Resistance to Citrus Canker in Key/Mexican Lime Induced by β-Aminobutyric Acid and Green Tea

Citrus bacterial canker, caused by Xanthomonas citri subsp. citri (Xcc), is a destructive disease. So far used chemicals to control this pathogen are either not effective or have harmful effects on the environment. To improve control of this disease, lime (Citrus aurantifolia) plants inoculated with Xcc were treated with β-Aminobutyric Acid (BABA), ascorbic acid (vitamin C), thiamin (vitamin B1), green tea (Camellia sinensis), copper oxychloride and distilled water. Lesion diameters of inoculated leaves were evaluated twenty days after treatment. The results showed that BABA and green tea had inhibitory effects on disease development. None of the agents used for plant treatment had direct antimicrobial activity on Xcc, except copper oxychloride. This indicated that the inhibitory effects of BABA and green tea resulted from strengthening the defense capacities of the plant. To support this claim, partial coding sequences of Pathogenesis-Related (PR) genes from lime were cloned and sequenced. Analysis of PR gene expression showed increased mRNA levels of β-1,3-glucanase and chitinase, during disease development. Reduction in lesion size and lack of antimicrobial activity indicate that BABA and green tea might be useful treatments against Xcc infection.