Enhancement of biocontrol efficacy of antagonistic yeasts by salicylic acid in sweet cherry fruit

Salicylic acid (SA) and two yeast antagonists, Rhodotorula glutinis and Cryptococcus laurentii, were investigated separately and together for controlling Penicillium expansum and Alternaria alternata in sweet cherry fruit. Applied separately, both SA (0.5 mm, pH 3.6) and antagonists inhibited decay caused by P. expansum and A. alternata. Biocontrol activity of R. glutinis was enhanced in combination with SA, whereas the efficacy of C. laurentii was not affected. Application of SA did not affect the growth of R. glutinis and C. laurentii in cherry wounds. Results of in vitro studies showed that SA at low concentrations had little effect on the growth of the yeasts or the pathogens. SA treatment induced a significant increase in polyphenoloxidase, phenylalanine ammonia-lyase, and beta-1,3-glucanase activity in cherry fruit, but did not alter the levels of peroxidase. The mechanism by which SA enhanced the biocontrol efficacy of the antagonistic yeast may be related to its ability to induce biochemical defense responses in sweet cherry fruit rather than its fungitoxicity effects on the pathogens. (C) 2003 Elsevier Ltd. All rights reserved.