Molecular phylogeny of the Leptosphaeria maculans-L. biglobosa species complex

Leptosphaeria maculans (anamorph Phoma lingam), the ascomycete causing stem canker of crucifers, is a species complex that can be separated into at least seven distinct subgroups using a combination of biochemical and molecular criteria. In the present study sequences of the entire ITS region, including the 5.8S rDNA, of 38 isolates representing the seven subgroups, along with specimens from culture collections, were analysed, compared to those of closely related Leptosphaperia species, and the phylogeny inferred using parsimony and distance analyses. A well-supported clade encompassed all isolates of the seven subgroups along with L. conferta, a known saprobe of dried crucifer stems. The L. maculans isolates were further separated into two well-supported clades corresponding to L. maculans s. str. and the recently named L. biglobosa. Parsimony and distance analyses further separated groups within both species, usually corresponding to specific host plants or geographic origin, e.g. L. maculans 'brassicae' from cultivated Brassica, L. maculans 'lepidii'. from Lepidium sp., L. biglobosa 'brassicae', from various Brassica species, L. biglobosa 'thlaspii' from Thlaspi arvense, L. biglobosa 'erysimii' from Erysimum sp., and L. biglobosa 'canadensis' mostly found in central Canada. The oldest L. maculans specimens maintained in international collections clustered with either L. maculans 'brassicae', L. biglobosa 'brassicae', or a still different group closely related to L. biglobosa 'thlaspii'. The evolutionary relationships between the seven infraspecific groups are discussed in terms of phytopathological relevance and species isolation linked with specific life cycle, geographic isolation or host specificity.