Fusarium virguliforme
Figure 1. Interveinal chlorosis of a soybean leaf from subsequent infection with F. virguliforme
Primarily known as the causal agent of soybean sudden death (SDS) in the United States, Fusarium virguliforme (O’Donnell & Aoki) is an ascomycete fungus within the family Nectriaceae, that colonizes soybean roots during cool-wet spring. This fungus is persistent within the soil and produces necrosis symptoms in roots while colonizing to the xylem tissues, where the pathogen secretes phytotoxins. The host response creates a characteristic symptom of interveinal leaf scorch associated with SDS (Figure 1). Root infection and leaf scorch leads to a reduction of overall plant biomass, flowering and pod loss, and thus yields. As the soybean plants mature, blue sporodochia fruiting bodies will develop on the tap root averaging <5 mm in size till they coalesce (Figure 2).
Figure 2. Blue sporodochia mass developing on a soybean tap root.
The sporodochia contain macroconidia, a canoe shaped muti-septate (2-5) asexual spore structure averaging 50-60 μm long by 5-5.5 μm long (Aoki et al., 2005) (Figure 3). Macroconidia act as inoculum for the following season, but microconidia and chlamydospores (resting spore structures) are produced and can overwinter till the next growing season as well.
Recently, a broader host range was documented for Fusarium virguliforme, including alfalfa, pinto bean, navy bean, red and white clover, Canadian milk vetch, sugar bean, canola, corn, wheat, ryegrass, pigweed and lambsquarter (Kolander et al., 2012). The broad host range of this pathogen may limit efficacy of cultural management practices.
Figure 3. Macroconidia of F. virguliforme
This species was first described in 2003 by Aoki and O’Donnell, formerly described as Fusarium solani f. sp. glycines. This fungus was first reported in 1971 in the United States (Hirrel, 1983).
Literature Cited:
Aoki T, O’Donnell K, Homma Y, Lattanzi AR 2003. Sudden-death syndrome of soybean is caused by two morphologically and phylogenetically distinct species within the Fusarium solani species complex-F. virguliforme in North Ameria and F. tucumaniae in South America. Mycologia 95: 660-684
Aoki T, O’Donnell K, Scandiani MM 2005. Sudden death syndrom of soybean in South America is caused by four species of Fusarium: Fusarium brasiliense sp. nov., F. cuneirostrum sp. nov., F. tucumaniae and F. virguliforme. Mycoscience 46:162-183
Hirrel M 1983. Sudden-death syndrome of soybean-a disease of unknown etiology. Phytopathology 73: 501-502
Kolander TM, Bienapfl JE, Kurle JE, Malvick DK (2012) Symptomatic and asymptomatic host range of Fusarium virguliforme, the causal agent of soybean sudden death syndrome. Plant Disease 96: 1148-1153
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