In vitro Organogenesis, Regeneration and Flowering of Wild Peanut (Arachis paraguariensis): II.

Tissue culture and biotechnology techniques offer potential routes for overcoming hybridization barriers that have long existed among Arachis species. But as with many legumes, these species are generally recalcitrant to regeneration in vitro. This study investigated the roles and interactions of different genotypes, explant sources, and growth regulators in tissue culture regeneration of Arachis paraguariensis Chodat & Hassl. De-embryonated cotyledon and embryonic axis explants dissected from mature seeds of A. paraguariensis were grown in vitro under continuous light on modified MS medium that was supplemented with 22 different combinations of thidiazuron (TDZ) and benzyl-aminopurine (BAP). A factorial experiment in a complete randomized design led to the development of an efficient regeneration protocol for A. paraguariensis through organogenesis. Across the six genotypes that were studied, de-embryonated cotyledons on MS medium supplemented with 4.4 mgl^-1 TDZ and 1.1 mgl^-1 BAP gave the highest number of shoots per explant and highest plantlet height of 14.8 ± 1.6 and 7.3 ± 0.7 respectively. Shooting frequency increased until the third subculture, but declined rapidly throughout additional subcultures. Shoots were transferred onto semi-solid MS medium containing 0.5 mgl^-1 BAP and 0.2 mgl^-1 NAA for elongation before they were rooted on reduced strength MS medium. Prior to acclimatization, 55% of the shoots exhibited flowering while peg formation was observed for 13% of the flowering shoots.  An experiment is currently underway to further elucidate the influence of photoperiod on in vitro reproductive development in A. paraguariensis.