Chitosan Reduces Bacterial Spot Severity and Acts in Phenylpropanoid Metabolism in Tomato Plants

摘要

Chitosan has recently shown potential for the control of plant diseases and can act as an elicitor in the induction of defence mechanisms. This study was made to assess the effect of chitosan on bacterial spot control caused by Xanthomonas gardneri in tomato plants. The chitosans used were commercial (Ccom), low molecular weight (Clmw) and medium molecular weight (Cmmw). Chitosans provided disease protection of up to 56%, with best results from Clmw at 3 mg/ml, applied 3 days prior to bacterial inoculation. The spectrophotometric profile of tomato plants that were treated with Clmw showed an increase of absorbance between wavelengths 280 and 300 mm, indicating that the polysaccharide may have induced the plants into synthesizing different compounds as a response to X. gardneri. The analysis of total phenolic compounds and flavonoids supported the results obtained in spectrophotometric scanning, showing a significant increase of those metabolites 3 days after inoculation. Therefore, chitosan has the capability of controlling bacterial spot in tomato plants, which is thought to be attributable to the induction of defence mechanisms in the plant.