Submitted to: Phytopathology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/16/2009
Publication Date: 1/1/2010
Citation: O Donnell, K., Sink, S.L., Scandiani, M.M., Luque, A.M., Colletto, A., Biasoli, M., Lenzi, L., Salas, G., Gonzalez, V., Ploper, L.D., Formento, N., Pioli, R.N., Aoki, T., Yang, X.B., Brice, A.J. 2010. Soybean Sudden Death Syndrome Species Diversity within North and South America Revealed by Multilocus Genotyping. Phytopathology. 100(1):58-71. Interpretive Summary: Soybean production within the United States and South America is constrained by the fungal disease commonly known as sudden death syndrome (SDS). Recent studies have shown that four closely related but genetically distinct Fusarium species native to South America cause the disease on this continent. In the present study, we determined that published molecular diagnostic assays failed to distinguish these four pathogens. Therefore, we developed and validated a novel, high-throughput DNA-based typing scheme and employed it to compare SDS pathogen diversity in Argentina and the United States. The results of this study show that, of the four species present in Argentina, Fusarium tucumaniae comprised 87.2% of the SDS pathogens recovered in this survey. By way of contrast, F. virguliforme accounted for close to 100% of the SDS pathogens within the United States. The novel molecular diagnostic system developed in the present study provides plant pathologists and quarantine officials with the only DNA-typing scheme for distinguishing the four SDS pathogens, thereby providing them with a robust tool for preventing the introduction of foreign SDS pathogens into the United States.
Technical Abstract: Sudden-death syndrome (SDS) of soybean and has become a serious constraint to the production of this crop in North and South America. Recently published phenotypic and multilocus molecular phylogenetic analyses, and pathogenicity experiments have demonstrated that four morphologically and phylogenetically distinct fusaria can induce soybean SDS (2,3). Because the species limits of these four pathogens were only recently resolved, published molecular diagnostic assays for the detection and identification of these pathogens have reported these pathogens as F. solani, F. solani f. sp. glycines or F. solani f. sp. phaseoli. In light of the recent discovery that soybean SDS is caused by four distinct species, multilocus DNA sequence analyses were conducted to assess whether any of the published molecular diagnostic assays were species-specific. Prompted by the finding that none of these assays were species-specific, we developed a multilocus genotyping (MLGT) assay which accurately differentiated the soybean SDS and two closely related Phaseolus and mung bean root rot (BRR) pathogens based on nucleotide polymorphism within the nuclear ribosomal intergenic spacer region (IGS) rDNA and two anonymous intergenic regions designated locus 51 and 96. The single-well diagnostic assay, employing flow cytometry and a novel fluorescent microsphere array, was validated by independent multilocus molecular phylogenetic analysis of a 65 isolate design panel. The MLGT assay was used to reproducibly type a total of 261 soybean SDS and 9 BRR pathogens. The validated MLGT array provides a unique high-throughput molecular diagnostic for the accurate identification and molecular surveillance of these economically important pathogens.