Micropropagation of Achras sapota through enhanced axillary branching

Abstract

A complete protocol for micropropagation of Achras sapota using cotyledonary node segments has been developed. Multiple shoots were induced in vitro from nodal segments through forced-axillary branching. Schenk and Hildebrandt's medium supplemented with 2.0 mg l −1 BAP induced up to three shoots per node with an average shoot length of 2.17 cm in 42 days. Further multiplication of shoots required continued culturing up to three passages of 21 days each on the same medium after establishment of cultures. Thereafter, a 3-fold multiplication rate was achieved during every subculture. Incorporation of GA 3 (1.0 mg l −1) in the medium during first subculture after establishment and initiation of shoot buds not only improved the shoot elongation but also enhanced the rate of shoot multiplication. One time use of GA 3 during first subculture, eliminated the need for prolonged culturing on BAP medium. Three-fold rate of shoot multiplication could be achieved after this treatment. Further use of GA 3 in the medium was not useful. The shoots could be multiplied for at least 24 months without loss of vigour. Implantation of shoots on half-strength SH medium after a pulse treatment of pre-autoclaved IBA (200 mg l −1) for half-an-hour induced rooting in 66% shoots with moderate degree of callusing. Seventy-seven percent callus-free rooting was obtained when shoots after treatment with pre-autoclaved IBA (200 mg l −1) for 2 h were directly implanted on autoclaved Soilrite™ contained in culture bottles and irrigated with 1/4 SH solution. This allowed rooting and partial hardening simultaneously. Ninety percent of such plantlets could be transferred to pots. Of 500 plantlets, 440 have been successfully established in soil.