Molecular differentiation of Fusarium solani f. sp glycines from other F-solani based on mitochondrial small subunit rDNA sequences

Fusarium solani is a soilborne plant pathogen that infects many different h osts. Within the species, there is some specialization, and a number of for ma specialis have been described based on host affiliation. One of these, F . solani f. sp. glycines, infects soybean and causes sudden death syndrome. To differentiate between F. solani f. sp. glycines and other F. solani iso lates, a partial sequence of the mitochondrial small subunit (mtSSU) rRNA g ene was amplified by polymerase chain reaction and sequenced from 14 F. sol ani f. sp. glycines and 24 F. solani isolates from various plant hosts. All F. solani f. sp. glycines isolates had identical sequences. A single, uniq ue insertion of cytosine occurred in all F. solani isolates but not in any of the F. solani f. sp. glycines isolates. Two major lineages, distinguishe d by sequence divergence and the presence or absence of multiple insertions , occurred in F. solani isolates. Cladistic analysis produced a single most -parsimonious tree with three major clades. The first clade contained all F . solani f. sp. glycines isolates. A second clade grouped together all of t he F. solani isolates that had only a single nucleotide insertion differenc e from the first clade. Genetic distance between these two clades was 0.016 . A third clade was formed by five F. solani isolates that had multiple ins ertions. Isolates in the third clade had a genetic distance of 0.040 from t he first and second clades. Based on the sequence data, it is likely that F . solani f. sp. glycines has a shorter evolutionary history than other F. s olani isolates that have either single or multiple nucleotide insertions. T he differences in nucleotide insertions in part of the mtSSU rRNA gene betw een F. solani f. sp. glycines and other F. solani isolates provide a direct and reliable way to distinguish isolates off solani.