Somatic Embryo Maturation and Germination of Persian Walnut (Juglans regia L.)

In spite of recent progress in micropropagation of walnut, low efficiency of embryo maturation, germination and conversion of embryos to plantlets remains a major problem. In this study, the effect of exogenous abscisic acid (ABA) and sucrose, as a low weight osmoticum, was investigated on somatic embryo maturation and secondary embryogenesis of Persian walnut (Juglans regia) with a view to improving embryo quality, increasing the incidence of normal embryo development and enhancing embryo germination. Individual globular somatic embryos were grown on a maturation medium supplemented with different combinations of ABA and sucrose. The number of germinated somatic embryos was influenced by the concentrations of ABA. The best treatment for maturation in which both well developed shoot and root were obtained, was 2 mg L-1 ABA with 41% conversion into plantlet. Different concentrations of ABA had reducing effects on secondary embryogenesis. The concentration of sucrose in this medium had a little influence on maturation. Plantlet regeneration was reduced at the high levels of ABA. In this study, normal and abnormal mature somatic embryos were compared histologically.