Partition of the Botrytis cinerea complex in France using multiple gene genealogies

Abstract

In micro-organisms biodiversity is often underestimated because relevant criteria for recognition of distinct evolutionary units are lacking. Phylogenetic approaches have been proved the most useful in fungi to address this issue. Botrytis cinerea, a generalist fungus causing gray mold, illustrates this problem. It long has been thought to be a single variable species. Recent population genetics studies have shown that B. cinerea is a species complex. However conflicting partitions were proposed. To identify the most relevant partitions within the B. cinerea complex we used a multiple-gene genealogies approach. We sequenced portions of four nuclear genes, of which genealogies congruently clustered into two well supported groups corresponding to Groups I and II previously described, indicating that they represent phylogenetic species. Estimates of migration rates and genetic differentiation showed that these groups had been isolated for a long time, without detectable gene flow. This was confirmed by the high number of polymorphic sites fixed within each group. The genetic diversity was lower within Group I, as revealed by DNA polymorphism and vegetative incompatibility tests. Groups I and II exhibited phenotypic differences in their phenology, host range, size of asexual spores and vegetative compatibility. All these morphological and molecular aspects suggest that B. cinerea Groups I and II may be different cryptic species, isolated for a long time. Phylogenies and molecular analyzes of variance revealed no genetic structure according to the other suggested partitions for the B. cinerea complex (i.e., among host plants, between strains with and without transposable elements, nor between strains responsible for noble rot and gray mold. This suggests that recombination regularly occurs, or occurred until recently, within B. cinerea Group II. This also was supported by recombination rates at each locus. Multiple-gene genealogies showed their utility by providing a relevant partition criterion for the B. cinerea complex.