Submitted to: Mycoscience
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/28/2011
Publication Date: 8/25/2011
Citation: Aoki, T., Scandiani, M.M., O Donnell, K. 2011. Phenotypic, molecular phylogenetic, and pathogenetic characterization of Fusarium crassistipitatum sp. nov., a novel soybean sudden death syndrome pathogen from Argentina and Brazil. Mycoscience. 53(3):167-186. Interpretive Summary: This research was conducted to characterize a novel Fusarium pathogen isolated from soybean plants exhibiting sudden death syndrome (SDS) in Argentina and Brazil. Cultural and microscopic studies revealed that the pathogen could be distinguished from all other known soybean SDS pathogens in the production of diagnostic yellowish colonies on potato dextrose agar. The fungus also produced tall, stout mostly unbranched aerial spore bearing structures which were diagnostic in that their base was thick-walled. Deoxyribonucleic acid (DNA) sequence analyses of six marker loci corroborated the morphological data by indicating the soybean pathogen represented a novel species. The novel soybean SDS pathogen was formally described herein as F. crassistipitatum. Koch’s postulates were completed by demonstrating that isolates of F. crassistipitatum were able to induce typical SDS foliar and root-rot symptoms on two soybean cultivars that were indistinguishable from those caused by three other SDS pathogens (i.e., F. virguliforme, F. brasiliens,e and F. tucumaniae) in a pathogenicity experiment. The results of this study will be of interest to quarantine officials and plant pathologists who are trying to control the spread of this pathogen and plant breeders who are focused on developing cultivars with broad based resistance to this economically devastating disease.
Technical Abstract: A novel soybean sudden death syndrome (SDS) pathogen from Argentina and Brazil is formally described herein as Fusarium crassistipitatum based on detailed phenotypic analyses of macro- and microscopic characters and phylogenetic analyses of multilocus Deoxyribonucleic acid (DNA) sequence data. Fusarium crassistipitatum can be distinguished from the other soybean SDS and Phaseolus/Vigna root rot pathogens (BRR) phenotypically by the production of yellowish colonies on PDA; and tall, stout and mostly unbranched conidiophores with a thick-walled base, which form mutiseptate conidia apically. Phylogenetic species recognition based on genealogical concordance of a six-gene dataset strongly supported the reciprocal monophyly of F. crassistipitatum with respect to the other SDS and BRR pathogens. Isolates of F. crassistipitatum were able to induce typical SDS foliar and root-rot symptoms on soybean that were indistinguishable from those caused by three other SDS pathogens (i.e., F. virguliforme, F. brasiliense and F. tucumaniae) on susceptible cultivars A 6445RG and N 4613RG in a pathogenicity experiment.