THE EFFECTIVENESS OF ECTOMYCORRHIZAL FUNGI IN INCREASING THE GROWTH OF EUCALYPTUS-GLOBULUS LABILL IN RELATION TO ROOT COLONIZATION AND HYPHAL DEVELOPMENT IN SOIL

Forty-seven different isolates of ectomycorrhizal fungi, from 16 diffe rent genera, were screened for their effectiveness in increasing the g rowth of Eucalyptus globulus Labill. where supply of P is deficient. P lants were grown in a P-deficient sand, in pots, in a temperature-cont rolled glasshouse. Seedlings were harvested 63 and 87 d after planting , and were assessed for dry matter production and mycorrhizal coloniza tion. Selected treatments were also assessed for P concentrations in t he plant and hyphal development in the soil. Dry weights of inoculated plants ranged from 50 to 350% of the dry weights of uninoculated plan ts. Growth increases in response to ectomycorrhizal inoculation corres ponded with increased P uptake by the plant. 'Early' colonizing fungal species (Descolea maculata, Hebeloma westraliense, Laccaria laccata a nd Pisolithus tinctorius) were generally more effective in increasing plant growth than 'late' colonizing species (cortinarius spp. and Hyst erangium spp.), although there was also variation in effectiveness amo ng isolates of the same fungal species. Plant dry weights were positiv ely correlated (r(2) = 0.79-84) with the length of colonized root, ind icating that fungi which colonized roots extensively were the most eff ective in increasing plant growth. For some fungi, however, plant grow th responses to inoculation were not related to colonized root length. These responses could not be related to the development of hyphae in soil by the mycorrhizal fungi.