Fungi Science
Effect of adding fossilised shell in Auricularia polytricha cultivation
Global demand for wood ear mushroom, including Auricularia polytricha, is high, with expanded production in Asia in particular making it the third most-produced mushroom after shiitake and oyster mushrooms. By contrast, in Japan the yield of wood ear mushrooms centered on A. polytricha is 2,315 tonnes, which constitutes a mere 8.4% of the 27,546 tonnes (fresh weight equivalent) consumed domestically. However, with fraudulent origin claims, residual pesticides and other risks with imported agricultural products also arising with imported mushrooms, the use of domestically produced mushrooms is being actively promoted and wood ear mushroom production in Japan has increased more than sevenfold in the last ten years. Further, A. polytricha favours a warm climate, so the ability to cultivate it in simple facilities without the need for strict temperature control has also contributed to its increased production in Japan.
A. polytricha has traditionally been imported so, compared to other mushroom varieties, there has been limited research into and development of its cultivation conditions and substrate composition. In recent years, however, there has been more research on substrates and nutrition supplementation with public research institutes publishing the results of studies on cultivation conditions with the aim of introducing them across Japan. Although such efforts towards achieving stable A. polytricha production are steadily progressing, further research is still needed to enhance Japan’s production capacity.
Increased yields with the addition of materials high in calcium carbonate such as fossilised shells and oyster shells have been reported for shiitake, bunashimeji, maitake and other major mushroom varieties. Although there are many cultivation instructions and cultivation test reports on A. polytricha that talk about adding calcium carbonate, to our knowledge there are no studies on the effect of its addition.
Therefore, in this study, we clarified the effects of adding of fossilised shells, which are widely distributed throughout Japan and are largely composed of calcium carbonate, on mycelial growth. Further, A. polytricha generally has an incubation period of at least 60 days. However, because increased yields and a shortened cultivation period are crucial for enhancing domestic productivity, in the incubation process we also investigated the possibility of reducing the incubation period by creating subgroups with incubation periods under 60 days with a focus on improving yield.
In this study, we tested the Kinko AP1 variety of A. polytricha (variety registration pending; application number 34132) (see Fig. 1). This [Kinko AP1] strain is stored as TMIC 36441 at the Tottori Mycological Institute of the Japan Kinoko Research Center Foundation. The spore-producing part of the A. polytricha fruiting body is naturally dark brown to black, but becomes lighter in colour when cultivation conditions are suboptimal. This is a high-yield strain that is less prone to lightening.
Table 1 shows the substrate compostion (all in absolute dry weight ratios) used in our mycelial growth tests and cultivation tests. Table 2 shows the main components of the fossilised shell used in this study.
The base and nutrition supplementation was mixed at a ratio of 8:2. We created test group B with a base of only beech sawdust (from Takebayashi Mokuzai Kogyo in Hokkaido) and, in response to the recent rising price of hardwood sawdust, test group BS with a 6:4 mixture of beech sawdust and cedar sawdust (left outside for over two months, from Rekisha Shoten in Okayama Prefecture). The nutrition supplementation was wheat bran (or excess wheat bran equivalent from Masuda Flour Milling in Hyogo Prefecture) and rice bran (from Tottoriken Shoku in Tottori Prefecture) mixed at a ratio of 6:4. The moisture content was prepared to 63 ± 2% and the fossilised shell (from Toyo Kogyo in Tochigi Prefecture) was added in increments of 0.5% in relation to the substrate weight after the addition of water from 0-3.5% in eight B subgroups and 0-2.0% in five BS subgroups.