Postharvest efficacy of resistance inducers for the control of green mold on important Sicilian citrus varieties

The disease reducing activity of acibenzolar-S-methyl (ASM), chitosan and ?-aminobutyric acid (BABA) against postharvest green mold (GM) of citrus fruit, Penicillium digitatum, was investigated by tests performed in in vitro and in vivo conditions. The inhibition of the mycelial growth of P. digitatum by ASM, chitosan and BABA at different concentrations was evaluated on potato dextrose agar and on orange peel extract agar. The pathogen was totally inhibited (100% growth inhibition) by chitosan at concentrations >= 0.1% and by BABA at 1000 mmol and only poorly inhibited by ASM at 0.5% (47% growth inhibition). Inhibitory effects of chitosan and BABA were confirmed by P. digitatum conidial germination tests. The performances of these chemical compounds were evaluated in vivo on artificially inoculated orange, lemon and grapefruit cultivars. On the whole, chitosan significantly reduced GM decay on 'Valencia' and 'Washington Navel' orange, 'Femminello' lemon and grapefruit cv. Marsh Seedless at the concentration of 0.5% (6-20% disease incidence), and BABA provided the best results on 'Tarocco Scirè' and 'Valencia' orange and grapefruit cv. Marsh Seedless at the concentration of 1000 mmol (12-16% disease incidence). ASM did not show any efficacy. This study demonstrated that the effects of chitosan and BABA on GM in citrus fruits may be associated with their direct fungitoxic properties against the pathogen. Treatments with chitosan and BABA could be recommended for inclusion in postharvest decay management programs for citrus packinghouses and their use may be an effective method to improve the integrated pest management strategy. © Eugen Ulmer KG, Stuttgart.