To establish a theoretical method of log cultivation of shiitake, Lentinula edodes (Berk.) Pegler, the biology of the fungus was studied. Comparing the amounts of chemical components in Quercus serrata wood and the fruiting bodies revealed that N, P, and K contents in logs limited fruiting body yield. A log of 10,000cm^3 in volume could produce ca. 260g of dried fruiting bodies in the course of its life. The process of log cultivation is divided into three stages: preparation of bedlogs, formation of fruiting body primordia, and development of fruiting bodies. After the preparation of bedlogs, mycelial amounts of bedlogs, which were estimated with chitin content, were positively correlated with fruiting body yield. The degree of wood decay also affected fruiting; a shiitake strain with a specific gravity of ca. 0.4 of oven-dried wood showed good fruiting, although the ability of shiitake to decay wood varied among strains. Formation of fruiting body primordia requires light, water, and moderate temperatures (15-25℃). In Quercus serrata logs, outer bark more than 2mm in thickness completely prevented both light transmission to the inside and the formation of primordia. In three-year-old bedlogs, a moisture content of more than 35% was necessary for primordia formation. Number of primordia tended to increase from spring to autumn but not in winter. Low temperatures induced fruiting body development which accompanied the enhancement of enzyme activities such as acid protease and the accumulation of nutrients around a developing fruiting body. Logs consist of wood substance, water (bound water and free water), and air. Each bedlog had its own optimum water content for fruiting, depending on the degree of wood decay. For example, a high content of free water, more than 20%, together with a high content of air, more than 30%, resulted in a good fruiting. Damage of bedlogs by Trichoderma spp. such as T.harzianum and T.polysporum reduces fruiting body yield. They often attack and kill shiitake mycelium in bedlogs by producing antifungal substances and mycolytic enzymes. However, shiitake are more or less able to resist a Trichoderma attack. Shiitake cultures produced at least five straight-chain antibiotic alcohols, which act as anti-Trichoderma substances because the kind and amount of the substances increased after a Trichoderma attack. A Trichoderma inoculation test for shiitake cultures showed that the resistance of shiitake in a wood-powder medium was correlated positively with that in bedlogs. A screening assay using the wood-powder medium selected some highly resistant and highly susceptible strains. Crossing between these strains revealed that resistance was dominant to susceptibility.

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Severe brown rot disease on Lentinula edodes cultivated on bed logs was reported in Oita Prefecture during the period of 1994-1996. A causative bacterium was isolated from young and old fruit bodies. The isolated bacterium produced the rotting symptoms on shiitake mushroom formed on the bed logs following artificial inoculation and also on slices of fruit bodies, gill, and mycelium of several different kinds of mushrooms cultivated in Japan. The causal bacterium was identified as Ewingella americana according to its bacteriological characteristics and 16S rRNA gene analysis. The name brown rot (Fuhai byo) was proposed for this disease.

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Clinical studies in humans have reported that the intake of dietary Flammulina velutipes (Curt.: Fr.) Singer extracts results in a significant decrease in the visceral fat area as measured by computed tomography. The fatty acid composition of F.velutipes extracts was found to include constituents that bind to cells expressing the β-adrenoceptor. Here, we investigated the effect of F.velutipes extracts on lipid accumulation in primary culture of rat visceral adipocytes. Morphological examination showed a marked reduction in lipid droplets compared with the control, demonstrating an inhibitory effect on lipid accumulation. The triglyceride (TG) to DNA ratio in cells after the culturing with F.velutipes extract was significantly lower. These findings suggest that F.velutipes extracts have an inhibitory effect on visceral fat accumulation.

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We used random amplified polymorphic DNA (RAPD) analysis with six kinds of 10-mer primers to type Cladobotryum varium and Trichoderma cf. pleuroticola strains isolated from Japanese mushroom cultivation facilities. Strains of C.varium isolated in Fukuoka, Nagano, and Saitama Prefectures had similar amplification patterns. Similarly, strains of T.cf. pleuroticola isolated in Nagano, Kumamoto, Fukuoka and Niigata Prefectures had similar amplification patterns. Strains of C.varium and T.cf. pleuroticola isolated in different years from the same facilities had similar respective amplification patterns. This result indicated that a certain strain continued to disturb mushrooms cultivated within the same facility. In one system in which the inoculation and culture facility was separated from the fructification facilities, the RAPD patterns of a C.varium strain isolated from the inoculation and culture facility had amplification patterns similar to strains isolated from the fructification facilities.

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