In vitro flowering of Boronia megastigma Nees. and the effect of 6-benzylaminopurine

Abstract

Successful flower bud initiation and development was achieved on Boronia megastigma in vitro. The effect of cytokinin on flowering was investigated in environmental conditions that promote flowering as well as under conditions that stimulate vegetative growth (nonfloral promotory conditions). Flower initiation and differentiation was enhanced by cytokinin; however, many flower buds reverted when the media contained high levels of cytokinin. Anthesis occurred only on media that had no cytokinin added and under floral promotory conditions. Boronia megastigma Nees. is a woody understorey shrub 1-2 m in height, bearing a profusion of strongly scented brown, purple, and yellow flowers in early spring. They are initiated in autumn and continue to differentiate during the winter. Floral and vegetative buds are normally initiated from uncommitted primordia located in the axils of nonexpanding leaves, on current season's node-bearing structures, under a range of environmental conditions. More flowers initiate (up to three per leaf axil) under low night temperatures (5-7~ with short days (10 h) and 50-100% full sunlight (floral promotory conditions) (Roberts and Menary 1989a,b).Differentiation and development of preexisting flower buds in vivo is enhanced by exogenous cytokinin under floral promoting conditions. However, when applied under long days (16 h) and moderate night temperatures (> 15~ many flower buds revert to vegetative differentiation rather than abort (Roberts 1989). Successful reversion to vegetative growth depends partly on the stage of flower bud differentiation when the cytokinin is applied. A flowering gradient exists along most laterals where the more mature flowers are usually located in the axils of the fourth leaves below the apex; flower maturity decreases both acropetally and basipetally from this point (Roberts and Menary 1990). The presence of the flowering gradient makes it difficult to carry out investigations on buds that initiate at the same time and have the same degree of sink strength; however, this can be achieved in vitro. The aim of this experiment was to investigate flower bud initiation and development in vitro using different levels of cytokinin and two environments. Materials and Methods Preliminary ExperimentsGenerally for woody species, embryos or young inflorescences must be used to regenerate shoot types or organs in vitro; hence, the explant must be in to a juvenile state (Tran Thanh van 1981).For example, in Citrus Altmen and Goren (1974), Garcia-Luis et al. (1989), andTisserat et al. (1990) used explants that consisted of the whole bud, portions of bark and wood from the branchlet and the stump end of the petiole; Tsujikawa et al. (1990) used axillary leaf buds or growing shoot apices for successful flowering of Japanese pear. Trial experiments were carried out with Boronia using explants derived from a variety of sources, including: shoot proliferations, in vitro grown shoots, and current seasons' laterals. These preliminary experiments showed that flower buds could be initi...

In vitro induction of inflorescence in Dioscorea zingiberensis

“…In vitro floral induction and development require presence of cytokinins (Roberts et al 1993). BA has been reported to be effective in floral induction of a number of plant species, such as orchids (Chang and Chang.…”