Characterization of the biocontrol activity of Debaryomyces hansenii in the control of Penicillium digitatum on grapefruit

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Abstract
Interactions between Debaryomyces hansenii and Penicillium digitatum were studied in culture and on fruit to better characterize the observed biological control of green mold on grapefruit by the yeast. The antagonist did not produce antibiotic substances in culture and was ineffective in protecting against the disease when killed by heat or chemicals. Incidence of green mold was dependent upon the concentration of both the pathogen spores and the antagonist yeast cells. Control of green mold was most effective at 109 cfu/mL of D. hansenii. The role of available nutrients in the biological control activity of D. hansenii was assessed. Significant inhibition of spore germination and hyphal growth of P. digitatum in culture was achieved by the addition of the yeast cells to a minimal synthetic growth medium. Inhibition of P. digitatum by the antagonist in culture and on the fruit peel could be overcome by the addition of exogenous nutrients. Our results indicate that competition for nutrients may play a role in the biocontrol of P. digitatum by D. hansenii on grapefruit.Key words: biological control, Penicillium digitatum, Debaryomyces hansenii, grapefruit.