Inhibition of Botrytis cinerea by Epirodin: A Secondary Metabolite from New Zealand Isolates of Epicoccum nigrum

摘要

Many isolates of the saprophytic fungus Epicoccum nigrum produce yellow compounds that diffuse readily into culture media. Historically, two such compounds have been identified; flavipin and epirodin both reported to have antimicrobial properties. Preliminary studies on 280 New Zealand isolates of E.nigrum confirmed that all but two produced a yellow, intensely pigmented substance in sufficient amounts to inhibit the germination of Botrytis cinerea conidia. The compound produced by the inhibitory isolates is epirodin, a polyene antibiotic. Five representative E.nigrum isolates were selected for further investigation. Two of these produced relatively large amounts of epirodin and, in a diffusible metabolite assay, reduced germination of B.cinerea conidia by up to 94%. Another isolate produced a trace amount of epirodin and had no effect on the germination of B.cinerea conidia or on germ tube morphology. The two remaining isolates produced intermediate amounts of epirodin and were only moderately inhibitory to the germination of B.cinerea conidia and to germ tube morphology. In slide dual-culture experiments, epirodin appeared to concentrate in conidia and mycelia of B.cinerea. In acid conditions, as on dual-culture slides of E.nigrum and B.cinerea, the yellow-coloured epirodin underwent a hypsochromic shift, changing colour to become red. The relationship between epirodin production and the suppression of Botrytis growth and development was further investigated using necrotic kiwifruit leaf discs. The E.nigrum isolate that produced the greatest amount of epirodin almost completely inhibited the growth and development of B.cinerea on the leaf discs. In contrast, the efficacy of E.nigrum isolates which produced less epirodin ranged from 78% to just 23%. This is the first report of epirodin production by New Zealand isolates of E.nigrum, and we conclude that isolates that produce high concentrations of epirodin may have potential for plant disease control.