ARS | Publication request: 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

Submitted to: Molecular Plant Microbe Interactions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 1, 1995
Publication Date: N/A

Interpretive Summary: Sudden death syndrone (SDS) is a fatal disease of soybeans caused by a fungal pathogen that is difficult and sometimes impossible to detect, isolate, and identify using standard microbiological techniques. This paper describes the development and successful application of molecular probes for the rapid detection and accurate identification of the SDS pathogen in diseased soybean plants. Since these molecular probes specifically detect the SDS pathogen, to the complete exclusion of other microbes, they can be used to screen fields for this soil-borne pathogen prior to planting. Also, the test can be run in hours compared with the several weeks required using microbiological procedures currently used.

Technical Abstract: Phylogenetic relationships of several species within the Fusarium solani complex were investigated using characters from the ribosomal DNA. Genetic variation within 24 isolates, including 5 soybean sudden death syndrone (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. The sequence data were used to design a PCR primer pair which could specifically amplify DNA from isolates of the SDS pathogen and from infected plants. In separate cladistic analyses, Plectosphaerella cucumerina and Nectria cinnabarina or F. ventricosum were used for rooting purposes. Bootstrap analysis and decay indices were used to assess clade stability, and these measures of branch robustness showed a positive correlation. Monophyly of the F. solani-complex was strongly supported. Parsimony analysis revealed that this complex is composed of a number of phylogenetically distinct species, including N. haematococca MPI, MPV, MPVI, Neocosmospora vasinfecta, and F. solani f.sp. phaseoli. Also, the teleomorph reported for the SDS pathogen is shown to be an unrelated fungus, P. cucumerina, and not N. Haematococca incorrectly reported. Limitations of the morphological and biological species concepts as applied currently to F. solani/N. haematococca are discussed and the adoption of a phylogenetic species concept is proposed.