Biological control of the post-harvest pathogens Alternaria solani, Rhizopus stolonifer, and Botrytis cinerea on tomato fruit by Pichia guilliermondii

The yeast, Pichia guilliermondii, was evaluated for its activity in reducing post-harvest decay of tomato fruit caused by Alternaria solani, Rhizopus stolonifer, and Botrytis cinerea. The potential of using P guilliermondii to control natural infections, and its effects on the post-harvest quality of tomato fruit were investigated. The results showed that a washed-cell suspension of the antagonistic yeast was effective at inhibiting all three pathogens, and tomato fruit treated with the antagonist at 10(7) CFU ml(-1) or 10(8) CFU ml(-1) had significantly lower incidences of disease and smaller lesion diameters. The concentration of antagonistic yeast had a significant effect. Higher concentrations of the antagonist gave a lower incidence of disease. Results for reducing the development of natural decay on intact fruit were similar to those for artificially-inoculated fruit, and the effectiveness of the antagonistic yeast as a biocontrol agent was significant for tomato fruit at three different stages of maturity. Compared to controls, the incidence of natural decay on antagonist-treated fruit decreased significantly, and none of the treatments impaired the quality parameters (e.g.; weight loss, total soluble solids content, titratable acidity, ascorbic acid content and fruit colour). Thus, we conclude that the yeast, P guilliermondii, can control several post-harvest diseases of tomato fruit and not affect tomato fruit quality.