RESISTANCE OF RICE TO XANTHOMONAS-ORYZAE PV ORYZAE IN NEPAL

Resistance to bacterial blight (BB), caused by Xanthomonas oryzae pv. oryzae in rice cultivars, was evaluated in the field and under greenhouse experiments from 1987 to 1991. In the field studies, plants were assessed by measuring lesion length (LL) and disease severity (percentage of leaf diseased). The area under the disease progress curves (AUDPC) and LL were used to compare rice cultivars. Rice cultivars BR-34-13, PAU-50-B-25, Laxmi, Sabitri, BW293-21, IR7167-33, Rodina, and Amonghaud had significantly (P < 0.05) shorter LL and smaller AUDPC than the susceptible check IR24. In the greenhouse studies, highly significant (P < 0.01) cultivar, strain, dose, cultivar X strain, and cultivar X dose effects were observed, indicating a differential host-pathogen interaction. Differences in virulence among bacterial strains and resistance among rice cultivars were observed. Inoculum that contained 10(9) cfu/ml induced larger differences in LL between resistant and susceptible cultivars. Laxmi consistently exhibited the highest level of resistance as indicated by reduced LL and AUDPC, and could be a source of resistance to BB in Nepal.