Application of ectomycorrhizal fungi in rooting of Scots pine fascicular shoots

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.