Effects of Vapor Pressure Deficit on Ovary Morphogenesis and Pollen-Tube Growth in Pistils of Cherimoya (Annona cherimola Mill.)

Abstract

To determine the suitable vapor pressure deficit (VPD) for cherimoya pollination, flowers were detached one day before anthesis and hand-pollinated with fresh pollen. Then, the pollinated flowers were incubated under 12 different VPDs for 18 h. Ovary morphogenesis and pollen-tube growth in pistils were anatomically observed using a fluorescence microscope. Pistil malformation associated with shrunken ovaries was observed at higher VPDs. Pollen-tube pathways were partly interrupted in malformed pistils. The percentage of normal flowers was less than 40% at higher VPDs (1.2–2.5 kPa), whereas it sometimes reached to 90% or at least it was more than 50% at lower VPDs (0.2–1.2 kPa). Pollen-tube growth was largely inhibited at higher VPDs. This may be caused by insufficient secretion in pistils due to drought. Embryo sac malfunction might be another cause of incomplete pollen-tube induction. Pollen tubes successfully reached the embryo sac in more than 20% of the observed pistils at lower VPDs (less than 1.0 kPa), suggesting that the optimum VPD for cherimoya pollination was less than 1.0 kPa.