Development of smut. Biological (technological) efficiency of spring wheat seed protectants
Smut mushrooms(part 1)
Cereals affected by smut usually do not produce a harvest, since their spikelets are either completely or partially destroyed and filled with black dust - spores of the smut fungus. The smut spores are small and there are a lot of them. This is why smut can spread extremely quickly. Smut spores retain the ability to germinate and infect new crops for 10 years. Ears and panicles of cereals affected by smut can be easily seen in the field, as the spikelets are destroyed and turn black from the spores that have accumulated on them. The spikelets take on a burnt appearance, which is why the disease is called “smut.”
Fig.1. Smut mushrooms. Dusty and hard smut:
1 - for oats; 2 - on millet; 3 - on wheat; 4 - on corn; 5 - bunt on wheat; 6 - stem smut on rye; 7 - smut spores; 8 - smut spores; 9 - a bunch of stem smut spores; 10 - germination of spores of hard and dusty smut; 11 - wheat grains affected by smut.Different kinds have bunts distinctive features in development. First we will dwell on the development of millet smut and the development of species similar to it.
During harvesting and threshing of millet, smut spores are spread in large numbers, and at this time they stick to the grain and overwinter. If infected grains are sown in the spring, smut spores begin to germinate along with the seeds. The hyphae of the fungus penetrate into the tissues of a young millet sprout, and the mycelium grows with the young plant through its intercellular spaces, without initially producing a noticeable destructive effect. The presence of smut fungi is invisible to the naked eye until the cereal begins to sweep a panicle. At this time, the hyphae of the fungus branch especially abundantly at the top of the plant and produce numerous spores of the smut fungus, called chlamydospores. These black spores arise from hyphal cells and are distinguished by a thick wall, formed inside the cell under the old cell wall, which later becomes mucus. The formation of chlamydospores is accompanied by partial destruction of the tissues of the affected part of the plant, in which many black chlamydospores accumulate. A destroyed panicle of millet often does not come out of the vagina at all top sheet or moves out in the form of an elongated black body, covered with a whitish, easily destroyed film of mycelium. Chlamydospores are spread during threshing, stick to the grains and get into the soil with them during sowing.
Stem smut of rye, dusty smut of oats and durum smut of wheat develop similarly. Oat smut spores that fall on a grain germinate on the plant, and the mycelium penetrates the pericarp and the scales of the grain. In spring, during germination
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Smut fungi are an interesting group of basidiomycetes in many respects. About 1000 species of smut fungi are known, grouped into 40 genera. Smut fungi infect most organs of their host plants, including vegetative and flower buds, leaves and stems, corolla petals and sepals, stamens and pistils, fruits and seeds. Less often they attack the roots. Affected plant parts appear charred or covered in soot. Therefore, diseases caused by smut fungi are called “smut”.
Smut mushrooms are distributed from the Arctic to the tropics, almost everywhere they grow higher plants, not excluding deserts and mountains.
Smut is a common and harmful disease that affects all cereals and wild cereal grasses. Caused by fungi from the class Basidiomycetes, subclass Teliomycetidae, order Ustilaginales.
Causative agents of smut.
Pathogens are fungi (class Basidiomycetes, order Ustilaginales). In their development cycle they have mycelium, smut spores (teliospores), gemmas and basidiospores.
The mycelium of smut fungi is well developed, endogenous, extends in the affected tissue along the intercellular spaces, sometimes penetrates cells, is capable of breaking up into smut spores. Before breaking down into spores, it branches strongly, the hyphae are divided by additional transverse partitions, the cell membranes mucus, then thicker pigmented membranes are formed, and the cells detach from the main mycelium. Such isolated areas of the mycelium are called smut spores; they form a dusty or dense dark mass (smut). After penetration into the affected organ of the plant, the mycelium spreads diffusely in it (especially in species that infect during the seedling phase). However, the mycelium does not permeate the entire plant. The defeat of individual or all parts of the ear is explained by the fact that soon after infection, the fungus penetrates through the growth point into the rudimentary ear, when the plant is in the initial phase of development, and then, with vigorous growth of the stem, it is quickly carried upward. The mycelium concentrates and develops, depending on the type of pathogen, in the ovary, parts of the ear, and stem.
Smut spores serve to spread and preserve the species in non- favorable conditions.
Diagnostics.
The causative agents of smut affect all cereals. Plant infection occurs in at a young age, more often in the embryonic period. Individual ovaries or entire inflorescences, stems, and leaves are subject to destruction. A black, dusty mass forms on the affected organs. Depending on the destruction of certain organs, as well as on the signs of the manifestation of the disease, several types of smut are distinguished on cereals: dusty, hard, vesicular, stem, dwarf (Fig. 1).
According to the nature of the manifestation of the disease on the ear, two types are distinguished - hard and dusty smut. With smut, only the grain is destroyed, the grain shell is preserved. Smut spores are found in a bag, as it were, hence the name - smut sacs.
Rice. 1. Various types of smut of grain crops:
1 - durum wheat; 2 - dusty smut of wheat; 3 - rye stem smut;
4 - dusty smut of millet; 5 - dusty smut of oats.
With loose smut, almost all parts of the ear are destroyed, and the spores are easily carried by the wind. The nature of the manifestation of the disease on the ear is not related to biological and environmental features types of smut. This is a sign that makes it easy to recognize closely related types of pathogens based on the manifestation of the disease, but it does not allow them to be combined based on other properties (type of infection, persistence of infection, specialization, morphology, etc.). For example, the biology of the causative agent of wheat head smut (Ustilago tritici) is not similar to the biology of the pathogen of oat head smut (U. avenae) or corn head smut (Sorosporium reilianum). Species of the genus Urocystis (U. occulta and U. tritici) destroy the upper part of the stem, leaf sheaths and leaves and form longitudinal black stripes.
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Biology of smut fungi
Smut fungi are an interesting group of basidiomycetes in many respects. About 1000 species of smut fungi are known, grouped into 40 genera. Smut fungi infect most organs of their host plants, including vegetative and flower buds, leaves and stems, corolla petals and sepals, stamens and pistils, fruits and seeds. Less often they attack the roots. Affected plant parts appear charred or covered in soot. Therefore, diseases caused by smut fungi are called “smut”.
Smut is a common and harmful disease that affects all cereals and wild cereal grasses. Caused by fungi from the class Basidiomycetes, subclass Teliomycetidae, order Ustilaginales.
Causative agents of smut. Pathogens are fungi (class Basidiomycetes, order Ustilaginales). In their development cycle they have mycelium, smut spores (teliospores), gemmas and basidiospores.
The mycelium of smut fungi is well developed, endogenous, extends in the affected tissue along the intercellular spaces, sometimes penetrates cells, and is capable of breaking up into smut spores. Before breaking up into spores, it branches strongly, the hyphae are divided by additional transverse partitions, the cell membranes become slimy, then thicker pigmented membranes are formed, and the cells are detached from the main mycelium. Such isolated areas of the mycelium are called smut spores; they form a dusty or dense dark mass (smut). After penetration into the affected organ of the plant, the mycelium spreads diffusely in it (especially in species that infect during the seedling phase). However, the mycelium does not permeate the entire plant.
The defeat of individual or all parts of the ear is explained by the fact that soon after infection, the fungus penetrates through the growth point into the rudimentary ear, when the plant is in the initial phase of development, and then, with vigorous growth of the stem, it is quickly carried upward. The mycelium concentrates and develops, depending on the type of pathogen, in the ovary, parts of the ear, and stem.
Smut spores serve to spread and preserve the species in unfavorable conditions.
The causative agents of smut affect all cereals. Infection of plants occurs at a young age, often during the embryonic period.
Individual ovaries or entire inflorescences, stems, and leaves are subject to destruction. A black, dusty mass forms on the affected organs. Depending on the destruction of certain organs, as well as on the signs of the manifestation of the disease, several types of smut are distinguished on cereals: dusty, hard, blistered, stem, dwarf.
Based on the nature of the manifestation of the disease on the ear, two types are distinguished - hard and dusty smut. With smut, only the grain is destroyed, the grain shell is preserved. Smut spores are located, as it were, in a bag, hence the name - smut bags.
With loose smut, almost all parts of the ear are destroyed, and the spores are easily carried by the wind. The nature of the manifestation of the disease on the ear is not related to the biological and environmental characteristics of the smut species. This is a sign that makes it easy to recognize closely related types of pathogens based on the manifestation of the disease, but it does not allow them to be combined based on other properties (type of infection, persistence of infection, specialization, morphology, etc.).
For example, the biology of the causative agent of wheat head smut (Ustilago tritici) is not similar to the biology of the pathogen of oat head smut (U. avenae) or corn head smut (Sorosporium reilianum). Species of the genus Urocystis (U. occulta and U. tritici) destroy the upper part of the stem, leaf sheaths and leaves and form longitudinal black stripes.
Smut on grain crops is one of the most harmful diseases. With smut, the part of the plant most often affected is the part of the plant for which this crop is cultivated - the ear, cob or panicle. The grain completely turns into a black spore mass or, if other organs are affected, often does not develop. In this regard, the harvest of diseased plants is completely destroyed.
In addition to obvious crop losses, smut causes losses that cannot be taken into account when external inspection crops. These are the so-called hidden losses. They are expressed in the fact that the pathogen, which is in the plant from the moment of grain germination until the ripening of the seeds, has a depressing effect on the plant: seed germination is reduced, infected seedlings are more strongly affected by soil fungi, plants are stunted, many of them do not emerge, the normal course of biochemical processes is disrupted. processes, grain filling decreases.
Most species of smut fungi persist from year to year in the form of smut spores on the surface of the grain or in the soil, and only in a few species the mycelium overwinters inside the grain. Smut spores do not persist in the soil for a long time; they do not require a period of rest and germinate under favorable conditions of humidity and temperature. As a rule, this happens in the same autumn or spring next year. The exceptions are spores collected in balls (Urocystis occulta), found in vesicular growths of plants (Ustilago zeae), and spores that require a dormant period (Tilletia controversa).
The period of infection of plants by smut fungi is limited by the age of the tissue. Some species infect only grain seedlings (T. caries, U. avenae), others are capable of infecting young above-ground parts of plants (T. controversa, U. zeae), while others infect ovaries during the flowering period (U. tritici, U. nuda).
The presence of heterothallism (dioeciousness) in smut fungi determines the possibility of obtaining new forms and races that are different from the parent ones either in morphological terms or in terms of specialization, virulence, cultural characteristics, biochemical and other features.
New forms and races are formed as a result of interspecific and intraspecific crossing. More often they arise from crossing between closely related species and forms of smut.
In nature, the number of forms and races within a species is not constant; the process of formation is continuous. Some species have one form, while others have several.
Knowledge of the specialization and racial composition of the pathogen is important not only for breeders in the work of developing resistant varieties, but also for practitioners who must correctly approach the selection of varieties, as well as replace affected varieties.
Solid smut. Pathogens: Tilletia caries (DC.) Tul. (syn. T. tritici Wint.) -- spherical spores with a reticulate shell, 14--22 μm in diameter and T. levis Kuehn. -- irregularly rounded spores, 15--23 μm in diameter or oblong, 17-- in size 25x14--19 microns, with a smooth shell. The ovary is affected. Instead of grain, a smut sac is formed, consisting of teliospores covered with a grayish shell. When the smut sac is crushed, a smearing, greasy to the touch, dark brown mass of spores with a herring odor is revealed. Infection of plants occurs in the soil from germinating spores located on the surface of the seeds. Seedlings become infected through the coleoptile.
Dwarf smut. The causative agent is Tilletia controversa Kuehn. The spores are round, with a mesh surface, often surrounded by a colorless mucous layer, 19-28 microns in diameter. Along with dark-colored teliospores, colorless (hyaline) spores with a smooth shell are also found. It affects the ovary, like smut. In the ear, instead of grain, smut sacs are formed, small, with a rounded upper cone and a small process - the remnant of the stigma.
A plant affected by dwarf smut is undersized (dwarf), with increased bushiness. Infection of plants occurs at the soil surface. Seedlings are infected in the phase of one to three leaves.
Dusty smut. Pathogen - Ustilago tritici (Pers) Jens Spores are small, spherical or oblong, 5-9 microns in diameter. Destroys all parts of the spikelets. Only the stem of the ear remains undestroyed. Diseased ears appear at the time of heading. Instead of a spike, a sooty mass of spores emerges from the leaf sheath. The spores are spread by air currents. Plants become infected during the flowering period from spores falling on flowers from neighboring diseased ears.
The causative agent of the disease is Tilletia Tritici and Tilletia levis (syn. T. foentes).
Class:Ustilaginomycetes; order : Ustilaginaceae
The causative agents of the disease differ only morphological characteristics sori and teliospores. In Ukraine, wheat bunt is common in all regions of crop cultivation.
The disease manifests itself in the milky-waxy phase of ripeness. Affected plants are slightly stunted in growth, have a flattened ear, and have a more intense green color with a blue tint, compared to healthy plants. The spikelet scales are moved apart, instead of white “milk”, a gray liquid with the smell of herring brine (trimethylamine) is formed in the grains; therefore, durum wheat is also called wet or stinky. Over time, as the wheat ripens, the difference in color between the affected and healthy ears disappears, but the affected ear remains erect. Instead of grains, longitudinal sori (smut sacs) are formed in them. The shell of the grains remains undestroyed, and they are filled with an olive-brown mass of smut spores - teliospores.
During threshing, the sori are destroyed, teliospores fall on the surface of healthy grain, in the straw, partially on the surface of the soil, the infection accumulates on harvesting and grain cleaning machines, vehicles, container All this can be a source of infection for healthy grain.
Grain affected by Durum smut of wheat – Tilletia Tritici photo Development cycle of wheat durum smut – Tilletia Tritici
Once in the soil, teliospores retain their vital activity for 1-3 weeks. Under the influence of moisture and saprophytic microorganisms, they lose their viability. In dry soil they retain the ability to germinate for no more than one year. Therefore, the main source of infection is seeds contaminated with teliospores.
When such seeds germinate, teleospores also germinate, forming basidia with basidiospores. As a result of copulation of basidiospores, an infectious hypha is formed, which penetrates the young wheat seedling. In affected seedlings, the mycelium spreads throughout the intercellular spaces. Reaching the ear during the period of its formation, it grows rapidly and subsequently breaks up into teliospores, forming sori.
Depending on the temperature, wheat seedlings are vulnerable to infection for 1-8 days after germination. Optimal temperature for their infection 6-13˚С and relative humidity soil 40-60%, so it occurs more intensely when too early sowing spring and late sowing of winter wheat, as well as with deeper seed placement.
Measures to combat wheat bunt
Sowing with healthy certified seeds is required. Seeds from fields where, according to testing results, plant damage exceeds 0.2-0.3% are not allowed to be sown.
The main method is seed treatment using chemical disinfectants with strict adherence to drug consumption standards.
Biologists classify mushrooms as special kingdom along with plants and animals. This group of organisms, numbering almost one hundred thousand species, has great importance for flora and fauna. They contribute to the natural circulation of substances. Fungi speed up the decay process of animals and plant residues and increase soil fertility. Finally, they are a source of food for animals and humans.
Now the study of smut, its signs and consequences is included in the programs of all universities that train future agricultural producers. Knowing the specifics, types and forms of pathogens is important for both breeders and agronomists. The first to develop varieties that are resistant to this dangerous disease, and the latter are required to carefully select varieties before sowing.
There are several types of this disease to which wheat is susceptible. Thus, hard smut affects the ovary of the spikelet. Moreover, infection begins in the soil. Instead of grain, a grayish process appears in the form of a sac, consisting of spores of smut fungi. If the bag is crushed, a black mass appears that has the smell of herring.
On smut Another type of the disease is similar - dwarf. Spores penetrate the plant on the soil surface. The consequences of infection are almost identical: a smut sac grows on the spikelet instead of a seed. Ears suffering from dwarf smut are stunted and bushy.
Stem smut attacks leaves and stems. The essence of the disease is as follows: the ears are covered with long dark stripes. This is the order in which smut spores destroy plant tissue. A black spore mass oozes from the stem. The development of the ear is inhibited. Moreover, the plant gets sick at the moment when its seeds begin to sprout.
Rye suffers from this disease in the same way as wheat. Among the types of smut on rye, the most common are hard, dusty and stem. The first damages the grains, the second destroys the ear, the third destroys the leaves and stems.
Stye sometimes hurts special kind firebrand - stone. Smut fungi, penetrating during seed ripening, destroy all parts of the plant. The spores are stored on the spikelet scales. They are a solid mass covered with a film.
The oat crop may be damaged by covered smut. Spores of smut fungi in this type of disease are stored in lumps that are covered with spikelet scales. When threshing begins, the lumps break up and the spores infect good, healthy seeds. Millet smut has the same consequences.