The tested cherry variety was “Hongfei”, a 6-year-old tree planted at the Little Cherry Planting Base in Dianjun District, Yichang City, Hubei Province, with a density of approximately 70 trees per 666.7 m² (plot size 3 m × 3.2 m). The trees exhibited a naturally open-crowned shape, uniform growth vigor, and were free from pests or diseases. The soil type at the test site was yellow-brown soil with a pH of 6.5 and 1.8% organic matter content. The glycine betaine used in the experiment was an analytical-grade reagent, and during the test, it was diluted with distilled water to prepare three spray solutions with mass concentrations of 0.1%, 0.3%, and 0.6%.

The experiment adopted a randomized block design with four treatments: T1 (0.1% glycine betaine solution), T2 (0.3% glycine betaine solution), T3 (0.6% glycine betaine solution), and CK (equal volume of distilled water as control). Seven uniformly growing cherry saplings were selected for each treatment, with three replicates (total 21 saplings) per treatment. Isolation rows (two rows) were established between plots to prevent interference. The experiment was conducted over two cycles (2024 and 2025). Spraying was performed at three key stages: the first during the budding stage (March 8, 2024; March 10, 2025), the second during fruit setting (April 8, 2024; April 10, 2025), and the third during early fruit enlargement (April 28, 2024; April 30, 2025). A backpack sprayer was used for foliar spraying, with optimal results achieved when water droplets covered both sides of the leaves without dripping. Throughout the experiment, all field management practices (including irrigation, pest control, and pruning) were conducted according to standard procedures, except for the spraying treatments.

2.3.1. Appearance Quality Assessment

During the maturation period of little cherry (May 10-12), 50 mechanically undamaged fruits were randomly collected from each treatment. The following indicators were measured according to the method described by Liu Kun et al. [14]: 1) Single fruit weight: Weighed using an electronic analytical balance (precision 0.01 g) and averaged. 2) Fruit dimensions: Measured with a vernier caliper (precision 0.01 mm) and averaged. 3) Fruit color: The surface L value (brightness) and a value (red-green chroma, with higher values indicating deeper red) were determined using a colorimeter (CR-400, Konica Minolta). Three measurement points were taken per fruit, and the average was calculated. The statistical software SPSS was used for analysis of variance and significance level.

2.3.2. Measurement of Intrinsic Quality

After removing the skin and core from the fruits with the measured appearance quality, homogenize them and conduct the following measurements according to the method described by Zhang Zaihua et al. [15]: 1) Soluble solids content: Determine using a handheld sugar meter, with three repetitions; 2) Vitamin C content: Determine by the 2,6-dichloroindophenol titration method, expressed as mg/100g; 3) Titratable acid content: Determine by acid-base titration (using 0.1 mol/L NaOH standard solution), measured as malic acid, expressed as %.

2.3.3. Yield Measurement

For each batch of 7 little cherry saplings, the fruits of each little cherry tree were weighed together and the fruit number per plant was recorded using photoelectric counter, and the average yield per plant was calculated. This yield was then converted to per-mu (666.7 m²) yield (calculated by planting 70 saplings per 666.7 m²).

As shown in Table 1, compared with the control (CK), spraying different concentrations of glycine betaine significantly improved the appearance quality of little cherry, with the T2 treatment (0.3% GB) showing the best effect. In 2024, the single fruit weight of the T2 treatment was 2.82 g, an increase of 34.3% compared to CK; the longitudinal and transverse diameters were 18.7 mm and 17.2 mm, respectively, representing increases of 15.4% and 12.4% over CK; the a-value (red-greenness) was 28.6, up 15.3% from CK, while the L-value (brightness) was 34.2, down 8.7% from CK, indicating deeper red coloration and more vibrant hues. The trend of each indicator in 2025 was consistent with 2024, with the single fruit weight, longitudinal diameter, transverse diameter, and a-value of the T2 treatment increasing by 35.8%, 16.0%, 12.3%, and 16.3% respectively compared to CK, and the differences between T2 and CK in both years were statistically significant (P < 0.01). The T1 treatment (0.1% GB) and T3 treatment (0.6% GB) showed weaker effects on appearance quality improvement compared to T2, with some fruits in the T3 treatment exhibiting slight surface wrinkling, suggesting that high concentrations of glycine betaine may have a certain impact on fruit skin development.

Table 1. Effects of different concentrations of glycine betaine on the appearance quality of little cherry.

As shown in Table 2, the application of glycine betaine significantly improved the intrinsic quality of little cherry, with the T2 treatment demonstrating the most optimal results. In 2024, the soluble solids content in the T2 treatment was 18.3%, an increase of 16.6% compared to the CK; the vitamin C content was 49.8 mg/100 g, up by 13.9% from the CK; and the titratable acid content was 0.62%, a decrease of 10.1% from the CK. In 2025, the soluble solids content and vitamin C content in the T2 treatment further increased to 18.7% and 50.5 mg/100g, respectively, representing increases of 17.6% and 14.5% from the CK; while the titratable acid content decreased to 0.60%, a reduction of 11.8% from the CK. The differences between the T2 treatment and CK were statistically significant (P < 0.01) in both years. Although the intrinsic quality indicators of the T1 treatment were superior to those of the CK, they were lower than those of the T2 treatment: in 2025, the soluble solids content in the T1 treatment was 17.2%, 8.0% lower than that of the T2 treatment; and the vitamin C content was 46.2 mg/100g, 8.5% lower than that of the T2 treatment. The intrinsic quality of the T3 treatment was similar to that of the T1 treatment, with its soluble solids content being 7.5% lower than that of the T2 treatment.

Table 2. Effects of different concentrations of glycine betaine on the intrinsic quality of little cherry.

As shown in Table 3, the application of glycine betaine significantly increased the yield of little cherry, with the T2 treatment demonstrating the most pronounced yield-enhancing effect. In 2024, the T2 treatment achieved a single-plant yield of 10.97 kg and a yield per 666.7 m² of 768.08 kg, representing a 36.0% increase compared to the control (CK). In 2025, the T2 treatment yielded 11.54 kg per plant and 807.79 kg per 666.7 m², showing a 37.7% yield increase over CK, with an average yield improvement of 36.9% over two years. The T1 treatment increased

Table 3. Effects of different concentrations of glycine betaine on little cherry yield.

yield by 19.8% - 20.7% compared to CK, achieving a yield of 702.58 kg per 666.7 m² in 2025. The T3 treatment increased yield by 23.4% - 24.2% over CK, yielding 723.51 kg per 666.7 m² in 2025. These results indicate that an appropriate concentration of glycine betaine enhances yield by increasing fruit weight and plant fruiting capacity, while concentrations that are either too low or too high may limit yield improvement.