Volvariella spp Paddy Straw Mushroom

Volvariella is a mushroom of the tropics and subtropics; it grows at a relatively high temperature of around 35°C. This is a very fast growing mushroom, it takes about 10 days from spawning to first harvesting, is easiest to cultivate with a cropping cycle of 3 weeks but does not give good economic yields and its shelf-life is poorest of all mushrooms. Understandably, its production in 1997 was only 0.18 million tonnes and it contributed only 3% to the world mushroom production while its share was 4.6% in 1986. Nevertheless, its significance lies in East Asian countries where staple food is rice and paddy straw can be utilized for growing this mushroom mostly for self-consumption or trade in the domestic market. Commonly cultivated species are V. volvacea and V. bombycina.

There are two commercial substrates for growing this mushroom: traditional paddy straw bundles made into beds and the other involves the use of cotton waste compost after a short period of fermentation. The latter has many advantages (Quimio 1993; Quimio et al. 1990). While outdoor seasonal farming is still done on paddy straw by small growers, modern indoor cultivation is done on fermented cotton waste. Grain (wheat, sorghum) or cereal straw spawn is used; however, cotton waste + tea leaves spawn has been found superior (Chang 1982). Several techniques have been used for the cultivation of V. volvacea in the tropics, which thrives in the temperature range of 30-35°C and R.H. of 75-85% (Quimio et al. 1990). However, the traditional method of cultivation in South-East Asia is on straw beds, both outdoor and indoor, while the more sophisticated indoor technique is preferred for industrial scale production on cotton waste compost; the latter gives higher yield but is capital-intensive process. While the traditional paddy straw cultivation has been described in detail by several authors (Chang 1982; Khanna 1997; Quimio et al. 1990), modern indoor cultivation technology under controlled conditions on cotton waste compost will be dealt here (Chang 1982; Quimio 1993). Since 1973, straw mushroom has been cultivated completely on cotton waste compost in controlled conditions in Hong Kong and the technology is now being practiced in Thailand, Indonesia, Vietnam, Singapore, and some parts of Malaysia and Philippines. It takes about 4 days to make compost of cotton waste mixed with rice bran and water. Compost is filled (10 cm) on beds in a plastic mushroom house fitted with blower and polyduct and pasteurized with live steam for 2 h at 60-62°C, conditioned at 50-52°C for 8 h and then allowed to cool to 34-36°C suitable for spawning. The amount of spawn used is 1.4% of the dry weight of compost or 0.4% of wet weight. Full growth is achieved within 3-4 days at 32-34°C of room temperature. During spawn-running no water and light is needed and a little ventilation is provided. Then white light is provided with fluorescent lamps and fresh air is introduced. After removal of plastic sheets and sprinkling with water, growth of other fungi and actinomycetes retards while V. volvacea continues to grow. On the fifth day after spawning primordia appear, which take about 4 days to reach the harvesting stage. Straw mushrooms are not allowed to grow to umbrella like structures but are picked for marketing at the stage before volva enclosing the cap breaks or just after

Volvariella Volvacea
Figure 5 Proper stage for harvesting of V. volvacea.

rupture; the former is "button stage" and the latter is "egg stage" (Figure 5). The first flush usually lasts for 4-5 days; four days later second flush starts but yield is just 10% of the first flush. For all purposes, only one flush is commercially taken and in this way, one mushroom house can give two crops a month or at least three corps every two months. The shelf life of Volvariella is very short; it liquefies even at 4°C and also at high temperature. While canning is done at the industrial scale it is generally traded fresh or dried by small farmers in the developing countries.

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