MATURATION AND GERMINATION OF WALNUT SOMATIC EMBRYOS

Walnut somatic embryos were multiplied by repetitive embryogenesis on a solid basal DKW medium at 25-degrees-C in the dark. When the embryos were isolated at early cotyledonary stage (1-2 mm long) from the primary embryos and cultured on the medium for 3 weeks, they developed into mature embryos showing white, enlarged cotyledons and shoot and root apex. After transfer to light on solid germination medium, however, few mature embryos (0-5%) germinated. Germination percentage increased to about 10% when the mature embryos were pretreated by a storage at 4-degrees-C in the dark for 2 months, or by desiccation at 25-degrees-C in the dark for 3 or 5 days under an air-humidity conditioned by saturated salt solutions (Mg(NO3)2.6H2O, or ZnSO4.7H2O). Similar results were obtained by the addition of gibberellic acid (GA3) to the germination medium. When mature embryos were desiccated and then placed on medical cotton compresses in liquid germination medium, 45% of the embryos germinated into complete plantlets. These plantlets continued their growth after transplanting to a mixture of peat and vermiculite in pots.