Genetic homogeneity of a recently introduced pathogen of chickpea, Ascochyta rabiei, to Australia

The study examined the genetic structure and potential for adaption to host genotype of Ascochyta rabiei, a major necrotrophic fungal pathogen of chickpea. For this, A. rabiei populations derived from six major chickpea growing regions in Australia were characterized using 20 polymorphic microsatellite markers. The overall gene (H = 0.094) and genotypic (D = 0.80) diversities among the entire population were low, indicating the establishment of a recent founder population. Since, no significant genetic differentiation was detected among growing regions, subsequent anthropogenic dispersal was proposed, mainly through seed movement. The highest genotypic diversity and allelic richness was detected at Kingsford, South Australia, thought to be one of the sites of industry establishment in the 1970s and hence the centre of introduction. Despite assessing 206 isolates collected in 2010 from host genotypes with differential disease responses, no significant co-occurrence of fungal haplotype with host genotype was detected. Rather a single haplotype that accounted for 70 % of the total isolates assessed was detected on all host genotypes assessed and from all regions. Therefore, we propose that up until 2010, host reaction was not a major influence on the Australian A. rabiei population structure. Additionally, the detection of a single mating type only, MAT1-2 indicated asexual reproduction, further influencing low haplotype diversity and resulting in a population comprising of multiple clones with relatively few haplotypes compared to populations in other continents.