ASSESSMENT OF GENETIC DIVERSITY OF THE CAUSAL AGENT OF BACTERIAL BROWN STRIPE OF RICE BY REP-PCR

Brown  stripe of rice disease was first reported from rice nursery in Mazandaran  province. The  agent was identified  as  Acidovorax  avenae  subsp. avenae (Aaa) (Rahimian. 1986, Iran Agric. Res. 5: 63-71). Assessment of the possible  genetic  diversity  of  Aaa isolates  in eastern Mazandaran was attempted in the present study. On the basis of biochemical and physiological characteristics, the isolates were identified, phenotypically, as Aaa. All isolates were oxidase and catalase positive and hydrolysed starch, casein and Tween 80. They did not assimilate sucrose or salicin but were capable of using sorbitol and monnitol as carbon sources (Rahimian. 1986, Iran Agricultural Res. 5: 63-71). Genomic DNA of isolates was extracted and subjected to rep-PCR using REP and BOX primers, under the previously described  conditions with only minor modifications (Versalovic  et al. 1991, Nucleic Acids Res. 19: 6823-6831). Dendrograms  were constructed using data sets obtained  from  amplified  fragments, using the Jaccard coefficient, the UPGMA algorithm and NTSYS-PC program. Comparison of the genomic fingerprints demonstrated that , at 20%, 50%, 80% similarity levels isolates formed 7, 16, 23 clusters with BOX primer, respectively and 5, 13, 19 clusters with REP primer at the stated levels of similarity, respectively. The clusters produced in REP-PCR  were highly congruent with those of BOX-PCR. There has been no report on the presence of such  any high level of genetic diversity in this bacterial subspecies elsewhere.