First microsatellite markers developed and applied for the genetic diversity study and population structure of Didymella pisi associated with ascochyta blight of dry pea in Montana.

Didymella pisi is the predominant causal pathogen of ascochyta blight of dry pea causing yield losses in Montana, where 415 000 acres were planted to dry pea in 2018. Thirty-three microsatellite markers were developed for dry pea pathogenic fungus, Didymella pisi, these markers were used to analyze genetic diversity and population structure of 205 isolates from four different geographical regions of Montana. These loci produced a total of 216 alleles with an average of 1.63 alleles per microsatellite marker. The polymorphic information content values ranged from 0.020 to 0.990 with an average of 0.323. The average observed heterozygosity across all loci varied from 0.000 to 0.018. The gene diversity among the loci ranged from 0.003 to 0.461. Unweighted Neighbor-joining and population structure analysis grouped these 205 isolates into two major sub-groups. The clusters did not match the geographic origin of the isolates. Analysis of molecular variance showed 85 % of the total variation within populations and only 15 % among populations. There was moderate genetic variation in the total populations (PhiPT = 0.153). Information obtained from this study could be useful as a base to design strategies for improved management such as breeding for resistance to ascochyta blight of dry pea in Montana.