Abstract
The rice seed disinfectant, ipconazole, had antifungal in vitro activities against a wide range of plant pathogenic fungi from the Ascomycotina, Basidiomycotina, Deuteromycotina and Zygomycotina. Most of the EC50 values for the tested fungi did not exceed 0.5μg/ml. Seed treatments with wettable powder containing 6% ipconazole protected against the major rice seed-borne and soil-borne diseases, “Bakanae” disease, Helminthosporium leaf spot, blast and seedling blights caused by Rhizopus sp. and Trichoderma viride. High concentrations of residual ipconazole, which varied with the method of application, were detected by HPLC analysis on the outer portion of seeds. Regardless of the method, the residual ipconazole in the intact seeds remained nearly the same after a period of water soaking. The isolation frequencies of Fusarium moniliforme, the causal fungus of “Bakanae” disease, from infected, untreated rice seeds were 75%, 25% and 15% from hulls, endosperm and embryo, respectively. Ipconazole permeated into the seeds in a sufficient amount to be fungitoxic or fungistatic during treatment conditions and successive water soaking. In shake culture, mycelial growth of F. moniliforme was reduced by 50% and gibberellin production was totally inhibited by 0.1μM of ipconazole. The inhibition of gibberellin production at the fungistatic concentration may partially contribute to its activity against “Bakanae” disease. In a paddy field trial, ipconazole-treated seedlings showed no “Bakanae” symptom through harvest time. The protective action of ipconazole appears to consist of both fungicidal and fungistatic activities.
