Introduction: The genus Fusarium comprises a wide and heterogeneous group of fungi important for the food and drug industry, medicine and agriculture. Fusarium solani (Mart.) Sacc. (teleomorph = Nectria haematococca (Berk. & Br.) is a phytopathogenic fungus and is an important causal agent of several crop diseases, such as root and fruit rot of Cucurbita spp., root and stem rot of pea, sudden death syndrome of soybean, foot rot of bean and dry rot of potato.

The morphological species Fusarium solani (Mart.) Sacc. was first described by C.F.P. Von Martius in 1842 as Fusisporium solani from rotted tubers of potato, Solanum tuberosum.  The species was transferred to the genus Fusarium by the Italian mycologist Piers A. Saccardo in 1881.  F. solani was emended by Snyder and Hansen in 1941 to comprise a complex group of species that are widely distributed in soils and cause tuber, root, and stem rots of plants worldwide.  There are at least 50 subspecies lineages (Desjardins, A.E., 2006).

The taxonomic rank of Fusarium solani is as follows: 

                                      Source:  Bugwood.org

Host range and distribution:  The predominant hosts for Fusarium solani are potato, pea, bean, and members of the cucurbit family such as melon, cucumber, and pumpkin.  Some strains may cause infections in humans.

Fusarium virguliforme sp. nov., formally known as F. solani f. sp. glycines, causes sudden death syndrome (SDS) in soybean.  The name "sudden death" refers to the early defoliation and death of the soybean plant (Koenning, S., 2001). SDS has become a serious problem in the commercial production of soybeans in North and South America since the early 1990’s (Aoki, T., et al, 2003).

Fusarium solani [Mart.] Sacc. f. sp. phaseoli [Burk.] W.C. Snyder & H.M. Hans. causes Fusarium root rot in common beans such as snap and dry bean.

Isolation: 

Identification: 

On potato dextrose agar medium, F. solani produces sparse to abundant, white cream mycelium.  Macroconidia have three to four septa on average, are slightly curved, are rather wide and thick walled, and may have a slightly blunted apical end.  Microconidia are abundant, oval to kidney shaped, and formed in false heads on very long monophialides.  Chlamydospores are abundant.

Colonies are fast growing, variable in color and texture, often granular or fluffy, rose-red, purple, or lavender, but may start out as white, cottony colonies that darken with maturity.

Symptoms: 

(Source:  B. Román-Avilés, S.S. Snapp and J.D. Kelly, Dept. of Crop and Soil Sciences, and W.W. Kirk, Dept. of Plant Pathology Michigan State University.)

The first symptoms of root rot in beans are narrow, long, red to brown lesions on the stems, and lengthwise cracks often develop.  Lesions extend down the main taproot, which may shrivel, decay and die. The symptoms in some cases extend up the hypocotyl to the soil surface. Clusters of fibrous roots (lateral roots or adventitious roots) commonly develop above the shriveled taproot. Severe Fusarium root rot kills primary and secondary roots of beans, and most times only adventitious roots are visible. Note the typical redbrown symptoms of Fusarium root rot on the taproot.

Ecology and life cycle: 

Fusarium solani produces asexual spores (microconidia and macroconidia).  Its sexual state is Nectria haematococca (Ascomycete).  It produces chlamydospores and overwinters as mycelium or spores in infected or dead tissues or seed.  It can be spread by air, equipment, and water.

The fungus can persist in the soil for several years. The spores and the mycelium are carried into the soil on tools and in bean straw manure. They may also be splashed by rain or carried by floods.  The chlamydospore is the survival structure in the absence of a host plant. 

Control

Beans

The best prevention strategy is to plant beans after soils have warmed up (55ºF) at a depth of 1/2 inch in a coarse, well-drained soil that has been optimally fertilized. A well-prepared seedbed promotes rapid seedling growth and minimizes root rot.  Soil compaction should be minimized, and hard pans should be broken up if they exist. The bean refuse should always be hauled where beans probably will not be grown for 6 or more years. It is not known how long the root rot fungus can live in the soil; but where a 6-year or longer rotation is practiced, the disease is held in check sufficiently to grow a profitable crop. Where the usual 3-year rotation is practiced, root rot increases until finally bean growing in those fields becomes impossible.

Squash and Pumpkin

Fusarium crown and foot rot occurs sporadically in most areas, and disease severity depends on soil moisture and inoculum density. Because the fungus survives in the soil for only two to three years, a four-year rotation is usually adequate for disease control. Planting fungicide-treated seed also reduces disease initiated from infected seed.

Potato

Most techniques for managing dry rot are aimed at preventing injury to the tubers, either seed or the harvested crop. Preventing bruises will greatly aid in avoiding infection.

Links to other sites: 

Aoki, T., O’Donnell, K., Homma, Y., Lattanzi, A.  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 America and F. tucumaniae in South America.  Mycologia, 95(4): 660–684.

Cho, J. H., Rupe, J. C., Cummings, M. S., and Gbur, E. E., Jr. 2001. Isolation and identification

of Fusarium solani f. sp. glycines from soil on modified Nash and Snyder’s medium. Plant Dis.

85:256-260.

Desjardins, Anne E.  2006.  Fusarium mycotoxins : chemistry, genetics and biology.  The American Phytopathological Society.  St. Paul, Minnesota.  APS Press.  PP 184-185.

Koenning, Stephen.  2001.  Soybean Sudden Death Syndrome, Soybean Disease Information Note 7.  Plant Pathology Extension, North Carolina State University, Raleigh, NC. 

Zaccardelli, M., Vitale, S., Luongo, L., Merighi, M.,  Corazza, L.  2008.  Morphological and Molecular Characterization of Fusarium solani Isolates J. Phytopathology: 156, 534–541.

Vincent W. Cochrane and Jean Conn Cochrane. 1971.  Chlamydospore induction in pure culture in Fusarium solani.  Mycologia: 63, 462-477.