This study was to select ectomycorrhizal fungi which were tolerant to heavy metals including zinc, copper, lead and cadmium and to examine the growth of Dipterocarpus alatus Roxb. seedlings inoculated with ectomycorrhizal fungi when exposed to heavy metals in order to use as future trends in remedial plantings on heavy metal-contaminated sites. Forty-three ectomycorrhizal fungal isolates of Gasteromycetes including Astraeus sp., Pisolithus sp. and Scleroderma sp. collected from several natural sites of Thailand were tested for heavy metals tolerance on modified Melin-Norkrans (MMN) agar, pH 4.3 supplemented with ZnSO₄, CuSO₄, Pb(NO₃)₂ and CdSO₄. The colony diameter and the mycelia dry weight of each isolate were determined every week and 4 weeks after inoculation respectively to compare the fungal growth and also analyse the effective concentration of heavy metals inhibiting growth by 50%, EC₅₀. The results exhibited that Scleroderma sp. isolate Ssp42 showed high zinc tolerance with the EC₅₀ value of 7.5 mM. High copper tolerance with the EC₅₀ value of 7.1 mM was detected in Pisolithus sp. isolate Psp32. Pisolithus albus isolate Pa33 showed high lead tolerance with the EC₅₀ value of 5.8 mM. Whereas, Astraeus asiaticus isolate Aa11 showed high cadmium tolerance with the EC50 value of 0.047 mM. The most four ectomycorrhizal fungal isolates tolerant of each heavy metal were inoculated in Dipterocarpus alatus Roxb. seedlings and then grown in substrate culture with addition of heavy metal. The results showed that there was no statistically significant differences between inoculated and uninoculated seedlings in terms of height, root collar diameter, fresh and dry matter of shoot and root. Furthermore, the ectomycorrhizal infection on the seedlings was not observed in all treatments.
