Monday, November 13, 2006

Sequence Analysis and Pathogenic Characterization of Fusarium spp. Associated with Sudden death syndrome of soybean.

Silvina Giammaria1, Zahi K. Atallah2, Walter R. Stevenson2, and John Rupe1. (1) Univ of Arkansas, 217 PTSC, Fayatteville, AR 72701, (2) Univ of Wisconsin, Dept. of Plant Pathology, 1630 Linden Dr, Madison, WI 53706

Sudden death syndrome (SDS) of soybean is a disease caused by the soilborne fungus Fusarium solani f.sp. glycines sensu lato. Recently, three species of the genus Fusarium were reported to cause SDS (namely F. virguliforme, F. tucumaniae, F.brasiliense) , and a change in the name of the causal organism was proposed. The etiology of the disease and the ability of certain species to cause disease remains controversial. Sequences of the internal transcribed sequence of the rDNA (ITS) and several protein coding genes were generated. The latter genes were: histone 3 (H3), histone 4 (H4), elongation factor 1-α (EF1), calmodulin (Cal), actin (Act) and two regions of the β–tubulin (Bt). The obtained nucleotide sequences were used in phylogenetic analyses to determine the relationship among the three fungi and ascertain the taxonomic name change. Additionally, pathogenicity tests were conducted under controlled conditions, by inoculating isolates representative of each of the species on a susceptible and resistant soybean cultivar. The phylogenetic results indicate that each species constitutes a distinct monophyletic taxonomic group. Nevertheless, discrepancies in the virulence on the soybean host were observed.