RESISTANCE TO XANTHOMONAS GARDNERI IN TOMATO LEAVES INDUCED BY POLYSACCHARIDES FROM PLANT OR MICROBIAL
C. Luiz, A.C. Rocha Neto, R.M. Di Piero
Bacterial spot (Xanthomonas gardneri) is a major disease of tomato affecting the yield of attacked crops. The application of polysaccharides can represent an effective way to control plant diseases. This work aimed at assessing the effect of xanthan gum (GUM) and polysaccharides extracted from X. gardneri (X. gardneri polysaccharides - XP) and Aloe barbadensis parenchyma (Aloe polysaccharides - AP) in the protection of tomato plants against bacterial spot and in vitro development of the bacterium. In vivo experiments were conducted with tomato plants, which were treated with polysaccharides, inoculated with X. gardneri and submitted to evaluation. Samples of treated leaves were collected 0, 2, 4 and 6 days after treatment for determination of the activities of peroxidase and polyphenol oxidases and quantification of total phenolic compounds and flavonoids. The hypersensitivity reaction of tomato plants submitted to polysaccharides was also examined. On average, XP reduced the in vitro growth of X. gardneri by 56%. GUM, AP and XP reduced the severity of bacterial spot up to 76.1, 76.6 and 67.4%, respectively, but GUM caused phytotoxicity in the plants. Plants treated with AP showed an increase in the content of flavonoids and polyphenol oxidase activity. Moreover, leaf cells of tomato plants treated with all tested polysaccharides exhibited accumulation of hydrogen peroxide and an increased peroxidase activity. Reduction of tomato bacterial spot is related to induced resistance, and AP and XP can represent an alternative to the conventional form of disease control.