Submitted to: Fungal Genetics Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 3/13/2001
Publication Date: N/A
Technical Abstract: Septoria passerinii causes speckled leaf blotch of barley. No teleomorph has been found and the pathogen is assumed to reproduce exclusively through asexual pycnidiospores. Recent phylogenetic analyses have shown that S. passerinii is closely related to the wheat pathogen Mycosphaerella graminicola, a species that undergoes regular sexual reproduction. Analyses of genetic variation within populations of S. passerinii revealed a high level of genotypic diversity, suggesting the possibility of sexual reproduction in nature. To test the hypothesis that S. passerinii is capable of sexual reproduction, mating type clones from M. graminicola were used as probes in Southern analyses. A 4 kb band was present in some isolates of S. passerinii when probed with a clone containing the hmg box from M. graminicola. This 4176 bp band contained a complete hmg box-like idiomorph of 2899 bp from S. passerinii, including sequence at both flanking regions. An open reading frame (ORF) of 101 amino acids had high similarity to the hmg box region of M. graminicola and other fungi. PCR primers were designed to amplify the other mating type idiomorph from isolates that did not hybridize to the hmg box probe. Sequencing of a 3637 bp PCR product revealed an alpha protein-containing idiomorph of 3050 bp. This clone contained an ORF of 345 amino acids with high similarity to alpha mating-type proteins from other fungi. Primers for multiplex PCR were designed to test the mating types from field isolates. This technique revealed that both mating types were present in the same fields in Minnesota and North Dakota. Therefore, this pathogen has the potential for sexual reproduction in nature, which may explain the high levels of genotypic diversity observed in barley fields in the north central U.S.