Phenotypic evaluation of rice germplasm against Xanthomonas oryzae pv. oryzae and its in-vitro management through antibiotics

Xanthomonas oryzae pv. oryzae (Xoo) which causes bacterial leaf blight (BLB) disease is one of the most destructive pathogen of rice. BLB incites more than 70% yield losses in epidemic conditions thus deteriorating the rice industry and export revenue. The use of conventional synthetic bactericides causes remarkable environmental hazards such as water and air pollution. This study was focused at the management of bacterial leaf blight disease through the application of antibiotics because injudicious use of bactericides results in the development of resistance in bacteria. The objectives were to evaluation of rice germplasm against BLB, biochemical characterization of the pathogen and its in-vitro management. There were very limited studies on the phenotypic evaluation of BLB disease and biochemical analyses of its causal organism. Twelve rice cultivars were screened against the disease in randomized complete block design. The isolated pathogen was subjected to Gram staining and microscopic examination. Biochemical characterization of the pathogen was done by methyl red, indole production, citrate utilization and Voges-Proskaure tests. Three antibiotics (Kanamycin, Streptomycin and Ampicillin) were used at three concentrations (0, 50, 100 and 150 ppm) against the pathogen. Among all the screened cultivars, none was highly resistant and resistant. Maximum disease severity (89.01%) was depicted by the variety Super Basmati. All isolate were Gram negative and these showed positive response in case citrate utilization test indicating that citrate permeases enzyme is abundant. In-vitro results showed that Kanamycin is the most effective against pathogen at all concentrations than Ampicillin and Streptomycin. It is concluded that none of the screened cultivars showed resistance against Xoo, so the Basmati varieties may be sown with appropriate antibiotic like Kanamycin. It is recommended to devise effective breeding programs for the development of resistance rice cultivars against this economically important disease.