[show abstract][hide abstract] ABSTRACT: In this letter, we advocate recognizing the genus Fusarium as the sole name for a group that includes virtually all Fusarium species of importance in plant pathology, mycotoxicology, medicine and basic research. This phylogenetically-guided circumscription will free scientists from any obligation to use other genus names, including teleomorphs, for species nested within this clade, and preserve the application of the name Fusarium in the way it has been used for close to a century. Due to recent changes in the International Code of Nomenclature for algae, fungi and plants (16), this is an urgent matter that requires community attention. The alternative is to break the longstanding concept of Fusarium into nine or more genera, and remove important taxa such as those in the F. solani species complex from the genus, a move we find unnecessary. Here we argue that our proposal will preserve established research connections and facilitate communication within and between research communities, and at the same time support strong scientific principles and good taxonomic practice.
[show abstract][hide abstract] ABSTRACT: We report on the phenotypic, molecular phylogenetic and pathogenic characterization of a novel azuki bean (Vigna angularis) root-rot (BRR) pathogen from Hokkaido, Japan, which formally is described herein as Fusarium azukicola. This species can be distinguished phenotypically from the other Phaseolus/Vigna BRR and soybean sudden-death syndrome (SDS) pathogens by the production of wider and longer four-septate conidia cultured on SNA. Molecular phylogenetic analyses of four anonymous intergenic loci, a portion of the translation elongation factor (EF-1α) gene and the nuclear ribosomal intergenic spacer region (IGS rDNA) strongly support the genealogical exclusivity of F. azukicola with respect to the other soybean SDS and BRR pathogens within Clade 2 of the F. solani species complex (FSSC). Evolutionary relationships of F. azukicola to other members of the SDS-BRR clade, however, are unresolved by phylogenetic analyses of the individual and combined datasets, with the exception of the IGS rDNA partition, which strongly supports it as a sister of the soybean SDS pathogen F. brasiliense. A multilocus genotyping assay is updated to include primer probes that successfully distinguish F. azukicola from the other soybean SDS and BRR pathogens. Results of a pathogenicity experiment reveal that the F. azukicola isolates are able to induce root-rot symptoms on azuki bean, mung bean (Vigna radiata), kidney bean (Phaseolus vulgaris) and soybean (Glycine max), as well as typical SDS foliar symptoms on soybean. Our hypothesis is that F. azukicola evolved in South America and was introduced to Hokkaido, Japan, on azuki bean but its possible route of introduction remains unknown.
[show abstract][hide abstract] ABSTRACT: Fusarium tucumaniae and F. virguliforme are the primary etiological agents of sudden-death syndrome (SDS) of soybean in Argentina and the United States, respectively. Five isolates of F. tucumaniae and four isolates of F. virguliforme were tested for relative aggressiveness to soybean, using a toothpick inoculation method and two versions of a soil infestation inoculation method. Partially resistant soybean cultivar RA629 and susceptible cultivar A6445RG were inoculated separately with each of the nine isolates. Two experiments for each inoculation method were performed. Analysis of variance identified a significant three-way interaction of soybean cultivar*experiment*SDS pathogen (P = 0.01) using the different methods. When the two soil infestation methods were used, F. virguliforme was more aggressive than F. tucumaniae; however, when using the toothpick method, isolates of F. virguliforme and F. tucumaniae were equally aggressive. Although all three methods discriminated levels of partial resistance of the genotypes to SDS, results of the present study indicated that soil inoculations with sorghum infested grain represent the best method for evaluating soybean cultivar resistance to SDS. The existence of interactions among the host, pathogen and environmental conditions highlights the need for additional studies to improve the reproducibility of tests for screening soybean germplasm for resistance to SDS
[show abstract][hide abstract] ABSTRACT: Sudden death syndrome (SDS) of soybean has become a serious constraint to the production of this crop in North and South America. Phenotypic and multilocus molecular phylogenetic analyses, as well as pathogenicity experiments, have demonstrated that four morphologically and phylogenetically distinct fusaria can induce soybean SDS. 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, primarily because the species limits of these four pathogens were only recently resolved. In light of the recent discovery that soybean SDS and Phaseolus and mung bean root rot (BRR) are caused by four and two distinct species, respectively, multilocus DNA sequence analyses were conducted to assess whether any of the published molecular diagnostic assays were species-specific. Comparative DNA sequence analyses of the soybean SDS and BRR pathogens revealed that highly conserved regions of three loci were used in the design of these assays, and therefore none were species-specific based on our current understanding of species limits within the SDS-BRR clade. Prompted by this finding, we developed a high-throughput multilocus genotyping (MLGT) assay which accurately differentiated the soybean SDS and two closely related Phaseolus and mung BRR pathogens based on nucleotide polymorphism within the nuclear ribosomal intergenic spacer region 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 262 soybean SDS and 9 BRR pathogens. The validated MLGT array provides a unique molecular diagnostic for the accurate identification and molecular surveillance of these economically important plant pathogens.
[show abstract][hide abstract] ABSTRACT: We investigated the sexual reproductive mode of the two most important etiological agents of soybean sudden death syndrome, Fusarium tucumaniae and Fusarium virguliforme. F. tucumaniae sexual crosses often were highly fertile, making it possible to assign mating type and assess female fertility in 24 South American isolates. These crosses produced red perithecia and oblong-elliptical ascospores, as is typical for sexual members of the F. solani species complex. Genotyping of progeny from three F. tucumaniae crosses confirmed that sexual recombination had occurred. In contrast, pairings among 17 U.S. F. virguliforme isolates never produced perithecia. Inter-species crosses between F. tucumaniae and F. virguliforme, in which infertile perithecia were induced only in one of the two F. tucumaniae mating types, suggest that all U.S. F. virguliforme isolates are of a single mating type. We conclude that the F. tucumaniae life cycle in S. America includes a sexual reproductive mode, and thus this species has greater potential for rapid evolution than the F. virguliforme population in the U.S., which may be exclusively asexual.
Fungal Genetics and Biology 09/2007; 44(8):799-807. · 3.26 Impact Factor
[show abstract][hide abstract] ABSTRACT: Soybean sudden death syndrome (SDS) pathogens and dry bean root-rot pathogens were studied taxonomically, phylogenetically, and pathologically. Detailed phenotypic comparisons of macro- and microscopic features and phylogenetic analyses of multilocus DNA sequence data, including those on the nuclear ribosomal intergenic spacer region and the single copy nuclear gene translation elongation factor 1-a, indicated that they comprised five distinct species of Fusarium. Two new species causing soybean SDS in Brazil, F. brasiliense and F. cuneirostrum, are formally described. Fusarium cuneirostrum is responsible for soybean SDS in Brazil and dry bean or mung bean root-rot in the United States, Canada, and Japan. Strains of each species, including F. cuneirostrum isolates from dry bean and mung bean and F. phaseoli isolates from dry bean, were inoculated on soybean cultivar Pioneer 9492RR to determine their pathogenicity. Although intraspecific variation in pathogenicity was observed, all the species were able to induce typical SDS symptoms on soybean plants in the artificial inoculation tests. Comparisons of the key diagnostic morphological features reveal that all five species can be diagnosed using conidial morphology.
[show abstract][hide abstract] 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 DNA sequence
data. Fusarium crassistipitatum can be distinguished from the other soybean SDS and bean (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 multiseptate 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.