Biological properties of procymidone-resistant field isolates of Botrytis cinerea.

Abstract

Botrytis cinerea resistant to procymidone was isolated from the vegetables grown in greenhouses. All of them showed low level of resistance (ED50 values were approximately 10 times), and no isolate with high level of resistance was found. Although the resistant isolates were indistinguishable from the sensitive strain in growth rate of hypha, ability to sporulate and spore germination on a nutrient agar, some of them did not grow after incubation at a high temperature of 32C. When the resistant strain was inoculated to tomato fruits together with the sensitive strain, the resistant strain rapidly decreased in a population and often disappeared during successive inoculations to other fresh fruits. In cases that procymidone was treated preventively or curatively against the resistant strain on the leaves of cucumber, the controlling efficacy was inferior to that against the sensitive strain. On the other hand, when the resistant and sensitive strains were mixedly inoculated to the plants, curative application of procymidone was more effective in controlling the disease than when the resistant strain was singly inoculated. The fungicide sensitivity of B. cinerea isolates from 7 greenhouses in Kochi Prefecture, where the resistant strain was extremely dominant in a population in March of 1982, was examined in December of 1982. The resistant strain was still dominant in 1 greenhouse, but no resistant B. cinerea was detected in 5 greenhouses and only a few in 1 greenhouse. These results suggest that the population of procymidone-resistant B. cinerea would be unstable in the concomitant presence of the sensitive strain.