NUTRITIONAL ENHANCEMENT OF BIOCONTROL OF BLUE MOLD ON APPLES

Thirty-six carbohydrates and twenty-three nitrogenous compounds were evaluated for their effect on germination, and germ tube and radial growth of the pathogen Penicillium expansum, and for stimulation of growth of an antagonist Pseudomonas syringae (strain L-59-66). Compounds that strongly stimulated growth of the antagonist but had little or no stimulatory effect on germination and growth of the pathogen were evaluated for their effect on enhancing biocontrol of blue mold on ripe Golden Delicious apple. Seven amino acids and two carbohydrates met the required criteria. myo-Inositol and L-arabinose at 50 mug/ml had no effect and at concentrations ranging from 0.1 to 12.8 mg/nil actually reduced biocontrol. L-Asparagine and L-proline greatly enhanced biocontrol at concentrations of 20 and 80 mM. Enhancement effects were strongest at the highest concentrations of the antagonist (1.7 and 5.4 X 10(8) du/ml). Both amino acids enhanced the population of the antagonist on fruit by more than one order of magnitude. Thus, nutrients can be used to enhance antagonist population size and the resulting biocontrol of blue mold on ripe apple. Both amino acids strongly stimulated germination of P. expansum but had little effect on radial growth, indicating that inhibition of the mycelial phase of fungal development is the most important factor in this biocontrol system.