Optimization of the induction, germination, and plant regeneration system for somatic embryos in apomictic walnut ( Juglans regia L.)

The low efficiency of somatic embryo induction, proliferation, germination, and conversion to plantlets is a major problem in walnut. In this study, we used the cotyledons of immature embryos of apomictic seeds in walnut plus trees ‘Y17’ as explants. The optimum medium and culture conditions of somatic embryo induction, proliferation, and germination were tested through comparative experiments. The results showed that the optimum formula for somatic embryo induction, proliferation, and germination medium was DKW medium with 1.0 mg L −1 6-BA, 2.0 mg L −1 KT, and 0.01 mg L −1 IBA, DKW medium with 30–40 g L −1 sucrose and 7–8 g L −1 agar, and DKW medium with 2.0 mg L −1 concentrations of GA 3 , respectively. Meanwhile, the optimum time of seedling training was 36 h, and the substrate ratio was perlite: peat soil: vermiculite (1: 2: 1) after plant transplanting. The inter simple sequence repeat marker banding patterns of the primary embryo, secondary embryo and regenerated plants were all identical to that of the mother plant and proved the genetic stability of regenerated plants. An excellent walnut tissue culture system from walnut somatic embryo to the whole plant was formed, which can accelerate the speed of walnut genetic improvement.