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 gibberellic acid (GA 3) on intact plants and cultured phylloclades of 'Crimson Giant' Easter cactus [Rhipsalidopsis gaertneri (Regel) Moran]. Responses of intact plants depended on GA3 concentration, number of spray applications, and application time. Single GA3 applications delayed flowering and reduced the percentage of apical phylloclades flowering and number of flower buds per plant when applied before floral primordia formation [from 20 days before to the start of long days (LDs)], but hastened flowering and did not affect the percentage of apical phylloclades flowering or number of flower buds per plant when applied during floral bud development (20 days after the start of LDs). When sprays were applied at or before the start of LDs, increasing the GA3 concentration resulted in fewer plants flowering, longer flowering delays, and further decreases in the number of flower buds per plant. Multiple GA3 applications were more inhibitory to flowering than single applications. Whole plants and cultured phylloclades exhibited similar reactions to GA3, but cultured phylloclades were more responsive to GA3 than intact plants. Intact plants and cultured phylloclades generally produced more new phylloclades as GA3 concentration increased. Spine growth also increased when phylloclades were cultured in a GA3-containing medium. Flowering was accelerated by almost-equal-to 5 days when GA3 was applied to intact plants with 1- to 2-mm-long flower buds. GA3 may be horticulturally useful for Easter cactus crop scheduling.