Abstract

Plant activators provide an appealing management option for Asiatic citrus canker. The ability of β-aminobutyric acid (BABA) and green tea extract (GTE) to induce resistance in lime (Citrus aurantifolia) plants against Xanthomonas citri subsp. Citri(Xcc) was investigated. Green house experiments showed that BABA (250 ppm) and GTE {5 % (w/v)} treatment protects lime plants against Xcc. Lime plants treated with BABA, green tea extract (Camellia sinensis), copper oxychloride and distilled water were inoulated with Xcc. Lesion expansion of inoculated leaves were evaluated 5,10 and 20 days after treatment. The results showed that BABA and GTE had inhibitory effects on disease development. Base on previous experiments, none of the applied agents for plant treatment had direct antimicrobial activity onXcc, except copper oxychloride. This indicated that the inhibitory effects of BABA and GTE was as a result of strengthening the defense capacities of the plant. To support this claim, two pathogenesis-related (PR) genes from lime, β-1,3-glucanase and chitinase, used for defense signaling pathway was studied. Analysis of PR genes expression showed increased mRNA levels of β-1,3-glucanase and chitinase, after treatment. Reduction in lesion size and lack of antimicrobial activity indicates that BABA and GTE might have an important role in turning on defense signaling pathway against Xcc infection.

Key words: Pathogenesis-related genes, Xanthomonas citri subsp. Citri, plant activator, disease resistance.

Abbreviation

Abbreviations: ACC, Asiatic citrus canker; SAR, systemic acquired resistance;PR, pathogenesis-related; PR3, chitinase; PR2, glucanase; BABA, β-aminobutyric acid;  BTH, benzothidiazoles; ASM, acibenzolar-S-methyl; RT-PCR, reverse transcriptase-polymerase chain reaction; NAS, nutrient-agar-sucrose; EF1,elongation factor 1-alpha; GABA, γ-aminobutyric acid.