Floral Differentiation and Development in Cherimoya (Annona cherimola Mill.) under Warm (30/25.DEG.C.) and Cool (20/15.DEG.C.) Day/night Temperatures.

Abstract

To clarify the floral inhibition in cherimoya in warm environments, the number of flowers, floral morphology, nodal position, days to flowering, and flowering period were determined under 20/15°C and 30/25°C day/night temperature conditions throughout two years. Floral differentiation of cherimoya was more favorable at 20/15°C than at 30/25°C. More flowers were produced at 20/15°C and the flowering period was longer. Flowers were also larger at 20/15°C, however, the growth rate of floral organs was faster at 30/25°C. The temperature effects were more pronounced in the second year. The floral responses to temperature were different depending on the nodal positions, because of the different developmental processes. The number of the floral buds at the basal part of new shoot (at the 1st-3rd nodes) at 30/25°C was similar to that at 20/15°C in the first year, but it became smaller than that at 20/15°C in the second year. On the other hand, no distal buds of new shoot (at the 4th-more distal nodes) were produced at 30/25°C throughout the experiment period. The floral buds at the basal nodes differentiated almost a year previous to their anthesis, whereas the distal buds differentiated in synchronization with the shoot extension, about 5 weeks before anthesis. The axillary buds for basal flowers of the next season had already differentiated even in one-week-old leaf axils. Cherimoya produced an axillary multiple bud complex for the subsequent bloom and flush. In a 4-week-old leaf axil, a few floral buds with one or two vegetative buds usually developed at 20/15°C, while none or one floral bud with several vegetative buds developed at 30/25°C. The bud differentiation period was found to be the most temperature sensitive stage to influence flower number and morphology. Thus, exposure of cherimoya trees to a warm environment a year previous to the flowering and during shoot extension, respectively, was suggested to inhibit flowering at the basal and distal nodes.