Optimizing secondary somatic embryo production in English walnut (Juglans regia L.)

One repetitive somatic embryo line, initiated from the embryonic axes of immature zygotic embryos of English walnut (Juglans regia L.) was used for study on secondary somatic embryo production. The efficient production of morphologically normal somatic embryos depended on physical and chemical factors. Somatic embryos of 1 similar to2 and 2 similar to4 mm were more efficient than those of other sizes in producing new somatic embryos. L-glutamine (250 mg l(-1)) and casein hydrolysate (500 mg l(-1)) were ineffective on, malt extract (500 mg l(-1)) and yeast extract (500 mg l(-1)) were inhibitory to somatic embryo production in comparison with basal medium. Secondary somatic embryo production was sucrose-dependent and 30 similar to 50 g l(-1) sucrose yielded better results than the other concentrations tested. At the same concentration of 30 g l(-1), maltose, glucose and fructose decreased, mannitol and sorbitol strongly suppressed somatic embryo production when compared with sucrose. DW (1/2 DKW + 1/2 WPM) and MW (1/2 MS + 1/2 WPM) media were more effective than DKW, MS, WPM and MD (1/2 MS + 1/2 DKW) in the improvement of secondary somatic embryo production, especially using Gelrite as gelling agent.