The causative agent of the disease is the basidiomycete Ustilago zeae. It affects leaves, stems, internodes, leaf sheaths, cobs and panicles of corn. The disease manifests itself in the form of swellings and nodules of various shapes and sizes. They are initially whitish-pink or greenish-yellow in color and filled with white pulp. Then the nodules darken, crack, and a dark brown dusty mass of fungal teliospores appears from the cracks. Telio spores are spherical, light brown, with a faintly visible mesh pattern and spines.
The disease leads to the death of young plants or there is infertility of the cobs and a shortage of grain and green mass. The harmfulness of smut depends on the age of the plants at which infection occurred, the number and size of nodules. Damage to corn at a younger age is most harmful.
The causative agent of bladder smut infects corn throughout the entire growing season. But only young, growing organs are always infected.
The disease develops most often according to the local type. In the area where the infection occurred, a pale, swollen spot forms, which, growing, turns into a swelling. Swelling - the nodule consists of overgrown cells of the host plant, penetrated by the mycelium of the fungus, the cells of which gradually become denser, covered with a dense membrane and turn into teliospores. The nodule dries out, darkens, its shell cracks, and ripe spores, scattering across the field, carry out secondary infections of plants. The number of re-infections depends on weather conditions (high humidity and a temperature of 23-25° C are optimal for the fungus). The pathogen is preserved by teliospores in smut nodules in the soil and with plant residues, on the surface of healthy seeds.
In the spring, under favorable conditions, teliospores that have overwintered in the soil or got there on the surface of seeds germinate, forming four-celled basidia with four basidiospores. Basidiospores are carried by air currents and, falling on the organs of corn with young meristematic tissue, copulate and infect the plants.
The development of the disease is facilitated by sharp fluctuations in temperature and humidity, and soil depletion of nutrients, especially potassium and phosphorus. Affection increases with mechanical damage from insects (Swedish fly, etc.). At the same time, a high agricultural background, the application of potassium and phosphorus fertilizers, as well as seed treatment with microelements (zinc, boron, copper, manganese) increase the resistance of corn to smut.
Control measures. Crop rotation. Spatial isolation (1000 m) of corn seed plots from the previous year's crops. Selection of predecessors (winter wheat, beets, buckwheat, etc. helps cleanse the soil of smut). Selection, sorting, calibration and disinfection of seeds. Sowing at the optimal time and at the optimal depth. Application of phosphorus-potassium fertilizers. Optimal timing of harvesting and removal of post-harvest residues from the field. Removal of smut nodules before teliospores form.
All actively growing parts of the plant can be infected with the fungus. Their predisposition to damage given their growth potential results in the most severe symptoms. Plants are most susceptible to infection at the germination stage. In this case, the plants show signs of stunted growth and may not produce inflorescences or ears. On older plants, infection leads to the formation of tumor growths - a combination of host tissue and fungus. Smut blisters are greenish-white in early stages and turn black as they mature. Their appearance is especially typical on cobs, where a separate bubble can form on each individual grain. When these bubbles burst, dusty black contents are revealed. The blisters on the leaves usually remain small and dry without bursting.
Trigger
Corn smut is caused by the fungus Ustilago maydis, which can remain in the soil and remain viable for several years. Spores are spread to plants by wind, soil dust and rain. The infection process is favored by the presence of damage that can be caused by insects, animals, careless actions during agricultural work or hail. There is no secondary transfer from plant to plant. Symptoms of the disease are most severe on tissues with the greatest growth potential (such as cobs or growing tips). Extreme weather conditions that result in decreased pollen production and low pollination rates (such as drought followed by heavy rain) lead to the spread of the fungus.
Biological Control
Direct control of this pathogenic fungus is very difficult, and at the moment no effective control methods have been developed.
Chemical Control
Always give preference to an integrated approach, combining preventive measures with biological treatment whenever possible. Treating seeds and foliage with fungicides does not reduce the incidence of smut infection in corn.
Preventive Measures
- Plant hardy varieties if available.
- When planting plants, keep a sufficiently wide distance between them.
- Watch for bubbles, collect and destroy them before the dark fungal spores are released.
- Prevent plants from being damaged by insects and other pests.
- Avoid damaging plants during agricultural work.
- Avoid over-fertilizing with nitrogen.
- After harvesting, remove all residues and do not use contaminated plant parts when making compost.
- Plan long-term crop rotations with non-host plants.
- Clean all tools and equipment thoroughly.
- After harvesting, plow the soil deeply and bury plant remains.
Belongs to the higher fungi of the class Basidiomycetes, subclass Teliomycetes, order Golovnevye.
Cultures.
Affects corn.
Prevalence.
It is found in all regions of the Russian Federation where corn is cultivated.
Symptoms of the disease.
The disease affects corn throughout the growing season. It is characterized by the formation of whitish swellings and nodules of various sizes. On shoots and nodes it appears in the form of spherical-tuberous swellings with a diameter of up to 15 cm or more. On the leaves, swellings form along the veins and have an elongated shape. On the cobs, individual ovaries are affected, the development of which is delayed or stopped. They can also grow and take on an irregular shape. On sultanas, individual flowers are affected, which grow, forming blisters.
Biology of the pathogen.
At sites of infection, a pale or greenish-yellow swelling forms on all plant organs. Later, by the time the teliospores mature, the nodule darkens and is covered on top with a whitish-gray film that takes on a silvery sheen. Later, the nodule dries out, the covering film cracks and the released teliospores disperse, causing secondary infection. Some teliospores are retained in the affected ears of grain and in the field on post-harvest residues. Teliospores are able to germinate immediately as soon as they ripen, but in dry form they can persist for 5 years or longer. In natural humid conditions, they quickly lose their germination capacity, but, remaining in undisintegrated lumps in the field, they can serve as a source of primary infection for seedlings. Teliospores can also be introduced into the field with seed material. Teliospores, germinating, form basidia with basidiospores, which reproduce by budding. Sporidia sprout with growth tubes and penetrate only into young meristematic tissues. Haploid hyphae are formed from the germ tubes. The yield of green mass of corn due to disease is reduced by 25...50%, grain - by 50%.
Sources of infection.
Infected ears, plant residues, soil.
Preparations for protection.
Agrotechnical control measures.
Introduction to the production of resistant varieties, scientifically based seed production, compliance with crop rotation. Compliance with spatial isolation of seed plots from commercial crops, disinfection of agricultural machinery and equipment.
Distributed in all corn growing areas. It appears on cobs, plumes, stems, reproductive buds, leaves and aerial roots in the form of bubble-like swellings (galls) of various shapes and sizes. The disease is not detected on the roots. The development of the swelling begins with a pale, slightly swollen spot, which gradually grows and turns into a large nodule, filled first with white pulp, and later with a grayish-white or pinkish mucous mass, which then turns into a black-olive dusty mass of spores. The largest swellings occur on the cobs and stems. On the leaves they are usually small in the form of a group of rough wrinkles, often drying out to form spores.
Symptoms of the disease are first detected on young leaves and their sheaths, and sometimes on aerial roots located on the stem.
Severe damage is observed on seedlings when the apical bud is infected. Infected tissues of the buds (leaf and stem primordia) turn into smut growths and grow greatly, many times exceeding their original volume, as a result of which the impression of “diffuse” damage to the plant is created.
From the phase of 5-8 leaves, damage to leaves, leaf sheaths and stems is detected. Then the disease appears on the panicles, and from the beginning of flowering and with the appearance of stigmas, the ears are affected. After emergence and the beginning of flowering, axillary buds located under the leaf sheaths and below the cobs become infected.
The most severe form of the disease is damage to the stem. In this case, the plant becomes distorted, the entire part of it above the affected area turns into smut growths and dies.
The causative agent of the disease is the basidiomycete fungus Ustilago zeae Unger of the order Ustilaginales. When the swellings ripen, its mycelium breaks up into a huge number of teliospores. In mass they are black-olive, and single ones under a microscope are yellow-brown, spherical, with a mesh pattern and large bristles, 8-13 microns in diameter.
When the swelling shell bursts, teliospores scatter across the field and serve as a source of infection of young plant organs. They germinate in the presence of dripping moisture within a few hours. The optimal temperature for their germination is +23-25°, at + 15...18° it slows down, and at 12° and below it stops. In germinating teliospores, after 15-20 hours, a rapidly developing sprout appears - the basidium, on which unicellular colorless elongated basidiospores measuring 3 X 1.2 microns are formed. They often reproduce by budding, producing large numbers of sporidia, which are sometimes called secondary conidia.
The hyphae of the haploid mycelium coopulate with the hyphae of the mycelium of the opposite sex and give rise to the development of a diploid mycelium, consisting of thick knotty hyphae. From the diploid mycelium, after 20-24 days, a swelling with teliospores develops at the sites of infection.
During the growing season of corn, the fungus can produce 3-4, and sometimes 5 generations, which explains the strong manifestation of the disease at the beginning of harvesting.
The fungus U. zeae does not spread diffusely throughout the plant, so each swelling forms in the area where the plant was infected.
Dry teliospores can remain viable for up to four years, whereas in natural conditions, when exposed to water wetting, they quickly lose their viability. However, teliospores, which are in the form of lumpy swellings, are poorly wetted and do not die during autumn, winter and spring. In the spring, when cultivating the soil, they break up and the spores are carried by the wind, being the primary source of plant infection. In rare cases, the pathogen may be introduced into the field with seeds, which sometimes retain viable teliospores.
The degree of development of bladder smut depends on soil moisture. At optimal humidity (60% PV), plant damage is always less than at low (40%) or high (80%). Fluctuations in soil moisture lead to increased damage to plants, which should be taken into account when cultivating corn on irrigated lands (Shkodenko V.I., 1966).
The harmfulness of blister smut lies in the death of affected young plants, infertility of cobs when infected early and a significant loss of yield. The latter depends on the size and number of swellings on the plant. With large swellings, the yield is reduced on average by 60%, with medium swellings - by 25, small ones - by 10%. The harmfulness of two swellings on one plant is three times greater than the harmfulness of one same swelling (Nemlienko F. E., 1957).
When studying the characteristics of the development of bladder smut against the background of natural and artificial infection, T. A. Kulik (1975) found that the formation of galls is determined by genotypic differences in self-pollinated lines and the reaction of the host plant to the introduction of the pathogen.
Data on the toxicity of bladder smut are contradictory. Most authors believe that young growths in which teliospores have not yet formed are non-toxic, and when the latter form, they can be as toxic as ergot. Therefore, parts of plants affected by bladder smut are not recommended for use as animal feed.
The main measures aimed at protecting corn from smut are observing scientifically based crop rotation, breeding and zoning of resistant hybrids and varieties, seed treatment, sowing at optimal times and at optimal depth, applying phosphorus-potassium fertilizers, removing post-harvest residues, spatial isolation seed plots at least 1 km from fields where corn was grown in the previous year.
The disease is common in all corn growing areas. It appears on cobs, plumes, stems, leaves and aerial roots in the form of bubble-like swellings of various sizes (up to 15 cm in diameter or more). The disease is not detected on the roots. Development begins with a pale, slightly swollen spot, which gradually grows and turns into a large nodule, filled first with white pulp, and later with a grayish-white or pinkish mucous mass, which then turns into a black-olive dusty mass of spores. The largest swellings occur on the cobs and stems. On the leaves, the swellings are usually small in the form of a group of rough wrinkles, often drying out until spores form.
Bladder smut is first found on young leaves and their sheaths, sometimes on knotty (aerial) roots located on the stem. Severe damage is observed on seedlings when the apical bud is infected, from which all plant organs subsequently develop. Infected tissues of the buds (leaf and stem primordia) turn into smut growths and grow greatly, many times exceeding their original volume, giving the impression of “diffuse” damage to the plant.
From the 5th-8th leaf phase, damage to the leaves, leaf sheaths and stem is noted. Then the disease appears on the panicles, and from the beginning of flowering and with the appearance of stigmas, the ears are affected. After emergence and the beginning of flowering, the axillary buds located under the leaf sheaths below the cobs become infected. The most severe form of the disease is damage to the stem: the plant becomes bent, the entire part of it above the affected area turns into smut growths and dies.
The causative agent of the disease is basidiomycete Ustilago zeae Unger out of order Ustilaginales. When the swellings ripen, its mycelium breaks up into a huge number of teliospores, which, scattering, serve as a source of infection of young growing plant organs. In bulk, teliospores are black-olive, and single ones under a microscope are yellow-brown, spherical, with a reticulate pattern and large bristles, 8-13 microns in diameter.
In the presence of dripping moisture, teliospores germinate within several hours. The optimal temperature for their germination is considered to be 23-25°C. At 12°C and below, spores do not germinate. In germinating teliospores, after 15-20 hours, a rapidly developing sprout appears - the basidium, on which unicellular colorless elongated basidiospores measuring 3x1.2 microns are formed. Additionally, they reproduce by budding and form a large number of sporidia (secondary conidia). Basidiospores and sporidia tolerate low humidity well and die only after 30-36 days.
During the germination of sporidia and basidiospores, and sometimes directly from the basidium, a germ tube is formed, which penetrates the plant through the delicate epidermis, which explains the infection of only young meristematic tissues.
From the germ tubes in the tissues of the plant, a haploid thin filamentous mycelium is first formed, the hyphae of which copulate with the hyphae of another mycelium of the opposite sex and give rise to the development of a diploid mycelium consisting of thick knotty hyphae. From the diploid mycelium, after 20-24 days, swellings with teliospores develop at the sites of infection. During the growing season of a plant, the fungus can produce 3-4, and sometimes 5 generations, which explains the strong manifestation of the disease at the beginning of harvesting.
Mushroom U. zeae does not have the ability to diffusely spread throughout the plant, so each swelling is formed in the place where the plant was independently infected.
One more feature of the fungus should be noted - it affects only vegetative cells. In grains on the cob, the outer shell of the pericarp is affected; the mycelium does not penetrate into the embryo and nucellus, as well as into the endosperm; when young ovaries are damaged, these cells atrophy. In panicles, smut swellings are formed from bracts and anther stalks; The anther shells are also affected, and the pollen grains atrophy.
Dry teliospores can remain viable for four years, whereas under natural conditions, when exposed to water wetting, they quickly lose their viability. However, teliospores, which are in the form of lumpy swellings, are poorly wetted by water and do not die during autumn, winter and spring. In the spring, when cultivating the soil, the lumpy swellings are broken and the spores are easily carried by the wind, being the primary source of plant infection. In rare cases, seeds, which sometimes retain viable teliospores, can be a source of infection in the field.
The degree of development of bladder smut depends on soil moisture. At optimal soil moisture (60% of total moisture capacity), plant damage is always less than at low (40%) or high (80%) conditions. A temporary decrease or increase in soil moisture (from optimal) before and after infection leads to increased damage, which should be taken into account when cultivating corn in irrigated areas.
The harmfulness of blister smut lies in the loss of affected young plants, infertility of cobs when they are infected early, or in a significant loss of yield due to damage to various plant organs. The reduction in yield, as studies have shown, depends on the size and number of swellings on one plant. With large swellings, the yield is reduced on average by 60% or more, with medium-sized swellings - by 25% and with small swellings - by 10%. The harmfulness of two swellings on one plant is three times greater than the harmfulness of one same swelling.
There are conflicting data in the literature regarding the toxicity of bladder smut. Most authors are inclined to believe that young growths in which teliospores have not yet formed are non-toxic, and when they form they can be as toxic as ergot. Therefore, it is not recommended to use parts of plants affected by bubbly smut for animal feed fresh or for ensiling.