Pilot Testing of Pichia guilliermondii: A Biocontrol Agent of Postharvest Diseases of Citrus Fruit

The efficacy of the yeast Pichia guillierrnondii (US-7) in controlling postharvest decay of citrus fruit was evaluated in small-scale and pilot tests in commercial packinghouses. In scale-up fermentation on cheap industrial waste materials, P. guillierrnondii grew efficiently and maintained its antagonistic activity, as tested in in vitro assay against spore germination of Penicilliurn digitatum. In small-scale experiments with injured and non-injured fruits dipped in the yeast cell suspension, the development of decay in several citrus cultivars was effectively inhibited. The yeast was compatible with a mixture of commonly used waxes containing a low concentration of a chemical fungicide. In packinghouse tests, combining the yeast with 200 ppm thiabendazole (TBZ) resulted in a reduction in the incidence of decay to a level equal to that of the commercial treatment of 2000 ppm TBZ. The efficacy of US-7 could also be maintained under packinghouse conditions at a cell concentration of the yeast antagonist as low as 107 cells/ml. No significant difference in the efficacy of P. guilliermondii was found in either the drench or the spray application systems tested in citrus packing-houses