''Fusarium culmorum'' is a fungal

plant pathogen Plant diseases are diseases in plants caused by pathogens (infectious organisms) and environmental conditions (physiological factors). Organisms that cause infectious disease include fungi, oomycetes, bacteria, viruses, viroids, virus-like orga ...

and the causal agent of seedling blight, foot rot, ear blight, stalk rot, common root rot and other diseases of

cereals A cereal is a grass cultivated for its edible grain. Cereals are the world's largest crops, and are therefore staple foods. They include rice, wheat, rye, oats, barley, millet, and maize (Corn). Edible grains from other plant families, suc ...

, grasses, and a wide variety of monocots and dicots. In coastal dunegrass ('' Leymus mollis''), ''F. culmorum'' is a nonpathogenic symbiont conferring both salt and drought tolerance to the plant.

Identification

Colonies grow rapidly on potato dextrose agar. The aerial

mycelium Mycelium (: mycelia) is a root-like structure of a fungus consisting of a mass of branching, thread-like hyphae. Its normal form is that of branched, slender, entangled, anastomosing, hyaline threads. Fungal colonies composed of mycelium are fo ...

is whitish to yellow, tan or pale orange, but becomes brown to dark brown to red-brown with age. Under alternating conditions of light and temperature, rings of spore masses may be formed by some isolates.

Macroconidia

Microconidia are absent, but macroconidia are usually abundant. The sporodochia are orange to brown color and relatively common. The

macroconidia A conidium ( ; : conidia), sometimes termed an asexual chlamydospore or chlamydoconidium (: chlamydoconidia), is an Asexual reproduction, asexual, non-motility, motile spore of a fungus. The word ''conidium'' comes from the Ancient Greek word f ...

are thick and bluntly pointed at their apex, and conspicuously wider above the center of the spore. The dorsal side is somewhat curved, but the ventral side is almost straight. The distinguishing characteristic from '' Gibberella pulicaris'' (''Fusarium sambucinum'') is the broader macroconidia. Their size ranges from 4 to 7 μm wide and from 25 to 50 μm long; the septae are usually three or five in number. They develop singly from phialides (5 x 15–20 μm). They are loose at first and are later aligned in sporodochia.

Chlamydospores

Chlamydospores are usually abundant and form relatively quickly, requiring 3–5 weeks on carnation leaf agar. They are found in both

hypha A hypha (; ) is a long, branching, filamentous structure of a fungus, oomycete, or actinobacterium. In most fungi, hyphae are the main mode of vegetative growth, and are collectively called a mycelium. Structure A hypha consists of one o ...

e and macroconidia. Those found in the macroconidia persist longer than those found in the hyphae under field conditions. They are thick-walled and globose in shape, found singly, in clumps or chains. Their size ranges from 9–14 μm in diameter.

Disease cycle

''Fusarium culmorum'' causes seedling blight, ''Fusarium'' head blight (FHB) as well as foot and root rot (FRR), and is considered one of the most serious pathogens of

wheat Wheat is a group of wild and crop domestication, domesticated Poaceae, grasses of the genus ''Triticum'' (). They are Agriculture, cultivated for their cereal grains, which are staple foods around the world. Well-known Taxonomy of wheat, whe ...

and other small grain cereals besides ''

Gibberella zeae ''Gibberella zeae'', also known by the name of its anamorph ''Fusarium graminearum'', is a fungus, fungal plant pathogen which causes fusarium head blight (FHB), a devastating disease on wheat and barley. The pathogen is responsible for billions ...

'' (''Fusarium graminearum''). Different from ''F. graminearum,'' the teleomorph of ''F. culmorum'' is not known, which means the

ascospore In fungi, an ascospore is the sexual spore formed inside an ascus—the sac-like cell that defines the division Ascomycota, the largest and most diverse Division (botany), division of fungi. After two parental cell nucleus, nuclei fuse, the ascu ...

s are not produced. Instead, it reproduces asexually by developing conidia, which is also the main mode of dispersal.Scherm B, Balmas V, Spanu F, Pani G, Delogu G, Pasquali M, Migheli Q (2013), ''Fusarium culmorum'': causal agent of foot and root rot and head blight on wheat. ''Mol Plant Pathol.'',14(4):323-41. Chlamydospores can survive in host debris during winter, whereas the microconidia are usually not produced in natural conditions.Wagacha J.M. & Muthomi J.W. (2007), ''Fusarium culmorum'': Infection process, mechanisms of mycotoxin production and their role in pathogenesis in wheat. ''Crop Protection'' 26 (2007) 877–885 As a soil-borne fungus, ''F. culmorum'' could survive on or within the infected seeds and result in pre- or post-emergence seedling death. However, seedborne inoculum has not been confirmed to contribute to the FHB. When causing FHB, macroconidia in soil and crop residues are dispersed by wind, rain splash or transmitted by insects to reach the host. The ear of wheat is most susceptible to ''F. culmorum'' conidia during ''anthesis'' and FHB can last from anthesis to grain

harvest Harvesting is the process of collecting plants, animals, or fish (as well as fungi) as food, especially the process of gathering mature crops, and "the harvest" also refers to the collected crops. Reaping is the cutting of grain or pulses fo ...

. Systematic infection has been reported, and the infection of wheat head leads to kernel contamination with

mycotoxin A mycotoxin (from the Greek μύκης , "fungus" and τοξικός , "poisonous") is a toxic secondary metabolite produced by fungi and is capable of causing disease and death in both humans and other animals. The term 'mycotoxin' is usually rese ...

s. Chlamydospores can also infect

coleoptile Coleoptile is the pointed protective sheath covering the emerging shoot in monocotyledons such as grasses in which few leaf primordia and shoot apex of monocot embryo remain enclosed. The coleoptile protects the first leaf as well as the growing ...

s as well as primary and secondary roots, causing FRR during the crop growing period, which is a monocyclic disease .

Hosts

Wheat, barley, among others.

Environment

Fusarium head blight (FHB)

A warm and moist environment is preferred by ''F. culmorum'' in order to cause FHB. Frequent rains between anthesis and kernel filling stages facilitate the occurrence of FHB. The level of pathogen presenting in the soil also increases the risk of this disease. Temperature and moisture in the microclimate play an important role once the inoculum reaches the ear of crops. The optimum temperature is . Long moist periods and temperatures above is needed for the infection. Germination of macroconidia is limited to a minimum humidity of 0.86 aw (water activity).

Foot and root rot (FRR)

The development of FRR can be affected by several factors, such as residue management, previous crop, plant density, nitrogen fertilization and environmental conditions. Wheat

monoculture In agriculture, monoculture is the practice of growing one crop species in a field at a time. Monocultures increase ease and efficiency in planting, managing, and harvesting crops short-term, often with the help of machinery. However, monocultur ...

and rotation with other

cereal A cereal is a grass cultivated for its edible grain. Cereals are the world's largest crops, and are therefore staple foods. They include rice, wheat, rye, oats, barley, millet, and maize ( Corn). Edible grains from other plant families, ...

crops contribute to maintaining the survival of inoculum in the soil and thereby increases the FRR severity. High planting density and nitrogen fertilization level are shown to boost the likelihood of FRR occurrence. Warm and droughty conditions that may trigger water stress also increase the pathogen sensitivity and make the FRR severe.

Management

The inoculum can be controlled by applying cultural practices,

fungicide Fungicides are pesticides used to kill parasitic fungi or their spores. Fungi can cause serious damage in agriculture, resulting in losses of yield and quality. Fungicides are used both in agriculture and to fight fungal infections in animals, ...

, resistant cultivars and biological control agents. From the cultural practices aspect, plowing is better than

minimum In mathematical analysis, the maximum and minimum of a function are, respectively, the greatest and least value taken by the function. Known generically as extremum, they may be defined either within a given range (the ''local'' or ''relative ...

or no tillage in ''F. culmorum'' management.

Crop rotation Crop rotation is the practice of growing a series of different types of crops in the same area across a sequence of growing seasons. This practice reduces the reliance of crops on one set of nutrients, pest and weed pressure, along with the pro ...

with noncereal host could also decrease the occurrence of the disease.Kurowski, T.P., Majchrzak, B., Jankowski, K. and Jaz’win’ska, E. (2011) Influence of Brassicacea as a previous crop on intensity of winter wheat root and foot rot. ''Progr. Plant Protect''. 51, 1319–1322. Since ''F. culmorum'' causes pre- or post-emergence

damping off Damping off (or damping-off) is a horticultural disease or condition, caused by several different pathogens that kill or weaken seeds or seedlings before or after they germinate. It is most prevalent in wet and cool conditions. Symptoms There ar ...

by colonizing seeds, sowing healthy seeds with a fungicide coat is one of the most efficient approaches of management; however, which is usually limited to the early states of the crop's growth since the

s can not maintain long periods of sufficient protection. Fungicides mainly belonging to the strobilurin and

azole Azoles are a class of five-membered heterocyclic compounds containing a nitrogen atom and at least one other non-carbon atom (i.e. nitrogen, sulfur, or oxygen) as part of the ring. Their names originate from the Hantzsch–Widman nomenclature. Th ...

classes are reported to reduce the disease by up to 70% in the field. The ideal strategy to control the disease is the adoption of resistant cultivars, however, wheat that is highly resistant to ''F. culmorum'' has not yet been found. Additionally, the integration of biological management methods can be effective. Developing biological control agents and applying natural antagonist microbes of ''F. culmorum'' onto the host plant or crop residues by seed dressing or spray decreases the severity of FHB or FRR.

Hosts

See: * List of asparagus diseases * List of carrot diseases * List of barley diseases * List of maize diseases * List of oat diseases * List of potato diseases * List of rye diseases * List of wheat diseases

References

External links

FusKey - Fusarium Interactive Key
{{Authority control Fungi described in 1884 Fungal plant pathogens and diseases Cereal diseases Vegetable diseases culmorum Fungus species