Differentiation of the sudden death syndrome pathogen of soybean, Fusarium solani f.sp. glycines, from other isolates of F. solani based on cultural morphology, pathogenicity, and mitochondrial DNA restriction fragment length polymorphisms

Forty-four isolates consisting of Fusarium solani (Mart.) Sacc. f.sp. glycines Roy, Fusarium solani f.sp. phaseoli (Burkholder) W.C. Snyder & H.N. Hans., and F. solani, collected from a variety of hosts and locations, were compared based on pathogenicity on soybean and mitochondrial DNA (mtDNA) restriction fragment length polymorphisms (RFLPs). The 24 isolates of F. solani f.sp. glycines caused more severe sudden death syndrome (SDS) foliar symptoms and root rot on soybean compared with all other isolates. All isolates of F. solani f.sp. glycines belonged to a single mtDNA RFLP haplotype. The other isolates of F. solani belonged to nine mtDNA RFLP haplotypes distinct from that of the SDS pathogen and did not cause significant levels of SDS. Three isolates of F. solani f.sp. phaseoli in a single mtDNA RFLP haplotype were very similar to isolates of F. solani f.sp. glycines in culture. One of these isolates consistently produced SDS-like symptoms in pathogenicity tests, although at a low frequency. Fusarium solani f.sp. glycines represent a genetically distinct subgroup within F. solani but may be related to F. solani f.sp. phaseoli.Key words: Fusarium solani f.sp. phaseoli, Glycine max, sudden death syndrome (SDS), mtDNA.