Cultivation and spawn production of the wood-decaying fungus, shiitake (Lentinula edodes): Optimization of spawn growth, production of degradative enzymes and interaction with wood inhabitants: Dissertation

The growth requirements and characteristics of six shiitake (Lentinula edodes) strains were evaluated. Of these only two produced a sufficient harvest of normal sporophores on artificial logs. The shiitake strains used in Finland turned out to belong to the "cold strains" which grow and form sporophores well at 18 - 25 oC and in an sawdust medium of about 64 - 76 % moisture content. The shiitake spawn was grown in a liquid medium. During the growth period a mycelial mat was formed over the medium which was broken up into mycelial fragments by homogenization. The homogenization had a very destructive effect on spawn growth and viability. The unfavourable effects of homogenization could be avoided by using mycelium of the correct age, the shortest possible homogenization time and by allowing the mycelium to recover for sufficient time before inoculating the sawdust logs. The production of liquid spawn was improved by sawdust or calcium sulphate supplementation. The supplementation of liquid spawn production medium by sawdust resulted in a great mycelial biomass yield and increased production of extracellular cellulases. The amount of xylanase activity was lower than the cellulase activity but it was clearly connected to the appearance of cellulase activity during the growth period. The addition of calcium sulphate to the liquid spawn production medium resulted in an almost four times greater yield of mycelium than in the control culture, and was followed by a sharp decrease in pH of the medium. Later, when sawdust logs were inoculated with spawn grown with calcium sulphate supplementation, a two fold mushroom harvest compared with the control was obtained. The mycelial growth and wood degradation of two shiitake strains were studied on alder and birch logs at four climatically and vegetatively different ripening fields. Preliminary laboratory tests showed that alder was degraded more efficiently than birch by both shiitake strains. The strain ELI2099 degraded both wood species faster than the strain ELI2094. However, during the field experiment little difference was observed in the degradation ability between the two strains. The moisture content of alder logs varied depending on weather conditions and season but by contrast birch logs maintained their moisture content better despite the climatic changes. The most suitable conditions for rapid mycelial growth were provided in sunny conditions, on sparse spruce or mixed wood with a slight west-east slope. The antagonistic activity of two Pseudomonas species was studied. These strains were isolated from alder logs inoculated with shiitake mycelium for mushroom cultivation. The bacteria were found to produce siderophores. P. chlororaphis was a stronger inhibitor of shiitake than P. fluorescens on yeast-malt extract medium. The iron addition neutralized the mycelial growth inhibition caused by P. fluorescens but not completely the growth inhibition caused by P. chlororaphis. The iron-specific chelator, EDDHA, showed also strong inhibitory action against the mycelial growth, which also suggested the involvement of siderophores in growth inhibition of shiitake caused by P. chlororaphis and P. fluorescens.