Prevalence of mating type idiomorphs in Pyrenophora teres f. teres and P. teres f. maculata populations from the Canadian prairies

The fungus Pyrenophora teres Drechs. occurs as two morphologically similar but genetically distinct forms, P. teres f. teres (Ptt) and P. teres f. maculata (Ptm), which cause the net form and spot form of net blotch of barley, respectively. A collection of 220 isolates from the Canadian prairie provinces (Alberta, Saskatchewan and Manitoba) was evaluated for mating type (MAT) idiomorph distribution and frequency. Fungal isolates were classified as Ptt or Ptm using form-specific polymerase chain reaction (PCR) primers. PCR analysis with MAT-specific primers indicated that the MAT1 and MAT2 idiomorphs of Ptt and Ptm could be identified within the same field, on the same plant, and on the same leaf. There was no significant departure from the expected 1:1 MAT1/MAT2 ratio for both forms in all three provinces or in the Canadian prairies population as a whole. Polymorphic simple sequence repeat primers were used to detect evidence of possible recombination between the two forms. Cluster analysis revealed that all P. teres isolates, including 30 isolates causing intermediate symptoms, clustered in two distinct groups conforming to either Ptt or Ptm. Therefore, hybridization was not detectable from the 220 isolates collected in western Canada. Pyrenophora teres f. teres is still the dominant form (58%) of the net blotch pathogen, and the data suggest both Ptt and Ptm go through regular cycles of sexual reproduction in the Canadian prairies.