Genetic Diversity of Zymoseptoria tritici Populations in Central and South-eastern Ethiopia

Septoria tritici blotch (STB), caused by the hemibiotrophic fungus Zymoseptoria tritici, is a serious threat to global wheat production, and a major bottleneck to wheat production in Ethiopia. Accurate identification and analysis of the pathogens genetic structure helps inform robust STB management. This study analyzed the molecular identity and genetic structure of 200 Z. tritici isolates retrieved from diseased crops in central and south-eastern regions of Ethiopia. Allelic diversity at 12 simple sequence repeat (SSR) loci was examined for all 200 isolates, and 165 isolates were identified by Sanger sequencing of the internal transcribed spacer (ITS) region of nuclear DNA (rDNA) region. The microsatellites were highly polymorphic, with mean number of alleles (Na) = 6.23, effective alleles (Ne) =2.90, Neis gene diversity (H) =0.57, and polymorphic information content (PIC) =0.59, and an analysis of molecular variance confirmed the presence of low population differentiation (Fixation Index (FST) = 0.02, Gene Flow (Nm) = 14.7), with 95% of the total genetic variation residing within populations, and only 5% residing between populations. The highest genetic diversity (Number of allele (Na) = 9.33, Effective number of allele (Ne) = 3.41 and Neis gene diversity (H) = 0.68) was observed in the Oromia special zone surrounding Finfinnee (OSZ) Z. tritici populations, followed by Arsi and North Shewa populations, indicating that these areas are ideal for multi-location germplasm resistance screening, and also pathogen genetic and genomic analyses. Cluster analyses did not clearly divide the populations into genetically separate clusters according to their geographic sampling areas, probably because of high gene flow. All individual samples showed genetic admixture, and shared genomic backgrounds from two subgroups (K=2). Overall, the SSR markers proved to be highly informative and effective genetic tools for unlocking the pathogens genetic structure. The Z. tritici populations of central and southeast Ethiopia exhibit high genetic diversity, indicating the need to deploy durable and diverse disease management strategies. North Shewa, OSZ, Arsi and West Arsi administrative zones represent hotspots for genetic and genomic analyses of Z. tritici. Moreover, these areas would be excellent locations for host-pathogen interaction studies, and wheat germplasm screening for STB resistance.