THE INFLUENCE OF NATURAL AND IN VITRO BUD FLUSHING ON ADVENTITIOUS BUD PRODUCTION IN SITKA SPRUCE [PICEA SITCHENSIS (BONG.) CARR.] BUD AND NEEDLE CULTURES.

The adventitious bud forming ability of Sitka spruce [Picea sitchensis (Bong.) Carr.] buds was found to be dependent upon the time of year at which they were introduced into culture. Adventitious bud production was at a maximum in the latter weeks of March, immediately prior to their natural flushing time, a period when the buds are naturally forming initials for lateral buds and bud scales and are in a highly active physiological state. Throughout the dormant period cultured buds were able to form adventitious buds, however, once the buds were in an advanced state of natural flushing their capacity for organogenesis declined and they became callused and senescent. The enhancement of adventitious bud production with the onset of natural flushing, and the detrimental effects of bud overdevelopment, were simulated by flushing dormant buds in vitro on a cytokinin free medium using juvenile tissues. In vitro flushing of buds from mature trees did not increase their organogenic capacity,. Increasing tree age also significantly reduced the number of adventitious buds forming throughout the natural growth cycle. Adventitious bud production in needle cultures, using needles excised from buds flushed to varying extents in vitro, was also found to be reliant upon their developmental state. Needles needed to be in an immature state (approx. I to 2 mm long) to produce optimum organogenesis on their basal tissues. Needles that were more differentiated became callused and senescent in culture. To maximize shoot multiplication rates with Sitka spruce bud and needle cultures, tissues need to be in a carefully controlled stage of differentiation. This can probably be best achieved by flushing dormant buds in vitro to precise extents prior to adventitious bud induction. [ABSTRACT FROM AUTHOR]