plant pathogen
Plant pathology (also phytopathology) is the scientific study of diseases in plants caused by pathogens (infectious organisms) and environmental conditions (physiological factors). Organisms that cause infectious disease include fungi, oomyc ...
and the causal agent of seedling blight, foot rot, ear blight, stalk rot, common root rot and other diseases of
cereals
A cereal is any grass cultivated for the edible components of its grain (botanically, a type of fruit called a caryopsis), composed of the endosperm, germ, and bran. Cereal grain crops are grown in greater quantities and provide more food en ...
, grasses, and a wide variety of monocots and dicots. In coastal dunegrass (''
Leymus mollis
''Leymus mollis'' is a species of grass known by the common names American dune grass, American dune wild-rye, sea lyme-grass, strand-wheat,Higman, P. J. and M. R. Penskar. 1999Special plant abstract for ''Leymus mollis'' (American dune wild-rye) ...
''), ''F. culmorum'' is a nonpathogenic symbiont conferring both salt and drought tolerance to the plant.
mycelium
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 substrate (biology), substrates. A typical single ...
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
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 ...
are absent, but macroconidia are usually abundant. The sporodochia are orange to brown color and relatively common.
The
macroconidia
A conidium ( ; ), sometimes termed an asexual chlamydospore or chlamydoconidium (), is an Asexual reproduction, asexual, non-motility, motile spore of a fungus. The word ''conidium'' comes from the Ancient Greek word for dust, ('). They are al ...
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
''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 ...
'' (''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
phialide
The phialide ( ; el, phialis, diminutive of phiale, a broad, flat vessel) is a flask-shaped projection from the vesicle (dilated part of the top of conidiophore) of certain fungi. It projects from the mycelium without increasing in length unless ...
s (5 x 15–20 μm). They are loose at first and are later aligned in sporodochia.
Chlamydospores
Chlamydospore
A chlamydospore is the thick-walled large resting spore of several kinds of fungi, including Ascomycota such as '' Candida'', Basidiomycota such as ''Panus'', and various Mortierellales species. It is the life-stage which survives in unfavourable c ...
s 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 or ...
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 grass widely cultivated for its seed, a cereal grain that is a worldwide staple food. The many species of wheat together make up the genus ''Triticum'' ; the most widely grown is common wheat (''T. aestivum''). The archaeologi ...
and other small grain cereals besides '' Gibberella zeae'' (''Fusarium graminearum''). Different from ''F. graminearum,'' the
teleomorph
In mycology, the terms teleomorph, anamorph, and holomorph apply to portions of the life cycles of fungi in the phyla Ascomycota and Basidiomycota:
*Teleomorph: the sexual reproductive stage (morph), typically a fruiting body.
*Anamorph: an ase ...
of ''F. culmorum'' is not known, which means the
ascospore
An ascus (; ) is the sexual spore-bearing cell produced in ascomycete fungi. Each ascus usually contains eight ascospores (or octad), produced by meiosis followed, in most species, by a mitotic cell division. However, asci in some genera or ...
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. doi: 10.1111/mpp.12011. 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 gathering a ripe crop from the fields. Reaping is the cutting of grain or pulse for harvest, typically using a scythe, sickle, or reaper. On smaller farms with minimal mechanization, harvesting is the most labor-i ...
. 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 τοξίνη , "toxin") is a toxic secondary metabolite produced by organisms of kingdom Fungi and is capable of causing disease and death in both humans and other animals. The term 'mycotoxin' ...
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. Monoculture is widely used in intensive farming and in organic farming: both a 1,000-hectare/acre cornfield and a 10-ha/acre field of organic kale are ...
and rotation with other
cereal
A cereal is any Poaceae, grass cultivated for the edible components of its grain (botanically, a type of fruit called a caryopsis), composed of the endosperm, Cereal germ, germ, and bran. Cereal Grain, grain crops are grown in greater quantit ...
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 biocidal chemical compounds or biological organisms used to kill parasitic fungi or their spores. A fungistatic inhibits their growth. Fungi can cause serious damage in agriculture, resulting in critical losses of yield, quality, ...
,
resistant cultivar
Plant disease resistance protects plants from pathogens in two ways: by pre-formed structures and chemicals, and by infection-induced responses of the immune system. Relative to a susceptible plant, disease resistance is the reduction of pathoge ...
plowing
A plough or plow (Differences between American and British spellings, US; both ) is a farm tool for loosening or turning the soil before sowing seed or planting. Ploughs were traditionally drawn by oxen and horses, but in modern farms are draw ...
is better than
minimum
In mathematical analysis, the maxima and minima (the respective plurals of maximum and minimum) of a function, known collectively as extrema (the plural of extremum), are the largest and smallest value of the function, either within a given ran ...
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. It reduces reliance on one set of nutrients, pest and weed pressure, and the probability of developing resistant ...
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
fungicide
Fungicides are biocidal chemical compounds or biological organisms used to kill parasitic fungi or their spores. A fungistatic inhibits their growth. Fungi can cause serious damage in agriculture, resulting in critical losses of yield, quality, ...
s can not maintain long periods of sufficient protection. Fungicides mainly belonging to the
strobilurin Strobilurins are a group of natural products and their synthetic analogs. A number of strobilurins are used in agriculture as fungicides. They are part of the larger group of QIs (Quinone outside Inhibitors), which act to inhibit the respiratory c ...
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. T ...
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
This article is a list of diseases of asparagus (''Asparagus officinalis'').
Fungal diseases
Viral and viroid diseases
Miscellaneous diseases and disorders
References
{{reflist
Common Names of Diseases, The American Phytopathological So ...
*
List of carrot diseases
This is a list of diseases of carrots (''Daucus carota'' subsp. ''sativus'').
Bacterial diseases
Fungal diseases
Nematodes, parasitic
, Cyst nematode
, ,
''Heterodera carotae''
, -
, Lance nematode
, ,
'' Hoplolaimus uniformis''
, -
...
List of wheat diseases
This article is a list of diseases of wheat (''Triticum'' spp.) grouped by causative agent.
Bacterial diseases
Fungal diseases
Viral diseases
Phytoplasmal diseases
Nematodes, parasitic
References
Common Names of Diseases, The Amer ...