Abstract
Attempts to characterise the growth conditions for Thelephora terrestris and Laccaria laccata were made, temperature,pH and medium composition were optimised. Both fungi were grown in submerged batch culture under carbon, nitrogen and phosphate limited conditions, and Laccaria laccata was also grown in continuous systems. The specific growth rates of Laccaria laccata and Thelephora terrestris were lower than those determined for most other filamentous fungi but the- yield and maintenance characteristics were comparable with other species. The growth morphology of the fungi in submerged culture varied from filamentous to pelleted types, depending on the species and conditions used. With Laccaria laccata a morphologically stable "floccular" growth form was observed. The infectivity of the CSTR grown cultures of Laccaria laccata and Thelephora terrestris to the conifer Picea sitchensis was determined. It was established that with both species the percentage of mycorrhizal short roots formed within the first six months was directly dependent upon the inoculum density (measured in terms of colony forming units). Pot trials revealed that approximately 100 colony forming units of each fungus were necessary to produce 90% infection of the root system. When environmental and/or soil conditions were adverse, increased levels of inoculum were required to produce adequate infection. Dry weight increase was observed in all of the inoculated treatments, however, the growth stimulation was reduced when excessive amounts of inocula were used. Reasons for this observation are discussed. The production of vegetative inoculum was successfully scaled up to the 200 litre level using a modified batch culture system. Each litre of inoculum was sufficient to inoculate approximately 500, 2 month old seedlings of Picea sitchensis. Two small scale field trials of the inocula were undertaken. The mycelial inoculum was formulated by immobilisation into alginate gel. The viability of the mycelium during and after immobilisation was dependant upon the morphology, growth phase, and nutrient status of the cells, together with the water content and storage temperature of the prepared gel. These parameters were optimised to the extent that 100% viability was maintained for 3 months. Half saturationconstants Ks) were determined for Thelephora terrestris and Laccaria laccata grown under glucose and phosphate limited conditions. The Ks values for glucose were high with both organisms, whilst the values for phosphate were found to be very low. These results indicate that these organisms have a low affinity to glucose but a high affinity to phosphate. The implication of this to the mycorrhizal symbiosis is discussed.