Sudden-Death Syndrome of Soybean Is Caused by Two Morphologically and Phylogenetically Distinct Species within the Fusarium solani Species Complex: F. virguliforme in North America and F. tucumaniae in South America

Abstract

Soybean sudden-death syndrome has become a serious constraint to commercial production of this crop in North and South America during the past decade. To assess whether the primary etiological agent is panmictic in both hemispheres, morphological and molecular phylogenetic analyses were conducted on strains selected to represent the known pathogenic and genetic diversity of this pathogen. Maximum-parsimony analysis of DNA sequences from the nuclear ribosomal intergenic spacer region and the single copy nuclear gene translation elongation factor 1-␣, together with detailed morphological comparisons of conidial features, indicate that SDS of soybean in North and South America is caused by two phylogenetically and morphologically distinct species. Fusarium virguliforme sp. nov., formally known as F. solani f. sp. glycines, is described and illustrated for the SDS pathogen in North America, and F. tucumaniae sp. nov. is proposed for the South American pathogen. The molecular phylogenetic results challenge the forma specialis naming system because pathogenicity to soybean might have evolved convergently in F. tucumaniae and F. virguli

Phenotypic, molecular phylogenetic, and pathogenetic characterization of Fusarium crassistipitatum sp. nov., a novel soybean sudden death syndrome pathogen from Argentina and Brazil

“…Moreover, F. virguliforme is the only SDS pathogen that has not been detected in Brazil, based on limited sampling . In contrast to F. virguliforme, which appears to possess a highly clonal population structure (Achenbach et al 1996;Li et al 2000;Rupe et al 2001;Aoki et al 2003Aoki et al , 2005O'Donnell et al 2010), F. tucumaniae has been shown to possess a heterothallic or self-sterile reproductive mode based on laboratory (Covert et al 2007) and field (Scandiani et al 2010) studies. Koch's postulates have been completed for F. virguliforme (Roy et al 1997) and F. tucumaniae (Scandiani et al 2004).…”

“…Methods for the examination of morphological characters followed Aoki et al (2003) and Aoki et al (2005) to compare the various species within the SDS-BRR clade. Fusarium strains grown on potato dextrose agar (PDA; Difco, Detroit, MI, USA) and synthetic low nutrient agar (SNA; Nirenberg 1990) in 9-cm-diameter plastic Petri dishes were incubated at 20°C in complete darkness, under continuous fluorescent light (FL40S-W; Mitsubishi, Yokohama, Japan) or under daylight to examine morphological and cultural characteristics.…”

“…This economically devastating disease is characterized by foliar chlorosis and necrosis, root rot, vascular discoloration of stems and roots, defoliation, and death. Recent morphological and molecular phylogenetic analyses have shown three closely related species within clade 2 of the Fusarium solani species complex can induce soybean SDS (i.e., F. virguliforme, F. tucumaniae, and F. brasiliense), and that these fusaria are very closely related to two root rot pathogens of mung bean (Vigna radiata (L.) R. Wilczek) and snap and dry edible bean (Phaseolus vulgaris L.) (Aoki et al 2003(Aoki et al , 2005O'Donnell et al 2010). The two bean (Phaseolus/Vigna) root rot (BRR) fusaria, which were described as F. phaseoli and F. cuneirostrum, are referred to as BRR pathogens hereafter to distinguish them from the soybean SDS fusaria.…”

Synergism in the interaction of Fusarium virguliforme with Heterodera glycines in sudden death syndrome of soybean

“…In the Midwest of the U.S., sudden death syndrome (SDS) of soybean, caused by Fusarium virguliforme (Aoki et al 2003), is a disease of increasing economic importance within the last two decades (Roy et al 1997, Wrather & Koenning 2009. Fusarium virguliforme infects soybean roots but does not move past the crown of the plant.…”

Utilizing Soybean Milk to Culture Soybean Pathogens

“…For example, Fusarium virguliforme produced aerial conidiophores and conidia on synthetic low nutrient agar [7]. Some Fusarium species, including F. virguliforme, produced chlamydospores when 10 mL of sterile distilled water was added to cultures grown on Bilay's medium [8,9].…”