Annona Species Monograph.pdf - Crops for the Future

Chapter 10. Agronomy
(1970) found that flower opening occurs from early morning until noon and
that the stigma is more receptive at this time on the first day, giving about
90% fruit set. Thereafter, receptivity decreases gradually, resulting in
minimal fruit set (8%) on the fifth day.
Pollen germination of cherimoya has been found to be optimal at 20-25°C,
which is the same temperature required for good fruit set in the orchard
(Rosell et al., 1999). Higuchi et al. (1998) studied the effects of warm
(30/25°C) and cool (20/15°C) day/night temperatures on fruit set and growth
in potted cherimoya under greenhouse conditions. They found that fruit set at
warm temperatures was very low, and ascribed this response to both pollen
and stigmatic damage from heat stress. In Madeira island, the best climatic
conditions for cherimoya self-pollination are temperatures equal to or above
22°C, with relative humidity of 70-80%, whereas temperatures below 22°C
with RH above 90% reduce pollination success (Nunes, 1997).
The stage of flowering phenology, pollen maturity and viability are factors
that affect fruit set and yield of Annona species. In New Zealand, Richardson
and Anderson (1996) compared fruit set at different flowering times by using
hand pollination methods in individual trees as main plots and time of
pollination on 20 flowers as sub-plots. They found that cherimoya pollination
is more successful at the beginning of the flowering period (January), with a
total yield of 34.8 kg/tree, than at the end of the flowering period (February)
with a total yield of only 0.1 kg/tree. It was also observed that pollen viability
varied from 20 to 50% and seediness increased from 11 seeds/fruit at the
beginning to 59 seeds at the end of the flowering period. In Chile, Saavedra
(1977) found that the first flowers of cherimoya to open gave poorer fruit set
with hand pollination than the later ones, probably because the majority of
the pollen grains at the beginning of flowering were still in the tetrad stage,
with thick walls and full of starch; at this stage, the pollen has a low viability
and, consequently, gives a low fruit set.
Grossberger (1999) commented that when pollen is used within 1-2 h of its
collection, more than 80% fruit set is generally obtained, as assessed by fruit
set two weeks after pollination. When pollen was stored for 12 h in a
standard refrigerator, fruit set fell to about 65% and to 35% after 24 h. This
would suggest that old pollen results in a low percentage of fruit set, even
using a brush or blower, which are appropriate tools for hand pollination.
Fruit set by hand pollination ranges from 44.4 to 60% depending upon the
species, while fruit set from open pollination is always less than 6%
(Mansour, 1997). Hand pollination is the only certain strategy to ensure
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