Benomyl-marked populations of Chaetomium globosum: survival on apple leaves with and without benomyl and antagonism to the apple scab pathogen, Venturia inaequalis

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Abstract
Resistance to the fungicide benomyl (BenR) was induced with N-methyl-N''-nitro-N-nitrosoguanidine in C. globosum isolated from apple leaves. The population densities of a resistant strain reintroduced to leaves on apple trees in an orchard were determined at 3 h and 1 and 3 wk following inoculation. Relative to wild-type parents, BenR populations declined more rapidly on orchard trees, but the rate of decline was reduced by amending initial inoculum with 18.5 ppm benomyl. Survival of BenR C. globosum increased 40-58% relative to BenR C. globosum applied without benomyl. In growth chamber experiments with potted apple seedlings, the BenR strain was as antagonistic as were the wild-type parents to the scab pathogen. V. inaequalis. The marked strain alone did not significantly reduce scab infection on saplings in the field; when it was applied with benomyl, scab severity was significantly (P = 0.01) less than with benomyl alone.