The mushroom defined as “a macro fungus with a distinctive fruiting body, large enough to be seen with the naked eye and to be picked up by hand” (Chang and Miles, 1992). In a narrow sense, the world mushroom also refers only to the fruit body. Unlike green plants, mushrooms are heterotrophs. Not having chlorophyll, they cannot generate nutrients by photosynthesis, but take nutrients from outer sources. Fungi cultivation develops with the advance of science and technology. In history, human beings only hunted and collected wild mushrooms at the beginning. After a long period they observed and learned how to cultivate fungi. Presently, mushrooms have become popular throughout the world since they have wonderful food and medicinal values. The local demand for mushrooms is also steadily increasing [2].
Population increases are creating an alarming situation in the food supply in Sri Lanka. Malnutrition in terms of 'protein' deficiency is becoming a major hazard in developing countries. Exploiting non-traditional food resources can make a substantial breakthrough to meet the serious food deficit. In this circumstance, popularizing mushroom as part and parcel of every day food is of paramount importance. No food is so wrapped in mystery as mushroom. It is amazing to see tiny pin heads on a composting medium growing into buttons rich in protein, vitamins and minerals. Not only because that mushrooms have a marvelous medicinal values. Mushroom is a protein source without cholesterol. On the other hand, they have an ability to maintain the blood cholesterol at the optimum level. In addition to that there are some other medicinal values that also can be found in mushrooms [3].
Mushroom farming is becoming successful because of its very low inputs. In Sri Lanka, mushroom cultivation is highly rewarding because of the prevailing climatic conditions. The technology profitably is located in areas where land is limiting factor and agricultural residues are abundantly available.
Although the history of the world mushroom cultivation goes back to thousands years the commercial mushroom cultivation in Sri Lanka was started in the middle of 1980's with the cultivation of Oyster (Pleurotus ostreatus). However, compared to other countries technological improvements of mushroom cultivation are not satisfactory in Sri Lanka. Oyster, Paddy straw (Volvariella volvacea) and Milky (Calocybe indica) mushrooms are some of the high potential cultivable mushrooms in Sri Lanka since they can grow well under tropical and subtropical condition. Paddy straw mushroom is a popular variety among people because of its distinct flavor, pleasant tastes, higher protein content and shorter cropping duration compared to other cultivated mushrooms. Presently, Sri Lanka imports canned paddy straw mushrooms from China and this mushroom is available in most of the supermarkets. It originally grows in rice straw stack in tropical and sub tropical zones that have high temperature and a rainy climate. Chinese growers developed its cultivation more than 300 years ago. Therefore, it was named “Chinese Mushroom” (Zhanxi and Zhanhua, 2000). Volvariella requires a high temperature (35 ± 2 ºC) for better and early hyphal growth. Also 32±2 ºC and 80-90 % RH (relative humidity) are needed for the formation of fruiting bodies [4]. The yield of straw mushroom depends on the cultivation methods and compost (growing) medium. Prior to 1970, rice straw was practically the only material used for preparing the growing medium for Volvariella volvacea. Straw alone is not sufficient as a composting material as it contains a little quantity nutrients and has a slow rate of decomposition [5]. Therefore, straw mushrooms presently are grown in some other materials such as cotton waste, sugar cane bagasse, dried banana leaves, oil farm bunch waste etc [4]. However, paddy straw is the material freely available in Sri Lanka and therefore, this cultivation is ideal in rural area where paddy straw is abundant after each paddy harvest and it can provide additional income.
An outdoor cultivation method was introduced for paddy straw mushroom by the Department of Agriculture in the middle of the 1980’s. However, farmers are reluctant to produce mushrooms using this method because of the uncertainty of production with irregular and low yield, due to difficulties to control environment factors such as temperature, RH and pest problems. Unlike the oyster mushroom, the straw mushroom is highly sensitive to the climatic conditions and their fluctuation. To overcome these problems, indoor cultivation method under controlled environment may be an effective alternative [6].
Therefore, an experiment was conducted to identify the suitability of an indoor cultivation method for paddy straw mushroom under Sri Lankan conditions, using locally available low cost raw materials.