Effects of different growth regulators on fruit quality of Yanfu No. 3 apple on the Loess Plateau

【Objective】The study aimed to systematically evaluate the regulatory effects of different plant growth regulators on quality formation during the fruit development of Yanfu No. 3 apple, and to elucidate their physiological impacts on fruit appearance characteristics, nutritional quality, and aroma substance formation.【Methods】The experiment was conducted in the main apple- producing area of Jingning County, Gansu Province, using widely cultivated 6- year- old Yanfu No. 3 (Malus domestica Bork.) apple trees as research material. Treatments were applied at the young fruit stage, approximately 20 days after flowering, using a randomized block design with seven spray treatments: T1 (gibberellin GA4), T2 (gibberellin GA7), T3 (spraying gibberellin GA4+7 compound), T4 (chlorogenic acid), T5 (sodium nitrophenolate), T6 (gibberellin (GA4+7) + sodium nitrophenolate), T7 (gibberellin (GA4+7) + sodium nitrophenolate + chlorogenic acid). water spray treatment served as the control (CK). Each treatment was replicated three times. All treated trees received unified water and fertilizer management, pest and disease control, and pruning techniques to minimize interference from non-experimental factors and en-sure the feasibility of the experimental data. The full-bloom date of Yanfu No. 3 apple is April 28, and the fruits are ripe and harvested on October 22, which is 170 days after full bloom, and relevant indicators were immediately tested and analyzed. Appearance characteristics included fruit weight and fruit shape index; internal quality indicators included the contents of vitamin C, total phenols, total sugars, soluble solids, soluble protein, flavonoids, and tannins in the fruits.【Results】The research results showed that all different spray treatments affected the quality formation of Yanfu No. 3 apple fruits, with significant differences observed among treatments for the various indicators. Although single regulator treatments performed well in certain individual indicators, the combination treatments demonstrated superior comprehensive regulatory effects. Notably, the T7 treatment (GA4+7 + chlorogenic acid + sodium nitrophenolate) showed significant advantages in enhancing fruit nutritional components. The fruits under T7 treatment exhibited significantly higher contents of vitamin C, total sugars, soluble solids, and soluble protein compared with other treatments and the control, indicating a strong synergistic effect of the regulator complex in promoting nutrient accumulation. In addition, T7 treatment significantly reduced the contents of flavonoids and tannins in the fruits and effectively improved their flavor. Regarding appearance characteristics, the fruits from T3 and T7 treatments showed better shape indices. The analysis identified the main aroma components of Yanfu No. 3 apples as esters, alcohols components. The T7 treatment was particularly effective, resulting in the fruits exhibiting a more intense overall aroma. The underlying mechanism would be presumed to be related to the regulators promoting the synthesis and conversion of aroma precursors and enhancing fatty acid metabolism and related enzyme activities, thereby increasing the accumulation level of volatile aroma compounds.【Conclusion】Based on the systematic analysis of the appearance characteristics, nutritional quality, and aromatic compounds of the Yanfu No. 3 fruits in this experiment, it can be concluded that the application of 10 mg·L-1 gibberellic acid GA4 + 7 plant growth regulators and 12 mg · L- 1 gibberellic acid (GA4 + 7) + sodium nitroprusside + chlorogenic acid plant growth regulators had a positive effect on improving the fruit quality of Yanfu No. 3 in the Loess Plateau region, with the T7 treatment showing the most significant effect.