Evolution of Fusarium oxysporum f. sp vasinfectum races inferred from multigene genealogies

Fusarium wilt of cotton is a serious fungal disease responsible for signifi cant yield losses throughout the world. Evolution of the causal organism Fu sarium oxysporum f. sp. vasinfectum, including the eight races described fo r this specialized form, was studied using multigene genealogies. Partial s equences of translation elongation factor (EF-la), nitrate reductase (NIR), phosphate permase (PHO), and the mitochondrial small subunit (mtSSU) rDNA were sequenced in 28 isolates of F oxysporum f. sp, vasinfectum selected to represent the global genetic diversity of this forma specialis. Results of a Wilcoxon Signed-Ranks Templeton test indicated that sequences of the fou r genes could be combined. In addition, using combined data from EF-1 alpha and mtSSU rDNA, the phylogenetic origin of F oxysporum f. sp. vasinfectum within the F oxysporum complex was evaluated by the Kishino-Hasegawa likeli hood test. Results of this test indicated the eight races of F oxysporum f. sp. vasinfectum appeared to be nonmonophyletic, having at least two indepe ndent, or polyphyletic, evolutionary origins. Races 3 and 5 formed a strong ly supported clade separate from the other six races. The combined EF-1 alp ha, NIR, PHO, and mtSSU rDNA sequence data from the 28 isolates of F oxyspo rum f. sp. vasinfectum recovered four lineages that correlated with differe nces in virulence and geographic origin: lineage I contained race 3, mostly from Egypt, and race 5 from Sudan; lineage Il contained races 1, 2, and 6 from North and South America and Africa; lineage III contained race 8 from China; and lineage IV contained isolates of races 4 and 7 from India and Ch ina, respectively.