Fungitoxicity of oxine and copper oxinate: activity spectrum, development of resistance and synergy

The antifungal activity of oxine and copper oxinate was investigated using standardized methods to compare efficacy, discriminate activity patterns, e lucidate mechanisms of action and establish attributes of relevance to fiel d use. Both agents were shown to be active against a broad range of physiol ogically diverse fungi. Species of Aspergillus, Penicillium, Fusarium, Rhiz opus, Candida, Rhodotorula and Saccharomyces were significantly more resist ant than Pythium, Phytophthora. Sclerotina and Trametes, the difference bei ng greater for oxine than for copper oxinate and in Sabouraud than in Czape k-Dox media. Copper oxinate was generally more active and more broadly and rapidly fungicidal than oxine. Both are fungicidal at low concentrations ag ainst significant plant pathogens and relatively active against important s poilage and mycotoxin producing moulds. The MIC (minimum inhibitory concent ration) and MFC (minimum fungicidal concentration) for both agents were dep endent on method and medium. Neither agent produced changes in morphology, asexual reproduction or differentiation. Oxine and copper oxinate were resi stant to inactivation by organic materials, interacted synergistically in v itro and did not elicit resistance on long term exposure. Differences in ac tivity pattern suggest independent modes of action. Oxine is worthy of revi sitation as a useful agricultural fungicide and preservative.