Single strand conformation polymorphism is a sensitive method for screening nucleotide variations in Mycosphaerella graminicola.

Single Strand Conformation Polymorphism (SSCP) and sequencing were performed in order to assess molecular polymorphism of mating type sequences in the heterothallic ascomycete Mycosphaerella graminicola, the causal agent of Septoria tritici blotch of wheat. The screening was undertaken on mat1-1 and mat1-2 partial sequences of 341 and 657 bp, respectively, amplified with multiplex PCR from 510 French single-conidial strains plus the two reference isolates IPO323 and IPO94269 from The Netherlands. After restriction with Taq1 in order to reduce the fragment sizes, all digested amplicons were subjected to SSCP. Sequencing was then performed when a SSCP pattern deviates from the most frequently occurring profile. Among the assessed strains, 228 ones plus IPO323 were MAT1-1 and 282 ones plus IPO94269 were MAT1-2. Among the MAT1-1 strains, only a single one exhibited a SSCP profile distinct to the other MAT1-1 strains, whereas 10 MAT1-2 strains (among which 2 and 4 with same profiles, respectively) showed a SSCP profile differing to the other MAT1-2 strains. Sequencing revealed that all polymorphisms observed on SSCP gels were single nucleotide variations and all strains displaying the same SSCP profiles showed identical nucleotide sequences. Among the seven disclosed nucleotide variations, only two were non-synonymous and both were non-conservative. This study reports a high sensitivity of SSCP allowing detection of single point mutations in M. graminicola, shows a conservation of mating type idiomorphs in the fungus at both sequence and population scales, but also suggests a difference in polymorphism level between the two mating type sequences.