Phylogenetic Relationships of the Soybean Sudden Death Syndrome Pathogen Fusarium solani f. sp. phaseoli Inferred from rDNA Sequence Data and PCR Primers for Its Identification. Kerry O'Donnell. Microbial Properties Research, National Center for Agricultural Utilization Research, Agriculture Research Service, U.S. Department of Agriculture, Peoria, IL 61604 U.S.A. Lynn E. Gray(2). (1)Microbial Properties Research, National Center for Agricultural Utilization Research, Agriculture Research Service, U.S. Department of Agriculture, Peoria, IL 61604 U.S.A. (2) U.S. Department of Agriculture, Agriculture Research Service, Plant Protection Research, and Department of Plant Pathology, University of Illinois, Urbana, IL 61801 U.S.A. MPMI 8:709-716. Accepted 2 June 1995. Copyright 1995 The American Phytopathological Society.

Phylogenetic relationships of several species within the Fusarium solani-complex were investigated using characters from the nuclear ribosomal DNA. Genetic variation within 24 isolates, including 5 soybean sudden death syndrome (SDS) strains, was assessed using rDNA sequence data and restriction fragment length polymorphic markers. By these techniques, the causal agent of soybean SDS was identified as F. solani f. sp. phaseoli. In separate cladistic analyses, Plectosphaerella cucumerina and Nec-tria cinnabarina or F. ventricosum were used for rooting purposes. Monophyly of the F. solani-complex was strongly supported by bootstrap and decay analyses. Parsimony analysis indicates that this complex is composed of a number of phylogenetically distinct species, including Neocosmospora vasinfecta, F. solani f. sp. phaseoli, and biological species designated as MPI, MPV, and MPVI of N. haematococca. The results demonstrate complete congruence between biological and phylogenetic species within the N. haematococca-complex. In addition, DNA sequence data were used to design a PCR primer pair which could specifically amplify DNA from isolates of the SDS pathogen from infected plants.