MOLECULAR CHARACTERIZATION OF SYRIAN RACES OF XANTHOMONAS AXONOPODIS pv MALVACEARUM
M. Abdo-Hasan, H. Khalil, B. Debis, N. MirAli
Xanthomonas axonopodis pv. malvacearum (Xam), the causal agent of cotton angular leaf spot disease, causes severe qualitative and quantitative losses in most cottongrowing areas of the world. Forty virulent strains of Xam originally selected from 200 isolates were tested against a set of ten differential cotton varieties. Forty isolates representing nine defined races were used to detect the genetic diversity among these races using RAPD and ISSR PCR-based techniques. Both techniques revealed high degrees of polymorphisms among the studied races. Combined data showed that percent disagreement values (PDV) ranged between 0.13 and 0.37. RAPD identified 7 isolates with the majority having several unique bands. ISSR, on the other hand, identified 9 isolates with the majority having less unique bands. A single isolate (race 32) was not characterized by any unique band and thus was not distinguishable by both methods. The combined dendrogram based on UPGMA analysis contained two main clusters. The first cluster contained four isolates (races), three of which were the lowest in virulence, and the second cluster contained three highly virulent isolates (races). The two outgrouped races, namely 11 and 26, were of medium virulence and were characterized as being the most distinguishable by both methods (15 and 17 unique bands for races 11 and 26 respectively). It was concluded that analysis of genomic DNA using RAPD and ISSR is a suitable typing method for since both techniques proved to be fast, sensitive, and reliable for determining genetic relationships among Xam isolates.