Citrus exhibits unique nutritional values. Most citrus cultivars are derived from mutations. However, the effect of these mutations on fruit quality is unclear. We have previously found a yellowish bud mutant in the citrus cultivar ‘Aiyuan 38’. Therefore, this study aimed to determine the effect of the mutation on fruit quality. ‘Aiyuan 38’ (WT) and a bud mutant variant (MT) were used to analyze variations in fruit color variation and flavor substances using colorimetric instruments, high-performance liquid chromatography (HPLC), headspace solid-phase microextraction-gas chromatography–mass spectrometry (HS-SPME-GC–MS), and odor activity values (OAVs). The mutation in MT conferred yellowish characteristics to its peel. Although the differences in total sugar and acid content of the pulp were not statistically significant between WT and MT, the MT glucose content was significantly lower and the malic acid level was significantly higher. HS-SPME-GC–MS analysis revealed that the MT pulp released more types and contents of volatile organic compounds (VOCs) than the WT, whereas the opposite trend was observed for the peel. Analysis of the OAV revealed that the MT pulp contains 6 unique VOCs, whereas the peel contains only 1. This study provides a useful reference for the study of flavor substances associated with citrus bud mutations.

The interstock, a stock between the rootstock and scion, has a significant regulatory effect on the stock and scion, and its function is highly dependent on graft compatibility. To assess the graft compatibility of the interstock and scion, ‘Yuanxiaochun’ was top grafted onto ‘Ponkan’, ‘Shiranuhi’, ‘Harumi’, ‘Tarocco’, and ‘Kumquat’. The results showed significant differences in the survival ratio and preservation ratio among different combinations. Grafting compatibility in the early stages of grafting was associated with the genetic relationship. The biomass accumulation revealed that the interstock could influence both the rootstock and the scion. The physiological and biochemical traits analysis suggested that SPAD reading and soluble sugar could be employed as preselected indices to evaluate graft compatibility in the late stage of grafting. These results indicated that the evaluation of graft compatibility was a dynamic process. The findings provided a new approach for studying the stock and scion interaction mechanisms mediated by interstock, and directly provided a theoretical and practical basis for the high-grafting of ‘Yuanxiaochun’ citrus.

Interstock, located between rootstock and scion, plays a critical role in determining graft compatibility. This study aimed to elucidate the physiological mechanisms mediated by interstock in graft compatibility by comparing various leaf and root system parameters between compatible and incompatible graft combinations. These parameters included growth parameters, photosynthetic pigments, carbohydrates, antioxidant enzyme systems, and hormones. The study found that both PG (‘Yuanxiaochun’/‘Ponkan’/‘Trifoliate orange’) and JJ (‘Yuanxiaochun’/‘Kumquat’/‘Trifoliate orange’) treatments exhibited a noticeable phenomenon of “small feet” (scion diameter exceeding interstock), indicating mild graft incompatibility. Compared to grafted compatibility groups, chlorophyll content in PG and JJ treatments leaves was significantly reduced, particularly in carotenoids (Car). Additionally, PG and JJ treatments leaves showed lower levels of total soluble sugars, fructose, sucrose, gibberellin A4, zeatin-Riboside, and N6-(delta2-isopentenyl) adenosine, as well as catalase (CAT) activity. In contrast, peroxidase (POD) activity, glucose, soluble proteins, hydrogen peroxide (H₂O₂), malondialdehyde (MDA), aminocyclopropane carboxylic acid, and abscisic acid content were higher. In roots, PG and JJ treatments had elevated starch, sucrose, jasmonic acid, and jasmonic acid-isoleucine content, but showed lower levels of total soluble sugars, MDA, indole-3-acetic acid, and abscisic acid. Comprehensive analysis revealed that total soluble sugar content in both leaves and roots under PG and JJ treatments were reduced. These findings offer valuable insights into enhancing citrus grafting practices, particularly by guiding the selection of compatible rootstock-scion combinations. By elucidating the physiological mechanisms underlying graft compatibility, this research enables researchers and growers to refine grafting strategies, thereby improving citrus grafting success rates.

Peelability, a crucial commercial trait for fresh-eating citrus, has received limited research attention regarding its underlying mechanisms. This study investigated three late-maturing citrus cultivars, namely ‘Qingjian’ (QJ), ‘Mingrijian’ (MRJ), and ‘Chunjian’ (CJ), analyzing their peelability development using texture analysis and exploring the physiological and biochemical factors influencing peeling difficulty. The results showed that peelability improved with fruit maturation, reaching its peak at full ripeness, with the following order of peeling difficulty: QJ (hardest) > MRJ (intermediate) > CJ (easiest). At full maturity, QJ (the most difficult to peel) exhibited more regularly shaped peel cells with fewer intercellular spaces, lower intracellular organic matter accumulation, and higher levels of cell wall polysaccharides, calcium (Ca), and abscisic acid (ABA). These characteristics may be linked to the lower relative expression of soluble sugar (TS)-related genes (CCR4A, SPP1) and the titratable acid (TA)-related gene (CsCit1), as well as the higher relative expression of ABA biosynthesis genes (NCED1, NCED2). Correlation analyses demonstrated that citrus peel firmness and adhesion strength are significantly associated with multiple growth and developmental characteristics, including fruit morphometric parameters, peel cellular architecture, intracellular organic compound content, cell wall polysaccharide levels and related degradative enzyme activities, calcium concentrations, and endogenous phytohormone profiles. These findings provide valuable insights for studying peelability mechanisms and improving fruit quality in citrus breeding.