TOWARDS GENETIC TRANSFORMATION OF QUINCE AND PEAR

Quince (Cydonia oblonga) is widely used as a dwarfing rootstock for pear (Pyrus communis). We have devised procedures for Agrobacterium-mediated gene transfer using leaf discs of quince. The following factors were particularly important for recovery of shoots after incubation of leaf discs with Agrobacterium: an efficient regeneration system, the use of an effective antibiotic to eliminate Agrobacterium while maintaining a high regeneration frequency, and the choice of selectable markers. The regeneration frequency of control leaf discs on a medium containing 30 μM thidiazuron and 0.3 μM naphthaleneacetic acid was 100%. The frequency decreased linearly with increasing concentrations of antibiotics. Timentin. which consists of ticarcillin and a 6-lactamase inhibitor, was more effective in eliminating Agrobacterium than cefotaxime and carbenicillin. Vectors with the bar gene (bialaphos resistance) were better than those with the npt 11 gene (kanamycin resistance), since kanamycin bleached the leaf discs, resulting in poor regeneration. Bialaphos-resistant quince shoots which were positive in Southern hybridization have been obtained. The same procedures are being applied for transformation of pear.