The ectomycorrhizal fungi, Pisolithus tinctorius (Pers.) Coker & Couch and
three Paxillus involutus (Batsch) Fr. strains, were used to enhance in vivo
rooting in fascicular shoots of 49 Scots pine (Pinus sylvestris L.) genoty
pes representing seed families from southern and northern Finland. Inoculat
ion with specific fungi either increased the rooting percentage or accelera
ted root formation expressed as an increased number of adventitious roots p
er cutting. Only one of the six seed families gave no positive response. Th
e relationship between the in vitro production of free and conjugated forms
of indole-3-acetic acid (IAA) by the fungi and rooting was also investigat
ed. Pisolithus tinctorius was the only significant producer of IAA in the a
bsence of exogenous tryptophan. All the Paxillus involutus strains also syn
thesized both free and conjugated IAA but did that actively only from exoge
nous tryptophan. In vitro production of IAA did not correlate with root ind
uction in vivo, but the rooting responses depended on the fungus strains an
d the Scots pine seed families and (or) genotypes within families. This ind
icates that in vitro IAA production capacity cannot be the only criterion w
hen selecting ectomycorrhizal fungi for rooting in vivo and that specific g
enotype-genotype interactions play a key role in root initiation.