Maturation and germination of walnut somatic embryos

Abstract

Walnut somatic embryos were multiplied by repetitive embryogenesis on a solid basal DKW medium at 25°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°C in the dark for 2 months, or by desiccation at 25°C in the dark for 3 or 5 days under an air-humidity conditioned by saturated salt solutions (Mg(NO3)2.6HzO, or ZnSO4.7H20 ). 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.

Secondary somatic embryogenesis and applications in plant breeding

“…(Krikorian & Kann, 1981), Juglans nigra (Deng & Cornu, 1992), Manihot esculenta (Raemakers, 1993), Picea glauca (Kong & Yeung, 1992) and P. glauca x engelmannii (Eastman et al, 1991). The production of embryos is determined by the number of responding explants and the number of embryos produced per responding explant.…”

“…In some species it continued for one or two cycles of secondary embryogenesis (Cheema, 1989;Dhahnalakshmi & Lakshmanan, 1992;Lu & Vasil, 1981;Tremblay & Tremblay, 1991;, probably because of a carry-over effect of the auxin. It is a common observation of growth regulator free or CYT induced embryogenesis that the process of secondary embryogenesis is difficult to stop (Adu-Ampomak et al, 1988;Aguilar et al, 1992;Ammirato, 1977;Cornu, 1988;Deng & Cornu, 1992;Druart, 1990;Jha et al, 1992;Kochba et al, 1972;Parrott & Bailey, 1993;Plata & Vieitez, 1990;Rangaswamy, 1961;Rashid & Street, 1974;Southworth & Kwiatkiowski, 1991;Thomas & Wenzel, 1975;Tulecke & McGranahan, 1985;Vieitez et al, 1991;Zatyk6 et al, 1976). In Brassica napus (Huang et al, 1991), Carum carvi (Ammirato, 1977) and Medicago spp (Lupotto, 1986;Parrott & Bailey, 1993) ABA stopped proliferation.…”

“…In Brassica napus (Huang et al, 1991), Carum carvi (Ammirato, 1977) and Medicago spp (Lupotto, 1986;Parrott & Bailey, 1993) ABA stopped proliferation. In Juglans spp (Deng & Cornu, 1992;Tulecke & McGranahan, 1985) proliferation could be reduced by either a desiccation treatment, cold storage, liquid culture instead of solid and culture on GA3 supplemented media. In Theobroma cacao (Adu-Ampomak et al, 1988) where new embryos were formed from the cotyledons and the embryogenic axis, proliferation can be interrupted by excision of the cotyledons.…”

“…In Vitis longii (Gray & Mortensen, 1987) a cold treatment of mature embryos was essential for development into shoots. Cold treatment also stimulated germination in Brassica napus (Huang et al, 1991), Fagus sylvatica (Vieitez et al, 1992), Juglans spp (Deng & Cornu, 1992;Tulecke & Granakou, 1985) and Querqus spp (Gingas & Lineberger, 1989;Gingas, 1991). Another frequently used treatment is desiccation.…”

“…Another frequently used treatment is desiccation. It enhanced germination in Arachis hypogaea (Durham & Parrott, 1992), Brassica napus (Huang et al, 1991), Glycine max (Christou & Yang, 1989), Juglans regia × nigra (Deng & Cornu, 1992), Mangifera indica , Manihot esculenta (Mathews et al, 1993) andQuerqus alba (Gingas & Lineberger, 1989).…”