AbstractYoung seedlings and calli of European larch (Larix deciduaMill.) but not jack pine (Pinus banksianaLamb.) were rapidly infected withAgrobacterium rhizogenes(Riker et al.) Conn. Calli were extensively colonized and necrotic within 2 weeks. Seedlings swelled at the wound site, and developed multiple buds, blue‐colored needles with dense aggregations of stomates, or adventitious roots. Inoculation of juvenile conifer tissues with selected strains of plasmid donors may offer opportunity to clone engineered superior tree genotypes throughin vitromicropropagatio