INVITRO CULTURE OF VANHOUTTE SPIREA EXPLANTS FROM SECONDARY CULTURES AND DORMANT STEMS FORCED IN SOLUTIONS CONTAINING PLANT-GROWTH REGULATORS

Explants from new growth of forced dormant stems and 'secondary cultures' of Vanhoutte's spirea were cultured on Linsmaier and Skoog (L.S.) medium containing benzyladenine (BA), indoleacetic acid (IAA), thidiazuron (TDZ), and zeatin. The dormant stems were forced by immersing their basal portions in forcing solutions containing 626 muM 8-hydroxyquinoline citrate (8-HQC) and 2% sucrose. BA and gibberellic acid (GA3) were also added into the forcing solutions to determine if explants obtained from the new growth will benefit from this treatment when cultured in vitro. L.S. medium supplemented with 5 muM BA alone, 5 muM BA plus 1 or 5 muM IAA, and 0.5 or 0.75 muM TDZ alone produced the best shoot proliferation for both sources of explants. BA and GA3 appeared to be taken up from the forcing solution by the new softwood growth. BA in the forcing solution stimulated in vitro shoot proliferation in different degrees depending on the period of treatment, while GA3 caused less in vitro shoot proliferation. It is proposed that forcing solutions containing plant growth regulators (P.G.R.) are a useful approach for manipulating responses of plant tissues cultured in vitro.