ANTIBIOTIC ACTIVITY AGAINST XANTHOMONAS GARDNERI AND PROTECTION OF TOMATO PLANTS BY CHITOSAN

D.S.O. Coqueiro, R.M. Di Piero

Abstract


Xanthomonas gardneri is an important species associated with bacterial leaf spot of tomato in Brazil. The losses caused by the disease can reach 100% if preventive measures are not adopted. The polysaccharide chitosan has antibiotic activity and the ability to activate defense mechanisms and may constitute a tool for managing plant diseases. This study aimed at evaluating the antibacterial effect of chitosans with different molecular weights on X. gardneri development and tomato plants protection. Three types of chitosan, i.e. commercial (Ccom), low molecular weight (Clmw), and medium molecular weight (Cmmw), were incorporated in nutrient agar medium to assess bacterial growth. In greenhouse tests, tomato plants were treated with chitosans and inoculated with X. gardneri, and the disease severity was evaluated 15 days after inoculation. Leaf samples were collected at 0, 3, 4, and 6 days after the treatment to evaluate peroxidase and ß-1,3-glucanase activities. Chitosans with different molecular weights showed a similar level of antimicrobial effect on X. gardneri. The polysaccharides at concentrations of 1 and 3 mg ml-1 reduced the leaf spot severity by 70%, when applied up to 3 days before inoculation of tomato plants. Enzymatic analysis showed an increase of peroxidase activity in Clmw-treated plants. Thus, the antibiotic activity of chitosan associated with induction of resistance may explain the control level of bacterial spot observed in this study.

Keywords


bacterial spot; chitosan; induced resistance; peroxidase

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DOI: http://dx.doi.org/10.4454/jpp.v93i2.1188

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