Postharvest Biological Control of Rhizopus Rot of Nectarine Fruits by Pichia membranefaciens

Abstract

A new yeast antagonist, Pichia membranefaciens, isolated from wounds of peach fruit, was evaluated for its biocontrol capability against Rhizopus stolonifer on nectarine fruits at different temperatures and with other treatments. P. membranefaciens at 5 × 10⁸ CFU/ml of washed-cell suspension completely inhibited Rhizopus rot in nectarine wounds artificially inoculated with 5 × 10⁴ spores per ml at 25, 15, and 3°C. A culture filtrate of the yeast antagonist failed to provide any protection against Rhizopus rot in nectarine fruits. The yeast mixed with iprodione at 100 μg a.i./ml gave better control of R. stolonifer than either yeast or iprodione alone. A solution of 20 g CaCl₂ per liter enhanced the efficacy of P. membranefaciens (10⁷ to 10⁸ CFU/ml) as an aqueous suspension. Rapid colonization of the yeast in wounds was observed during the first 48 h at 25 and 15°C. P. membranefaciens at 5 × 10⁸ CFU/ml was effective when applied 0 to 72 h before the pathogen, while at 1 × 10⁸ CFU/ml, its efficacy was best when applied 24 to 48 h prior to inoculation with R. stolonifer. However, its efficacy was significantly reduced when the yeast was applied simultaneously with the pathogen, with disease incidence of 60% and lesion diameter of 37 mm.