Phylogenetic analysis of globally distributed Mycosphaerella graminicola populations based on three DNA sequence loci.

DNA sequence data from three nuclear loci were collected from 384 isolates representing fourteen globally distributed populations of the plant pathogenic fungus Mycosphaerella graminicola. Gene genealogies were constructed for the actin and beta-tubulin loci as well as for the previously characterized RFLP locus STS2. The STS2 and beta-tubulin loci showed greater potential for phylogenetic studies than the actin locus. Greater sequence diversity was found in the "Old World" populations (Middle East and Europe) than in the "New World" populations (North and South America and Australia). The gene trees were rooted using homologous DNA sequences of Septoria passerinii, the closest known relative to M. graminicola, as well as coalescent rooting. Based on the rooted trees, a tentative phylogenetic history of these populations was inferred. The Middle East appears to be the most likely center of origin, while European populations are more ancient than New World populations. A test for neutrality indicated that the intron in the actin locus could be under selection, while the other two sequence loci were neutral.