Effect of Metalaxyl on Capsidiol Production in Stems of Pepper Plants Infected with Phytophthora capsici. Byung Kook Hwang, Professor, Department of Agricultural Biology, Korea University, Seoul, Korea. Nak Kyu Sung, Department of Plant Pathology, Institute of Agricultural Sciences, Suweon, Korea. Plant Dis. 73:748-751. Accepted for publication 13 February 1989. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/PD-73-0748.

Capsidiol production, associated with control of Phytophthora blight of pepper plants by the systemic fungicide metalaxyl, was determined in the infected stems of pepper cultivars resistant and susceptible to Phytophthora capsici. Increasing concentrations of metalaxyl in soil treatments 1 day before stem-inoculation with P. capsici gradually retarded the lesion development on the stems of pepper plants, but stimulated capsidiol production in the infected stems. Metalaxyl treatments did not change the rapidly growing stem lesions into brownish necrotic ones of the hypersensitive reaction. In particular, the accumulation of capsidiol by metalaxyl treatment was more pronounced in the resistant cultivar Kingkun than in the susceptible cultivar Hanbyul. At metalaxyl concentrations of 1 and 5 ?g/ml, lesions appeared on the stems 2 days after inoculation, with a maximum production of capsidiol. As the stem lesions developed and enlarged, the production of capsidiol in metalaxyl-treated, infected stems declined to a final base level similar to that in the infected control stems 5 days after inoculation. The metalaxyl treatments of 1 and 2 days after inoculation produced more capsidiol in the susceptible seedlings than before inoculation.