Mitochondrial DNA-based genetic diversity and population structure of Zymoseptoria tritici in Tunisia

A total of 108 isolates of the wheat pathogen Zymoseptoria tritici were collected from four distinct locations of Tunisia and characterized for three mitochondrial DNA sequences to provide insight into the genetic diversity and population structure of the fungus in this country. The number of different alleles averaged over all loci within locations ranged from 3.33 to 5.67, with an average of 4.42 per location. Multilocus analysis identified 27 (25 %) distinct haplotypes among the 108 assessed isolates, revealing a high mtDNA-based clonality within the population. Three of the highlighted haplotypes occurred in all locations and nine of them covered at least two locations. Significant levels of genetic diversity were found for the whole population and within each of the sampled locations, as indicated by the Nei’s gene diversity (0.52), unbiased gene diversity (0.58) and allele richness (4.43) indices. Further analyzes using Bayesian and non-Bayesian statistical models, as well as AMOVA, showed a lack of mtDNA-based genetic structure (GST = 0.06), hence supporting previous reports on Z. tritici in Tunisia performed using nuclear-DNA markers. A high level of gene flow (Nm = 8.27) corroborates the lack of structure and suggests regular cycles of sexual reproduction, leading to allelic pool homogenization via wind-born ascospores in the Tunisian population of Z. tritici.