Effects of rootstock-scion interaction on peel coloration and nutrient absorption in Orah Mandarin

【Objective】Rootstock selection is a critical determinant of citrus productivity and fruit quality. This study systematically evaluated the impact of four commercially significant rootstocks, Trifoliate orange (Poncirus trifoliata), Red tangerine (Citrus reticulata), Ziyang Xiangcheng (C. junos Sieb. ex Tanaka), and Carrizo citrange (C. sinensis × Poncirus trifoliata), on peel coloration and leaf mineral nutrients in Orah mandarin (C. reticulata Blanco cv. Orah). The objective was to identify optimal rootstocks tailored to specific soil conditions and production objectives, thereby offering a scientific foundation for precision orchard management in Orah mandarin cultivation.【Methods】A three-year field experiment was conducted from 2018 to 2020. The study utilized five-year-old Orah mandarin trees grafted onto the above four rootstock types. The experimental trees were selected based on consistent tree age, canopy size, and management practices. Annually, at commercial maturity, fruit peel color was assessed using a colorimeter to measure CIE L* (lightness), a* (red-green), and b* (yellow-blue) values, and the Citrus Color Index (CCI) was calculated to evaluate color saturation. Leaf samples were collected concurrently and analyzed for macronutrients (N, P and K), secondary nutrients (Ca, Mg and S), and micronutrients (Fe, Mn, B, Cu and Zn) following standard analytical procedures. Data were subjected to analysis of variance (ANOVA), Duncan’s multiple range test, and principal component analysis (PCA). For PCA, 15 indicators, including color parameters (L*, a*, b*, CCI) and nutrient contents from 12 samples (three replicates per rootstock) were standardized. Principal components with eigenvalues greater than 1 were extracted to develop a comprehensive evaluation model.【Results】The genotype of the rootstock significantly influenced both fruit peel coloration and leaf nutrient content, with consistent patterns observed across the three-year study period. Regarding fruit coloration, annual variations were evident, yet rootstock- specific performance remained stable. The Red tangerine rootstock consistently yielded fruit with the highest peel lightness (L*), recording values of 57.18 (2018), 59.95 (2019), and 57.12 (2020), and a three-year average of 58.08, which was significantly higher (P＜0.05) than that of Carrizo citrange (54.52). Similarly, Red tangerine also induced the most intense yellowness (b*), peaking at 55.69 in 2020, with a three-year average of 54.72. In contrast, Carrizo citrange and Trifoliate orange rootstocks consistently generated deeper red hue (a*) and higher color saturation (CCI), with a* values of 38.60 and 38.21, and CCI values of 13.92 and 13.51, respectively, which were significantly higher than those of Ziyang Xiangcheng and Red tangerine. A declining trend in yellowness (b*) was observed in fruits from Ziyang Xiangcheng over the three years. In terms of mineral nutrition, different rootstocks exhibited distinct elemental absorption preferences. Ziyang Xiangcheng led to the highest accumulation of macronutrients, with leaf N and P contents of 2.89% and 0.13%, respectively, and K content significantly higher (1.33% ) than the other rootstocks, along with the highest S content (0.25% ). Trifoliate orange showed a strong ability to enrich Mg (0.34%), which was significantly higher than the other rootstocks, and also accumulated the highest levels of Cu (407.43 mg·kg-1 ). Carrizo citrange demonstrated a high efficiency in absorbing specific micronutrients, with the highest Mn (80.81 mg · kg- 1 ) and B (221.64 mg · kg-1 ) contents, which significantly exceeded the other rootstocks. Red tangerine also promoted Zn accumulation (78.98 mg·kg-1 ) and exhibited intermediate values for most of the nutrients, suggesting a more balanced nutritional profile. Notably, rootstock genotype had no significant effect on Fe absorption. Principal component analysis (PCA) revealed that the first three principal components explained 81.19% of the total variance, identified as the“macronutrient factor”(PC1, 45.49%),“color factor”(PC2, 21.67%), and“secondary/micronutrient factor”(PC3, 14.03%). The comprehensive evaluation model, based on weighted factor scores, ranked the rootstocks as follows: Red tangerine (0.867- 0.935)＞Trifoliate orange (0.528-0.632)＞Ziyang Xiangcheng (0.342-0.452)＞Carrizo citrange (-0.896 to -0.958), indicating that Red tangerine provided the best overall performance.【Conclusion】The results demonstrate a pronounced rootstock-specific influence on the performance of Orah mandarin. No single rootstock demonstrated universal superiority; selection should therefore be tailored to local soil conditions and production objectives. Carrizo citrange and Trifoliate orange are recommended for orchards aiming to enhance red fruit coloration. Carrizo citrange is particularly suitable for soils deficient in Mn or B. Trifoliate orange and Red tangerine are better adapted to acidic soils or those low in Cu and Zn, though potential Cu excess under Trifoliate orange requires monitoring. Ziyang Xiangcheng is ideal for poor soils or situations demanding vigorous tree growth. Notably, Red tangerine, achieving the highest comprehensive evaluation score, exhibited well-balanced performance in both coloration and nutrient uptake, establishing it as a preferred choice for Orah cultivation in southern Guangxi. However, its fruit quality is strongly dependent on harvest timing: it is unsuitable for early harvest (e.g., January) and attains optimal quality with delayed harvesting (recommended until February). For established orchards showing nutrient deficiency symptoms, inarching with a complementary rootstock represents a viable remedial approach. This study offers a scientific framework for evidence- based rootstock selection in Orah mandarin production, facilitating the synergistic improvement of fruit quality and nutrient use efficiency.