Anatomical Observations of Pollen Starch Accumulation and Pollen Germinability as Affected by Pre-anthesis Night Temperatures in Cherimoya (Annona cherimola Mill.)

Abstract

Pre-anthesis night temperatures (1800–0900 h) surrounding cherimoya flowers were sectionally regulated at 4–35ºC, and pollen germination was examined immediately after their anthesis. Developmental changes in pollen starch were also anatomically observed, and the night temperature effects on pollen starch and germinability were discussed. Pollen germination percentage was largely affected by pre-anthesis night temperatures, being highest (≈70%) at 20–22ºC. Germination decreased at temperatures below 14ºC, and decreased remarkably below 6ºC. Tube elongation was also restricted below 6ºC. At 4ºC, the pollen often shriveled. Germination also decreased over 27ºC. Germination and elongation were low at 35ºC. Night temperatures also affected anthesis time. The time was earliest at 18–22ºC (1500–1600 h) and was delayed at higher and lower temperatures. Pollen starch only accumulated in the generative cell until 1 week before anthesis. From 3 days before anthesis to the morning of the anthesis day, starch accumulation was sometimes observed in the whole portions in pollen. The accumulation was not affected by temperatures. At 10–20 minutes before anthesis, the pollen was filled with starch. Immediately after anthesis, starch was observed in only half of the pollen. The disappearance of starch was not affected by temperatures. No apparent relationship between germination and starch accumulation was found. Cherimoya pollen germination declined remarkably when flowers were exposed to temperatures lower than 14ºC or higher than 27ºC even for one night previous to anthesis.