Biological control of postharvest sour rot of citrus by two antagonistic yeasts

Abstract

To investigate antifungal effects of two antagonistic yeasts on postharvest sour rot caused by Geotrichum citri-aurantii in citrus and evaluate possible mechanisms. Cell suspension of Cryptococcus laurentii at 10(8) to 10(9) cells per ml effectively reduced sour rot incidence from 55.6% among untreated control fruit to 29.9-20.7% after 5 days of incubation at 26 degrees C. Application of cell-free culture filtrate of C. laurentii was effective in reducing the sour rot, but the effectiveness was lower than that of the cell suspension (1 x 10(8) cells per ml). In addition, C. laurentii multiplied more rapidly than Rhodosporidium paludigenum at 26 degrees C. The fruit inoculated with the two yeasts demonstrated changes in peroxidase and superoxide dismutase activity. Cryptococcus laurentii, in particular, was capable of inducing a striking response in treated citrus fruits. The antifungal ability of C. laurentii can be attributed to the competitions of nutrients and space, defensive responses and possible secretion of antibiotic compounds. The use of such antagonists may constitute an important alternative to synthetic fungicides for controlling postharvest sour rot in citrus.