Anatomical Study on Seasonal Changes in Pistil Receptivity of Cherimoya (Annona cherimola Mill.)

Abstract

Morphogenesis of reproductive organ was correlated with external appearance of flower buds in cherimoya, and then pollen-tube growth in pistils incubated after pollination was observed chronologically to explain low pistil receptivity in early spring and mid summer. In April, when minimum temperatures were approximately 10°C, pollen-tube growth was suppressed and many impaired ovules were observed, suggesting a shortage of photosynthate accumulation in flowers. After May, when the minimum temperature increased to more than 15°C, faster pollen-tube growth and less impaired ovules were observed, although a large deviation in pistil receptivity was observed until mid May. This deviation might have been a result of nutrient competition between pistils in a multiple-flower. In late May to late June, when temperatures were 15-30°C, pistil receptivity was highest throughout the season with small deviation. After late June, when night temperatures often exceeded 25°C, pistil receptivity decreased, and many impaired ovules were observed in July. Increased respiration and thereby exhaustion of floral organs might be caused by high night temperatures. Besides the effects of low pollen viability, the low fruit set in early and late season was considered to be attributed to the impaired pistil development.