Astraeus asiaticus and A. odoratus are edible ectomycorrhizal fungi associated with dipterocarp tree. Dipterocarpaceae is commercial hardwoods and important to tropical forest ecosystem in South East Asia especially in Thailand. Dipterocarp plantations are now not quite successful due to poor ectomycorrhizal association there is a need to develop inoculation programs for forest nurseries. In this study, 45 strains of Astraeus asiaticus and 9 strains of A. odoratus collected from various localities in Thailand were isolated and cultured on PDA medium. A. asiaticus strain KANII6 and A. odoratus strain TAK8 were selected for inoculum production based on giving the highest colony growth rate on PDA medium at 14 days. The effects of different media and pH on growth from both strains were studied with the aim of improving mycelial production. Among media and pH tested, MMN medium at pH 5.5 was found to be the best medium and pH for the both strains with the maximum mycelial dry weight of 1.95 mg/ml in A. asiaticus strain KANII6 and those of 2.17 mg/ml in A. odoratus strain TAK8 at 35 days. The effects of different inoculation techniques (mycelial suspension, mycelial inoculum grown in peat-vermiculite, mycelial inoculum grown in coconut dust-rice husk, alginate-entrapped mycelium) of both strains on mycorrhizal formation and growth stimulation of 8- months-old Dipterocarpus alatus seedlings were also evaluated. The results showed that no mycorrhizal infection was found in noninoculation treatments. The percentage of mycorrhizal infection showed similar values for both fungal species. The percentage of infection in treatments inoculated with the strain KANII6 was ranging from 5.67% to 13.44 %. The strain TAK8 colonized seedling roots ranging from 5.33% to 14.78%. The seedlings inoculated with mycelia inoculum grown in coconut dust-rice husk mixed with growing medium in a proportion 1:6 (v/v) of both strains had the highest percentage of infection. The both strains significantly stimulated growth of D. alatus seedlings having mycorrhizal colonization > 12%. The seedlings inoculated with mycelia inoculums of fungal strain TAK8 grown in coconut dust-rice husk mixed with growing medium in proportion 1:6 and 1:3 (v/v) had shoot height, stem diameter, shoot and root dry weight and total biomass significantly greater than non-inoculated seedlings. The results in this study indicated that the seedling colonization level was very variable depending on inoculums dose and inoculation techniques. Moreover coconut dust and rice husk are promising alternative substrates for commercial mycelial inoculum production because of their availability and cheapness.
