Clonal propagation in the genus Ulmus: Improvement of rooting ability by Agrobacterium rhizogenes T-DNA genes

Elm clones may be propagated by grafting, but graft incompatibility is a ma jor problem. Rooting by cuttings does not always give satisfactory results. Shoots of elm clones resistant to Dutch Elm Disease (caused by Ophiostoma ulmi Buism.) and with poor rooting ability, were air layered after one of t he following five treatments: application of growth regulator mixture; inoc ulation with Agrobacterium rhizogenes wild type 1855 (A.r. 1855) or Agrobac terium tumefaciens-ORF11 (A.t. ORF11); application of growth regulator mixt ure and inoculation with A.r. 1855 or A.t. ORF11. Shoots treated only with growth regulators exhibited low percentage of rooting; shoots inoculated wi th only Agrobacterium strains produced very low percentage of rooting; shoo ts treated with growth regulator and inoculated with Agrobacterium strains exhibited the best percentage of rooting. The results demonstrated the poss ibility of rooting of these recalcitrant clones, with clear advantage for t he propagation of elm clones with growth regulator and A.t. ORF11.