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Fusarium solani

Sarah Luginbuhl

A class project for PP728 Soilborne Plant Pathogens, Fall 2010

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: 

Kingdom

Fungi

Phylum

Ascomycota

Subphylum

Pezizomycotina

Class

Sordariomycetes

Subclass

Hypocreomycetidae

Order

Hypocreales

Family

Nectriaceae

Genus

Fusarium

                                      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 damping-off, corn rot, fruit rot, root rot, and surface rot are caused by Fusarium solani (Mart.) Sacc.and are found in most states in the United States (http://www.bugwood.org/fungi.html).

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: 

fusarium_in_culturesmall2.jpg

Figure:  Colonies of A, Fusarium virguliforme, B, Paecilomyces sp., C, F. solani, D, Pythium sp., and E, F. merismodes on modified Nash and Snyder’s medium.

(Figure from Cho, J. H., et al, 2001).

To isolate the pathogen from the soil, samples are mixed with deionized water and shaken.  A series of dilutions are then made, and then 1 ml aliquot from each dilution is spread over modified Nash & Snyder’s medium (MNSM) in petri dishes (Cho, J.H., et al, 2001). Plates can be incubated at room temperature and light.  After 7 days, colonies that are thought to be F. solani can be transferred to potato dextrose agar (PDA).

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.

mycelium.jpg

This image shows the white, fungal mycelium on a gourd (Cucurbita spp. L), after incubation, that was infected with Fusarium fruit rot by the fungus Fusarium solani.

Source:  Paul Bachi, University of Kentucky Research and Education Center, Bugwood.org

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: 

Bean root rot(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.

 

fusarium_cucurbit_speciessmall.bmp

Photo courtesy of T.A. Zitter, Cornell University, Ithaca, NY

Fusarium crown and foot rot of squash and pumpkin is caused by Fusarium solani f. sp. cucurbitae.  The first symptom is wilting of the leaves. Within several days, the entire plant may wilt and die. If the soil is removed from around the base of the plant, a very distinct necrotic rot of the crown and upper portion of the taproot can be seen. The rot develops first as a light-colored, water-soaked area which becomes progressively darker. It begins in the cortex of the root, causes cortex tissue to slough off, and eventually destroys all of the tissue except the fibrous vascular strands. Infected plants break off easily about 2-4 cm below the soil line. The fungus generally is limited to the crown area of the plant.

PotatoFusariumCollsmall.jpg

Rosemary Loria, Department of Plant Pathology, Cornell University

Fusarium dry rot is characterized by an internal light to dark brown or black rot of the potato tuber-and it is usually dry. The rot may develop at an injury such as a bruise or cut. The pathogen penetrates the tuber, often rotting out the center. Extensive rotting causes the tissue to shrink and collapse, usually leaving a dark sunken area on the outside of the tuber and internal cavities. Yellow, white, or pink mold may be present.

Ecology and life cycle: 

life_cyclesmall.bmp

Source: HGCA.com

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.

Asexual spore.jpg

This image shows the asexual spores of Fusarium solani that have infected a gourd (Cucurbita spp. L.), causing Fusarium fruit rot. 

Source:  Paul Bachi, University of Kentucky Research and Education Center, Bugwood.org

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: 

Selected References: 

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.