REGULATING VEGETATIVE GROWTH AND FLOWERING WITH GIBBERELLIC-ACID IN INTACT PLANTS AND CULTURED PHYLLOCLADES OF CRIMSON GIANT EASTER CACTUS

Investigations were performed to determine the influence of gibberelli c acid (GA 3) on intact plants and cultured phylloclades of 'Crimson G iant' Easter cactus [Rhipsalidopsis gaertneri (Regel) Moran]. Response s of intact plants depended on GA3 concentration, number of spray appl ications, and application time. Single GA3 applications delayed flower ing and reduced the percentage of apical phylloclades flowering and nu mber of flower buds per plant when applied before floral primordia for mation [from 20 days before to the start of long days (LDs)], but hast ened flowering and did not affect the percentage of apical phylloclade s flowering or number of flower buds per plant when applied during flo ral bud development (20 days after the start of LDs). When sprays were applied at or before the start of LDs, increasing the GA3 concentrati on resulted in fewer plants flowering, longer flowering delays, and fu rther decreases in the number of flower buds per plant. Multiple GA3 a pplications were more inhibitory to flowering than single applications . Whole plants and cultured phylloclades exhibited similar reactions t o GA3, but cultured phylloclades were more responsive to GA3 than inta ct plants. Intact plants and cultured phylloclades generally produced more new phylloclades as GA3 concentration increased. Spine growth als o increased when phylloclades were cultured in a GA3-containing medium . Flowering was accelerated by almost-equal-to 5 days when GA3 was app lied to intact plants with 1- to 2-mm-long flower buds. GA3 may be hor ticulturally useful for Easter cactus crop scheduling.