Acquisition of competence for shoot regeneration in leaf discs ofSaintpaufla ionantha xconfusa hybrids (African violet) cultured in vitro

Abstract

Leaf discs fromSaintpaulia ionantha xconfusa hybrids (African violet) were transferred between basal medium (BM) containing no hormones and shoot-inducing medium (SIM) containing 2.0 mg 1⁻¹ indole acetic acid and 0.08 mg l⁻¹ 6-benzylaminopurine to determine whether there is a “window” of competence for shoot regeneration. Leaf discs precultured on BM prior to transfer to SIM formed buds 3 days earlier than the controls (leaf discs not precultured) regardless of whether the discs were placed upside down or right side up on the medium. This suggests that cultured leaf cells were not competent for shoot induction during the first 3 days of culture. Leaf discs cultured right side up (abaxial surface to the medium) did not form buds on BM alone, unlike discs cultured upside down. Leaf disc survival was affected by a delay in hormonal exposure, but surviving leaf discs produced as many shoots as control leaf discs. This suggests that in the absence of exogenous plant hormones, cellular competence to regenerate shoots is not lost in excised leaf discs of African violet.