''Fusarium'' dry rot is one of the most common

potato The potato is a starchy food, a tuber of the plant ''Solanum tuberosum'' and is a root vegetable native to the Americas. The plant is a perennial in the nightshade family Solanaceae. Wild potato species can be found from the southern Unit ...

diseases. It is caused by fungi in the genus ''

Fusarium ''Fusarium'' is a large genus of filamentous fungi, part of a group often referred to as hyphomycetes, widely distributed in soil and associated with plants. Most species are harmless saprobes, and are relatively abundant members of the soil mi ...

''. This fungi causes a variety of colored rots in potatoes. This pathogen, while having both a sexual and asexual form, stays in an asexual cycle due to the way it spreads. Preferring warmer climates, it is not uncommon to find this pathogen in the northern United States where it has been reported to affect yield as much as 60%.

Hosts and symptoms

''Fusarium'' dry rot of potato is a devastating

post-harvest losses (vegetables) Post-harvest losses of vegetables and fruit occur at all points in the value chain from production in the field to the food being placed on a plate for consumption. Post-harvest activities include harvesting, handling, storage, processing, packag ...

disease affecting both seed potatoes and potatoes for human consumption.Rowe, R.C., Miller, S.A, & Riedel R.M. ''Fusarium'' Dry Rot and Seed Piece Decay of Potato. Retrieved from http://www.oardc.ohio-state.edu/sallymiller/extension/factsheets/fuspotato.pdf Dry rot causes the skin of the tuber to wrinkle. The rotted areas of the potato may be brown, grey, or black and the rot creates depressions in the surface of the tuber. Seed pieces may rot completely before they have the chance to be planted. The genus that causes dry rot of potato, ''Fusarium'', is a fungus. Signs of ''Fusarium'' can be seen on an infected potato, and include white or pink

mycelia Mycelium (plural mycelia) is a root-like structure of a fungus consisting of a mass of branching, thread-like hyphae. Fungal colonies composed of mycelium are found in and on soil and many other substrates. A typical single spore germinates in ...

(masses of vegetative fungal tissue) and very colorful spores that can be blue, black, purple, grey, white, yellow, or pink.

Disease cycle

The most prevalent ''Fusarium'' species is ''

Fusarium sambucinum ''Gibberella pulicaris'' is a fungus, fungal plant pathogen infecting several hosts including List of potato diseases, potato, List of strawberry diseases, strawberry, List of hop diseases, hop, List of alfalfa diseases, alfalfa and List of Dougl ...

''. There are thirteen known dry rotting species of ''Fusarium'' but ''Fusarium sambucinum'' causes the most problems in the United States. ''Fusarium'' species are asexual but some do have a sexual stage. The sexual stage for ''Fusarium sambucinum'' is known as ''

Gibberella pulicaris ''Gibberella pulicaris'' is a fungal plant pathogen infecting several hosts including potato, strawberry, hop, alfalfa and Douglas-fir The Douglas fir (''Pseudotsuga menziesii'') is an evergreen conifer species in the pine family, Pinacea ...

'' but little is known about it other than it is an

ascomycete Ascomycota is a phylum of the kingdom Fungi that, together with the Basidiomycota, forms the subkingdom Dikarya. Its members are commonly known as the sac fungi or ascomycetes. It is the largest phylum of Fungi, with over 64,000 species. The defi ...

. Potatoes are not your typical vegetation. Each tuber is capable of producing a brand new plant from various eye spots. This allows farmers to culture an identical plant from each tuber and in turn cuts costs as each tuber can sprout a dozen new plants. And dozens of new sources of

dry rot Dry rot is wood decay caused by one of several species of fungi that digest parts of the wood which give the wood strength and stiffness. It was previously used to describe any decay of cured wood in ships and buildings by a fungus which resul ...

. Tubers are stored over winter and in the spring, they are cut up so that each piece yields a new plant. ''Fusarium'' takes advantage of this overwintering and spring cutting. The pathogen is unable to enter the tuber until it is either wounded through harvest, storage, or cutting Loria, Rosemary. "Vegetable Crops: ''Fusarium'' Dry Rot of Potato." Vegetable MD Online. Department of Plant Pathology, Cornell University, Aug. 1993. Web. 22 Oct. 2013. https://www.vegetablemdonline.ppath.cornell.edu/factsheets/Potato_Fusarium.htm and thus if there is any inoculum present in the soil, it has to wait until harvest occurs to infect the tuber. Once in, the fungus, along with other opportunistic pathogens like soft rot, begin to decompose the tubers and are able to kill off the plant before it emerges.Warton, Phillip, Ray Hammerschmidt, and William Kirk. "Potato Diseases: ''Fusarium ''Dry Rot." Potato Diseases. Michigan State University, May 2007. Web. 22 Oct. 2013. http://www.potatodiseases.org/dryrot.html Depending on the time of year, this pathogen moves and infects in different manners. As ''Fusarium'' is a soil borne pathogen,

International Potato Center The International Potato Center (known as CIP from its Spanish language, Spanish-language name ''Centro Internacional de la Papa'') is a research facility based in Lima, Peru, that seeks to reduce poverty and achieve food security on a sustaine ...

(CIP). Major Potato Diseases, Insects, and Nematodes. CIP, Sept. 1996. Web. 22 Oct. 2013. http://cipotato.org/publications/pdf/002408.pdf if there is sufficient wounding to the tubers, it may infiltrate that way. Because of the way this ''Fusarium'' species spreads, it does not need to produce any above ground fruiting bodies. It is only necessary to form

microconidia A conidium ( ; ), sometimes termed an asexual chlamydospore or chlamydoconidium (), is an asexual, non-motile spore of a fungus. The word ''conidium'' comes from the Ancient Greek word for dust, ('). They are also called mitospores due to th ...

late in the season or remain in the tubers to infect in the following season. The general cycle is as follows: # Overwinters in/on infected and healthy tubers in warehouse. # During the spring, tubers are cut to create seeds for planting. This allows for increased spread. # "Seeds" are then put in storage before planting and disease continues to spread. # During later spring when the crop is planted, less than 50% of planted seed sprouts due to rot. # As the season progresses, rotted seed and sprouts leave behind sparse fields of smaller, weaker potatoes # Potatoes that were not infected can still cause a problem as ''Fusarium'' can produce

and rest in the soil and on tubers. # During late summer harvest, damage is caused to the newly grown tubers allowing for ''Fusarium'' to infect. #In the fall, tubers are put into storage with ideal growing conditions for ''Fusarium'' to spread and allow for opportunistic species to infect.

Environment

Warmer climates are preferred. However; different species of ''Fusarium'' may be more prevalent in different areas. Michigan is currently having trouble with ''Fusarium sambucinum''. ''Fusarium sambucinum'' can be found in Ohio, Michigan, Wisconsin, North Dakota, and Montana. ''Fusarium'' requires higher moisture to grow and is not able to when conditions are only periodic. Temperatures preferred for growth and spread are above 50F. There are currently no listed vectors known to carry and transmit ''Fusarium sambucinum''. However, humans are very good at transmitting the pathogen through the creation of cull piles, agricultural equipment, or warehouse storage where temperatures and moisture are ideal for growth.

Management

There are many ways to manage

. Application of

thiabendazole Tiabendazole (INN, BAN), also known as thiabendazole (AAN, USAN) or TBZ and the trade names Mintezol, Tresaderm, and Arbotect, is a preservative, an antifungal agent, and an antiparasitic agent. Uses Preservative Tiabendazole is used primar ...

, also known as Mertect, was a common and efficacious method used from 1970-1985. Eventually, however, the pathogen developed resistance to the chemical treatment, and while some people still use

, it is no longer an effective treatment. Effective chemical control of dry rot can be achieved with chemicals like Tops MZ, Maxim MZ, and Moncoat MZ. These chemicals protect not only against dry rot, but also against other potato diseases like

rhizoctonia ''Rhizoctonia'' is a genus of fungi in the order Cantharellales. Species form thin, effused, corticioid basidiocarps (fruit bodies), but are most frequently found in their sterile, anamorphic state. ''Rhizoctonia'' species are saprotrophic, but ...

silver scurf ''Silver scurf'' is a plant disease that is caused by the plant pathogen ''Helminthosporium solani.'' Silver scurf is a blemish disease, meaning the effect it has on tubers is mostly cosmetic and affects "fresh market, processing and seed tuber ...

, and black dot. These chemical treatments can delay emergence of the young plants, but this doesn't mean these chemicals shouldn't be used. Many fungicides, including

, work best when they are applied to tubers before they are cut into seed pieces.Schwartz, Howard F., and David H. Gent. "''Fusarium'' Dry Rot." Major Potato Diseases, Insects, and Nematodes. N.p., 29 Mar. 2005. Web. http://wiki.bugwood.org/uploads/FusariumDryRot-Potato.pdf. Cultural practices can also limit the spread of

. Farmers are advised to only use certified, disease-free seed, and to inspect seed pieces personally to ensure that they are symptom-free. Seed should be stored at 40-42 degrees Fahrenheit, but gently warmed to 50 degrees prior to cutting. The cooler temperatures antagonize growth of ''Fusarium'', and the warmer temperature encourages potato tubers to heal any post-harvest wounds, minimizing the chance that ''Fusarium'' will get inside the tuber. Sanitation is very important in controlling

. Storage facilities and cutting equipment should be disinfected frequently. The blades used for cutting should be sharp to ensure clean cuts. Farmers also should not keep “cull piles” of potato tubers. . Before planting, cut seed pieces should be treated with fungicide, such as Tops MZ, Moncoat MZ, or Maxim MZ. The seed pieces should be planted in warm, well-drained soil within 24 hours of cutting; this environment is conducive to sprout growth and emergence. The seed pieces should be shielded from wind and sunlight before they are planted, to prevent dehydration. Tubers shouldn’t be harvested until their skins have set and their internal temperature is greater than 50 degrees Fahrenheit. These measures minimize the risk of harvest injury, which could give the ''Fusarium'' pathogen entrance into the tuber. Biological control of

is an intriguing concept, but currently nothing is available commercially. Researchers at Michigan State University are investigating the efficacy of ''

Bacillus subtilis ''Bacillus subtilis'', known also as the hay bacillus or grass bacillus, is a Gram-positive, catalase-positive bacterium, found in soil and the gastrointestinal tract of ruminants, humans and marine sponges. As a member of the genus ''Bacillu ...

'' and '' Bacillus pumilis'' (both

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...

) and ''

Trichoderma harzianum ''Trichoderma harzianum'' is a fungus that is also used as a fungicide. It is used for foliar application, seed treatment and soil treatment for suppression of fungal pathogens causing various fungal plant diseases. Commercial biotechnological p ...

'' (a fungus) in controlling ''Fusarium'' dry rot. Scientists in Tunisia have found that several bacterial species of the genus ''

Bacillus ''Bacillus'' (Latin "stick") is a genus of Gram-positive, rod-shaped bacteria, a member of the phylum ''Bacillota'', with 266 named species. The term is also used to describe the shape (rod) of other so-shaped bacteria; and the plural ''Bacilli ...

'', commonly found in the salty soils of

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, can reduce the amount of rot seen due to ''Fusarium sambucinum''. ''

Bacillus thuringiensis ''Bacillus thuringiensis'' (or Bt) is a gram-positive, soil-dwelling bacterium, the most commonly used biological pesticide worldwide. ''B. thuringiensis'' also occurs naturally in the gut of caterpillars of various types of moths and butterflie ...

'' can help control dry rot when applied to older cultures.Sadfi, N, M Cherif, I Fliss, A Boudabbous, and H Antoun. Evaluation of Bacterial Isolates From Salty Soils and ''Bacillus thuringiensis'' Strains for the Biocontrol of ''Fusarium'' Dry Rot of Potato Tubers. Journal of Plant Pathology 83.2 (2001): 101-18. Google Scholar. Web. 3 Dec. 2013. http://sipav.org/main/jpp/volumes/0201/020104.pdf

Importance

Dry rot Dry rot is wood decay caused by one of several species of fungi that digest parts of the wood which give the wood strength and stiffness. It was previously used to describe any decay of cured wood in ships and buildings by a fungus which resul ...

is not just a cosmetic problem like many other pathogens. It destroys tubers and leaves them completely inedible or unusable as seed in the future. Long-term storage losses have been reported to be as high as 60% while annual

losses can range from 6 to 25%.Gachango, E, L E. Hanson, A Rojas, J J. Hao, and W W. Kirk. "Fusarium spp. Causing Dry Rot of Seed Potato Tubers in Michigan and Their Sensitivity to Fungicides." Plant Disease 96.12 (2012): 1767-74. Print. In Michigan, over 50% of seed lots have reported having variable levels of dry rot.

References

{{reflist, 2 Potato diseases