Rooting and Other Characteristics of a Transgenic Walnut Hybrid (Juglans hindsii × J. regia) Rootstock Expressing rolABC

Abstract

<jats:p>Walnuts (<jats:italic>Juglans</jats:italic> spp.) are difficult-to-root woody plants. The <jats:italic>rolABC</jats:italic> genes (<jats:italic>rolA</jats:italic> + <jats:italic>rolB</jats:italic> + <jats:italic>rolC</jats:italic>), derived from the bacteria <jats:italic>Agrobacterium rhizogenes</jats:italic>, have been shown to increase the rooting potential of other difficult-to-root woody plants. We inserted the <jats:italic>rolABC</jats:italic> genes into somatic embryos of a `Paradox' hybrid (<jats:italic>J. hindsii</jats:italic> × <jats:italic>J. regia</jats:italic>) clone PX1 using the <jats:italic>A. tumefaciens</jats:italic> gene transfer system. A transgenic sub-clone, designated PX1 <jats:italic>rolABC 2-2</jats:italic> was selected and compared to the untransformed clone for a variety of phenotypic characteristics, including rooting potential. Transformed and untransformed shoots were budded onto seedling <jats:italic>J. regia</jats:italic> rootstock in the greenhouse and established in the field. Transformed trees displayed reduced internode length, an increase in lateral branching, and wrinkled leaves. In another test, a commercial persian walnut cultivar <jats:italic>J. regia</jats:italic> `Chandler' was grafted onto rooted cuttings of both the untransformed and transformed plants. The presence of the <jats:italic>rolABC</jats:italic> genes in the rootstock had no visible effects on the grafted scion. Several of these trees were excavated from the field and the root systems of each genotype were examined for root number, diameter, and biomass. Trees with the <jats:italic>rolABC</jats:italic> rootstock had significantly more small diameter roots compared to the controls and less recovered biomass. Tests of the rooting potential of leafy semi-hardwood cuttings for two years resulted in 14% to 59% rooting of the transformed cuttings compared to 51% to 81% rooting of the control. Both transformed hardwood cuttings and microshoots in tissue culture also rooted significantly less (52% and 29% respectively) than untransformed hardwood cuttings and tissue cultured shoots (82% and 54% respectively). Thus, although the <jats:italic>rolABC</jats:italic> genes induced a shorter internode length and a more fibrous root system (typical of <jats:italic>rol</jats:italic>-tranformed plants), they were not useful for increasing the rooting potential, and as rootstock they did not affect the phenotype of the scion.</jats:p>

Production and rooting behaviour of rolB-transgenic plants of grape rootstock ‘Richter 110’ (Vitis berlandieri × V. rupestris)

“…van der Salm et al 1997;Welander et al 1998;Vahdati et al 2002;Zhu et al 2003). Compared to non-transgenic 'Richter 110', the most notable features of rolB-transgenic clones are their overall higher rooting ability and that they are able to root well even in the absence of auxin.…”

“…Rooting of difficult-to-root woody plants has been significantly improved by rol gene transformation, e.g. in rose (van der Salm et al 1997), apple (Welander et al 1998), pear (Zhu et al 2003) and walnut (Vahdati et al 2002). In addition to promoting root initiation, rol genes are known to affect root architecture (Chriqui et al 1996) and thereby might influence plant productivity (Lynch 1995).…”

Effect of exogenous ABA on somatic embryo maturation and germination in Persian walnut (Juglans regia L.)

“…1,700,000 tons in-shell nuts annually and its wood is valued for furniture, veneer and gunstock (Vahdati 2001;FAO 2005). Walnut trees are more difficult to propagate clonally than most fruit trees (Dhuria et al 1977;Roghani 1977;Kuden and Kaska 1997;Ozkan et al 2000;Ozkan and Gumus 2001;Vahdati et al 2002;Rezaee et al 2008).…”

Characterization of hairy root-phenotype in transgenic Hypericum perforatum L. clones

“…Increased formation of adventitious roots on the stem has been observed on transgenic tobacco plants expressing rolB gene (Schmülling et al 1988). On the contrary, rolA, B and C genes induced shorter internode length and a more fibrous root system typical for rol-transformed plants, but were not useful for increasing the rooting potential of a transgenic walnut hybrid (Vahdati et al 2002). Antirrhinum (Senior et al 1995) or an abundant root system (Handa 1992).…”