Fusarium oxysporum f. sp canariensis: evidence for horizontal gene transfer of putative pathogenicity genes

Fusarium wilt is a serious disease of the date palm Phoenix canariensis, caused by Fusarium oxysporum f. sp. canariensis (Foc). A previous study that characterized and compared the genetic diversity of the Australian Foc population with international strains suggested that the Australian population may have had an independent evolutionary origin. The current study compared the species phylogeny of the Australian and international populations and determined that Foc is not monophyletic, separating into three supported lineages across the two phylogenetic species of the Fusarium oxysporum species complex. This confirms an independent evolutionary origin for Foc in Australia. However, phylogenetic analysis of the putative pathogenicity genes Secreted In Xylem (SIX) did not reveal any separation of the Australian and international Foc strains. Furthermore, there was very low SIX sequence diversity within Foc. Horizontal gene transfer is argued to be the most parsimonious explanation for the incongruence between the species and SIX gene phylogenies.