<i>In vitro</i> Induction and Proliferation of Callus from Immature Cotyledons and Embryos of Juglans regia cv. 'Xiangling'

Callus holds great potential for biotechnology applications in plants. In this study, several experiments were performed to establish a protocol for in vitro induction of good quality callus by using immature cotyledons and embryos of Juglans regia cv. ‘Xiangling’ as the explants. DKW basal media supplemented with different concentrations of plant growth regulators were applied to determine the induction rate, texture and color of the recovered callus. Results showed that the optimum culture medium for the callus induction from these explants was a DKW basal medium consisting of 1 mg/L BA, 2 mg/L KT 250 mg/L glutamine, 500 mg/L casein hydrolysate, 200 mg/L Vc, 50 g/L sucrose and 2.8 g/L Gelrite (i.e., the T8 medium). The average rate of callus induction on the medium reached 80.7% for the immature cotyledons and 66.7% for the immature embryos, and all the callus was characterized by a friable, creamy or yellow appearance. In vitro proliferation of callus was not very successful as a result of the fact that the friable callus with creamy or yellow color grew very slowly, whereas the fast-growing callus was easy to turn brown and died eventually. Even though further investigation will be required to overcome the problem of browning and assess the regeneration ability of the callus, this approach for the production of friable callus may have valuable applications for walnut and other woody trees.