A combination of the yeast Candida utilis and chitosan controls fruit rot in tomato caused by Alternaria alternata (Fr.) Keissler and Geotrichum candidum Link ex Pers.

Abstract

SummaryThe antifungal activity of chitosan was tested in vitro against Alternaria alternata and Geotrichum candidum, two major post-harvest pathogens of tomato. Chitosan, at all concentrations, inhibited spore germination in A. alternata and G. candidum. Survival of the yeast biocontrol agent, Candida utilis, in chitosan solution was also studied in vitro, as well as in fruit wounds. Chitosan did not adversely affect the growth of C. utilis. In fruit wounds, populations of C. utilis with or without chitosan increased to the target level (107 CFU per wound) within 7 d, and thereafter became stable. In in vitro studies, populations of C. utilis increased in 0.25% (w/v) chitosan solution; while in 0.5% (w/v) and 1% (w/v) solutions, populations dropped initially, but resumed growth within 24 h. The addition of 0.25% (w/v) chitosan solution to a cell suspension of C. utilis significantly enhanced its efficacy in controlling post-harvest decay of tomato compared with treatments of C. utilis, or 0.25% (w/v) or 0.5% (w/v) chitosan alone. The efficacy of a combination of C. utilis and chitosan was not increased by increasing the concentration of chitosan from 0.25% (w/v) to 0.5% (w/v).