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Pimaricin: A new post-harvest fungicide for selected citrus, stone, and pome fruits
D. Chen (1), H. Förster (1), J. Adaskaveg (1) (1) Department of Plant Pathology and Microbiology, University of California, Riverside, U.S.A.

Pimaricin (natamycin) is a polyene macrolide antimycotic produced by Streptomyces natalensis. It has been demonstrated to block fungal growth by binding to ergosterol within cell membranes. In use as a food preservative for many years, no resistance to pimaricin has ever been observed in Penicillium spp. populations. Pimaricin has potential to be an effective naturally derived fungicide for postharvest management of fruit decays when used by itself (e.g., stone fruits) or in mixtures with conventional fungicides (e.g., citrus and pome fruits) for improved efficacy and as an anti-resistance strategy. We tested the in vitro toxicity of pimaricin against selected postharvest pathogens of fruit crops. Mean EC50 values for inhibition of mycelial growth of isolates of Alternaria alternata, Botrytis cinerea, Geotrichum citri-aurantii, P. digitatum, and P. expansum were 0.92 mg/L, 0.79 mg/L, 3.20 mg/L, 1.47 mg/L, and 1.14 mg/L, respectively. Treatments of inoculated citrus (G. citri-aurantii, P. digitatum), stone fruits (B. cinerea, Monilinia fructicola, Rhizopus stolonifer), and pome fruits (A. alternata, B. cinerea, P. expansum, Mucor piriformis) with 1000 mg/L pimaricin were mostly effective with a reduction in decay incidence by 65 to 95% as compared to the control. However, reduced efficacy or treatment failures were observed in some pathosystems (e.g., P. expansum on pears). The mechanism for this unique selective performance is currently being investigated.