Genotypic and phenotypic characterization of isolates in the Fusarium oxysporum species complex from soybean roots
M. L. ELLIS (1), D. R. Cruz Jimenez (1), B. F. Linn (1), L. F. Leandro (1), G. P. Munkvold (1). (1) Iowa State University, Ames, IA, U.S.A.
The <i>Fusarium oxysporum</i> species complex (FOSC) includes economically important pathogens to many hosts. In Iowa, <i>F. oxysporum</i> is the most frequent <i>Fusarium</i> species isolated from soybean roots, and isolates range from aggressive seedling and root rot pathogens to non-pathogenic isolates. The objective of this research was to characterize the genotype and phenotype of isolates within the FOSC from soybean roots. Sequence analyses of the elongation factor 1-α (TEF) gene and the mitochondrial small subunit (MtSSU), identification of mating type loci, and vegetative compatibility (VC) tests were used to genotypically characterize 102 soybean isolates from Iowa. Pathogenicity was tested using a rolled towel assay in which soybean seed was inoculated with 100 μl of 1x10<sup>6</sup> conidia/ml. Phylogenetic analysis of the TEF and MtSSU identified four previously described clades, including <i>F. commune</i>. Mating type loci MAT1-1 and MAT1-2 were present in isolates from all clades. Isolates differed in aggressiveness within and among clades; one clade had many isolates that were significantly less aggressive (P <0.0001) when compared to isolates from the other <i>F. oxysporum</i> clades and <i>F. commune</i>. Current data indicate that aggressiveness may correspond to VC group. Analysis of pathogenic and non-pathogenic isolates will be done to determine if conditionally dispensable chromosomes may be responsible for pathogenicity to soybean.
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