Mushrooms are the fruiting bodies which are edible. They are cultured in many parts of the world. They were used as food since long back, probably from 3000 B.C The Greeks and the Romans described mushrooms as "food for the god". Since that time, people consumed mushrooms after collecting them from their natural habitats. The cultivation was started in the early part of the 18th century in France. The World Health Organization (WHO) recommended some mushrooms can be used as nutritious food for human consumption.
The body of mushrooms divides into vegetative body - the mycelium and reproductive body - fruiting body. The mycelium comprises a profusely branched thread like septate (segmented) hyphae grown in the substratum. Hypha is the individual thread-like filament that forms the mycelium and the fruiting body. The mycelium absorbs soluble food from the substratum. The mycelia are of two types -the monokaryotic primary mycelia and dikaryotic secondary mycelia. Primary mycelia are short-lived. They give rise to long-lived secondary dikaryotic mycelium through somatogamy i.e. fusing of their two compatible hyphae. Secondary mycelium or spawn produces aerial basidiocarps. Basidiocarp has a fleshy stalk or stipe and an umbrella-shaped cap or pileus.
A membranous annulus occurs on the upper part of the stipe. The undersurface of the pileus is flat and has a number of radiating rows of vertical plates called lamellae or gills. The two sides of each gill bear numerous basidia and paraphyses. Each basidium develops four sterigmata with a basidiospore at its free margin. Basidiospores of mushrooms are brownish.
On germination, each basidiospore forms a primary mycelium. A volva is a cup- like structure at the base of a mushroom that is a remnant of the veil. The veil or velum is a very thin membrane that covers a young mushroom. When the pileus of a mushroom opens, it leaves its remnant as volva (near the base of the stalk) and annulus (near the pileus at the stalk).
Internal structure of pileus through gills: A vertical section of the pileus through the gills shows three distinct regions: trama, sub- hymenium and hymenium. The trama is the innermost portion of the gill. It is formed by a mass of elongated hyphae. Outside the trama, a compact layer of short branches forms a sub-hymenium. The outer layer is the hymenium that consists of two types of cells: larger club-shaped cells, the basidia and a shorter sterile cell, called paraphyses. Both the basidia and the paraphyses are binucleate. Later, the basidia produce basidiospores.
Basidiocarp of the mushroom consists of pileus, gills and stipe. There are many thin vertical plates-like gills or lamellae present under the surface of the pileus. Gills produce the spores or basidiospores for reproduction and protect them.
The internal structure of the gills shows three distinct regions: trama, sub-hymenium and hymenium. The outer layer of the hymenium consists of larger club-shaped basidia and shorter sterile paraphyses. Both the basidia and the paraphyses are binucleate. The two nuclei of each basidium get fused to form the diploid nucleus (karyogamy) and the basidium represents the zygote. Now, the zygote is the only diploid stage in the life cycle.
The zygote (2n) immediately undergoes meiosis to form four haploid nuclei (n). The basidium develops into four slender outgrowths called sterigmata. Each of the four nuclei along with cytoplasm migrates into each sterigma. The tip of sterigmata finally develops into basidiospores. In this way, each basidium produces four basidiospores. Among four, two basidiospores are of one mating type or positive strain (+ve) and the other two are another mating type or negative (-ve) strain. On maturity, basidiospores are pinched up and are blown away by wind. On falling on suitable substratum, all the basidiospores germinate and form four uninucleate primary hyphae or monokaryons (two +ve strain and two-ve strain). The two hyphal cells between compatible monokaryons fuse together to form dikaryon or dikaryotic hyphal cells. The dikaryon develops secondary mycelium. The secondary mycelium is long and branched. Several secondary mycelia are twisted forming a cord-like structure, the rhizomorph. During reproduction, the rhizomorph develops many rounded structures on its surface. This stage is called the button stage. The button stage expands and develops the mature basidiocarp. Thus, once mature, mushrooms produce basidiospores, releasing them to the suitable environment and continuing the life cycle of mushrooms.
Generally, mushrooms grow in moist humid and dark places; on rotten logs of wood, tree trunks, and soil rich in organic matter, dung cakes, decaying organic matter, etc. Mushrooms are the members of the kingdom Fungi. They are achlorophyllous they do not contain green pigment called chlorophyll. They cannot make their own food. They get food from decomposing dead and decaying organic matter. So, mushrooms are called saprophytic fungi and their mode of nutrition is heterotrophic. ll the mushrooms growing in the forest are not edible. Some of them are very poisonous.
Pleurotus ostreatus, Agaricus brunnescens, field mushroom (Agaricus campestris), Lentinus edodes), Paddy straw mushroom (Volvariella volvacea), wood mushroom (Laccaria leccata), Oyster mushroom (Pleurotussajor-caju), etc. are some common examples of edible mushrooms.
Mushrooms are the richest source of vegetable protein which ranges its value very high. They are rich in protein content which varies from 19 to 35% by dry weight which is much higher than pulses, cereals (rice (7.3%), wheat (12.7%), chicken (18-20%), vegetables and fruits. They are useful for vegetarians and for the people who want to increase the protein content in their diet. The proteins of mushrooms contain essential amino acids including lysine (550 mg/gm) in much higher amounts. Amino acids help in healthy growth of the body.
There are different vitamins present in the mushroom; some of them are vitamin B2 (riboflavin), Pantothenic acid, thiamine (B1), biotin, folate, niacin, vitamin B12 and vitamin D. They are useful for vegetarians. They help to lower the cholesterol by the fiber which is present in mushrooms. It is important for the digestive system. Vitamin D is essential for the absorption of calcium.
Mushrooms are rich in important minerals such as sodium, phosphorus, calcium, iron, copper, potassium and selenium. Copper helps in absorbing oxygen and creating red blood cells; potassium regulates the blood pressure and helps in the functioning of cells properly. Selenium acts as an antioxidant to prevent cell damage which reduces the risk of cancer and other diseases. It contains low levels of fat, calories and sodium.
Mushrooms are highly valued in the medicinal system for curing. They contain antioxidants, anticancer, antiviral, immuno-modulatory and aphrodisiac. Most of the mushrooms have high medicinal value to reduce blood pressure, obesity, constipation, atherosclerosis (fat deposition inside blood vessels), joint pains, piles, etc. Mushrooms such as Ganoderma lucidum, Lentinus edodes etc. have potential anti-cancer property. So, it is used to make medicine for the treatment of cancer.
Wild mushrooms play a critical role in nearly every ecosystem. They function as the decomposers as well as the part of food chain to maintain a healthy ecosystem. They are a key in recycling dead vegetation and making nutrients available for the next generation of plant life.