Sclerotium

A sclerotium (/skləˈroʊʃəm/), plural sclerotia (/skləˈroʊʃə/), is a compact mass of hardened fungal mycelium containing food reserves. One role of sclerotia is to survive environmental extremes. In some higher fungi such as ergot, sclerotia become detached and remain dormant until favorable growth conditions return. Sclerotia initially were mistaken for individual organisms and described as separate species until Louis René Tulasne proved in 1853 that sclerotia are only a stage in the life cycle of some fungi. Further investigation showed that this stage appears in many fungi belonging to many diverse groups. Sclerotia are important in the understanding of the life cycle and reproduction of fungi, as a food source, as medicine (for example, ergotamine), and in agricultural blight management.Sclerotia are often composed of a thick, dense shell with thick and dark cells and a core of thin colorless cells. Sclerotia are rich in hyphae emergency supplies, especially oil. They contain a very small amount of water (5–10%) and can survive in a dry environment for several years without losing the ability to grow. In most cases, the sclerotium consists exclusively of fungal hyphae, whereas some may consist partly of fungal hyphae plexus and partly in between tissues of the substrate (ergot, Sclerotinia). In favorable conditions, sclerotia germinate to form fruiting bodies (Basidiomycetes) or mycelium with conidia (in imperfect fungi). Sclerotia sizes can range from a fraction of a millimeter to a few tens of centimeters as, for example Laccocephalum mylittae, which has sclerotia with diameters up to 30 cm and weighing up to 20 kg.In the Middle Ages Claviceps purpurea sclerotia contaminated rye grain used in bread and led to ergot poisoning by way of which thousands of people were killed and mutilated. Claviceps purpurea sclerotia contain alkaloids that, when consumed, can cause ergotism which is a disease that causes paranoia and hallucinations, twitches, spasms, loss of peripheral sensation, edema and loss of affected tissues.For example, Claviceps purpurea sclerotia form and begin regrowth in the spring, infecting grass and rye plants by way of releasing their ascospores from perithecia. Claviceps purpurea can infect a wide variety of plants by infecting the ovaries. The fungal spores germinate at the anthesis and grow down the pollen tube without branching any hyphae outward. When the fungus reaches the bottom of the ovary, it leaves the pollen tube path and enters the vascular tissues where it branches its hypha. Approximately seven days into the infection, the mycelium produces conidia. The conidia are then secreted out of the plant in a sugary liquid that insects, attracted by the sugars, transfer to other plants. After two weeks of being infected by the fungus, the plant no longer generates the sugary liquid, and the fungus produces sclerotia. The sclerotium is an overwinter structure, which contains ergot alkaloids.Claviceps purpurea's life cycle is an interesting model for plant pathologists and cell biologists because:This sclerotium of Wolfiporia extensa (called 'Tuckahoe', or Indian bread) was used by Native Americans as a source of food in times of scarcity. It is a wood-decay fungus but has a terrestrial growth habit. It is notable in the development of a large, long-lasting underground sclerotium, which resembles a small coconut.Over billions of years of Earth's history, organisms have acquired the ability to produce secondary metabolites, that is chemical compounds that afford protection from pathogens and ultraviolet light damage from the sun. Fungi are no exception, and due to their exposure to a wide variety of environments, they have developed the ability to produce a large number of such chemical compounds that are very valuable in medicine.Many methods have been created to reduce the growth of agriculturally pathogenic sclerotia like changes in crop rotation, deeper ploughing and sifting out sclerotia. Fungicides, breeding disease resistance rye and cross breeding natural rye with hybrid rye have reduced C. purpurea infections.Sclerotium delphinii sclerotia on infected hostAthelia rolfsii sclerotia on Solanum lycopersicum (tomato)