Effect of pollination methods on fruit set, quality and pollination costs of a self-fertile sweet cherry variety under protected cultivation

【Objective】The effects of different pollination methods on the fruit set rate, fruit quality, endogenous hormone levels, and economic costs of the self-fertile sweet cherry cultivar 7-2-9 under greenhouse cultivation were investigated. Based on this premise, multiple pollination treatments, including manual pollination using a feather duster, plant growth regulator application, bee pollination, and a nonassisted control, were established to comparatively analyze the physiological and developmental responses during fruit set and growth. The study focused on evaluating differences in fruit set stability, fruit size, soluble solid content, coloration traits, and the dynamic changes of endogenous hormones such as auxins, cytokinins, and gibberellins under different pollination conditions. In addition, a comprehensive assessment of labor input, operational costs, and overall economic efficiency associated with each pollination strategy was conducted to reflect their practical applicability in greenhouse production systems. The results further revealed both commonalities and differences among treatments in terms of improving fertilization efficiency, regulating fruit developmental synchronization, and enhancing fruit commercial quality. This work provides a scientific and technical basis for optimizing pollination management strategies under protected sweet cherry cultivation and supports the large- scale promotion of self-fertile cultivars in controlled environments.【Methods】The 8-year-old self-fertile sweet cherry cultivar 7-2-9 (Prunus avium L.), grafted on Jingchun 2, was selected as the experimental material at the Tongzhou Cherry Base of the Forestry and Fruit Research Institute, Beijing Academy of Agriculture and Forestry Sciences. The experiment was conducted in a solar greenhouse under controlled environmental conditions (15-22 ℃, 50%-70% RH), where four pollination treatments were established: natural selfpollination (CK), hand pollination (HP) with feather dusters, plant growth regulator treatment (PGRT) involving a multi-component solution including GA3, 6-BA, and NAA, and bee pollination (BP) using Apis mellifera ligustica. To ensure experimental precision, isolating nets were employed for CK, HP, and PGRT until fruit set was stable. The self-fertility of 7-2-9 was first validated through pollen germination assays and scanning electron microscopy (SEM, Hitachi SU-8010) to assess pollen morphology and uniformity. During the reproductive stages, the fruit set rate was calculated by monitoring flower and fruit counts on representative primary branches. Upon fruit maturity, physical quality traits (weight, shape index, and firmness) were measured using analytical balances, calipers, and the Firmtech FT-7 tester, while nutritional components (anthocyanins, VC, total phenols, and flavonoids) were quantified via colorimetric and enzymatic assays. Furthermore, endogenous hormone levels (IAA, CTKs, GA, SA, and JA) were determined using an LC-MS/MS system (ExionLCTM AD UPLC coupled with QTRAP® 6500+), with samples stored at -80 ℃. Additionally, a standardized cost-benefit model was constructed to calculate pollination time, labor expenses (20 RMB/h), and material inputs per 666.7 m2 . Finally, all data were processed using SPSS 22.0 for one-way ANOVA and LSD tests, with graphical visualizations generated using GraphPad Prism 8.0.2.【Results】Significant differences were observed in the growth, development, fruit quality, and economic costs of greenhouse-cultivated 7-2-9 sweet cherries under different pollination treatments. Pollen assays and two-year field identification confirmed that 7-2-9 was a self- fertile cultivar with high pollen viability and a stable self- pollination fruit set rate (46.00%- 58.00%). Compared with the control, both hand pollination (HP) and plant growth regulator treatment (PGRT) significantly increased the fruit set rate, whereas bee pollination (BP) showed a limited promoting effect. Morphologically, PGRT induced pedicel elongation and inhibited endocarp development, resulting in seedless fruits with smaller endocarps, whereas HP and BP maintained fruit traits similar to those of the control. Regarding internal quality, PGRT optimized the sugar-acid ratio by reducing acidity, whereas HP significantly enhanced nutritional quality, producing the highest concentrations of anthocyanins (0.68 mg · g- 1 ) and ascorbic acid (0.34 mg · g- 1 ). Physiological analysis revealed that PGRT and BP decreased IAA and tZ levels, whereas PGRT significantly increased the concentrations of cytokinins (BAP), gibberellins GA1 and GA3, and JA. Finally, economic evaluation showed that PGRT incurred the highest total cost because of intensive labor and chemical inputs, followed by BP due to hive expenses. Overall, hand pollination (HP) was the most efficient strategy, significantly improving fruit set and nutritional quality with relatively low economic costs, thereby providing a balanced approach for highquality production under protected cultivation.【Conclusion】Different pollination methods had significant effects on the fruit set rate, fruit quality, and economic costs of the self-fertile sweet cherry 7-2-9 under protected cultivation. Both hand pollination (HP) and plant growth regulator treatment (PGRT) significantly improved the fruit set rate compared with the control. However, although PGRT promoted fruit set, it altered fruit morphology and endogenous hormone balance, and was associated with high labor intensity and production costs. Bee pollination (BP) maintained fruit quality but involved relatively high hive expenses with limited improvement in fruit set. In contrast, hand pollination (HP) not only effectively increased the fruit set rate but also minimized adverse effects on fruit quality, showing the highest economic feasibility. Therefore, hand pollination is recommended as the primary pollination strategy for self- fertile sweet cherries under greenhouse conditions. This study clarifies the trade- offs among different pollination methods and provides a technical basis for efficient production. Further research is needed to explore the molecular mechanisms by which different pollination stimuli regulate endogenous hormone metabolism during fruit development.