Abstract: (Fengqi Navel) orange fruits (Citrus sinensis L. Osbeck) were used as experimental subjects to evaluate the efficacy of different concentrations of benzothiadiazole (BTH) in controlling lesion diameters and disease incidence in citrus fruits inoculated with Penicillium italicum, Penicillium digitatum and Colletotrichum gloeosporides separately in the same and different wounds. At the same time, the optimum concentration of BTH to control these diseases was determined. The effects of BTH wound inoculation and dipping treatment on endogenous salicylic acid (SA) content and disease resistance-related enzymes activities in citrus peel were also investigated. The results indicated that BTH treatment at three concentrations (0.25, 0.50, 1.00 mmol/L) could reduce lesion diameters of citrus fruits inoculated with three pathogens and the best effect was observed at 0.50 mmol/L. All these three treatments controlled disease incidence at the early stage of disease, but the effect was marginal at the late stage. By comparison, BTH at 0.50 mmol/L was most effective. BTH wound inoculation at the optimum concentration could increase the content of endogenous SA in the peel. BTH dipping treatment had no significant effect on the content of endogenous free SA in the peel, but could promote the accumulation of endogenous bound SA content. Both BTH treatments could increase the activities of β-1,3-glucanase (GLU), chitinase (CHI), phenylalanine ammonia-lyase (PAL), peroxidase (POD) and polyphenol oxidase (PPO) in the peel. Therefore, BTH could be effective in inducing postharvest disease resistance in citrus fruits.

Key words: benzothiadiazole, citrus fruit, infectious diseases, induced resistance