Impact of CPPU and combined CPPU-thidiazuron treatments on fruit quality and volatile compounds in 'Jinling Xiangxin' grapes

(2-Chloro-4-pyridyl)-N′-phenylurea (CPPU) is a widely used plant growth regulator (PGR) in table grape production to promote seedlessness and increase berry size. However, the mechanisms by which PGRs influence aroma quality remain poorly understood. In this study, the effects of different CPPU and thidiazuron (TDZ) treatments on the exterior and nutritional quality of 'Jinling Xiangxin' grapes were evaluated, and a non-targeted volatile metabolomics analysis was conducted using gas chromatography-mass spectrometry (GC–MS). Results showed that the 5C–5C treatment (20 mg·L⁻¹ GA₃+ 5 mg·L⁻¹ CPPU at 3 d after bloom and 25 mg·L⁻¹ GA₃ + 5 mg·L⁻¹CPPU at 15 d after bloom) significantly improved the fruit exterior and nutritional traits, whereas the 5C–0C treatment (20 mg·L⁻¹ GA₃+ 5 mg·L⁻¹ CPPU at 3 d after bloom and 25 mg·L⁻¹ GA₃ at 15 d after bloom) enhanced aroma quality. A total of 113 volatile compounds were identified, with terpenoids (35 compounds) and esters (46 compounds) being predominant. Aldehydes and esters were confirmed as the primary contributors to grape aroma. Radar analysis revealed that grapes under the 5C−0C treatment exhibited stronger herbaceous, citrus, and caramelized flavors. K-means clustering further indicated that esters and terpenoids were mainly regulated by CPPU concentration, with <italic>β</italic>-terpinol and ethyl 3-oxohexanoate consistently affected. Moreover, 13 and eight differential compounds were identified as characteristic markers in CPPU-only and CPPU + TDZ treatments, respectively. Comprehensive evaluation of fruit exterior, nutritional, and aroma traits demonstrated that the 5C–0C treatment was optimal, enhancing marketability while minimizing negative impacts on aroma.