Corn bump brandy
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Corn blight ( Ustilago maydis ) |
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| ( DC. ) Corda |
The maize bite brandy ( Ustilago maydis ) or maize brandy (the edible stages are called Huitlacoche or Cuitlacoche ) is a parasitic smut fungus that only affects maize in Europe and causes the disease of the same name. Its narrow host range only includes in its home area Mexico occurring teosinte ( Zea mays subsp. Mexicana , syn. You Lena mexicana ), probably the wild form of maize culture is.
The fungus is found wherever corn is grown, but it prefers warm, moderately dry climates. The scientific name Ustilago comes from the Latin ustilare (= to burn) and refers to the “burnt” appearance of the plant when the tumor-like plant galls open and the blue-black burn spores are distributed over the plant.
Characteristics and infection
The corn bite brandy is a highly specialized fungus that only affects corn. It does not pose a threat to other agricultural crops. It occurs in all areas where corn is grown. Only in years with extreme weather conditions (rapid change between summer drought and high water supply) does the disease lead to greater losses due to cob infections, especially in grain maize.
Corn blight can affect all parts of the corn plant above ground. Macroscopically, it can be easily recognized on infected maize plants through the tumor-like growths and bile structures; in extreme cases, the galls can be the size of a child's head. These growths are stimulated by the growth substances released into the plant tissue. The fungal mycelium grows particularly strongly in the hypertrophied parts of the plant , where it forms large quantities of teliospores , which when released give the maize plants their smut appearance. The infestation of the cobs is particularly serious from an economic point of view, since these represent the most nutritious part of the forage crop maize.
The infection of the maize plant only takes place in the tissues that are still capable of dividing and are therefore still growing, mainly after emergence up to a plant height of 40 cm. The corn bumps therefore not only occur on the cob, they can also form on other parts of the plant. An infection can lead to the complete death of the plants. A low infestation of the maize plants does not seem to have any health consequences for the cattle during ensiling and feeding, nevertheless an increased tendency to miscarriages after ingestion of higher amounts of spores is discussed.
Investigations with dairy cows by the Bavarian State Research Center for Agriculture in Poing- Grub showed that maize silage with 100% infestation had a significant adverse effect on the feed value (18% less net energy and 27% less digestible protein). An impairment of feed consumption and animal health could not be determined. In bull fattening , there were no problems with feeding silage with a bump fire infestation of 10–15%. However, the silage made from infected maize contained an increased proportion of spoilage-causing fungi. It was concluded that it is less stable under aerobic conditions. Uncontaminated silage was stable for one day longer than silage with bump burn. This difference could be compensated by the use of silage additives .
"Low bubonic burns (<20%) have no influence on feed intake and nutrient concentration. But if every plant is infested (100%), a lower net energy and a higher protein breakdown must be taken into account. The increasing spread of year-round silage requires stable silage for feeding in summer. According to older studies, corn blight infestation shows a lower aerobic stability. It is therefore recommended that silage additives are used in the case of a very high level of corn blight infestation (Practical Guide for Feed Conservation 2006, 7th edition), which have the DLG quality mark for direction 2 improvement of aerobic stability. "( Bavarian State Institute for Agriculture - Institute for Animal Nutrition and Feed Management )
Development cycle
There is a risk of the fungus spreading via spores adhering to the seeds ; further spreading paths exist via wind movement or water splashes. Infection is promoted by stress factors that cause the maize to temporarily weaken: such as dry weather, temperatures between 26 and 34 ° C and late frosts.
The permanent spores (telio or teleutospores) that overwinter in the soil or plant residues and can survive up to ten years germinate after nuclear fusion ( karyogamy ) in spring to summer and form a basidia in which meiosis and mitosis take place. The basidia then divides ( septates ) lengthways and secretes a total of four haploid basidiospores . These basidiospores, also known as sporidia, are carried by the wind or by spray water onto young maize plants, where they can germinate on growing, meristematic plant tissue.
The ability to fuse successfully in the corn smut sporidia depends on two gene loci , named a and b . Two alleles of the gene locus a are known (a1 and a2) while about 33 of the gene locus b are now known. Crosses of the form a1b1 with a2b2 are compatible, but not a1b1 with a1b2. If the conditions are favorable, the haploid cells of the corn blight initially multiply in a yeast-like manner by sprouting on the surface of the plant. The sporidia initially grow saprotrophically and are not pathogenic. If two compatible sporidial cells meet, they form a connection via conjugation hyphae . The cell contents fuse by somatogamy to form a binuclear ( dikaryotic ) cell, which differentiates into a dikaryotic filament ( hypha ). The germination of the sporidia, the yeast-like growth and the formation of the dikaryotic filament can be traced in the laboratory without a maize plant on media containing activated carbon. All other stages require contact with the host plant.
The dikaryotic hypha forms an appressoric structure with which the fungus can penetrate the host tissue - preferably through wounds. The hyphae of the dikaryotic mycelium now penetrate further into the plant tissue and continue to grow there between the maize cells, especially in the direction of meristematic plant tissue. As the fungus now secrete growth substances, the surrounding plant cells are stimulated to grow in size and increase cell division. Tumor-like, bilious growths form. Usually these are limited to the immediate vicinity of the infection and often go completely unnoticed. The conspicuous galls rarely develop. If female flowers are infected, the infection can grow into the young corn cobs via the “hairs” of the flowers and destroy them.
During the formation of the galls , the hyphae grow intercellularly, i. That is, between the cells, but from a certain degree of maturity the mycelium penetrates the hypertrophied plant cells and digests them for the most part, so that in the end only the mycelium and cell debris remain in the galls. Most of the mycelium then transforms into teliospores, which are released after the bile shell has burst. If these teliospores immediately reach meristematic maize cells, they can immediately germinate there into infection hyphae. Otherwise they survive in the soil or on plant remains.
Countermeasures
A direct, i.e. That is, chemical control of the fungus is difficult. As a preventive measure against the corn bite burn , the seeds are coated (encrusted) to prevent infestation by the frit fly. Their activity causes wounds on the maize plants, which can serve as entry portals for infection hyphae.
Cultivation breaks of three years prevent the occurrence of corn smut. Far-standing maize stands favor an infestation with maize blight. Sowing, e.g. B. of rye, significantly reduce the circulation of smut spores from the soil into the maize crop (filter effect). Resistance breeding is the cheapest control measure. The risk of infestation can be reduced by growing less susceptible varieties. All measures to improve the vitality of the plants, as well as optimal cultivation, reduce the susceptibility of the maize to infestation and damage caused by infestation. The risk of infestation can be reduced by avoiding excessive nitrogen administration. Under irrigation conditions, kernel and cob diseases of maize are generally promoted. But: Not all infections lead to the formation of bumps; this is particularly favored by stressful situations such as long periods of drought. The still divisible tissue tries to compensate the growth residue after the dryness with enough water. In the process, burn bumps are then increasingly formed. In longer periods of drought, an additional water supply could reduce the risk of large-scale occurrence of maize fire.
toxicity
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Ustilago maydis spores can cause allergies . "Ustilaginism" is the name given to poisoning caused by corn bite burn, which can occur in humans and animals. The cause is suspected to be ergotamine-like alkaloids , as can also be found in a rye parasite , ergot . In the United States spores extracts were the African-American population abortions used.
It has not been clearly proven that the corn bruise is said to trigger allergies or is toxic. According to recent studies, e.g. B. by the Bavarian State Institute for Agriculture, the mushroom is non-toxic. According to information from AgroMais Saatzucht GmbH and Industrieverband Agrar e. V. (IVA) 2007 maize bite blight is a fungus that does not produce toxins. In several feeding experiments, no negative effects on animal health were found. Plants that have been infected with bump burn, however, are often infected with mold , which in turn can form mycotoxins . This means that any mycotoxins that occur would not come from the corn bite burn, but from the secondary mold infestation. As a precautionary measure, it is recommended not to feed heavily bubbled corn to high-bearing or freshly lactating cows. In young cattle or beef rations, the proportion should not be higher than 30 percent of the dry matter of the total ration.
Very few original publications indicate toxicity or triggering of allergenic reactions. In 1938, for example, a paper reported on the poisoning of Yugoslav children who, after consuming maize porridge that was presumably contaminated with maize blight spores, showed signs of poisoning such as diarrhea and skin changes. Feeding trials of this maize porridge with mice gave similar results in these animals. However, the pathogens were not isolated in this investigation and it was not examined whether an artificial infection with the pathogen caused the same symptoms. The further work describes the neurotoxicity and organ changes caused by the fungus in rats. It is therefore at least likely that a very high consumption of this mushroom over a long period of time can have negative effects on the organism because of the alkaloid content.
According to the current state of knowledge, direct, negative effects of the bump fire on the fermenter biology and gas yields are not to be expected when using the silages in biogas plants.
Use of the corn smut fungus
Ustilago maydis in research
Since the haploid, yeast-like developing fungal cells are easy to cultivate in the laboratory, the corn smut has become a popular research subject. The entire genome of the fungus is now known. Since Ustilago maydis can also be genetically modified relatively easily, the processes during the infection can be traced on the genetic level.
Genetic recombination and DNA repair mechanisms are also being investigated with the help of the corn smut. In this way, the mode of action of the BRCA2 gene , which can lead to breast cancer if it malfunctions , was discovered. A gene from Ustilago maydis BRH2 that is homologous to BRCA2 , in the absence or dysfunction , causes cells to be extremely sensitive to UV light and ionizing radiation, because DNA repair then no longer works. This type of gene appears to be very original, as homologues to BRCA2 have been found not only in mammals and fungi, but also in completely different organisms such as thale cress ( Arabidopsis thaliana ) and nematodes ( Caenorhabditis elegans ).
More recently, Ustilago maydis has continued to become a model system for studying the molecular basis of polar growth. The role of cell cycle regulators and the cytoskeleton are currently the focus of research by some scientists.
Since Ustilago maydis has inhibitors prevent the other blight pathogen on growth, was at the ETH Zurich gene transfer made on wheat, which then under laboratory conditions successfully resistant against bunt of wheat ( Tilletia caries was).
Food value
In eastern Mexico in particular , the corn smut is considered a food and delicacy and the infection of the corn by the fungus is therefore not viewed as harm, but as a benefit. The infected cobs are harvested before the fungus has fully matured and begins to spore. The mushroom, which is referred to here as Huitlacoche or Cuitlacoche, is usually fried with garlic and various other ingredients and served on tacos and quesadillas or used in soups and casseroles.
In Europe and the USA, Huitlacoche is only prepared as an exotic dish in upscale gastronomy, here it is called, among other things, "Mexican truffle " (advertising, not biologically durable).
According to the Swiss Edible Mushroom Ordinance, the corn bump brandy is approved for wholesale as a marketable edible mushroom. The gall stages are harvested a few weeks after the plant is infected, when it is still immature and the interior is still moist. The boiled galls should take on a mushroom-like, sweet aroma when cooked. Sotolon , vanillin and glucose have so far been identified as flavor components .
In Germany , Ustilago maydis is not listed in the German Food Book under “Principles for mushrooms and mushroom products”. Thus, the corn smut is not an edible mushroom in Germany. The German Food Book is an orientation aid based on Section 15 of the Food and Feed Code (until 2005: Section 33 of the Food and Commodities Act ). Ustilago maydis is also not mentioned in the Austrian Edible Mushroom Ordinance of 1997 and is therefore not marketable in Austria .
Industrial biotechnology
In the presence of alkanes or triglycerides, corn smut is able to produce cellobiose lipids , which act as biosurfactants and are of potential interest for industrial biotechnology . In addition, Ustilago maydis is becoming more and more important in the biotechnological production of itaconic acid .
Individual evidence
- ↑ a b page of the Bavarian State Agency for Agriculture on the corn bite brand ( Memento from October 15, 2010 in the Internet Archive )
- ↑ a b c D. Seidel, T. Wetzel, H. Bochow: Plant protection in plant production. Deutscher Landwirtschaftsverlag, Berlin 1983.
- ↑ a b U. Beckmann, H. Kolbe: Maize cultivation in organic farming. Information for practice and advice. Saxon State Agency for Agriculture, 2002
- ↑ Anonymous: Corn smut Ustilago maydis. LfL Bayerische Landesanstalt für Landwirtschaft 2007.
- ↑ F. Bigler, M. Waldburger, G. Frei: Four corn cultivation methods: Diseases and pests. Agricultural Research 2, 1995; Pp. 380-382.
- ↑ a b H. Imgraben: New mushrooms, new problems. Plant protection practice. DLG-Mitteilungen 8, 2004; Pp. 40-44.
- ↑ Mayerhofer, Dragisic: Another report on childish maize fire poisoning (Ustilaginism). Journal of Pediatrics 59, 1938; Pp. 543-552
- ↑ S. Pepeljnjak, J. Petrik, M. Klaric Segvic: Toxic effects of Ustilago maydis and fumonisin 1 in rats. In: Acta Pharmaceutica 55, 2005; P. 339–348 ( full text (PDF file; 83 kB))
- ↑ Department of the Interior (Switzerland): Ordinance on edible mushrooms, amendment of March 27, 2002 - PDF, 56 kB
- ↑ Austrian Edible Mushroom Ordinance of 1997 ( Memento of June 29, 2006 in the Internet Archive ) (PDF), amendment 2004 ( page no longer available , search in web archives ) (PDF)
- ^ Rolf D. Schmid: Pocket Atlas of Biotechnology and Genetic Engineering. 2nd edition Wiley-VCH, Weinheim 2006; Pp. 58-59, ISBN 978-3-527-31310-5 .
- ↑ Elena Geiser, Vincent Wiebach, Nick Wierckx, Lars M. Blank: Prospecting the biodiversity of the fungal family Ustilaginaceae for the production of value-added chemicals . In: Fungal Biology and Biotechnology . tape 1 , January 1, 2014, ISSN 2054-3085 , p. 2 , doi : 10.1186 / s40694-014-0002-y .
literature
- George N. Agrios: Plant Pathology Third Edition. Academic Press, San Diego 1988, ISBN 0-12-044563-8 .
- Roth, Frank, Kormann: Poisonous mushrooms, fungal poisons - molds, mycotoxins . Nikol, Hamburg 1990, ISBN 3-933203-42-2 .
