Abstract: The resistance mutants of wild-type Xanthomonas oryzae pv.oryzae to amicarthiazol were got by ultraviolet(UV) irradiation in laboratory. These mutants could grow in the medium containing 100 μg·ml-1 of amicarthiaol. However the wild-type sensitive strain could not grow at 10 μg·ml-1. The activity of succinate dehydrogenase(SDH) was strongly inhibited by amicarthiazol while the activity of SDH from resistant mutants was very low and was not inhibited by the chemical. Six pairs of special primer based on the conserved region of Xanthomonas axonopodis pv.citri were designed and used to amplify the gene encoding succinate dehydrogenase from X.oryzae. Whole gene of succinate dehydrogenase has 3 616bp, 1 115 deduced amino acids and two introns. The homology of the nucleotide sequence and deduced amino acid of X. oryzae with that of X.citri was 93% and 97% respectively. Compared with that of other six bacteria, the homology of deduced amino acid of succinate dehydrogenase was from 43% to 95% respectively. Sequence comparison among sensitive and five mutants revealed that mutant gene encodes a modified iron-sulpher subunit of succinate dehydrogenase with a amino-acid substitution (His 229→Tyr).

Key words: Xanthomonas oryzae pv.oryzae, Amicarthiazol, Succinate dehydrogenase, Mode of action, Resistance