Evaluation of the phenotypic and genotypic diversity of the bacterial species causing gummy spike blight of wheat and barley

Gummy spike blight is a disease of wheat (Triticum aestivum) in several cereal growing areas of Iran. Rathayibacter iranicus, as the causative agent of the disease of wheat and barley ,appears to be confined to Iran. To evaluate possible phenotypic and genotypic diversity of strains infecting wheat and barley, infected spikes were collected from East Azarbaijan , Ilam, Isfahan, Fars and Khuzestan provinces and the associated bacteria were isolated from the spikelets and characterized. Fifteen strains were selected as representatives of groups displaying one or a few differences in phenotypic features or total protein electrophoretic patterns and were used in genotypic comprisons. DNA was extracted from these isolates and from the type strains of Rathayibacter spp. To evaluate the genetic diversity of the studied strains, minisatellite marker, with primers M13 and (GTG)R5R, was used. 7TFragments of the genes for 7T16S rDNA, ITS, gyrase (gyrB) and recombinase (recA) were amplified and sequenced. Combined PCR fingerprints obtained with the minisatellite primers indicated identity of the strains isolated from wheat with R. iranicus. Strains isolated from barley formed a distinct branch closer to that of R. iranicus and furthest from those of the other Rathayibacter species including R. tritici and R. rathayi. R. toxicus and other Rathayibacter species formed a distinctly different branch. Comparison of the sequences of the ITS, 16S rDNA, gyrB and recA genes with those deposited in GenBank, verified, further, the identity of the strains isolated from wheat and barley as R. iranicus.