Marigold can protect crops against soil-borne diseases. However, the effects of intercropping with marigold on apple rhizosphere soils are not known. In this study, we investigated the metabolite profiles and bacterial community structures in rhizosphere soils of the apple-marigold intercropping system by high-throughput sequencing and soil metabolomics. The results show that intercropping marigold could significantly enhance soil moisture, nitrogen, and enzyme activities compared with clean tillage. The soil metabolite profiles and the soil bacterial community structures in the rhizosphere soils were different between the inter-and mono-cropping systems. Among nine metabolites, carbohydrates were more increased in the intercropping system than in the monocropping system. Pathway enrichment analysis revealed that the greatest differential, in terms of metabolic pathway, was starch and sucrose metabolism. Moreover, intercropping marigold significantly increased the relative abundance of plant growth promoting bacteria in rhizosphere soils, such as Rhizobiales, Pseudomonadales, and Bacillales. These results indicate that marigold intercropping positively affected the apple orchard’s soil quality and may provide a new intercropping technique to improve soil fertility in orchards and promote plant growth.

Cold stress restricts the growth and development of plants. Lignin plays an important role in stress resistance. However, there are few studies on lignin mechanisms regulation under low-temperature stress. In this study, the contents of both acid-soluble and -insoluble lignin were reduced after a short period of cold treatment. A targeted metabolomics analysis showed that the contents of caffeate, ferulic acid, coniferaldehyde, and p-coumaraldehyde decreased after cold stress, while the contents of L-phenylalanine and sinapaldehyde increased. The C3′H (p-coumaroylshikimate 3-hydroxylase) and COMT (caffeic acid O-methyltransferase) families, which catalyze the formation of caffeate and coniferaldehyde, were analyzed. Among them, the transcriptional levels of PtrC3′H1, PtrCOMTL4, and PtrCOMT1 were positively correlated with the decreased lignin after cold stimulation. The lignin-related transcription factor PtrMYBs, such as PtrMYB021, PtrMYB074, PtrMYB125/85, and PtrMYB103/46, were clearly induced by cold stress. The reverse transcription-quantitative real-time polymerase chain reaction (RT-qPCR) further verified that the level of transcription of key genes was consistent with the transcriptomic data. The identified key genes and metabolic intermediates in lignin synthesis provide a foundation for the functional characterization of the molecular mechanism of lignin biosynthesis under cold stress, which should help to efficiently utilize lignin in forest resources.

Many studies have demonstrated that anthocyanin synthesis in apple peel is induced by light, but the color of bagged apple peel continues to change under dark conditions after light induction has not been characterized. Here, transcriptional and metabolic changes associated with changes in apple peel coloration in the dark after different light induction treatments were studied. Apple pericarp can achieve a normal color under complete darkness followed by light induction. Metabolomics analysis indicated that the expression levels of cyanidin-3-O-galactoside and cyanidin-3-O-glucoside were high, which might be associated with the red color development of apple peel. Transcriptome analysis revealed high expression levels of MdUFGTs, MdMYBs, and MdNACs, which might play a key role in light-induced anthocyanin accumulation under dark conditions. 13 key genes related to dark coloring after light induction was screened. The results of this study provide new insights into the mechanism of anthocyanin synthesis under dark conditions.

Fruit wine is favoured by consumers because of its low alcohol content and unique taste, but there are few studies on apricot wine. In order to explore the quality of apricot wine obtained by fermentation of different varieties of apricots and the typical volatile substances in apricot wine, and to find apricot varieties that can brew better quality apricot wine, the gas chromatography-mass spectrometry (GC-MS) method was used to detect Jinkaite, Katy, Jintaiyang apricots and brewed apricot wine, and the correlation and difference of key odour substances were analyzed. A total of 25 aroma components in 6 categories were detected in the 3 varieties of apricots. Among the components, esters account for the largest proportion at 14 types, followed by both ketones and alcohols at 5 types. Compared with the original juice, the types of volatile substances in fermented apricot wine increased significantly. After aroma component analysis, 42, 36 and 38 odour components were screened out in Jinkaite wine, Kate wine and Jintaiyang wine. They were mainly composed of alcohols and esters. Among the three varieties, the total content of aroma components in “Katy” wine was the highest (114.09 mg·L⁻¹), followed by Jinkaite wine (112.17 mg·L⁻¹), and the total content of aroma components in Jintaiyang wine was lower (108.72 mg·L⁻¹). The following substances were the most important aromatically active compounds identified, and they had low olfactory thresholds: linalool (25 μg·L⁻¹), β-ionone (0.007 μg·L⁻¹), ethyl caprylate (12.87 μg·L⁻¹), methyl caprate (6 μg·L⁻¹), which has a larger OAV value and strongly influences the aroma characteristics. Multi-factor analysis showed that compared with other varieties of apricot wine, the highest score of Kinkate apricot wine is 89 points, which is golden yellow, showing rich floral and fruity aromas, soft and full body, good stability and strong typicality. Jinkaite apricot, as an early-maturing and excellent new variety selected from the natural hybrid seedlings of Katy apricot, can be used as a high-quality new wine-making raw material. The aroma components and content of apricot wine made from different varieties of apricots showed significant differences, which provided an important basis for the selection of raw materials for deep processing of apricots. The research and development of apricot wine products can not only solve the problem of deep processing of apricots, but also conform to the current development trend of the wine market and have a good market prospect.