The potential applicability of bamboo in the sawdust based cultivation substrate of Pleurotus ostreatus was evaluated using bamboo sawdust with/without aging treatment. Regarding with cultivation period, the complementary relationship in untreated bamboo sawdust and aged bamboo sawdust was observed between required days for spread medium by mycelium and the days for fruit-body after spread over medium. And accordingly almost same period was required for both cultivations in untreated bamboo sawdust and aged bamboo sawdust. The fruit-body yield in the culture substituting with 50% untreated bamboo sawdust for hardwood was significantly higher than that in control cultivation, and almost identical yields with control cultivation were observed in the cultures substituting with 25, 75, and 100% untreated bamboo sawdust. These clearly indicate that untreated bamboo sawdust is applicable as a substrate for sawdust based cultivation of P. ostreatus. To examine the effect of the aging periods on the fruit-body yield, bamboo sawdust was aging-treated for different periods (from 1 to 6 months). In the case of substitution ratio of 100% bamboo sawdust aged for 4 months, the fruit-body yield reached the maximum value which was 1.3 folds higher than that in the control cultivation. Content of alcohol-benzene extracts in bamboo sawdust was decreased a little and soluble carbohydrate was decreased considerably in the course of aging treatment. Therefore it was suggested that the increase of fruit-body yield by aging treatment was caused by other factors than these components.

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The glucoamylase 1 gene (PnGlu1) from the saprophytic fungus Pholiota microspora has been previously cloned and characterized. In this study, a second glucoamylase gene (PnGlu2), 1719 bp long and encoding 573 amino acids, was identified in the P. microspora genome. PnGlu1 and PnGlu2 show 70% amino acid identity. Transcriptional analyses showed that PnGlu1 and PnGlu2 expression in minimal media containing different carbon sources are far lower than that in sawdust medium. In sawdust medium, transcription level of PnGlu1 is high in vegetative dikaryotic mycelia and that of PnGlu2 is high in primordia and at the fruiting body stage. These data suggested that the two glucoamylase gene PnGlu1 and PnGlu2 may be differentially regulated in each developmental stage such as mycelial growth and fruiting body formation.

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To enhance reliability of population estimation by increasing the number of samples inspected, we examined the efficiency of nondestructive inspection methods. The nondestructive inspection system consists of detectors made from a combination of high-sensitivity scintillator crystals (Ce:Gd3(Al,Ga)5O12(Ce:GAGG)) and semiconductor devices. The radiation count rate (CPS) within the shiitake logs measured by the nondestructive inspection system was converted into Bq/kg. The moisture content of shiitake logs in the felling season was between 40 and 43%. The shiitake log density was between 1.0 and 1.1. This inspection resulted in differences in the slant of the regression line and sample weight. The differences were caused by the moisture content of the shiitake logs and standard sample. The standard sample was modified by processing fresh shiitake logs into a cylinder, wrapping it with radiocesium infiltrated paper and also by increasing its surface area with fiber-reinforced plastic (FRP). Based on examining the results of inspecting the modified shiitake mushroom logs, those covered with FRP most represented actual shiitake logs.

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We investigated the radiocesium (Cs-134 + Cs-137) concentration in trees (Quercus serrata) used in shiitake mushroom log cultivation in Tochigi Prefecture (where the concentration of radiocesium differs among three areas) by nondestructive inspection methods. Most of the logs in the Sakura city area exceeded the index value (50 Bq/kg or less at 12% log water content as specified by the Forestry Agency of Japan); therefore, trees of this area cannot be used as shiitake mushroom logs. On the other hand, all logs in the Ichikai town area were below the index value. Furthermore, 9.4% of logs in the Utsunomiya city area exceeded the index value. The surfaces of logs from Utsunomiya were rinsed, and then the radiocesium concentration of the rinsed logs was measured. An average 20 Bq/kg decrease was observed for all logs. Based on these test results, we calculated the reliable minimum sampling number (to determine whether logs meet a specified value allowing their use for shiitake cultivation) from a t-distribution (small sample theory method). With a confidence level of 95%, 202 logs need to be removed for sampling from the Sakura city set and 188 logs need to be removed for sampling from the Utsunomiya city set.

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