Exopolysaccharides from Xanthomonas citri pv. malvacearum induce resistance in cotton against bacterial blight

Xanthomonas citri pv. malvacearum (Xcm ) is known to infect the cotton plant (Gossypium hirsutum ) and causing the disease known as cotton bacterial blight. While resistant plants show a hypersensitive reaction, susceptible plants suffer from water-soaking spots before death. In this study, we attempted to control the infected susceptible Gossypium hirsutum by spraying the cotyledons with exopolysaccharides (EPS) extracted from the same virulent race of Xcm that infected the plants. Our studies confirmed that EPS succeeded as an elicitor in decreasing bacterial populations in the susceptible G. hirsutum variety (-28 times compared to water-treated plants). Moreover, Gossypium treatment with this elicitor stimulated some defence in plants. We detected a significant increase in total peroxidase (POD) and superoxide dismutase (SOD) activities; however, no gene expression for G. hirsutum Fe-superoxide dismutase (GhFeSOD) was detected under the treatment conditions. Moreover, there was an increase in the gene expression of lipoxygenase (GhLOX1 ). In conclusion, in this study, we observed an increase in expression of the GhLOX1 gene, decrease in bacterial populations and a stimulation of POD activity after EPS treatment. The results confirmed that EPS treatment may stimulate certain defence responses against Xcm in susceptible Gossypium hirsutum plants.