**2. Mushroom cultivation and stimulation for fruiting body development**

*Ganoderma lucidum* are cultivated for special medicinal mushroom. Mushroom is fruiting body mainly in basidiomycetous fungi and some ascomycetous fungi. Therefore, mushrooms are developed for spore formation at reproductive growth phase. Mushroom farming is mainly based on two methods: log-grown or fungus bed-culture which using a pot fill with sawdust-based substrate. The later method offers controllable conditions so that effective mushroom growth can be expected. Biological efficiency has been improved by optimizing various factors, such as substrate formula, strain type, culture maturity, water condition and

Physical phenomena in cells caused by external pulsed electromagnetic energy have a variety of applications on biotechnologies [1]. The electrical stimulation can either destroy the cells and plants or promote its growth rate, depending on the degree of stimulation. In nature, mushrooms extraordinary grow-up around a hit point of a lightning have been reported by some mushroom farmers. Early studies of mushroom growth promotion by artificial lightning were carried out on edible mushroom cultivation using an impulse generator [2]. The output voltage of the impulse generator was more than 500 kV. After that, the high-voltage pulsed power supplies were designed to generate an output voltage from 50 to 130 kV for the electrical stimulation on mushroom cultivation bed. The promotion effects of high-voltage stimulation on sawdust-based substrate of *L. decastes* and natural logs hosting *L. edodes, Pholiota microspora* and *Hypholoma lateritium* were evaluated using the developed compact pulsed power generator [3]. Typical stimulation effects are shown in **Figure 1** as a photograph of cultured *L. edodes* taken on the same day. The upper bed-log was used in cultivation without the high-voltage stimulation. The lower bed-log was used in cultivation and a 50 kV voltage was applied 50 times as stimulation. *L. edodes* in the stimulated log grew faster than that in the bed-log without stimulation. The high-voltage electrode is located on the left side of the log. The fruiting bodies mainly grow near the high-voltage electrode. In this chapter, the effect of high-voltage electrical stimulation on induction of fruiting body of mushroom is described.

**Figure 1.** Typical photograph of the cultured *L. edodes* with (**bottom**) and without (**top**) electrical stimulation.

other environmental conditions of the cultivation room.

96 Physical Methods for Stimulation of Plant and Mushroom Development

Mushroom is fruiting body mainly in basidiomycetous fungi and some ascomycetous fungi. Therefore, mushrooms are developed for spore formation. Multiple environmental factors such as light, temperature, nutrient, gaseous components influence fruiting body induction and development. These environmental factors are used for sensing appropriate conditions for spore formation and dispersal.

Condition for fruiting body induction is one of critical factor for mushroom cultivation. To establish high yield cultivation method, it is very important to understand effects of environmental factors for fruiting body induction. Environmental factors for fruiting body induction are classified into physiological and physical factors. Gaseous condition and nutrient, or hormones are classified as physiological factor, and wounding or striking as physical factors. Light is one of the important factors for fruiting body induction, and blue light is the effective wavelength. For example, light promotes fruiting body induction in *L. edodes*. In contrast, some species can induce fruiting body in complete darkness. Therefore, light can promote fruiting body development in some species, but not really necessary. Temperature is one of the critical factors for fruiting body induction in basidiomycetes. Especially, down shift of temperature stimulates fruiting body induction in many mushroom species. For example, fruiting body of *F. velutipes* can induce temperature down shift (e.g. 23 → 16°C) in complete darkness. Interestingly, fruiting body formed in complete darkness has tiny cap on its head [4]. It is revealed that proteins expressed specifically during fruiting body formation are regulated by temperature but not by light in *F. velutipes*. Nutrient is another critical factor for fruiting body induction. Especially, high concentration of carbon and nitrogen sources inhibits fruiting body induction. Wood decay fungi are major species for commercially cultivating mushrooms, therefore, wood decay is closely related to fruiting body induction.

Wounding or striking are used for commercial cultivation in several mushroom species. For example, scrapping mycelia on surface of the media (so called Kinkaki in Japanese) is used for fruiting body induction in several mushrooms. Striking log wood is used for stimulation of fruiting body induction especially in *L. edodes*. Electrical stimulation is also a physical factor for fruiting body induction similar to Kinkaki or striking. Japanese farmers have their elders' wisdom that lightning comes crashing into the ground provokes a plentiful mushroom harvest. Electrical stimulation used for stimulating fruiting body induction by mimicking the effect of lightning in nature.
