Effects of exogenous plant growth regulators at different growth stages on fruit quality of blueberry

【Objective】Blueberries are rich in nutrients such as vitamin C, flavonoids, and anthocyanins, offering health benefits including vision protection, eye fatigue relief, and enhanced immunity. This study investigated effective methods to improve the quality blueberry fruit by spraying exogenous regulators at different growth stages and conducting comprehensive evaluation of fruit quality indices through principal component analysis.【Methods】Three-year-old O’Neal blueberry plants were used as experimental materials. Different concentrations of abscisic acid (ABA), 3-indoleacetic acid (IAA), 6- benzylaminopurine (6-BA), and gibberellic acid (GA3) were applied at three growth stages: Full bloom stage, fruit setting stage, and berry veraison stage, with clear water as the control (CK). The four exogenous regulators were tested at three concentration gradients: ABA: T1 (10 mg·L-1 ), T2 (50 mg·L-1 ) and T3 (100 mg·L-1 ); IAA: T4 (50 mg·L-1 ), T5 (100 mg·L-1 ) and T6 (150 mg·L-1 ); 6-BA: T7 (50 mg·L-1 ), T8 (100 mg·L-1 ) and T9 (200 mg·L-1 ); GA3: T10 (50 mg·L-1 ), T11 (100 mg·L-1 ) and T12 (200 mg·L-1 ). Each treatment comprised three blueberry plants. The entire plant was sprayed until fully moistened with dripping liquid, with applications repeated at 7-day intervals (twice total). Samples were taken after the berries were fully ripe. The measured parameters included: berry transverse diameter, longitudi-nal diameters, single berry mass, 100-grain mass, color parameters (L*, a* and b*), soluble solids, titratable acid, soluble sugars, vitamin C, total phenolic, and anthocyanin. Color parameters were measured using an PS2020 colorimeter; the soluble solids content was determined by using PAL-1, ATAGO, Japan; the titratable acid content was determined by pH potentiometric titration; the soluble sugar content was determined by anthrone colorimetric method; the vitamin C content was determined by molybdenum blue colorimetric method; the total phenolic content was determined in accordance with T/AHFIA 005—2018 standard; the total anthocyanin content was determined by the pH differential method. Differential and correlation analyses were performed on quality indices, followed by comprehensive evaluation using principal component analysis.【Results】1. Full bloom stage: Compared with CK, the fruit transverse diameter of T2 treatment increased most significantly, while T8 treatment showed the most notable enhancement in single fruit mass. T9 treatment increased the amount of fruit powder on fruit surface and significantly elevated the contents of vitamin C, total phenolic, and anthocyanin by 140.78% , 28.82% , and 140.00% , respectively. Correlation analysis revealed non- significant associations between fruit shape index, soluble solids content, and other quality parameters (P＞0.05). Transverse diameter exhibited significant positive correlations with single fruit mass and 100-grain mass (P＜ 0.05), while total phenolic content showed a highly significant positive correlation with anthocyanin (P＜0.01). Principal component analysis extracted five principal components with a cumulative contribution rate of 84.146%, identifying T9 as the optimal treatment for comprehensive fruit quality. 2. Fruit setting stage: The contents of soluble solids, vitamin C, total phenolic and anthocyanin in the fruits treated with T2 were significantly higher than those in the CK, increasing by 18.87%, 185.00%, 37.83% and 150.76% , respectively. The contents of transverse and longitudinal diameters, single fruit mass, 100- grain mass, soluble sugar, vitamin C and anthocyanin in the fruits treated with T5 were all significantly increased. The average single fruit mass of the T7 treatment was the maximum at 1.94 g, and the anthocyanin content of the fruits of the T11 treatment was as high as 2.29 mg·g-1 . Correlation analysis indicated no significant association between fruit shape index and other quality parameters (P＞0.05). Transverse diameter showed highly significant positive correlations with longitudinal diameter and single fruit mass (P＜0.01), and total phenolic content was strongly positively correlated with anthocyanin (P＜0.01). Principal component analysis extracted five principal components accounting for 91.123% of cumulative variance, identifying T5 as the optimal treatment for comprehensive fruit quality. 3. Berry veraison stage: With the T6 treatment, the contents of soluble sugar and ascorbic acid in the fruits increased by 39.20% and 102.36%, respectively, compared with the CK, while the total phenol content decreased. The T12 treatment enhanced transverse diameter, longitudinal diameter, single fruit mass, soluble sugar content, and vitamin C content by 2.91%, 7.19%, 9.25%, 47.69%, and 27.71%, respectively. T7, T9, and T11 treatments showed significant differences in fruit L* values compared to CK, potentially due to thicker fruit powder. Correlation analysis revealed no significant associations between soluble solids content, vitamin C content, and other quality parameters (P＞0.05). Transverse diameter exhibited highly significant positive correlations with longitudinal diameter and single fruit mass (P＜ 0.01), and total phenolic content demonstrated a strongly positive correlation with anthocyanin (P＜ 0.01). Principal component analysis extracted five principal components with a cumulative contribution rate of 89.475%, identifying T12 as the optimal treatment for comprehensive fruit quality.【Conclusion】Through comprehensive analysis and evaluation of blueberry fruit quality indicators using difference analysis, correlation analysis, and principal component analysis, it was determined that spraying 200 mg ·L-1 6-BA at the full bloom stage, 100 mg·L-1 IAA at the fruit setting stage, and 200 mg·L-1 GA3 at the berry veraison stage can significantly enhance the fruit quality of O'Neal blueberry.