Distribution of mating type alleles in Iranian populations of Pyrenophora graminea, the causal agent of barley leaf stripe disease, using a multiplex PCR approach

Pyrenophora graminea is the main fungal species associated with barley leaf stripe disease worldwide. Even though a heterothallic mating strategy has been proven for P. graminea, this species is mainly known based on the asexual morph in nature and there is no available information on the prevalence of an active sexual cycle within the populations of this species in Iran as well as many other barley-producing countries. The feasibility of a cryptic sexual cycle within Iranian isolates of P. graminea was assessed through analyzing the distribution and frequency of the mating type alleles on micro-spatial and macro-geographical scales. A total number of 306 P. graminea isolates were obtained from 93 fields in 45 geographical regions across East Azerbaijan province during 2016–2017. A multiplex PCR assay was developed for simultaneous identification of P. graminea and screening of its mating type alleles using previously designed primer sets. Using the multiplex PCR assay, a 435-bp band was consistently amplified from all P. graminea isolates; while a 1300-bp fragment or a 1150-bp fragment was only amplified from the isolates harboring MAT-1 and MAT-2 alleles, respectively. The mating type identity of 164 isolates was determined as MAT-1 and 142 isolates as MAT-2. Results of the present study revealed a nearly equal distribution (1:1 ratio; X²=1.582) of mating type alleles within and between different populations of P. graminea. Results of the micro-spatial and macro-geographical distribution of mating types showed that both mating types were often present on almost all studied scales, including: within the same lesion of each leaf from a single barley plant, from the same field or different fields in the same region, and from different regions. Based on the results of the current study and referring to the earlier reports on the population structure of P. graminea, it is concluded that this pathogen undergoes regular cycles of sexual recombination in most of the examined regions.