UC Davis

Hybridization plays a central role in plant evolution, but its overall importance in fungi is unknown. New plant pathogensare thought to arise by hybridization between formerly separated fungal species. Evolution of hybrid plant pathogens fromnon-pathogenic ancestors in the fungal-like protist Phytophthora has been demonstrated, but in fungi, the most importantgroup of plant pathogens, there are few well-characterized examples of hybrids. We focused our attention on the hybridand plant pathogen Verticillium longisporum, the causal agent of the Verticillium wilt disease in crucifer crops. In order toaddress questions related to the evolutionary origin of V. longisporum, we used phylogenetic analyses of seven nuclear lociand a dataset of 203 isolates of V. longisporum, V. dahliae and related species. We confirmed that V. longisporum was diploid,and originated three different times, involving four different lineages and three different parental species. All hybrids shareda common parent, species A1, that hybridized respectively with species D1, V. dahliae lineage D2 and V. dahliae lineage D3,to give rise to three different lineages of V. longisporum. Species A1 and species D1 constituted as yet unknown taxa.Verticillium longisporum likely originated recently, as each V. longisporum lineage was genetically homogenous, andcomprised species A1 alleles that were identical across lineages.