ISOLATION, CHARACTERIZATION, PRESERVATION AND PATHOGENICITY TEST OF XANTHOMONAS ORYZAE PV. ORYZAE CAUSING BLB DISEASE IN RICE

The present study was conducted to isolate the Xanthomonas oryzae pv. oryzae obtained from infected rice foliar samples collected from all agro ecological zones of Pakistan. Infected leaf samples when plated gave yellow, circular, smooth, convex and viscous bacterial colonies on (YDCA). Out of 123 isolates, 105 showed hypersensitive reaction on tobacco leaves (Nicotiana rustica). Six biochemical tests were conducted to characterize 17 isolates of pathogen. All isolates consistently gave similar results. Gram staining demonstrated that pathogen is a gram negative rod shaped, KOH test was performed in order to confirm gram staining results, further all isolates showed positive reaction and confirmed that they are gram negative. The egg yolk reaction was negative for the 7 isolates (Xoo 20, Xoo 36, Xoo51, Xoo 65, Xoo 75, Xoo 99 and Xoo 105). At 0.1 and 0.02 % concentration of TTC these seven isolates failed to produce colonies. In the oxidase test 7 isolates proved negative. In the starch hydrolysis above mentioned 7 isolates showed positive reaction. The Pathogenicity test of 7 isolates tested on eight rice varieties (Basmati 385, IRRI 26, Basmati 386, Dilroosh 97, JP 5, Super Basmati, Basmati 2000 and Ks 282). Analysis showed that out of eight tested varieties IRRI 6 was significantly resistant whereas the varieties Basmati 385, Basmati 386, Jp5, Super Basmati and Basmati 2000 were significantly susceptible and var. Dilroosh 97 and Ks 282 were moderately resistant.