Characteristics of induced dicarboximide fungicide-resistant strains conferred by filtrates of the resistant strains of Botrytis cinerea.

Abstract

The characteristics of induced dicarboximide fungicide-resistant strains of Botrytis cinerea developed by post-cultures in the filtrates of the field resistant strains were investigated. Mycelial growth curves of these induced resistant strains were divided into three groups, which were rapid in both radial and non-radial growth, slowed down in growth transiently at about 4 days of inoculation followed by fast growth again, and poor in nonradial growth. Sporulation was scarcely observed on PSA, YGA and V8 agar media except for PSA media containing cucumber leaf (Cu-PSA). But by illuminating with BLB, it was stimulated on PSA media, but not on the other media. Pathogenicity to cucumber plants was examined by cucumber leaf disc method with the mycelia cultured on distilled water agar (WA), WA media containing glucose (GA) and GA containing inosine (IGA), respectively. Any induced resistant strain cultured on WA did not form lesion on cucumber leaf discs. Six strains cultured on GA formed non-spreading lesions (disease incidence rate; DIR=2.5-7.5%), and one strain formed spreading lesion (DIR=37.5%) on the discs. Six strains cultured on IGA formed non-spreading lesions (DIR=0-17.5%), and other ten strains formed spreading lesions (DIR>42.5%), in which four strains showed high pathogenicity (DIR=80-100%). These characteristics of the induced strains had been stable through consecutive subcultures, and were different from those of the original strains of B. cinerea.