PLANT-REGENERATION FROM INVITRO CULTURE OF EMBRYONIC AXIS EXPLANTS IN COMMON AND TEPARY BEANS

A new in vitro protocol was developed for multiple bud induction and plant regeneration from embryonic axis explants of four common bean (Phaseolus vulgaris L.) and two tepary bean (P. acutifolius A. Gray) lines. The explants were prepared from two embryo sizes, 3 to 4 mm and 5 to 7 mm, corresponding to pods collected after 15 and 25 days from flowering, respectively. The embryonic axis was cultured on Gamborg's B5 basal medium with 0, 5, 10, or 20-mu-M BA in combinations with 0, 1, or 2-mu-M NAA. The cultures were maintained at 24 to 25C under continuous light or incubated in darkness for 2 weeks followed by continuous light before transfer to the secondary B-5 medium (0 or 2-mu-M BA or 2-mu-M BA plus 4-mu-M GA3). Adventitious roots or a single shoot with roots formed on the explants cultured on media without plant growth regulators. Multiple buds were induced on all BA media, but more were produced with 5 or 10-mu-M for most lines. Dark incubation greatly enhanced multiple bud initiation. Shoot buds were not produced on media containing NAA alone or in combinations with BA. On the secondary medium, six to eight shoots per explant for common bean and up to 20 shoots per explant from tepary bean were observed after 3 weeks. Mature, fertile plants were produced from these shoots. Chemical names used: benzyladenine (BA); 1-naphthaleneacetic acid (NAA); gibberellic acid (GA3).