Apical and lateral meristems of Paradox walnut (Juglans hindsii x J. regia) were used to investigate the possibility of accomplishing in vitro propagation of Paradox rootstock. A walnut specific medium, DKW, has been defined supporting optimum multiple shoot development under 4.5 μm benzyladenine (BA) and 5 nm indolebutyric acid (IBA) treatment. The method of analysis to determine the optimum level of constituents in tissue culture medium is discussed. Also reported is the in vivo rooting of tissue culture derived shoots.
In vitro propagation of mature cultivars of Juglans regia L. (Persian or English walnut) could have several major advantages over propagation by grafting on seedling black walnut [J. hindsii (Jeps.) Jeps.] rootstock. If commercial cultivars perform satisfactorily on their own roots, the expensive and time-consuming process of grafting could be avoided, genetic uniformity could be assured, and trees would not be subject to the lethal girdling of blackline disease (5). In addition, mature clones on their own roots might be more precocious than grafted seedlings. These factors are becoming increasingly important as walnut growers change to high-density or hedgerow orchards (D.E. Ramos, personal communication).