Biocontrol Efficacy of Yeast on Blue Mold in ‘McIntosh’ Apples

A yeast antagonist, Metschnikowia pulcherrima, was tested for efficacy against blue mold caused by Penicillium expansum on ‘McIntosh’ apples in 2003-04. The trial was conducted on commercially ripe apples. Apples were disinfested in 10% household bleach (5% sodium hypochlorite) and 0.01% Tween 20 (Fisher Scientific) for 4 min and rinsed in reverse osmosis water for 4 min. After disinfestation, apples were placed on plastic packing inserts contained in plastic boxes. The apples were punctured and inoculated within 45 min of wounding with a 20 micro litre (1,000 micro litres = 1 ml) drop consisting of one of the three concentrations of M. pulcherrima with Penicillium expansum isolate PS-1R. Treated apples were incubated at 4^oC for 3 months. Apples in each of the experiments were evaluated for decay after the respective incubation periods. To determine the efficacy of the biocontrol agent on fruit shelf-life, after the first fruit decay evaluations following incubation at 4^oC, the fruit were moved to 20^oC, 85% RH and incubated for 6 days. The fruit were again evaluated for blue mold incidence. The data obtained were analyzed with SigmaStat statistical package. The results indicate that initial low decay incidence increased with time. After 28 days of incubation, 28% blue mold infection was observed in the inoculum only treatment, while the treatments with combination of M. pulcherrima and the pathogen ranged between 0 to 8%. Better control was achieved with the lower concentrations of the pathogen inoculum. The combinations of M. pulcherrima at 1.6 x 10⁷ CFU/ml and 1 x 10⁴ conidia/ml of P. expansum resulted in no decay and only 2.8% decay after 28 and 58 days of storage, respectively. Control declined to 39% after storing for 86 days. A second year study is in progress.