Preparation and partial characterization of Xanthomonas oryzae phytotoxin

A synthetic medium containing ammonium nitrate, urea, D-glucose, glycerol, and sodium glutamate was developed for growth of Xanthomonas oryzae and preparation of its phytotoxin. Culture filtrates and partially purified toxin preparations caused blight symptoms when inoculated in leaves of 30 days old rice plant cv. T(N)1. Toxin elicited quicker response than living cells. This activity was due to a non-dialysable, partial acid and heat labile glycopeptide. There was a sharp decrease in activity when culture filtrates and crude toxin preparations were heated at 100 degrees C for 30 min. Maximum activity was observed in pH range of 6.0-7.0 and a gradual loss at lower pH (5.0-3.0) and higher pH values (8.0-10.0). Unlike living cells which caused continuous lesion enlargement, toxin inoculation caused maximum attainment of lesion length within 4-6 weeks. Toxin preparation in concentration of 45 micrograms glucose/ml failed to evoke response. The study demonstrates that the purified toxin being easy in storage and causing quicker response than living cells when inoculated in rice leaves, may be used to screen rice varieties for bacterial blight resistance.