Plantlet regeneration from somatic embryos of American chestnut

Embryogenic cultures were induced from ovules and immature zygotic embryos of American chestnut (Castanea dentata (Marsh.) Borkh.). Across all treatments, genotypes: and explant types, embryogenic response was 0.9%. Most efficient induction of embryogenic cultures was achieved from ovules, zygotic embryos not greater than 4 mm in length, and cotyledons smaller than 6 mm(2). Only cultures continuously maintained on 2,4-D sustained production of somatic embryos. Benzyladenine (BA), at concentrations tested, reduced induction of embryogenic cultures approximately 3-fold. Most rapid growth of embryogenic cultures was achieved in liquid woody plant medium supplemented with 3 mg/L 2,4-D and 0.25 mg/L BA. Activated charcoal enhanced yield and growth of somatic embryos. Sucrose promoted development of greater numbers of somatic embryos than did fructose, but fructose promoted higher rates of development of single (not fused) somatic embryos than did sucrose. Chilling at 4 degrees C enhanced root development from somatic embryos, but epicotyl elongation and formation of true leaves was infrequent. Plantlets survived more than 60 days after being transplanted to potting mix, but failed to continue growth. Damage by fungus gnat larvae and a high percentage of peat in the potting mix are believed to be major factors contributing to failure of ex vitro survival of plantlets. Improvement of embryo maturation and conversion should quickly increase efficiency of the system.