Abstract
Septoria tritici blotch (STB) caused by Zymoseptoria tritici is the primary biotic stress for durum wheat production in Tunisia. The present study was aimed to decipher the genetic diversity and population structure of Z. tritici bread wheat isolates; in the northern regions of Tunisia this pathogen infected exclusively bread wheat. A total of 162 single-spore isolates were sampled during the 2015-2016 growing season from nine naturally infected bread wheat fields at four locations in the three main wheat-growing regions in Tunisia, previously reported as hot spots for Septoria disease (Cap Bon, Bizerte, and Beja). Collected isolates were fingerprinted using twelve polymorphic microsatellite markers to assess the genetic diversity and population structure of Z. tritici. All the microsatellite loci were polymorphic and a high genetic diversity was observed within the whole population. The highest Nei's index value (0.42), Shannon Index (0.84) and private allele numbers (36) were found at the El Haouaria location (Cap Bon region). Furthermore, a moderate genetic differentiation within and among the surveyed locations (73% and 27%) was confirmed by analysis of molecular variance (AMOVA). On the other hand, the STRUCTURE program was shown to be less sensitive in revealing genetic structure especially at low levels of diversity. Thus, information on the genetic structure of the pathogen population collected from bread wheat is useful for designing and implementing durable and effective management strategies.