Chitosan effects on blackmold rot and pathogenic factors produced by Alternaria alternata in postharvest tomatoes

Stem scar application of chitosan inhibited growth and production of pathog enic factors by blackmold rot [Alternaria alternata (Fr,:Fr,) Keissl.] in c hallenged tomato (Lycopersicon esculentum Mill.) fruit stored at 20 degrees C for 28 days, Blackmold lesions were visible within 4 days of inoculation in control fruit, compared with >7 days in chitosan-treated fruit. Macerati ng enzyme activity (polygalacturonase, pectate lyase, and cellulase) in the tissue in the vicinity of the lesions was <50 % in chitosan-treated fruit compared with control fruit. Chitosan also inhibited production of oxalic a nd fumaric acids (chelating agents) and host-specific toxins such as altern ariol and alternariol monomethylether by the fungus. The pH of the infected tissue decreased from 4.7 to 4.0 in the control fruit, the optimum for pol ygalacturonase activity, while the pH of chitosan-treated fruit remained at 4.6, In addition, chitosan also induced production of rishitin (a phytoale xin) in tomato tissue. Such chitosan-pathogen-host interactions may be expl oited in the control of postharvest pathogens of fresh fruit and vegetables .