Take-all | |
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Wheat plants displaying symptoms of take-all root disease. | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Fungi |
Division: | Ascomycota |
Class: | Sordariomycetes |
Order: | Magnaporthales |
Family: | Magnaporthaceae |
Genus: | Gaeumannomyces |
Species: | |
Trinomial name | |
Gaeumannomyces tritici subsp. Hernández-Restrepo et al (2016) | |
Synonyms | |
Ophiobolus graminis var tritici, Gaeumannomyces graminis var "tritici" Contents |
Take all | |
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Causal agents | Gaeumannomyces tritici |
Hosts | wheat and barley |
Take-all is a plant disease affecting the roots of grass and cereal plants in temperate climates caused by the fungus Gaeumannomyces tritici (previously known as Gaeumannomyces graminis var. tritici). [1] All varieties of wheat and barley are susceptible. It is an important disease in winter wheat in Western Europe particularly, and is favoured by conditions of intensive production and monoculture.
The pathogen survives in the soil on infected cereal and grass residues. The fungus infects the root tissue of young plants and can spread from plant to plant in the form of hyphae growing through the soil which is why the disease is often seen in patches. The fungus blocks the conductive tissue of the plants and reduces water uptake. Early symptoms of the disease include yellowing and stunting, tillering is reduced and plants mature prematurely and often exhibit bleached seed heads. The affected roots are blackened and the plants are easy to pull from the soil. [2] These symptoms give rise to an alternative name for the disease, "whiteheads". Yield loss levels of 40 to 50% are often recorded in severe attacks.
Although disease levels are normally low in the first wheat crop in a rotation, the fungal inoculum builds up in the soil nearby wheat roots, which is known as take-all inoculum build-up (TAB). In the ensuing 2–4 years disease levels increase, which may be followed by take-all decline (TAD).
Chemical control measures have traditionally had little success, although a modern seed treatment shows promise. Crop nutrition imbalances exacerbate the disease, as does excessive liming. Modern varieties are stiff and short-strawed which allows relatively high spring nitrogen applications without serious lodging. This can limit damage from the disease.
The most appropriate control measure is the use of a clean one-year break crop of a non-cereal crop. This reduces the fungus to an acceptably low soil contamination level in about 10 months although stray volunteer grasses may reduce any beneficial effects.
Experiments performed on the famous "Broadbalk" field at Rothamsted Research where continuous monoculture winter wheat is grown, show that take-all build-up (TAB) occurs in successive crops to reach a peak in the 3rd to 5th cropping year, after which the disease declines (TAD), ultimately restoring yields to 80 to 90% of 1st and 2nd year levels. The decline cycle is destroyed by the introduction of a crop other than wheat or barley.
Although no resistant wheat varieties are currently commercially available, it has been found that wheat lines differ in their capacity to build-up take-all inoculum in the soil during their first year of a rotation. [3] The Low-TAB trait influences disease severity and wheat yield in second wheats, [4] and it is associated to changes in the rhizosphere microbiome. [5] [6] The genetic mechanism of the Low-TAB is still unknown, but the low TAB can still be exploited by farmers, making short wheat rotations more profitable.
Some wheat relatives such as strains of T. monococcum have comparable resistance to wheat varieties that have already been bred for resistance, [7] but genetic analysis suggests that they have different genetic bases for this, both different from wheat cultivars [7] and also from each other. [7] This may be a useful genetic resource to draw upon for introgression into wheat. [7]
Gaeumannomyces tritici causes disease in the roots, crown, and stem base of wheat, barley, rye, along with several grasses such as Bromegrass, Quackgrass, and Bentgrass. [8] Oats are the only cereal crops that are able to have resistance [9] being naturally resistant. [10] The majority of infected plants can withstand mild root infection and appear symptomless. [8] There are also cases where entire fields can be affected, [11] but typically premature death occurs in circular patches in the field. [12] Infected plants are identifiable through stunting, mild chlorosis (yellowing), and a decreased number of tillers, which are additional stems that develop of the main shoot of the plant. [8] [13] When tillers die due to disease they are white, creating a "white-head" that can be described as a sterile environment that isn’t able to germinate. [14] Signs include perithecia that are shown in infected root and stem tissues which are black in color. [15] This blackening of the crown and stem base allow the plant to be easily pulled from the soil with no attached root system. [9] Given its name "Take-all", it has been known to destroy entire stands of wheat. [16]
Gaeumannomyces tritici is a soil borne fungus that was first identified over 100 years ago in Australia. [14] Although the disease term originated in this region of the world, it is seen throughout the world under temperate climates as well as regions with tropical climates or high elevations. [17] Given that it is an ascomycete, it favors damp climates, but can proceed to persist in dry climates where irrigation is used. [12] Take-all becomes more severe in sandy, infertile, compact, and poorly drained soils, [8] where air, and therefore soil temperatures are 11 °C to 20 °C. [12] The second half of the growing season is favorable. The pathogen favors a basic environment and increases in severity of the pathogen when the pH reaches 7. Soils deficient in nitrogen, phosphorus, and copper also intensify growth of the pathogen. [12] Therefore, liming is not a suitable form of control. [8] There have been tested areas in Larslan and Toston, Montana, where two different fungi found in particular soil have reduced the severity of take-all through mycoparasitism. [18]
Gaeumannomyces tritici persists through unfavorable climates in infected host plants and host debris. [14] It can be spread from area to area through this debris. [8] There are two inoculum that contribute to the spread of the pathogen, hyphae and ascospores. Hyphae are the predominant inoculum, [14] because roots become infected as they grow through infested soil. Most of the plant-to-plant spread of take-all occurs via runner hyphae moving across "root bridges". In addition, ascospores are moved through splashing and in some instances wind. [14] The pathogen then causes whiteheads to accumulate on the top of the plant. When the plant eventually dies, the cycle repeats and the fungi once again overwinters as an ascocarp inside the host plant and plant debris. [19] This pathogen may be considered polycyclic because initial inoculum is by mycelial growth by the resting spores, ascomata. Alloinfection may be relatively less frequent within a season, yet secondary inoculum can also occur during the same season. [15]
Rusts are fungal plant pathogens of the order Pucciniales causing plant fungal diseases.
Powdery mildew is a fungal disease that affects a wide range of plants. Powdery mildew diseases are caused by many different species of ascomycete fungi in the order Erysiphales. Powdery mildew is one of the easier plant diseases to identify, as the signs of the causal pathogen are quite distinctive. Infected plants display white powdery spots on the leaves and stems. This mycelial layer may quickly spread to cover all of the leaves. The lower leaves are the most affected, but the mildew can appear on any above-ground part of the plant. As the disease progresses, the spots get larger and denser as large numbers of asexual spores are formed, and the mildew may spread up and down the length of the plant.
The smuts are multicellular fungi characterized by their large numbers of teliospores. The smuts get their name from a Germanic word for 'dirt' because of their dark, thick-walled, and dust-like teliospores. They are mostly Ustilaginomycetes and comprise seven of the 15 orders of the subphylum. Most described smuts belong to two orders, Ustilaginales and Tilletiales. The smuts are normally grouped with the other basidiomycetes because of their commonalities concerning sexual reproduction.
The cereal grain wheat is subject to numerous wheat diseases, including bacterial, viral and fungal diseases, as well as parasitic infestations.
Stem rust, also known as cereal rust, black rust, red rust or red dust, is caused by the fungus Puccinia graminis, which causes significant disease in cereal crops. Crop species that are affected by the disease include bread wheat, durum wheat, barley and triticale. These diseases have affected cereal farming throughout history. The annual recurrence of stem rust of wheat in North Indian plains was discovered by K.C. Mehta. Since the 1950s, wheat strains bred to be resistant to stem rust have become available. Fungicides effective against stem rust are available as well.
Blumeria graminis is a fungus that causes powdery mildew on grasses, including cereals. It is the only species in the genus Blumeria. It has also been called Erysiphe graminis and Oidium monilioides or Oidium tritici.
Elvin Charles Stakman was an American plant pathologist who was a pioneer of methods of identifying and combatting disease in wheat. He became an internationally renowned phytopathologist for his studies of the genetics and epidemiology of stem rust. Stakman is credited with improving crop yields both in North America and worldwide as part of the Green Revolution.
Loose smut of barley is caused by Ustilago nuda. It is a disease that can destroy a large proportion of a barley crop. Loose smut replaces grain heads with smut, or masses of spores which infect the open flowers of healthy plants and grow into the seed, without showing any symptoms. Seeds appear healthy and only when they reach maturity the following season is it clear that they were infected. Systemic fungicides are the major control method for loose smut.
Rhizoctonia solani is a species of fungus in the order Cantharellales. Basidiocarps are thin, effused, and web-like, but the fungus is more typically encountered in its anamorphic state, as hyphae and sclerotia. The name Rhizoctonia solani is currently applied to a complex of related species that await further research. In its wide sense, Rhizoctonia solani is a facultative plant pathogen with a wide host range and worldwide distribution. It causes various plant diseases such as root rot, damping off, and wire stem. It can also form mycorrhizal associations with orchids.
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Alternaria triticina is a fungal plant pathogen that causes leaf blight on wheat. A. triticina is responsible for the largest leaf blight issue in wheat and also causes disease in other major cereal grain crops. It was first identified in India in 1962 and still causes significant yield loss to wheat crops on the Indian subcontinent. The disease is caused by a fungal pathogen and causes necrotic leaf lesions and in severe cases shriveling of the leaves.
Pyrenophora tritici-repentis (teleomorph) and Drechslera tritici-repentis (anamorph) is a necrotrophic plant pathogen of fungal origin, phylum Ascomycota. The pathogen causes a disease originally named yellow spot but now commonly called tan spot, yellow leaf spot, yellow leaf blotch or helminthosporiosis. At least eight races of the pathogen are known to occur based on their virulence on a wheat differential set.
Zymoseptoria tritici, synonyms Septoria tritici, Mycosphaerella graminicola, is a species of filamentous fungus, an ascomycete in the family Mycosphaerellaceae. It is a wheat plant pathogen causing septoria leaf blotch that is difficult to control due to resistance to multiple fungicides. The pathogen today causes one of the most important diseases of wheat.
Tilletia caries is a basidiomycete that causes common bunt of wheat. The common names of this disease are stinking bunt of wheat and stinking smut of wheat. This pathogen infects wheat, rye, and various other grasses. T. caries is economically and agriculturally important because it reduces both the wheat yield and grain quality.
Ascochyta is a genus of ascomycete fungi, containing several species that are pathogenic to plants, particularly cereal crops. The taxonomy of this genus is still incomplete. The genus was first described in 1830 by Marie-Anne Libert, who regarded the spores as minute asci and the cell contents as spherical spores. Numerous revisions to the members of the genus and its description were made for the next several years. Species that are plant pathogenic on cereals include, A. hordei, A. graminea, A. sorghi, A. tritici. Symptoms are usually elliptical spots that are initially chlorotic and later become a necrotic brown. Management includes fungicide applications and sanitation of diseased plant tissue debris.
Pyrenochaeta terrestris is a fungal plant pathogen that infects maize, sweet potatoes, and strawberries. This plant pathogen causes a disease in onion that is commonly called pink root. P. terrestris is also known to infect shallots, garlic, leeks, chives, cantaloupe, carrots, cauliflower, cowpea, cucumbers, eggplants, lima beans, millet, oats, peas, peppers, potatoes, spinach, sugarcane, and tomatoes.
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Ruth Florence Allen (1879–1963) was an American botanist and plant pathologist and the first woman to earn her Ph.D. in botany from the University of Wisconsin. Her doctorate research focused on the reproduction and cell biology of ferns, particularly the phenomenon of apogamy. Later in her career, Allen shifted her focus to plant pathology. Her major contribution to the field of mycology was furthering the understanding of rust fungi, a group of economically important plant pathogens. Allen completed many studies on Puccinia graminis, once considered a catastrophically damaging disease-causing agent in cereal crops before the discovery of current management measures.
Stephen Denis Garrett was a British plant pathologist and mycologist who did pioneering work on soil-borne pathogens, root pathology and soil ecology. He was the first to apply ecological concepts to interactions in the soil. Much of his research used as a model system the fungus Gaeumannomyces graminis, which causes the important cereal disease take-all. He also studied Armillaria root rot of trees, among other plant diseases.
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