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.

The early-ripening peach industry has undergone rapid development in the Panxi region of the Sichuan Basin in recent years. However, after the introduction of some new peach varieties to the high-altitude peach-producing areas in Panxi, the titratable acid content in peach fruit has significantly increased. This study compared the fruit quality indicators of early-ripening peach varieties cultivated in Xide County (a high-altitude peach-producing area) and Longquanyi District (a low-altitude peach-producing area) in Sichuan Province and analyzed the differences in organic acid metabolism by combining primary metabolomic and transcriptomic approaches. The results showed that the ‘Zhongtaohongyu’ fruit from the high-altitude peach-producing area had a much higher accumulation of malic acid and, accordingly, a significantly higher organic acid content than the other samples. The lower annual average temperature and stronger ultraviolet radiation in high-altitude peach-producing areas may lead to the increased expression of genes (PpNAD-ME1, PpNADP-ME3, and PpPEPC1) in the organic acid synthesis pathway and the decreased expression of genes (PpACO2, PpNAD-MDH2/3/4/5, and PpPEPCK2) in the organic acid degradation pathway in peach fruit, ultimately resulting in the accumulation of more organic acids. Among them, the downregulation of the key genes PpNAD-MDH3/4/5 involved in malic acid metabolism may be the main reason for the higher malic acid accumulation in peach fruit from high-altitude peach-producing areas. Overall, this study elucidates the mechanism by which environmental factors enhance the accumulation of organic acids in peach fruit from high-altitude peach-producing areas from a multi-omics perspective, as well as providing a theoretical basis for screening key genes involved in organic acid metabolism in peach fruit.

Kiwifruit canker disease, caused by different bacterial pathogens, was observed in Sichuan Province, China. Specifically, in the winter and spring seasons, Pseudomonas syringae pv. actinidiae (Psa) was identified as the primary pathogen, causing reddish-brown exudates, branch dieback, and phloem decay. In contrast, during the summer months, Pectobacterium carotovorum subsp. actinidiae (Pca) emerged as the primary causal agent of kiwifruit canker, exhibiting similar symptoms to those caused by Psa, such as exudates from leaf scars and lenticels, xylem necrosis, and branch desiccation. From 55 symptomatic samples, 34 bacterial isolates were obtained, with 28 identified as Psa and 6 as Pca. Pathogenicity tests revealed significant variation in virulence, with Psa isolate G5 and Pca isolate M5 showing the highest pathogenicity on leaves and branches, respectively. Both pathogens caused characteristic necrosis and lesion expansion, fulfilling Koch’s postulates. Phylogenetic analyses confirmed the distinct evolutionary relationships of Psa and Pca isolates. These findings highlight the seasonal variability of kiwifruit canker pathogens and emphasize the need for targeted disease management strategies.

Anthocyanins, as natural pigments belonging to the flavonoid group, play a crucial role in plant reproduction, stress resistance and human fitness. Kiwifruit, which is rich in anthocyanins, demonstrates significant potential for promoting health benefits. Although light is widely recognized as an inducer of anthocyanin accumulation, we observed that kiwifruit accumulates more anthocyanin after bagging treatment. This unexpected finding suggests that anthocyanin biosynthesis in kiwifruit may also be regulated by other environmental or physiological factors influenced by bagging, such as humidity, temperature, or gas exchange. This implies that bagging may trigger specific regulatory pathways that promote anthocyanin accumulation through multiple environmental cues beyond light. Therefore, RNA-seq was performed to find the potential pathway. A total of 260 differentially expressed genes were found, including 8 transcription factors and 1 anthocyanin biosynthesis gene F3GT1 (glucosyltransferase). Dual-luciferase reporter assays revealed that bHLH transcription factors could activate the promoter of F3GT1 by 2.45-fold. We infer that bagging treatment increases the kiwifruit anthocyanin content through the bHLH291-F3GT1 pathway. This study not only highlights the potential agricultural applications and commercial value of bagging treatment but also provides new theoretical support for improving fruit coloration and optimizing breeding strategies.