The soursop flower is the reproductive structure of the Annona muricata tree, a tropical evergreen known for its distinctive fruit. These flowers are integral to the soursop tree’s life cycle, serving as the starting point for fruit development.
Anatomy and Characteristics of the Soursop Flower
Soursop flowers are notable for their unique appearance and structure. They typically measure between 1.5 to 2 inches (4-5 cm) in length and width, appearing plump and triangular-conical in shape. Each flower has six fleshy petals arranged in two rows of three. The three outer petals are yellow-green and slightly spreading, while the three inner petals are pale yellow and remain close together even when the flower is fully open.
These flowers can emerge anywhere on the trunk, branches, or twigs of the tree, often borne singly. They possess both male and female reproductive parts, making them hermaphroditic. The flowers emit a fruity odor, which is particularly noticeable when they are in their receptive female phase, helping attract potential pollinators.
The Soursop Flowering Process
The development of a soursop flower from bud formation to full bloom takes approximately 27-35 days. The tree can flower continuously throughout the year in suitable tropical climates, though some regions may experience peak flowering periods. A soursop tree typically begins to flower around three to four years after planting.
Soursop flowers exhibit a unique temporal flowering pattern, often opening in distinct phases. The floral anthesis, or opening, primarily occurs between noon and 8 p.m., and again from 4 a.m. to 8 a.m. Pollen release, however, usually happens later, specifically between 4 a.m. and 8 a.m. This asynchronous timing contributes to challenges in self-pollination.
Pollination and Fruit Set
The soursop flower’s structure presents a challenge for natural pollination. The flower is protogynous, meaning its female parts (stigma) become receptive before its male parts (stamens) release pollen. This asynchronous maturity prevents effective self-pollination within a single flower. Natural pollination is primarily carried out by insects, particularly beetles, which are attracted by the flower’s fragrance. Ants are also known to visit the flowers, but they are considered less efficient pollinators.
Due to the specific timing of male and female phases and often a scarcity of efficient natural pollinators, soursop trees frequently experience poor natural fruit set. This often results in a low yield of fruits, or the formation of misshapen fruits if only some ovules are fertilized. To overcome these limitations and increase fruit production, hand pollination is a widely adopted practice in soursop cultivation.
Hand pollination involves collecting pollen from a flower in its male phase, typically in the early morning before 10 a.m. when pollen viability is high. This pollen is then applied to the receptive stigma of a different flower that is in its female phase. The female stage is identifiable when the outer petals are open and the inner petals may also be slightly open, making the stigma accessible. This manual intervention ensures pollen transfer, significantly improving the chances of successful fruit development and resulting in well-shaped fruits.
Common Issues Affecting Soursop Flowers
Soursop trees can face issues that impact their flowers and fruit production. Flower drop is often caused by nutritional deficiencies, environmental stressors like extreme temperatures or humidity fluctuations, and water stress (under- or overwatering).
Pest infestations, such as thrips, mealybugs, root grubs, and carpenter moth larvae, can damage flowers and hinder fruit set. Fungal diseases, like anthracnose, can also cause lesions on flowers and lead to their decay.