REPETITIVE SOMATIC EMBRYOGENESIS IN PEANUT COTYLEDON CULTURES BY CONTINUAL EXPOSURE TO 2,4-D

Somatic embryos from immature cotyledons in peanut (Arachis hypogaea) were initiated on media supplemented with 2, 4-dichlorophenoxyacetic acid (2, 4-D). Over 90% primary embryogenesis and 41-46% repetitive embryogenesis were obtained 12 weeks after initiation by maintaining embryogenic cultures on medium containing 20 mg 1(-1) 2, 4-D. Maintenance of cultures on medium with 30 or 40 mg 1(-1) 2, 4-D resulted in lower primary and secondary embryogenesis, and proliferation of nonembryogenic callus. Transfer of embryogenic cultures to a secondary medium with 10 or 20 mg 1(-1) 2, 4-D significantly enhanced secondary embryogenesis compared to basal medium without the growth regulator. The use of Murashige and Skoog versus Finer's media had no significant effect on embryogenesis (85-95%), repetitive embryogenesis (11-37%) or mean embryo number. Secondary embryogenesis was also maintained for over one year by repeated subculture of isolated somatic embryos on medium with 20 mg 1(-1) 2, 4-D.