Flowering Behavior, Pollination, and Fruit Set



From the Horticultural Sciences Department, Florida Cooperative Extension Service
Institute of Food and Agricultural Sciences, University of Florida


Sugar apple trees produce flowers on -1 to 2-year-old wood and newly emerging shoots. Natural fruit set ranges from near zero to about 3% and fruit production may be severely limited by poor fruit set and fruit shape. This is due in part to the absence of their natural Nitidulid beetle pollinators in some areas and/or a lack of sufficient pollination during flowering. Misshapen fruit is caused by incomplete pollination.

Sugar apple have complete flowers, however, the male and female flower parts are functional at different times of the day (called protandry) (Table 4). Sugar apple flowers first open during the day and the female parts are receptive to pollen (female stage); early the next morning the flowers open wider and shed pollen (male stage). Subsequently, in the late afternoon and early evening, the male flowering stage occurs and the anthers release pollen. 

Table 4. Flowering behavior of sugar apple flowers

 Stage of flowering
Day Time of Day Female Male
1 Mid-day Receptive Not functional
Morning Receptive Pollen shedding


Annona squamosa (Custard Apple) flower in Hyderabad
Annona reticulata flower, male stage
Sticky stigma covered in pollen
Fig. 1 magnifying glass
Annona flowering,
female stage
Fig. 2 magnifying glass
A. reticulata flower,
male stage
Fig. 3  magnifying glass
Sticky stigma covered in pollen in A. muriticata

Flowers of sugar apple in the female stage are characterized by only a slight opening of the petals and a glistening appearance to the stigmatic surfaces. Flowers in the male stage are characterized by flower petals being wide open, petals may easily fall when touched and stamens may have a brownish color. This arrangement of having male and female flower parts functional at different times during the day makes cross pollination among different flowers necessary.

Sap beetle Carpophilus lugubris entering a Annona muriticata flower
Fig. 4 magnifying glass
Sap beetle Carpophilus lugubris entering a A. muriticata flower 


The natural pollinators of sugar apple and atemoya are nitidulid beetles (Coleoptera: Nitidulidae); sometimes called sap beetles. Nitidulid beetles are commonly found feeding and breeding on decomposing fruits and vegetables and are attracted to the strong, sweet odor of annona flowers during bloom. They feed on the nectar and pollen of the annona flowers and effect pollination by transferring pollen from functional male flowers to other flowers in the female stage.

Flowers which open under conditions of high humidity and warm temperatures are more likely to set fruit than those flowers opening during low humidity and/or cool temperatures. This is because a dry atmosphere more rapidly desiccates the female flower parts than a humid atmosphere.

Hand pollination of sugar apple is possible and may be very effective in improving fruit set (up to about 50%) and fruit shape. In general, pollen is collected from stamens of flowers in the male stage, which may be late afternoon, early evening, and early morning. The collected flower may be placed on paper where the anthers (male flower parts) are allowed to dehisce (release pollen). The next morning the pollen may be mixed with talcum powder to improve handling and transferred to flowers in the female stage of development. Hand pollination is usually most successful in the early to mid-morning hours (sunrise to about 11:00 am) and is done by using a thin camel-hair paint brush (like the brush found in water color paint set) to transfer pollen through the slightly open flower petals of the female stage flowers to the stigmatic surfaces at the base of the flower.


Further Reading
Artificial pollination of sugar apple and atemoya from AgriFoodGateway pdf
Hand Pollination of Custard Apples from the Archives of the Rare Fruit Council of Australia


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Atemoya Page
Cherimoya Page
Custard Apple Page
Soursop Page
Sugar Apple Page



Bibliography

Crane, Jonathan H., Balerdi, Carlos F. and Maguire, Ian. "Atemoya Growing in the Florida Home Landscape." edis.ifas.ufl.edu. This document is HS64, one of a series of the Horticultural Sciences Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Publication date 1980. Reviewed July 2013. Web. 29 Jan. 2014.

Photographs

Fig. 1 Garg, J.M. Annona squamosa (Custard Apple) flower in Hyderabad.2008. wikipedia.org. Web 27 Aug. 2014.
Fig. Ks. mini. "Annona reticulata." 2011. commons.wikimedia.org. Web.31 Dec. 2014.
Fig. 3  Daida, G. Sticky stigma covered in pollen. N.d. botany.hawaii.edu. University of Hawaii, Botany Department, Manoa Campus Plants. Web. 29 Aug. 2014.
Fig. 4 Sap beetle Carpophilus lugubris entering a Annona muriticata flower. N.d. In Insect/Mite Management in Annona spp. edis.ifas.ufl.edu. Web. 29 Jan. 2014.

Published 20 Jan. 2016 LR
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