Molecular characterisation of a Xanthomonas oryzae pv. oryzae isolated from an infected rice (Oryza sativa L) plant in Vellore district, India

Rice (Oryza sativa L) is a widely consumed cereal in India. Rice plants are susceptible to leaf blight disease caused by Xanthomonas oryzae pv. oryzae. The infection leads to yield loss and premature crop death. Genomic characterization of pathogenic strains isolated from infected plants grown in different geographical locations can help to devise molecular level control strategies. In this study, infected leaves were collected from rice plants grown in an agricultural field of Vellore district. The yellow mucoid colonies, observed upon incubation of infected leaves in Luria Bertani (LB) and nutrient broth yeast extract (NBY) medium, were isolated and characterised by biochemical tests and Gram staining. In vitro pathogenicity test relating to exopolysaccharide (EPS) production was carried out for six of the Gram negative rod isolates, which also tested positive for 3% KOH, citrate and catalase tests. Isolate IL8 had the highest EPS level of 2275 +/- 0.3 mu g/ml and it was characterised by fourier transform infrared spectroscopy (FTIR) spectroscopy for related functional groups. This isolate was then used for in vivo pathogenicity test on Ponni variety rice plants wherein progression of severe leaf blight disease was noted upon infection. Disease severity was measured in terms of diseased leaf area and disease scoring index was recorded. IL8 was characterised by 16S rRNA sequencing and confirmed as Xanthomonas oryzae pv. oryzae. The sequence was submitted to NCBI GenBank and an accession number of VITXO MK547277.1 was obtained.