Pathogenicity, mitochondrial DNA RFLPs, and colony morphology comparisons of isolates of Fusarium virguliforme and F. tucumaniae capable of causing SDS of soybean

Sudden death syndrome (SDS) is a recurrent problem in soybean growing areas of South America and the US. Recent reports have concluded that SDS is caused by two different species within the 'Fusarium solani' complex, Fusarium virguliforme and F. tucumaniae (syn. F. solani f. sp. glycines) (Aoki et al. 2003). The objective of this study was to compare ten representative isolates of each species for pathogenicity on soybean and greenbean, intDNA RFLPs, colony morphology, and growth rate. The isolates examined included 10 of F. tucumaniae from South America and 10 of F. virguliforme from the US. Pathogenicity tests were performed on the green bean cv. Top Crop and the SDS-susceptible soybean cv. Essex by scoring for root-rot and SDS-foliar symptoms. Significant differences in aggressiveness were measured for foliar SDS symptoms within each species. Conversely, no significant differences in aggressiveness were measured for root-rot. All SDS isolates failed to cause disease on the green bean cultivar. Minor differences in pigmentation and growth rate were observed among US isolates of F. virguliforme, while a considerable variation in pigmentation and growth rates were observed among the isolates of F. tucumaniae. MtDNA RFLP profiles were different between species while similar within each species. The results provide further support of the genetic differences between the two taxa capable of causing SDS symptoms.