The king oyster mushroom (Pleurotus eryngii) is classified as a white rot fungus capable of digesting lignocellulose (Sharma and Arora, 2015). Currently, lignocellulosic materials such as sawdust obtained from various tree species are widely used for commercial production of this mushroom (Peng, 1997; Yamanaka, 2011). Due to the crisis of global warming, the role as carbon sink of forest trees has received much attention, with the aim of reducing use of raw tree materials. Thus, many research efforts have focused on finding lignocellulosic wastes suitable for mushroom production to replace sawdust, which is often associated with deforestation (Baysal, 2003; Kurt and Buyukalaca, 2010; Obodai et al., 2003; Petre and Teodorescu, 2012; Rani et al., 2008; Yildiz et al., 2002; Zervakis, 2005).
According to Poppe (2000), at least 200 agroforestry wastes can be used for oyster mushroom production. However, numerous studies have indicated that individual mushroom species exhibit different growth responses to various cultivation substrates derived from particular agricultural residues. For example, Sherief et al. (2010) compared the growth and fruiting of a commercial strain of oyster mushroom cultivated on the two most commonly used substrates, namely rice straw and sawdust, and found that fruiting was earlier on rice straw. Obodai et al. (2003) evaluated eight lignocellulosic residues for growing the oyster mushroom Pleurotus ostreatus (Jacq. ex. Fr.) Kummer. They concluded that rice straw may be the best choice for oyster mushroom cultivation. Therefore, scientific evaluation of mushroom growth responses should be performed before any of the lignocellulosic wastes are recommended as alternative substrates for mushroom cultivation.
Current statistical data in Taiwan indicated that mushroom growers depend largely on imported sawdust: ≈5500 t annually at an average price of NT$15/kg (Customs Administration, R.O.C., 2014). Due to both the desire to limit deforestation and the increased demands for raw products, the free market supply of sawdust has decreased, creating an urgent need to reduce the reliance of mushroom growers on sawdust, particularly in markets that rely on imports. On the other hand, horticultural wastes, such as the trimmed branches of fruit trees, are a good source of lignocellulose. However, it is unknown whether pruned fruit tree branches can serve as an alternative substrate for king oyster mushroom growth. In Taiwan, around 5113 ha of land are devoted to wax apple [Syzygium samarangense (Blume) Merrill & Perry] cultivation, with 70% to 80% of wax apple tree branches pruned annually to achieve off-season production. Additionally, around 2048 ha of land in Taiwan are used for Indian jujube (Ziziphus mauritiana Lam.) production (Council of Agriculture–Taiwan, 2013), with annual tree pruning a common practice among growers to obtain higher yields. These pruned fruit tree branches are a horticultural waste and their removal from the orchard are an expense. In the present study, we investigated the potential of ground branches pruned from wax apple or Indian jujube trees to partially substitute sawdust in king oyster mushroom cultivation.
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