Assessment of the Resistance of Selected Rice Genotypes to Xanthomonas oryzae pv. Oryzae

Xanthomonas oryzae pv. oryzae, the causal agent of bacterial leaf blight disease of rice is one of the most important disease of rice (Oryza sativa L.) worldwide due to its growing concern, wide spread and destructive nature and lack of understanding of its control. The present study was carried out for assessment of rice varieties against X. oryzae pv. oryzae and to determine the phenolic contents of the physiology and biochemistry of diseased plants. Out of the 40 varieties tested none of them showed significant resistant response against the virulence of pathogen; only six were found moderately resistant, eight were graded as moderately susceptible, while 19 showed susceptible and six as highly susceptible in response. Highly significant disease severity (68.08%) was recorded on CO 39, whereas minimum (11.92%) was calculated on FARO 63. All the basmati varieties were found to be susceptible to highly susceptible against the disease and showed disease severity within a range of (51.21 to 65.05%), while the KSK genotypes presented (32.62 to 45.68%) disease severity. The total phenolics concentration significantly varied in response to treatment and showed negative correlation with the resistance of the variety. The highest phenolics compounds (183.42 mg 100-1) were produced in FARO 63, while the phenolics of CO 39 were not in the range of gallic acid standard. It appeared that resistant varieties showed higher concentration of phenolics than the susceptible ones, which played important role in reducing the disease severity. Thus, the study suggests that the exploitation of secondary metabolites in breeding programs and integrated management strategies could open the avenues to avoid future disease epidemics.