Strengthening Pollination Management to Increase Sweet Fruit Setting Rate
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Sweet cherries are one of the most efficient fruit tree species in terms of planting and production. Currently, regions such as Shandong, Liaoning, Hebei, Henan, Shaanxi, Sichuan, and Beijing are actively investing in and developing sweet cherry cultivation. However, a common challenge remains: low and unstable yields. This issue primarily stems from the fact that most sweet cherry varieties are not self-pollinating. Although some orchards use pollination varieties or even resort to artificial pollination, the fertilization rate is still low. The reason for this lies in the fact that while many sweet cherry varieties have strong cross-pollination potential among themselves, their compatibility between different varieties is often weak. Additionally, differences in flowering times can lead to mismatched pollination periods, especially when early-flowering varieties do not overlap with late-flowering ones. Therefore, it's essential to select pollination trees with similar flowering durations and strong pollination affinity to ensure high fruit set and stable production.
When choosing pollination varieties, the first principle is to match the pollination compatibility with the main cultivar. For known S-genotype varieties, the S-genotypes can help determine if other varieties outside the same group can serve as effective pollinators. For varieties with unknown S-genotypes, selecting those with distant genetic relationships and verifying their compatibility through field pollination tests is recommended. It's important to note that sweet cherry pollination affinity is controlled by a single gene locus with a pair of S alleles.
Flowering periods vary significantly among sweet cherry varieties. For example, Rabins, Laizhou Zaohong, and Naoeng tend to flower earlier, while Cevia and Regina bloom later. According to research from Michigan State University, there is typically a 5–12 day difference between early and late-flowering varieties. When selecting pollination varieties, it's crucial to consider the timing of each variety’s bloom. Ideally, the pollination variety should flower at the same time as the main cultivar or slightly earlier (1–2 days) to maximize pollination success.
In addition to compatibility, pollination varieties should also possess good economic traits and be able to effectively cross-pollinate with the main cultivars. Most varieties produce abundant pollen and have overlapping blooming periods, making them suitable as pollinators. The key is to choose varieties that can produce viable pollen and support strong cross-pollination.
To further increase fruit set, proper orchard management is essential. This includes controlling tree growth, promoting flowering, and ensuring adequate nutrient supply. Applying organic fertilizers, timely chemical inputs, and trace elements helps build up the tree's energy reserves. Techniques like branch spreading, bud scoring, and topping can help control vegetative growth and encourage flowering, especially in young, vigorous trees. During the flowering stage, spraying borax, potassium dihydrogen phosphate, or gibberellin can improve pollination success. Thinning flowers and fruits also helps boost fruit setting rates.
Proper configuration of pollination varieties is another critical factor. A typical ratio is 60% main cultivars and 40% pollination varieties. In smaller orchards, planting 3–4 different varieties together can enhance cross-pollination. In larger areas, multiple varieties should be planted according to maturity, with main and pollination varieties arranged in rows for easier harvesting and marketing.
During the flowering period, introducing bees can significantly boost pollination efficiency. It's recommended to place 3 hives or 3,000–5,000 bees per hectare. Moving beehives into the orchard two days before flowering allows bees to adapt. However, adverse weather conditions like rain, temperatures below 15°C, or strong winds can reduce bee activity. In such cases, manual pollination using simple pollinators can be an effective alternative.
Finally, covering the orchard during flowering can protect against environmental stressors like frost, cold, rain, or dry hot winds. These conditions can damage blossoms, hinder pollination, or prevent fruiting. Using simple greenhouses can reduce these risks, improve pollination success, and even advance fruit ripening, helping avoid issues like rain cracking and bird damage.