Phylogeographic population diversity of Bipolaris sorokiniana  causing spot blotch disease in wheat and barley

Abstract BackgroundThe spot blotch disease caused by Bipolaris sorokiniana is economically important fungal pathogen infecting wheat, barley and other crops. The disease is most prevalent in humid, warm wheat-growing regions and the Eastern Gangetic Plains of South Asia serving as a hotspot. very scanty and fragmentary information is available on its genetic variability, demography, and divergence period. The current study is the first detailed report to compare the phylogeographic patterns of B. sorokiniana isolates collected from different wheat and barley growing regions worldwide, with the goal of elucidating the demographic history and divergence time estimates. ResultsIn this study, we used multi-locus sequence (ITS, GAPDH and TEF-α1 genes) analysis to investigate the phylogeographic pattern of distribution and evolution of the 254 isolates of B. sorokiniana infecting wheat and barley . The degrees of differentiation among B. sorokiniana sequences from eighteen countries reflect the presence of a worldwide population that is broad and geographically undifferentiated. The analysis yielded fourty haplotypes. The ancestral haplotype was determined to be the dominant haplotype H_1 followed by H_29 and H_27, in which H_1 occupies a central position in the median-joining network and is shared by multiple populations from different continents. The phylogeographic patterns of multigene analysis of species as well as the preponderance of a single haplotype, suggest that human-mediated dispersal may have had a significant role in shaping the population of this pathogen.ConclusionsIn conclusion, the presence of one haplotype at a very high frequency and low genetic differentiation in B. sorokiniana suggests that the durability of resistance in host plants against pathogens could be improved by exchange of elite resistance lines from different countries. For the current distribution of species, divergence time analysis suggests that haplogroups began at the Plio/Pleistocene boundary.