| Quince (Cydonia oblonga Mill.) is widely used as a dwarfing rootstock for pear (Pyrus communis L.). The disadvantage of this rootstock is its inefficient uptake of Fe, resulting in leaf chlorosis. Application of tissue culture and gene transfer techniques may lead to production of quince clones with improved Fe efficiency. Pear may benefit from transformation by transfer of genes involved in disease resistance, insect resistance and delay of ripening. The objectives of this research were: (1) to determine the responses of two somaclonal variants, IE-1 and IE-2, to Fe-deficiency stress under greenhouse conditions; and (2) to establish transformation procedures for quince and pear.; Two somaclonal variants of quince, IE-1 and IE-2, with tolerance to low-Fe conditions were isolated previously (Dolcet-Sanjuan et al., 1992). These two variants were compared to the original Quince A clone under various conditions in the greenhouse in 1993 and 1994. Whereas Quince A was chlorotic under conditions with high pH (low Fe availability), the variants displayed only little chlorosis. Under those conditions, the chlorophyll and Fe{dollar}sp{lcub}2+{rcub}{dollar} concentrations in the leaves were significantly higher in the variants than in Quince A.; Agrobacterium-mediated gene transfer protocols for quince and pear were devised using leaves as explants. Efforts were directed at the following: improving the regeneration system, selecting the best antibiotic to eliminate Agrobacterium while maintaining a high regeneration frequency, and identifying a suitable selectable marker. Regeneration of Quince A was improved by replacement of agar with 1.6 g/l gelrite. Regeneration of the pear rootstock RV. 113 was enhanced by cold treatment of the shoot cultures used as explants. The antibiotic timentin, which consists of ticarcillin and a {dollar}beta{dollar}-lactamase inhibitor, was more effective in eliminating Agrobacterium and less inhibitory to regeneration than cefotaxime and carbenicillin. Vectors containing the bar gene (bialaphos resistance) were chosen for transformation experiments since bialaphos caused less damage to the leaf explants than kanamycin at effective concentrations for selection of transformants. GUS ({dollar}beta{dollar}-glucoronidase activity) assays showed chat under the proper conditions, transformed tissues were obtained. |
