DICARBOXIMIDE RESISTANCE AND OSMOTIC REGULATION IN PLANT PATHOGENS

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Dicarboximides have been applied on various crops against Botrytis cinerea. However, dicarboximide-resistant isolates of B. cinerea appeared on a variety of crops worldwide. To study mode of action and resistant mechanism of dicarboximides we use Neurospora crassa as a model fungus. The osmotic sensitive os-1, os-2, os-4 and os-5 mutants of Neurospora crassa were found to be resistant not only to iprodione but also to fludioxonil. Stimulation of glycerol biosynthesis by these fungicides observed in the wild-type strain was not induced in os mutant strains. The os-1 mutant alleles were classified into two groups based on sensitivity to fungicides and osmotic stress: Type I (highly resistant to fungicides but moderately sensitive to osmotic stress) and Type II (highly sensitive to osmotic stress but moderately resistant to fludioxonil). Sequence analysis of os-1 gene indicate that type I strains were null mutants. Thus we concluded that a os-1 product is essential for these fungicides to express their antifungal activity. Type II mutants have single amino acid substitutions within amino-acid repeats of os-1 gene, suggesting the amino-acid repeats may play a important rule for osmoreguylation.