Objective  To establish an efficient and stable somatic embryogenesis system, to provide technical and theoretical support for in vitro rapid propagation and its further research, and to lay a foundation for the construction of gene transformation of walnut.

Method  Two early-bearing walnut young fruits were sampled during 42-77 days after blooming. Somatic embryogenesis percentages were counted to screen the optimum development stage of the fruit. After subcultured for several times, the somatic embryos distortion percentage was calculated and then the optimum ABA concentration was tested. The somatic embryos were desiccated respectively for 0, 24, 48, 72, 96 and 120 h with saturated NH₄NO₃, and the germination rate of somatic embryo can be obtained.

Result  The highest somatic embryogenesis percentage of 'Zao Lin Xiang' and 'Zhong Lin 6' reached 88.32% and 86.7%, respectively, when the young fruits were sampled at 49 d and 56 d after flowering, respectively. Moderate concentration of ABA supplement not only reduced the rate of somatic embryos aberration, resulted from multiple subcultivation, but also increased the rate of somatic embryogenesis, and the optimum ABA concentration was 1 mg·L^-1. As the dehydration time was prolongated, the water loss increased gradually, while the germination rate increased at first and decreased later on. After dehydrated for 72 h, the germination rate of 'Zao Lin Xiang' and 'Zhong Lin 6' were up to the highest (56.67% and 53.33%), while the water loss was 38.73% and 40.56%, respectively.

Conclusion  In the process of young fruit development of early-bearing walnut, the inducing rate of somatic embryogenesis is changed with the development period. The suitable development period is the key to improve somatic embryo induction. Proper amount of ABA also plays an important role in regulating deformed embryo in the process of somatic embryo multiple subculture. What is more, moderate dehydration treatment has a well promoting effect on the regeneration of somatic embryo of walnut.