Treating pepper plants with phenolic compounds i.e. pyrogallol, catechol, caffeic, tannic and cinnamic significantly decreased bacterial spot disease of pepper plants. Treated pepper leaves 2 days before inoculation with Xanthomonas vesicatoria was more effective in reducing disease incidence and severity than inoculated plants with X. vesicatoria at once with spraying phenolic compounds. Spraying pepper leaves 2 days before inoculation, exhibited that, pyrogallol was the most effective treatment which reduced disease incidence and disease severity by 85.71 and 91.99% respectively followed by catechol and cinnamic which were reduced disease incidence with 80.96 and 76.19% and severity by 89.33 and 86.67% respectively. As for biochemical changes, the obtained results showed that, PO, PPO, PAL, chitinase and β-1,3-glucanase activities increased as a result of spraying pepper plants with the tested phenolic compounds compared to untreated control. As well as, all treatments led to an induction of PO isoenzymes in treated pepper plants. The data also illustrated that two unique bands were detected and specific to Pyrogallol 2 and Pyrogallol 3 and one unique band was detected as affected to Pyrogallol 1.
Polyacrylamide gel electrophoresis of protein showed that 15 protein bands with molecular weights ranging from 122 to 25 kDa are contained in pepper plants. New protein bands expressed as a result of treating pepper plants with phenolic inducers. Four new bands found between 25 and 56 Kda and a fifth band at 84 Kda.
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