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

SummaryElm clones may be propagated by grafting, but graft incompatibility is a major 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 the following five treatments: application of growth regulator mixture; inoculation with Agrobacterium rhizogenes wild type 1855 (A.r. 1855) or Agrobacterium tumefaciens-ORF11 (A.t. ORF11); application of growth regulator mixture and inoculation with A.r. 1855 or A.t. ORF11. Shoots treated only with growth regulators exhibited low percentage of rooting; shoots inoculated with only Agrobacterium strains produced very low percentage of rooting; shoots treated with growth regulator and inoculated with Agrobacterium strains exhibited the best percentage of rooting. The results demonstrated the possibility of rooting of these recalcitrant clones, with clear advantage for the propagation of elm clones with grow...