USE OF ROOT GRAFTING FOR CLONAL PROPAGATION OF PEST AND DISEASE RESISTANT WALNUT ROOTSTOCKS

Bench grafting of root pieces was investigated as a method for clonal propagation of pest and disease resistant genotypes including paradox hybrids and their backcrosses to Juglans regia. Grafting success has been achieved at acceptable levels for research using 10 clonal rootstock genotypes and three J. regia scion cultivars and at commercial levels (over 90%) for seedling paradox using several J. regia scions at a nursery in Argentina. Variables that have been identified which influence grafting success are genotype, diameter of the root piece and scion, concentration of potassium indolebutyric acid used to treat the base of the root piece to induce adventitious root formation and the temperature of the medium surrounding the graft union. The main advantages of bench root grafting for the propagation of clonal rootstocks are that a rooted plantlet is obtained rapidly (two to three months) and adventitious rooting is not limited by genotype as is often the case with stem cuttings and sometimes the case with microshoots.