Improvement of English walnut somatic embryo germination and conversion by desiccation treatments and plantlet development by lower medium salts

Summary

Well-developed somatic embryos were selected from a repetivively somatic embryo line derived from embryonic axes of immature zygotic embryos of English walnut ‘No. 120’ (Juglans regia L.) for germination and conversion studies. In germinating dishes, somatic embryos germinated into only shoots, only roots, or both shoots and roots. Without any pretreatment, 28% somatic embryos germinated, while those treated with 2.5–5.0 mg 1⁻¹ (7.2–14.4 μmol) gibberellic acid (GA₃) germinated at 25–28% and those receiving a cold treatment of 2–3 mo. at 3–4°C germinated at 30–43%. However, only 4–19% of the germinating embryos showed both shoots and roots. Treated with desiccation, either with CaCl₂·6H₂O or Ca(NO₃)₂·4H₂O at 20°C in the dark for 3 d, somatic embryos germinated at 85–91%, 57–69% of which had both shoots and roots. Treatment with 2 mo. cold storage in combination with desiccation using Ca(NO₃)₂·4H₂O resulted in 92% of somatic embryos germinating, 70% of which showed both shoots and roots. No significant differences were observed between solid and liquid germination media. After transferring the germinating embryos to plantlet development media, 52–63% of those with both shoots and roots developed into plantlets while 11% with only shoots or 9% with only roots converted into plantlets. Plantlet development was improved by using lower medium salts and sucrose concentrations. The addition of activated charcoal enhanced root development, particularly root branching. Of 131 plants transplanted, 91 plants were acclimatized to a greenhouse.