Benzyladenine-preconditioning in germinating mungbean seedlings stimulates axillary buds in cotyledonary nodes resulting in multiple shoot regeneration

Abstract

Tissue culture and histological studies were done to ascertain the effects of benzyladenine (BA)-preconditioning on direct shoot regeneration from cotyledonary node explants of mungbean. The highest direct shoot regeneration (93.3%), double-sided shoot initiation (65.0%) and average number of shoots per explant (2.7 shoots) were obtained when Pag-asa 7 explants are excised from seedlings germinated in basal medium (BM) consisting of MS salts and B5 vitamins with 1.0 mg l-1 BA, and subsequently cultured in fresh medium of the same composition. Histological inspection of sections from germinating seeds in BM and BM + 1.0 mg l-1 BA sampled at 1 to 4 days from germination revealed bigger and developmentally more advanced axillary shoots in BA-preconditioned seedlings, a built-in advantage which could attest to the improved regenerability in BA-treated seedling explants over the control (BM only). During shoot initiation from explants, two treatments namely doubling of the concentration BA to 2.0 mg l-1 and the addition of a non-ionic surfactant, Pluronic F-68 did not further increase the responses, but gave results comparable with those obtained using BM + 1.0 mg l-1 BA alone. Conversely, a BA-thidiazuron (TDZ) combination (each at 1.0 mg l-1) when added to BM significantly reduced shoot induction to only 48.3% possibly due to increased callusing at the nodes in 55% of the explants. The importance and applicability of the regeneration system in tissue culture and/or genetic manipulations of mungbean and other Asiatic Vigna species is discussed.