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INTRODUCTION

Mushrooms belong to the kingdom of Fungi, a group very distinct from plants, animals and bacteria. Fungi lack the most important feature of plants: the ability to use energy from the sun directly through Chlorophyll. Thus, fungi depend on other organisms for food, absorbing nutrients from the organic material in which they live. The living body of the fungus is mycelium made out of a tiny web of threads (or filaments) called hyphae. Under specific conditions, sexually compatible hyphae will fuse and start to form spores. The larger spore producing structures (bigger than about 1 mm) are called mushrooms. In nature this is the most striking part of the organism, but in fact it is just the fruiting body and the major part of the living organism is found under the ground or inside the wood.
Mushrooms are not plants, and require different conditions for optimal growth. Plants develop through photosynthesis, a process that converts atmospheric carbon dioxide into carbohydrates, especially cellulose. While sunlight provides an energy source for plants, mushrooms derive all of their energy and growth materials from their growth medium, through biochemical decomposition processes. This does not mean that light is an unnecessary requirement, since some fungi use light as a signal for fruiting. However, all the materials for growth must already be present in the growth medium.

REVIEW OF LITERATURE

Oyster mushrooms, Pleurotus spp, are edible fungi popularly known as wood fungi. Pleurotus is a genus of gilled mushrooms which includes one of the most widely eaten mushrooms, P. ostreatus. Species of Pleurotus may be called oyster, abalone, or tree mushrooms, and are some of the most commonly cultivated edible mushrooms in the world. Pleurotus fungi have been used in mycoremediation of pollutants such as petroleum and polycyclic aromatic hydrocarbons. The genus was established by Fries in 1821. There are a number of spp under this genus. According to Pegles (1970) and Singer (1986) this genus is known to contain 50 spp, of these about 25 spp are known to occur in India.
It is an 'oyster mushroom'. A number of different species are grown including, Pleurotus ostreatus, Pleurotus sajor-caju, Pleurotus cystidus, Pleurotus cystidus, Pleurotus citrinopileatus and Pleurotus flabellatus. This mushroom is cultivated on a wide range of plant wastes (cereal straw, sawdust, bagasse, waste cotton) often enclosed by plastic bags. Pleurotus mushrooms are the second most important mushrooms in production in the world, 25% of total world production of cultivated mushrooms. Pleurotus mushrooms are world-wide, China is the major producer.


METHODOLOGY

1. Isolation and maintenance of pure cultures of Pleurotus spp.
Isolation and maintenance of pure cultures of Pleurotus spp viz., Pleurotus florida, Pleurotus sajor-caju and Pleurotus eous were developed at the biotechnology lab in Mar Ivanios College by adopting tissue culture methods[Scarcye 1995].
Mycelium, or actively growing mushroom culture, is placed on growth substrate to seed or introduce mushrooms to grow on a substrate. This is also known as inoculation, spawning or adding spawn. Its main advantages are to reduce chances of contamination while giving mushrooms a firm beginning. Spores are another inoculation option, but are less developed than established mycelium. Since they are also contaminated easily, they are only manipulated in laboratory conditions with laminar flow cabinet.
Tissue from the junction of pileus and stipe of sporocarp was scooped out and surface sterilized by placing in 95% ethyl alcohol for one minute, after that the PDA slants were prepared, autoclaved for 15 minutes at 120C. Then inoculation of mycelium under the laminar flow in PDA slants and incubated at room temperature for 7-18 days. Following sub culturing it is maintained on PDA slants.


2. Spawn production
The mycelium will colonise the substrate and use the available nutrients. This is commonly referred to as the spawn run. When some nutrients run out, or when the weather changes, the mycelium will reach a different phase: the reproductive stage. A temperature of about 25 °C is optimal for the spawn run of most species. The environment can also enhance the growth of the desired mycelium: a high CO2 concentration is favorable for mycelial growth (but not for cropping). During spawn run stage the mycelium will grow through the substrate. The spawn run time is different for each species and depends on the size of the bag, amount of spawn, the strain used and the temperature.
Rice grain spawn of the three Pleurotus spp was prepared adopting the method described by Siva Prakasam (1980). Rice grains were boiled in water and are half boiled. After draining excess water, it was mixed with calcium carbonate at the rate of 50g per kg of rice grains to prevent adhesion of grains and for optimizing the pH for spawn. Bottles of 750ml capacity were filled with the grains to 2/3 of its capacity, plugged with cotton and autoclaved at 1.05kg cm-2 for 2 hours. The substrate should have cooled down (whether pasteurised by steam or by immersion in hot water) to 30 C. The spawn (3% to 8% of the weight of the substrate) can be mixed in with when filling the bags. Or a layer of substrate can be topped with some spawn, layer by layer.
Inoculation of the grains with pure cultures of pleurotus spp was carried out and incubated at room temperature. The nature of growth and time taken for completing mycelium colonization of the grains was recorded. The spawn thus prepared was utilized for laying out mushroom beds.
3. Preparation of mushroom beds
Preparation of bags : Use 60x30 cm polythene bags (both side open).Tie one end of bag, put two holes of 1 cm diameter in the middle.Put handful of cooked straw in the bag to a height of 5 cm; sprinkle about 25 g of spawn. Layer the straw to 25 cm height. Repeat the process to get four layers of spawn and 5 layers of straw. Tie the mouth and arrange beds in tiers in the spawn running room. After 15-20 days, cut and remove the polythene bag and transfer the beds to cropping room. Keep the beds moist by periodical spraying with water.
In the bed system mushrooms are grown in wooden receptacles which are approximately 65" wide×60 foot long. These receptacles may be wider or narrower than 65" and/or they can be shorter or longer than 60 feet long. The depth of these receptacles is generally from 6" to 8" deep, however, they can be any suitable size. In what is referred to as a mushroom house these receptacles are usually stacked in four tiers, In each of these tiers six receptacles are usually stacked in a superimposed arrangement so that one mushroom house contains 4 tiers and 24 receptacles.
In the tray system mushrooms are also grown in wooden receptacles. These receptacles or trays can be square or rectangular, however, the most popular size is 48" wide×72" long×8" deep. In a farm using the tray system approximately 220 of these trays are put into one growing room. The trays are generally stacked four to five trays high and are arranged in eleven rows four stacks to a row. A typical mushroom tray is about 175 cm. long by 120 cm. wide with the tray height being 17.5 cm. and the corner post extending upwardly from the tray sides a further distance of about 12.5-15 cm.
Mushrooms are grown on decaying organic material. This material can be horse manure, hay, cereal straw or a variety of other vegetable wastes. The breakdown of this organic material is accelerated by the mushroom grower by composting. The purpose of composting is to convert the crude, often variable, raw material into a medium rich in nutrition which is specific for the growth of mushrooms. Three different substrates were tried for mushroom production viz., paddy straw, non retted coir pith [obtained by manually extracting the mesocrap] and retted coir pith. Mushroom beds were prepared following the method described by Baskaran et al., (1978) in the case of paddy straw or non retted coir pith as the substrate and the method described by Theradinani and Marimuthu (1991) was adopted for the preparation of beds using retted coir pith as the substrate.
In the case of paddy straw and non retted coir pith, substrates were kept in water overnight, boiled for half an hour, drained and dried. In perforated polythene bags of size 60×30cm, 3 layers of substrate [each of 5 to 8cm thickness] was placed with spawning of each layer. 100gm spawn per mushroom beds was used. The bags were then tied and incubated in the dark for 15 days, after which they were opened and transferred to cropping room were adequate ventilation and moisture was maintained.
In the case of retted coir pith, well perforated polythene bags of size 30cm was first filled with 0.5kg of the substrate and inoculated with pleurotus spawn [at the rate of 100g per kg of the substrate] uniformly over surface and covered with another layer of 0.5kg of coir pith. This process was repeated till the bag was filled. The bag was tied and incubated in a room where adequate moisture and ventilation were present.
The nature and rate of growth and yield characteristics in all the substrates were recorded. Samples were drawn at 10, 20 and 30 days interval to study laccase production and also to estimate the laccase content.
4. Cultivation of oyster mushroom
Cultivation of Pleurotus spp on their natural habitat was first described at the beginning of 20th century [ Falck, 1917] and on a saw dust-cereal mixture by Kaufert (1935). The foundation for the industrial production of Pleurotus on different substrates was laid by several workers [Kalberes and Vogel, 1974; Zadrazil, 1974 and Kurtz man, 1979].
Pleurotus spp have been successfully cultivated of different agricultural wastes such as mixture of coconut fiber and coffee pulp [Bernabe et al., 1993], kidney bean stubbles [Sobal et al., 1993], sugarcane bagasse [Shi, 1994] and cotton wastes [Haq et al., 1994].