ENHANCEMENT OF MATURATION AND GERMINATION OF SOMATIC EMBRYOS OF PERSIAN WALNUT (JUGLANS REGIA L.) BY GELLAN GUM, COLD AND PGR

One of the potentially desirable propagation strategies for mass production of walnut cultivars, selected hybrids, or genetically engineered genotypes is somatic embryogenesis. Maturation and germination of somatic embryos of walnut has not been optimized yet. In this study, maturation of somatic embryos of Persian walnut (Juglans regia L.) was evaluated on media containing various concentrations of Gelrite (0.2%, 0.3%, 0.4% and 0.5%) and PEG (0.0%, 3.0%, 5.0% and 7.5%) in the presence of 2 mg L^-1 ABA and 3.0% sucrose. Gelrite was more effective in stimulating the production of mature somatic embryos than PEG. The highest number of cotyledonary (70.0%) and normal (50.0%) SEs was obtained with 0.3% Gelrite without PEG. Media containing 0.2% Gelrite (control) resulted in the highest secondary embryogenesis. With increasing concentrations of Gelrite, the number of matured somatic embryos was decreased. The combination of Gelrite and PEG was less effective for maturation of somatic embryos. The Gelrite 0.5% and PEG 7.5% caused the highest number of abnormal somatic embryos. For germination of matured somatic embryos, after growing the SEs on maturation medium for four weeks, four treatments including basal medium without PGR, basal medium with PGR, basal medium with cold pretreatment (four weeks at 4°C), basal medium with PGR and cold pretreatment were tested. The highest amount of normal germination and conversion to plantlets (55.0%) was achieved using 0.3% Gelrite and cold pretreatment and PGR.