The rooting ability of the dwarfing pear rootstock BP10030 ( Pyruscommunis) was significantly increased by introduction of the rolB gene

Abstract

The pear rootstock BP10030 ( Pyrus communis) is dwarf, frost hardy and compatible with most pear varieties, but very difficult to propagate due to its poor rooting ability. In order to improve its rooting ability, we transformed this rootstock with the rolB gene. Six transgenic clones were obtained and named 1-6. PCR and Southern hybridisation confirmed that all the transgenic clones contained the rolB and nptII genes, but only two of them contained the gus gene. The in vitro rooting results showed that the transgenic clones rooted from 67 to 100% without auxin, while the untransformed control did not root at all on the hormone free rooting medium. To further confirm the increased rooting ability of these clones, cutting experiments were carried out on four transgenic clones (1-4) and the untransformed control in the greenhouse. The rooting percentage ranged from 71 to 100 for the transgenic clones and only five for the untransformed control. Moreover, the root number was also greatly increased ranging from 11 to 17 for the transgenic clones, but only 3 for the untransformed control. Another important alteration by the insertion of the rolB gene was the root morphology. For the transformed clones, the roots were distributed evenly on the cut surface, but only on one side of the cut surface of the untransformed control. Growth analysis in the greenhouse, conducted on four transgenic clones (1-4) and the untransformed control, showed that three of the transgenic clones had a shortened stem length. The transgenic clones did not show any other visual alteration in shoot phenotype compared with the untransformed control plants.