Axillary Shoot Proliferation of Adult Eastern Black Walnut

Abstract

Softwood shoots of adult Juglans nigra (eastern black walnut) were forced from latent (epicormic) buds below the bark of large stem sections in a greenhouse. Once sufficiently long, the shoots were excised, surface-disinfested, and cut into 1-cm-long nodal or apical segments for establishment in culture vessels. Two experiments were conducted, each using explants of three different clones. The first experiment compared the effect of cytokinins: 0.3, 1.0, or 3.0 μM benzyladenine (BA) and 0.1, 0.3, or 1.0 μM thidiazuron (TDZ) arranged factorially. The basal medium was agar-solidified Long and Preece (LP) with 0.05 μM indole-3-butyric acid (IBA) and 30 g/L sucrose. The second experiment compared the agar-solidified basal media: Driver-Kuniyuki-Walnut (DKW), Woody Plant Medium (WPM) and LP, all with 1.0 μM BA, 0.3 μM TDZ, 0.05 μM IBA, and 30 g/L sucrose. Regardless of the BA concentration, explants on media containing 0.1 μM TDZ produced few, if any, axillary shoots while explants on media containing 1.0 μM TDZ excessive amounts of callus. Explants in media containing 0.3 μM TDZ, at all levels of BA, produced the greatest number of shoots and minimal callus. Male catkins were produced by 17 explants on various media. Fifteen of the catkin-producing explants were from one walnut clone. Axillary shoot number and callus production were not significantly affected by basal medium for any of the three clones.