Xueping Han

Non-bagging apple cultivation, which is time-saving, labor-saving, and cost-effective, represents the future direction of apple cultivation in China. However, compared with bagging cultivation, it degrades fruit appearance quality, characterized by rough peels and dull colors, with the underlying physiological and molecular mechanisms remaining unclear. This study used ‘Tianhong 2’ Fuji apples, grafted onto SH dwarfing rootstock, and integrated transcriptomics–metabolomics to explore these mechanisms. Results showed that non-bagging-cultivated apple peels had higher chlorophyll and carotenoid contents but lower anthocyanin content than those of bagging-cultivated ones. Transcriptome sequencing identified 1571 differentially expressed genes (DEGs: 1269 upregulated, 302 downregulated). Functional analysis revealed that the decline in fruit appearance quality was primarily associated with secondary metabolite biosynthesis, lipid metabolism, and carbohydrate metabolism, and 34 candidate genes were identified. Metabolomic analysis detected 394 differentially expressed metabolites (DEMs), 38 of which were closely related to the non-bagging-induced appearance degradation, mainly lipids, organic oxygen compounds, and organic acids and their derivatives. Integrated analysis of DEGs and DEMs indicated the involvement of multiple critical metabolic pathways, including cutin, suberin and wax biosynthesis; starch and sucrose metabolism; cyanoamino acid metabolism; and phenylpropanoid and flavonoid biosynthesis. Compared with bagging-cultivated apples, non-bagging-cultivated apples exhibited faster starch degradation and higher soluble sugar accumulation. Additionally, the accumulation of specific metabolites [e.g., quercetin (HMDB0005794, HMDB03249, LMPK12112097), and suberin components (LMFA01170020, LMFA01050437, HMDB0031885)], along with elevated organic acid levels, contributed to peel roughness and dull coloration. These findings further enrich the theoretical basis for the formation of fruit quality in Fuji apples under non-bagging cultivation and provide valuable theoretical guidance for the practical application of this cultivation mode.

The experiment was conducted at the Taidong Base of Shandong Institute of Pomology, Tai’an City, Shandong Province, China, from May to October 2022. Using Fuji Apple Tianhong.2/SH/Malus robusta (M. robusta) as experimental materials, the differences and mechanisms of the effects of non-bagging and bagging cultivation on the growth and changes in some substance content of Fuji apple fruits were studied. The results showed that compared with bagging, non-bagging cultivation increased single fruit weight and decreased fruit shape index, increased fruit sugar content, reduced acid content, and increased taste. It increased the content of vitamin C (VC) and protein in the fruit, increased the types and content of aromatic components in the fruit, significantly increased the activity of sugar- and acid-related enzymes, and improved the antioxidant capacity of the fruit. Compared to bagging cultivation, non-bagging cultivation improved the weight, taste (sugar acid ratio), and aroma of Fuji fruit, which is related to increasing the content of auxin (IAA), cytokinin (ZR), and salicylic acid (SA) and reducing the content of abscisic acid (ABA) in the fruit, as well as increasing the content of medium and trace elements calcium (Ca), iron (Fe), manganese (Mg), and boron (B). One of the mechanisms involved is the significant increase in gene expression related to phenylpropanoid biosynthesis, pentose and glucuronate interconversion, starch and sucrose metabolism, zeatin biosynthesis, microtubules, motor proteins microtubule movement, xyloglucan metabolic process, cell division, and peroxidase activity. In short, non-bagging cultivation is more conducive to improving the intrinsic quality and flavor development of Fuji apples, and one of the mechanisms is that non-bagging cultivation is beneficial for increasing the expression of related genes.

Introduction: Apricot fruits are edible and serve as a source of medicinal compounds. Flavonols are important plant secondary metabolites that have antioxidant and antitumor effects and may promote cardiovascular health. Methods: The flavonoid content in three stages of the ‘Kuijin’ and the ‘Katy’ was observed, followed by the combination of metabolome and transcriptome analysis to explore the metabolic basis of flavonol synthesis.Results: The differences in the metabolite contents between stages (of the same cultivar) and between cultivars (at the same stage) revealed decreases in the flavonoid content as fruits developed (i.e., from 0.28 mg/g to 0.12 mg/g in ‘Kuijin’ and from 0.23 mg/g to 0.05 mg/g in ‘Katy’). To decipher the regulation of flavonol synthesis in apricot (Prunus armeniaca L.), the metabolomes and transcriptomes of fruit pulp at three developmental stages of ‘Kuijin’ and the ‘Katy’ were analyzed. A total of 572 metabolites were detected in ‘Kuijin’ and the ‘Katy’ pulp, including 111 flavonoids. The higher flavonol content young ‘Kuijin’ fruits at 42 days after full bloom is mainly due to 10 types of flavonols. Three pairs of significant differences in flavonol content were identified. From these three comparison groups, three structural genes were strongly correlated with the levels of 10 types of flavonols (Pearson correlation coefficients > 0.8, p value < 0.05), including PARG09190, PARG15135, and PARG17939. The weighted gene co-expression network analysis showed that the turquoise module genes were highly correlated with flavonol contents (P < 0.01). There were 4897 genes in this module. Out of 4897 genes, 28 transcription factors are associated with 3 structural genes based on weight value. Two of the transcription factors are not only associated with PARG09190 but also with PARG15135, indicating their critical importance in the flavonols biosynthesis. The two TFs are PARG27864 and PARG10875.Discussion: These findings provide new insights into the biosynthesis of flavonols and may explain the significant differences in flavonoid content between the ‘Kuijin’ and the ‘Katy’ cultivars. Moreover, it will aid in genetic improvement to enhance the nutritional and health value of apricots.

This study was conducted at the Taidong Base of the Shandong Institute of Pomology, Tai’an City, Shandong Province, China, from May to October 2020. The effects of spraying calcium fertilizer on the photosynthetic characteristics, mineral element content, sugar and acid metabolism, and quality of apples were assessed. Fuji Apple Tianhong.2/SH/Malus robusta (M. robusta) was treated with the calcium fertilizers Niucui (Ca ≥ 100 g/L, B: 1–10 g/L) and Naipu 9 (Ca: 90 g/L, Mg: 21 g/L, N: 110 g/L) at the young fruit stage (25 May), the expansion stage (5 July), and the coloring stage (25 September). Water was sprayed as the control application. The results revealed that spraying calcium fertilizer increased the chloroplast pigment content and photosynthetic capacity of the apple leaves. Compared with the control, the net photosynthetic rate of apple leaves sprayed with Niucui increased by 4.3–34.6%, and that of leaves sprayed with Naipu 9 increased by 15.0–57.4%. Spraying calcium fertilizer promoted the accumulation of Ca, Mg, and B mineral elements in leaves and fruits while inhibiting the accumulation of Cu. Spraying calcium fertilizer improved the quality of apple fruit. Compared to the control fruit, the single fruit weight, fruit hardness, soluble solid content, and Vitamin C content of fruit sprayed with Niucui and Naipu 9 increased by 6.5 and 12.1%, 3.6 and 16.1%, 6.3 and 12.0%, and 30.5 and 29.4%, respectively. Spraying calcium fertilizer increased the sugar content and decreased the acid content of the apples. Naipu 9 was more effective at increasing fruit sugar content, especially sucrose and sorbitol, while Niucui was more effective at reducing the acid content, especially malic acid. This was observed because Naipu 9 increased the sugar metabolism enzyme activity, while Niucui increased the acid decomposition-related enzyme activity. In conclusion, according to the nutrition quality and flavor of the fruit, Naipu 9 application was determined to be the best fertilizer for the Fuji apple.