Pomegranate trees often face issues such as fruit drop, flower abortion, and abnormal flower development. These problems can be categorized into four main types:
(1) The pistil is taller than the stamen;
(2) The pistil is equal in height to the stamen;
(3) The pistil is shorter than the stamen and partially degenerated (about 1/2 to 1/3);
(4) The pistil is completely degenerated.
The timing of pollen release from the anthers and the stigma's ability to receive pollen plays a crucial role in fruit set. Environmental factors like temperature and light significantly affect this process. Adequate sunlight and suitable temperatures promote pollen loosening. Pomegranate flowers typically open between 8:00 and 10:00 AM. Pollen begins to loosen on the second day after opening, especially before May 20th. A large amount of pollen is released around 4:00 PM. As temperatures rise and light increases, some flowers may open and release pollen on the same day. However, by 6:00 PM, most pollen is scattered, and further loosening occurs the next morning at 8:00 AM. After June 20th, higher temperatures and stronger light lead to reduced anther production, with flowers becoming pale and weak, resulting in lower viability.
The stigma's ability to accept pollen directly influences fruit setting. Under natural conditions, pollination occurring two days before or on the same day as flowering yields the highest fruit set. Pollination three days after flowering usually results in poor fruit set, as the stigma loses its receptivity.
Insects are the primary pollinators for pomegranates, even though the tree has some self-fertility. Cross-pollination significantly improves fruit set rates. Before May 30th, low temperatures and limited insect activity are key factors affecting early fruiting. Therefore, increasing pollinator presence is essential during this period.
To improve fruit retention and quality, several measures can be taken:
1. Enhance flower quality by ensuring proper nutrition during the first two stages of flower bud differentiation. Applying additional fertilizer during this time helps promote healthy flower buds and increase the proportion of normal flowers.
2. Create favorable pollination conditions by planting multiple varieties when establishing a pomegranate orchard. A ratio of 6:4 between the main variety and pollinators is recommended. If bees are available, place hives in the orchard before flowering to assist with pollination. Avoid pesticide use during this time. Artificial pollination can also be performed using pollen from both female and abortive flowers. Collect pollen from flowers that have just started releasing it, remove the petals and buds, expose the anthers, and apply the pollen directly to the stigma of a fully opened flower. The best time for this is just before or immediately after the flower opens, when the stigma is most receptive.
3. Thin buds and fruits to concentrate nutrients. Remove 70% of abortive buds by the end of the flowering season. Leave only one top flower in clustered inflorescences and remove the rest. For double fruits, keep only one. This practice helps improve fruit set, size, yield, and overall quality.
4. Use a handheld sprayer to apply growth regulators. Spray 5–10 ml/L of gibberellin on fully open flowers, and 5–20 ml/L of 2,4-D sodium salt. Apply these treatments 2–3 times during the flowering period to enhance fruit set and development.
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