Microbial antagonists control postharvest black rot of pineapple fruit

Abstract

Incidence and severity of black rot (Chalara paradoxa (De Seyn.) Sacc.) of pineapple fruit were evaluated on fruit harvested every 2 weeks for 14 months. Rainfall did not play a major role in black rot incidence and severity. Total microbial counts on the fruit were correlated to rainfall in the month of harvest. Epiphytic antagonist microorganisms were apparently present on the pineapple fruit, as evidenced by the reduction of black rot severity when fruit were treated with pineapple fruit wash water. The most frequently isolated yeasts were able to inhibit Ceratocystis paradoxa growth in vitro and the most inhibitory isolated was Pichia guilliermondii. A mixture of five selected yeast isolates halved black rot severity compared to the control. Pichia and the yeast mixture reduced spore germination, germ tube length, and dry weight of C. paradoxa. The use of Pichia or the yeast mixture was comparable with current industry practice of holding fruit at a low temperature (8–10 °C) and fungicide. Combining the isolated Pichia or the yeast mixture with a half rate of fungicide resulted in complete control of black rot comparable to control achieved with a commercial rate of recommended fungicide. The mode of action by Pichia appeared to be competition for space and nutrients, while for the yeast mixture, mode of action appeared to be competition for space. Another possibility would be a growth inhibitor though no evidence was found to support this possibility.