Role of antioxidant scavenging enzymes and extracellular polysaccharide in pathogenicity of rice bacterial blight pathogen Xanthomonas oryzae pv. oryzae

Abstract

In the present work, we studied the role of antioxidant scavenging enzymes of plant pathogenic bacteria:  catalase, ascorbate peroxidase and a virulence factor; extracelluar polysaccharide production in determining the virulence of Xanthomonas oryzae pv. oryzae (Xoo) isolates and its differential reaction to rice cultivars. A varied level of antioxidant scavenging activity and exopolysaccharide production was observed among 34 isolates studied, and most of the Xoo isolates with higher catalase activity also exhibited higher ascorbate peroxidase activity. The maximum level of catalase (45 µM H₂O₂ min^-1 mg^{-1 protein), ascorbate peroxidase (29 µM ascorbate min-1 mg-1 proteins) activity and exopolysaccharide production (70 mg) was found in isolate Xoo32 which induced maximum lesion length on cultivar ‘Jaya’ upon clip inoculation in virulence assay. Among the 44 cultivars screened, cultivar ‘Jeerigesanna’ recorded least bacterial blight disease incidence, with 0.7 cm lesion length. The activity of catalase, ascorbate peroxidase and exopolysaccharide can be employed as bio-chemical markers in determining the virulence of Xoo under laboratory conditions.}

Key words: Paddy, plant pathogenic bacteria, antioxidant scavenging enzymes, exopolysaccharide,  virulence, bio-chemical markers.