potato industry in Russia: potato producing was concentrated in small private gardens. The part of resistant strains in populations from small private patches was less than at a big commercial potato fields. Small private gardens became the great source of sensitive genotypes. Last years the part of resistant strains in the majority of field populations was less than 30%. Small number of resistant strains in population occurs even if there was no treatment with metalaxyl—containing preparations during a long time. In some populations the frequency of resistant strains increased, it would be connected with treatments. A variation in the level of resistance to metalaxyl in one clonal linage is shown. Resistant strains occurred in potato leaves and tubers, in tomato leaves; they were rare in tomato fruits. Probably, the sensitive strains affecting fruits have selective advantage.

More than 370 strains from different regions were tested for resistance to dimethomorph. In several fields isolates were collected after treatment with dimethomorph—containing preparations. Resistant strains were not detected.