【Objective】Apple is the most widely cultivated deciduous fruit species in China, possessing considerable adaptability and economic value. Since the reform and opening-up, the apple industry has developed rapidly. However, the homogenized variety structure and its monotonous flavour profile can no longer meet consumers'growing demand for greater diversity in fruit. The cultivation of diverse, differentiated and personalized new apple varieties holds significant importance, with the development of small-fruit type apples emerging as one of the new breeding objectives. Therefore, we systemically investigated fruit quality traits of characteristic small-fruit type apple germplasm resources and conducted a comprehensive evaluation, thereby providing valuable reference and a theoretical basis for the innovative utilization of superior germplasm resources.【Methods】This study utilized 5 characteristic smallfruit type apple cultivars, namely Huangtaiping, Jinhong, Hesetiaowen, Whitney, and Xinhong, as exper-imental materials to measure and analyze their fruit morphological characteristics and quality trait indicators. Apple fruit phenotypic traits were surveyed and recorded in accordance with the‘Apple Germplasm Resource Description Specifications and Data Standards'. The determination of soluble sugars and organic acids in apples was carried out using high-performance liquid chromatography. The determination of polyphenolic components and their contents was performed using ultra-high-performance liquid chromatography-mass spectrometry. Five fruit sections including cross sectional, longitudinal sectional, cheeks, stem cavity and calyx-end were selected. After 24-hour fixation at room temperature to ensure complete penetration of the fixative, paraffin sections were prepared. Cytological observations were conducted on five-part fruit sections of apple varieties using paraffin sections. Finally, a comprehensive evaluation of fruit quality traits across different varieties was performed through correlation analysis and fuzzy membership function methods.【Results】Five characteristic small-fruit type apple varieties exhibit significant differences in fruit morphological characteristics and quality indicators. The fruit color of Huangtaiping and Hesetiaowen is pink, while Jinhong, Whitney and Xinhong are turkey red, brown red, and strong red, respectively. The fruit surfaces of Jinhong and Xinhong show arris, while other apple varieties have no arris. The fruit dots of Huangtaiping and Hesetiaowen varieties exhibit small dots, while Whitney and Xinhong display large dots. The fruit cores of Jinhong and Xinhong are small, while the cores of Huangtaiping, Hesetiaowen, and Whitney are medium. In terms of fruit morphological characteristics, the stem depression of Jinhong fruit is shallow and narrow, while Huangtaiping, Whitney and Xinhong are all deep and medium. Additionally, the range of fruit weight across different apple varieties is 42.03-82.55 g. Among these, Huangtaiping apples exhibit the lowest fruit weight, and both the transverse and longitudinal diameters of Huangtaiping apples are significantly smaller than those of other apple varieties. However, the titratable acidity, malic acid, citric acid, flavanols, phenolic acids, and total phenolic contents of Huangtaiping fruit are significantly higher than those of other apple varieties. Xinhong fruit exhibit the highest levels of fructose and sorbitol. Hesetiaowen fruit contain the highest levels of soluble solids, soluble sugars, sugar-acid ratio, sucrose, and dihydrochalcone. The Whitney apple variety exhibits the highest levels of glucose and flavonoids among all apple varieties, with a significantly higher content of phlorizine compared to other apple cultivars. Significant differences in cell morphology, size, and number also exist among different apple varieties. The fruit cells of Huangtaiping and Jinhong are arranged relatively densely, and exhibit consistent morphology across different parts. The fruit cells of Hesetiaowen are arranged in a relatively loose pattern. The cross section and longitudinal section of Whitney fruit show relatively dispersed cells with distinct intercellular spaces. The cell boundaries of Xinhong fruit exhibit an irregular shape. In terms of cell size and number in different fruit parts, the cross-sectional cell size and longitudinal cell number of Huangtaiping are significantly lower than those of other apple varieties, while there is no significant difference in cross-sectional cell size and longitudinal cell size, indicating that the volume difference between Huangtaiping fruit and other apple varieties mainly depends on the cross-sectional cell size and longitudinal cell number. There are significant differences in the number and size of cells in the stem cavity and calyx-end of various apple varieties, except for the number of cells in the cheeks. Significant differences exist in fruit size among varieties, with both the number of fruit cells and the volume of the fruit jointly influencing the final size of the fruit.【Conclusion】The comprehensive evaluation results based on the fuzzy membership function method indicate that the Hesetiaowen fruit exhibits the highest average membership function value, followed by the Huangtaiping, Whitney, Xinhong, and Jinhong fruits in a descending order. The evaluation results are consistent with the growth status and phenotypic characteristics of each apple germplasm resource. Based on the quality characteristics of each germplasm, specific traits such as high-quality fresh type, distinctive appearance type, and functional/processing type can be selected for germplasm breeding. The above research provides important references for the screening and comprehensive utilization of characteristic small-fruit type apple germplasm resources.

Peach trees exhibit vigorous growth that is often difficult to manage, frequently leading to canopy closure and the outward migration of fruiting positions, which ultimately results in diminished yield and fruit quality. Therefore, it is of great importance to study the key genes regulating peach tree vigor. Preliminary experiments identified PpNAC036 as a candidate gene potentially associated with vigor. In this study, we characterized the expression profile of PpNAC036 across various peach tissues. Our results demonstrate that PpNAC036 is most highly expressed in stems and responds rapidly to hormonal treatments, with expression levels increasing 3.6-fold and 3.9-fold under IAA and NPA treatments, respectively (5 min to 1 h). Subsequently, the PpNAC036 gene was cloned and overexpressed in Arabidopsis thaliana. Compared to the wild type, transgenic Arabidopsis exhibited a 28–50% reduction in primary root length and a 31.6–36.8% decrease in hypocotyl length. Conversely, at maturity, the transgenic Arabidopsis displayed enhanced vegetative vigor, with fresh and dry weights increasing by 37–48% and 29–46%, respectively. This growth was accompanied by a nearly two-fold increase in stem diameter and a 1.5- to 2-fold elevation in lignin content; simultaneously, genes related to lignin biosynthesis were upregulated. Hormonal profiling revealed that PpNAC036 overexpression led to a 7-fold increase in IAA, a 22–60% rise in GAs, and a 97–106% increase in CTKs, whereas ABA levels decreased by 5–6%. Furthermore, the transgenic Arabidopsis exhibited delayed germination and flowering, along with alterations in the number of floral organs. Transcriptomic analysis identified 2797 common DEGs, which were enriched in pathways related to cell wall organization and hormone signaling. Collectively, these findings elucidate the function of PpNAC036 as a pivotal regulator of plant vigor and secondary cell wall development, positioning it as a promising candidate gene for molecular breeding and architectural optimization in peach.

【Objective】Ornamental crabapples (Malus spp.) are primarily distributed across the Eurasian continent and North America. Due to their vivid flower colors, concentrated blooming periods, and abundant flowering, ornamental crabapples have been widely applied in scenic areas, gardens, urban greening, and container gardening. Many ornamental crabapples in China were introduced from North America and Europe, and hybrid breeding was primarily focused on improving fruit traits of dessert apples. As a result, the breeding of crabapples started relatively late and mainly targeted descriptive traits such as flowering time, phenology, and flower color. Heridity of quantitative floral organ traits has been far from clear. A deeper analysis of the genetic variation and inheritance patterns of floral traits in the F1progeny derived from the cross between Hongxun No.1 and Double-flowering crabapple can provide a foundation for breeding ornamental apple cultivars.【Methods】A total of 204 F1hybrid individu als derived from the cross between Hongxun No.1(Malus spp.)and Double-flowering crabapple(Malus spp.)were investigated for five quantitative floral traits(flower diameter, petal count, stamen count, pistil count, and peduncle length)and two descriptive traits(flower color and petal type: single or double). We organized experimental data using IBM SPSS Statistics 27, and generated figures with Origin 2018. The parental values(P1and P2), variances(Vp1and Vp2), mid-parent value(MP), hybrid population mean(F), standard deviation(S), variance(VH), coefficient of variation(CV, %), transmissibility(Ta, %), broad-sense heritability(H b2, %), heterosis rate(H, %), and high-parent rate(HH, %)were calculated to analyze the inheritance patterns. The mixed major gene plus polygene inheritance model was used to analyze the genetic models of the five quantitative traits in the F1population using the SEA software package. The optimal genetic model was selected based on the minimum Akaike's Information Criterion (AIC), and the corresponding major gene effects were estimated using the least squares method.【Results】Phenotypic identification of five quantitative and two descriptive traits in 204 F1progeny revealed rich genetic diversity. The flower color in the F1population showed clear segregation into four phenotypes: white (4.46%), pink (50.50%), red (33.66%), and purplish-red (11.38%). The petal type segregated into single-petaled (82.57%) and double-petaled (17.43%) individuals. Variants such as white single-petaled and red double-petaled were observed, demonstrating the high potential for selecting elite ornamental germplasm. All five quantitative traits showed varying degrees of phenotypic variation. The flower diameter had the lowest coefficient of variation (14.13%) and exhibited high genetic transmissibility and broad-sense heritability. Its optimal inheritance model was 2MG-EA, with a positive additive major gene effect and a major gene heritability as high as 98.79%. The petal count exhibited relatively high heritability and transmissibility, but with a negative heterosis(-27.57%). Most F1individuals had fewer petals than the mid-parent value, and the double-petal phenotype was unstable. The adaptability test suggested the optimal inheritance model for petal count was 2MG-AD. The stamen and pistil count both showed substantial variation in the F1generation, indicating the potential for genetic improvement. The stamen count exhibited strong positive heterosis, high-parent value, and high heritability. Its optimal model was 2MG-AD, with a positive additive effect(3.72)and a negative dominance effect(-2.45), indicating a degree of suppression from dominant genes. The major gene heritability was 92%, showing stable inheritance primarily under additive genetic control. The pistil count had a high coefficient of variation, heritability, and broad-sense heritability. The best model was 2MG-A, indicating the inheritance was dominated by additive effects, suggesting good selection potential. The peduncle length conformed to a normal distribution but had the highest coefficient of variation(417.24%), indicating strong phenotypic plasticity in response to environmental factors. It had relatively low transmissibility (20.5%) and broad-sense heritability (52.75%). The F1mean value was slightly lower than the mid-parent value, showing negative heterosis. The optimal genetic model was 2MG-AD, but the additive and dominance effects of the major genes were weak.【Conclusion】The floral traits of the F1progeny from the cross between Hongxun No.1 and Double-flowering crabapple displayed varying degrees of genetic variation and segregation. The flower diameter and stamen count showed high heritability and stable major gene control, making them priority traits for selection and fixation. The petal count was governed by a complex genetic mechanism involving both major genes and dominant suppression effects. Thus, breeding for double flowers should involve double-flowered parents on both sides. The pistil count exhibited significant variation and was regulated by additive effects of major genes, showing the potential for improvement. The peduncle length demonstrated low heritability and selectability, indicating the need for comprehensive evaluation integrating phenotype and environmental response.This study clarified the inheritance patterns of floral quantitative traits in the F1population from Hongxun No.1 × Double-flowering crabapple and would provide theoretical support and reference models for future floral organ trait improvement and molecular-assisted breeding.

With the increasing cost of bagging cultivation, non-bagging cultivation has become an important direction for green and sustainable development. In this study, the most representative ‘Fuji’ and ‘Ralls’ apple varieties were used as test materials to investigate bagging's effect on apple polyphenols and post-removal metabolic mechanisms using UPLC-MS/MS and metabolomics. For the first time, the feasibility of non-bagging apple cultivation was explored from the perspective of nutritional quality regulation and polyphenol antioxidant properties. Results showed that the total phenol contents of ‘Fuji’ and ‘Ralls’ varieties significantly decreased under bagging treatment at maturity. After bagging, ‘Fuji’ had higher flavanols, flavonols and anthocyanins but lower dihydrochalcones and phenolic acids; ‘Ralls’ showed higher dihydrochalcones and anthocyanins but lower phenolic acids. Comprehensive evaluation indicates that bagging treatment significantly reduces the antioxidant activity of apple fruit. Metabolomics identified 31 and 19 differential metabolites in ‘Fuji’ and ‘Ralls’, with shared enriched pathways including flavonoid biosynthesis. In summary, these findings provide new insights into non-bagging apple cultivation and offer a theoretical basis for regulating the nutritional quality of apple fruit.

Climate change poses an increasing threat to global biodiversity and food security. As a wild relative of cultivated apples, Malus baccata exhibits broad environmental adaptability and robust stress tolerance. However, its effective utilization in breeding is constrained by the absence of a complete reference genome and insufficient population-level genomic characterization. In this study, we assembled a haplotype-resolved, telomere-to-telomere genome for M. baccata, providing unprecedented resolution for a wild apple reference genome. Population genomic analyses revealed four distinct genetic clusters. Among these, the Hebei Group 2 harbors the highest genetic diversity and heterozygosity, alongside the lowest runs of homozygosity, suggesting a complex history of genetic admixture in this population. By integrating population genomics with genotype-environment association analyses, we identified a series of climate-associated single-nucleotide polymorphisms and structural variants. A substantial proportion of these adaptive variants is localized within the coding and regulatory regions of candidate genes, providing a genomic basis for their roles in environmental adaptation. Notably, DREB1A/D and NAC6 are associated with temperature seasonality and annual precipitation, respectively. Furthermore, future climate projections indicate that the Northeastern (NE) clusters face the highest risk of maladaptation, especially under high-emission scenarios. Collectively, these findings provide critical insights into the genetic basis of climatic adaptation in wild apples, establishing a solid foundation for the conservation of crop wild relatives and the breeding of climate-resilient cultivars.

With the rise in comprehensive production costs, non-bagging cultivation has replaced bagging as the core direction for the sustainable development of the apple (Malus × domestica) industry. Thus, a systematic analysis of bagging cultivation is crucial for modern agricultural innovation. However, the metabolic changes in apple fruit quality induced by bagging and their underlying gene regulatory networks remain poorly explored. This study utilized ‘Fuji’ and ‘Ralls’ apples which are distinct in flavor and integrated transcriptomics, metabolomics, and physiological and biochemical analysis to investigate the effects of bagging on fruit quality and the regulatory mechanisms of flavonoid and sugar metabolism. The results showed that bagging significantly improved the appearance quality of apple fruits, as well as soluble solids, soluble sugars, respiration rate, and ethylene release rate. However, it reduced firmness, vitamin C, titratable acid and total phenols. Further analysis revealed variety-specific impacts. The increase in content of ‘Fuji’ soluble sugar relied on the synergistic rises in fructose, sucrose, glucose and sorbitol, while that of ‘Ralls’ mainly depended on fructose and sucrose accumulation. The reduced titratable acid and total phenols in both varieties were linked to lower levels of malic, quinic, citric, shikimic acids, and phenolic acids under bagging. The integrated transcriptomic and metabolomics analysis indicated that differentially accumulated metabolites (DAMs) and differentially expressed genes (DEGs) of the flavonoid pathway in ‘Fuji’ were significantly upregulated, with higher expression levels than those in ‘Ralls’. In addition, through a comprehensive analysis of DAMs and DEGs of sugar metabolism, combined with co-expression networks, the regulatory mechanism of DEGs-DAMs mediated by differentially expressed transcription factors (DETFs) was revealed. These findings provide new insights into apple quality regulation and lay a theoretical foundation for high-quality industry development.

Apple germplasm resources exhibit substantial genetic and phenotypic diversity, offering great potential for fruit quality improvement. In this study, 1,217 apple accessions representing wild germplasms, landraces, and cultivars were systematically evaluated over three consecutive years (2020-2022) for eight key fruit traits, including fruit weight, firmness, soluble solids, titratable acidity, vitamin C, soluble sugar, sugar-acid ratio, and solid-acid ratio. High coefficients of variation and Shannon-Wiener indices were observed for several traits, particularly fruit weight, soluble sugar, and titratable acidity, reflecting rich genetic variation. Correlation analysis revealed strong interdependence among flavor-related traits, while vitamin C appeared genetically independent. PCA and LDA effectively differentiated germplasm types and highlighted key trait contributions. Wild germplasms showed the highest diversity, while cultivars exhibited more uniform traits due to intensive breeding. ANOVA confirmed significant genetic effects on key traits, with certain traits (e.g., titratable acidity, fruit weight) showing high interannual stability, while others (e.g., soluble sugar, firmness) were environmentally influenced. Hierarchical clustering revealed genotype-environment interactions and geographic differentiation, such as distinct trait patterns among Malus germplasms from different regions. This comprehensive phenotypic assessment provides valuable insights for apple breeding, germplasm selection, and genetic resource conservation, emphasizing the importance of wild germplasms and landraces in expanding the genetic base of cultivars.

Flavonols contribute significantly to both plant defense and human health. In apple (Malus domestica), flavonols accumulate at high levels in leaves and fruit skin but are present at low levels in the fruit flesh, the primary tissue consumed by humans. Enhancing flavonol content in the flesh requires a deeper understanding of the underlying molecular mechanisms. In this study, we investigated the expression patterns and functional roles of four apple flavonol synthase genes (MdFLS1, 2, 3, 4). MdFLS1, 2, 3 exhibited higher expression in fruit skin than in flesh, while MdFLS4 was not expressed in either tissue. Transient overexpression of each gene promoted flavonol accumulation in apple fruit flesh, indicating that all four genes encode functional flavonol synthases. This enzyme activity was further confirmed through stable overexpression in transgenic Arabidopsis and tomato plants. Notably, light exposure of apple fruit flesh enhanced the expression of MdFLS1 and MdFLS2 and increased flavonol accumulation. These findings advance our understanding of flavonol biosynthesis in apple.

Polyphenols are recognized as a class of compounds possessing a wide range of biological activities that provide numerous health benefits to humans. Apples are abundant in polyphenolic substances. As an integral part of the fruit's internal structure, the polyphenols found in fruit cores cannot be overlooked. This study examines the dynamic effects of six different dwarfing interstocks on the total phenolic content and polyphenol compounds in the core of 'Huahong' apples, aiming to gain a more comprehensive understanding of the phenolic components and their contents in fruit cores, providing novel insights into the comprehensive utilization of fruits. The 'CG24', 'SH38', 'SH3', 'MD001', 'Mac9', and 'CX5' were grafted onto Malus baccata (L.) Borkh. and 'Huahong' was grafted on six interstocks mentioned above, the self-root grafting Malus was used as a control (CK). The components and contents of polyphenols in cores were analyzed at seven periods during 'Huahong' apple growth by using High Efficiency Liquid Chromatography and Mass Spectrometry, and the content of total phenols was determined by the Folin-Ciocalteu method. The polyphenol concentration in the fruit core exceeds that of the peel but is lower than that found in the pulp, and this content, along with its constituent components, exhibits a gradual decline as the fruit undergoes development. At maturity, the polyphenol composition is consistent across dwarfing interstock combinations, primarily comprising Quercetindevelopment, but these levels drop below the control group in later stages. In contrast, 'MD001' effectively mitigates the reduction of polyphenols from mid- to late development, leading to substantial phenolic accumulation at maturity. Among the interstocks examined, 'MD001' demonstrates its superiority in enhancing phenolic compounds. Interstocks can increase the levels of polyphenolic compounds in the core of apples. The polyphenol content in the fruit core is intermediate between that of peel and flesh, exhibiting significant application value in processing and the extraction of polyphenol components.

CircRNAs, are a class of covalently closed non-coding RNAs; they have been identified in many plants and play an important role in the response to abiotic stresses. However, little is known about the response of the circRNAs of salt-tolerant apple rootstock resources in response to salt stress. In this study, the leaves and roots of the salt-tolerant Malus resource, ZM-4, and the salt-sensitive rootstock M9T337, were used as test materials and were exposed to 75 mmol/L NaCl stress for 0 h and 24 h. A total of 2502 circRNAs were identified, and 218 and 242 circRNAs were uniquely expressed in M9T337 and ZM-4, respectively. Furthermore, it was shown that the up-regulated parental genes of the differentially expressed circRNAs were enriched in the metabolic pathways and the biosynthesis of secondary metabolites pathway in the leaves and roots of ZM-4 under salt stress, respectively. There were potential regulatory networks of ceRNA among 150 circRNAs, 139 miRNAs, and 397 mRNAs. Novel_circ_000845 and novel_circ_000266 could target and inhibit the expression of mdm-miR156 and up-regulate the expression of the salt-responsive gene SPL6. Six circRNAs, including novel_circ_000898 and novel_circ_001519, could target and inhibit the expression of mdm-miR10995 and up-regulate the expression of the salt-responsive gene COBL7. In conclusion, this study laid the foundation for the post-transcriptional molecular regulation mechanism of salt tolerance in apple rootstock resources.

[Objective] With the improvement of residents' quality of life, consumers' demand for fruit has gradually changed from basic consumption to quality, individuation, and diversification. The interests of consumers are no longer limited to the basic nutritional value of fruit, but more concerned about its sensory properties, such as taste, aroma, appearance, and so on. In the fruit market with prominent consumption-driven and diversified demands, accurately grasping the attention and preference differences of different consumer groups on sensory attributes and traits of fruits is of vital significance for the production side to adjust product results, optimize product configuration, and enhance market competitiveness. This study aimed to investigate the importance consumers place on various sensory attributes and their specific preferences, providing empirical insights for optimizing fruit variety selection, improving product characteristics, and guiding targeted marketing strategies. Additionally, by focusing on consumer perceptions, this research seeked to generate a comprehensive data set that would support more informed decision-making for stakeholders across the fruit industry, ensuring that product development would be closely aligned with evolving market demands. Fruits, as an essential source of nutrition that meets people's aspirations for a better life, play a crucial role in implementing the broad food perspective and holistic health strategy. Therefore, the development of the fruit industry must adhere to a market-oriented approach, and technological research in the industry should fully consider market demands and consumer preferences. [Methods] This study selected apples, pears, grapes, peaches, strawberries, and durians as research subjects. The survey utilized a five-point Likert scale to collect first-hand data on consumers’ evaluations of the importance of sensory attributes and their specific trait preferences. In the first stage, respondents rated the importance of key sensory attributes, including sweetsour flavor, texture, flesh juiciness, color, and aroma. In the second stage, participants with high attention to specific attributes further detailed their preferences for those traits. Statistical analyses, including descriptive statistics and clustering methods, were applied to quantify consumer evaluations and identify patterns in sensory preferences. Moreover, the survey sample encompassed a broad demographic spectrum across various age groups, geographic regions, and socio-economic statuses to ensure representativeness. The reliability and validity of the questionnaire were confirmed through pilot studies and iterative refinements, thereby guaranteeing the robustness and reproducibility of the collected data. [Results] The findings revealed that sweet-sour flavor, flesh texture, and flesh juiciness were the most critical sensory attributes influencing consumer choices, while external attributes such as color and aroma exhibited greater variability in importance. Consumers generally favored fruits with a sweeter taste, delicate texture, and abundant juice. Specifically, sweet-sour flavor and flesh texture were the most important sensory attributes of fruits such as apples, pears, and peaches. Berry fruits are typically small, juicy, and contain multiple seeds. Consumers particularly valued the sweet and sour taste, pulp texture, flesh juiciness, color, and aroma types of strawberries and grapes. However, significant heterogeneity was observed in preferences for external attributes: For instance, preferences for fruit color varied depending on the fruit type, and the importance of aroma was more pronounced in specific fruits such as durians and strawberries. Detailed trait analysis further indicated that consumers generally favored fruits exhibiting pronounced sweetness, a delicate yet well-balanced texture, and abundant juice. In fruits like apples, pears, and peaches, a harmonious balance of sweet and sour flavors combined with optimal textural qualities played a pivotal role in shaping consumer preferences. High flesh juiciness consistently correlated with perceptions of freshness and superior quality, reinforcing its significance as a key selection criterion. In contrast, external sensory attributes such as color and aroma were subjected to considerable individual variability, reflecting differences in aesthetic and olfactory preferences across fruit types. [Conclusions] This study obtained the degree of consumers' attention to different sensory attributes of apples, pears, grapes, peaches, strawberries, and durians, and at the same time obtained the sensory traits that consumers paid more attention to, which would provide the data basis for breeders, producers, and sellers to breed, produce, and sell the above fruits. The conclusions could provide data support for the fruit industry to optimize variety structures, improve product characteristics, and implement targeted marketing strategies. Moreover, the results would support the breeding and development of new fruit varieties that align with consumer expectations, thereby improving market acceptance and promoting the sustainable development of the fruit industry. These insights would provide a robust foundation for stakeholders across the fruit industry. For producers and marketers, the findings would offer clear guidance for refining product characteristics and optimizing variety structures in order to better meet consumer expectations. For breeders, the delineated sensory trait targets could inform the development of new fruit varieties designed to enhance market acceptance. Overall, the study underscored the importance of integrating consumer feedback into the product development cycle to achieve improved market responsiveness and competitive advantage. Future research should explore regional and cultural variations in sensory attribute preferences, as well as examine the impact of emerging consumer trends on fruit selection.

To study the difference of polyphenol components and content in different apple strains, the components and content of polyphenol in peel and pulp of 55 apple cultivars, from four strains, were determined by ultra-performance liquid chromatography (UPLC), and liquid chromatography-mass spectrometry (LC-MS/MS). In the present study, a total of 21 polyphenolic components were detected from 55 cultivars, including 16 polyphenolic components in the peel, and 12 polyphenolic components in the pulp. Flavonols and procyanidins were the main components of peel polyphenol, while hydroxycinnamic acid and procyanidins were the main components of pulp polyphenol. The results of principal component analysis and cluster analysis showed that the Delicious-strains could be distinguished from other apple strains due to the high content of procyanidin C1 (PROC1), procyanidin B2 (PROB2), and epicatechin (EPI). Different breeding methods have different effects on polyphenolic compounds. The content of total phenol, flavonols, and hydroxycinnamic acids in the peel of Fuji-strains and Golden Delicious-strains descendants were increased by hybridized breeding, while the content of anthocyanins in the peel of Delicious-strains and Ralls-strains descendants was significantly increased by bud sport breeding. Meanwhile, eight cultivars, including 'Huafu', 'Shinsekai', 'Lysgolden', etc., were selected as breeding parents with high content of flavonols, procyanidins, and hydroxycinnamic acid, which could be used for germplasm innovation of high-polyphenol apple. This study explored the characteristics of polyphenolic components and content in different apple strains, and provided basic materials for functional breeding with high polyphenol content.

Fire blight, a devastating bacterial disease, primarily infects fruit trees of Rosaceous, leading to their decline and eventual death. This study aims to evaluate and screen the fire blight resistance in 19 Malus plants; additionally, the effectiveness and applicability of three inoculation methods were compared. The toothpick acupuncture method in young leaves, shoots in vitro, and young plants in vivo were used in this study. The results were significantly different from the three inoculation methods for some Malus plants. Under the inoculation conditions of young leaves in vitro, only Shidong Caiping No. 1 was tolerant to fire blight, exhibiting the highest resistance level, while others showed susceptibility at graded severity levels. Under the inoculation condition of young shoots in vitro, nine highly resistant resources were screened, such as OT3, SH3, SH6, etc. Under the inoculation condition of young plants in vivo, six highly resistant resources were obtained, included E Shanjingzi No. 2, Xiaogucheng Lenggunzi No. 1, Yingyehaitang, and so on. For practical applications, the evaluation of young shoots in vitro, and young plants in vivo should be integrated to achieve a comprehensive and accurate result. A total of three resistance resources were obtained, namely E Shanjingzi No. 2, Xiaogucheng Lenggunzi No. 1, and Yingyehaitang, which can be used for the breeding of parents of fire blight resistant varieties.

Malus zumi is an excellent saline-alkali tolerant apple rootstock resource and a valuable economic tree for greening due to its ornamental value. It is of great potential significance in the production of apples in saline-alkali areas. miRNA is a class of endogenous non-coding small RNA, which plays an important role in plant resistance to salt stress. However, the miRNA-mediated regulatory mechanisms underlying salt tolerance in Malus zumi remain unclear. In this study, the salt-tolerant apple resource Malus zumi ZM-4 and the salt-sensitive rootstock M9T337 were used as experimental materials. High-throughput sequencing was conducted on the leaves and roots of these plants treated with 75 mmol/L NaCl for 0h and 24h. The results showed that a total of 3,280 miRNAs were identified, with 274 and 323 miRNAs were specifically expressed in ZM-4 and M9T337, respectively. Under salt stress, 299 and 654 differentially expressed miRNAs were detected in leaves and roots, targeting 994 and 1,813 mRNAs, respectively. Furthermore, five (mdm-miR395j-TPS13; miR1507-y-RGA1; miR3699-z-SPL13A; novel-m0411-5p-MKK4; novel-m0641-3p/novel-m0642-3p-ALMT4) and three (miR168-y-PKS5; novel-m0474-3p-CNGC10; mdm-miR156a ∼ mdm-miR156o-SPL2/SPL6/SPL12) potential miRNA-mRNA regulatory modules were identified to response to salt stress in the leaves and roots, respectively. The qRT-PCR validation results were consistent with the RNA-seq results. A dual-luciferase assay further confirmed that mdm-miR156b negatively regulated the expression of MdSPL6. This study revealed the key regulatory network of miRNAs in the leaves and roots of ZM-4 to respond to salt stress, and the results laid the foundation for the post-transcriptional molecular regulatory mechanism of salt tolerance in ZM-4.

Calcium-dependent protein kinases (CDPKs) are unique serine/threonine kinases that play significant roles in response to environmental stresses in plants. In this study, we comprehensively characterized the CDPK gene family in the apple cultivar ‘Hanfu’ at the genome-wide level, and 38 MdCDPKs were identified. They were unevenly distributed across 14 chromosomes. Based on phylogenetic analysis, the MdCDPKs were classified into four subfamilies. Conserved domain analysis indicated that MdCDPKs contain the catalytic kinase domain and the Ca2+ binding domain. During Colletotrichum gloeosporioides infection, the expression level of MdCDPK24 was significantly upregulated. Subsequently, MdCDPK24 was fused to GFP to generate the MdCDPK24-GFP construct, and confocal microscopy imaging confirmed its cytoplasmic localization in Nicotiana benthamiana leaves. Using agrobacterium-mediated transformation, we generated the overexpression of MdCDPK24 transgenic calli. MdCDPK24-overexpressing calli demonstrated significantly reduced disease severity against C. gloeosporioides infection, indicating its positive role in apple bitter rot resistance. The analysis of the CDPK gene family in the apple cultivar ‘Hanfu’ provides a new insight into the identification of CDPK genes involved in biotic stress. MdCDPK24 represents a promising candidate for genetic manipulation to enhance apple bitter rot resistance.

As an important branch of agricultural science, fruit tree physiology and molecular biology have in recent years been driven by the intensification of global climate change and the upgrading of consumer demands towards high-quality and diversified products [...]

MicroRNAs are non-coding RNAs that play a crucial regulatory role in plant growth, development, and environmental stress response. 'Binzi' is an ancient apple cultivar renowned for its unique aroma, however, the mechanisms of miRNAs underlying aroma formation remain largely unknown. In this study, we performed small RNA sequencing to investigate the role of miRNAs during post-harvest storage of 'Binzi' apple. Peel samples from 'Binzi' fruit (namely BZP01 and BZP02) at two storage stages (20 +/- 1 degrees C) were sequenced. A total of 29 DEMs (15 miRNAs uniquely detected at specific storage periods and 14 miRNAs differentially expressed in different storage periods) were predicted to regulate aroma compound biosynthesis in 'Binzi' apple peels. A total of 604 genes were predicted to be targeted by 29 miRNAs. GO enrichment analysis was performed on the target genes, with 'cellular process', 'metabolic process', 'single-organism process', and 'catalytic activity' being the over-enriched biological processes. KEGG analysis showed that three pathways related to aroma synthesis ('fatty acid metabolism', 'biosynthesis of unsaturated fatty acid biosynthesis', and 'carotenoid biosynthesis') were enriched in the top 20 of the KEGG enrichment. We verified the regulatory relationship between miRNAs and their target genes by qRT-PCR. mdm-miR408c was negatively correlated with three target genes (two MdfabDs and one MdfabG) and was involved in the regulation of fatty acids biosynthesis. Furthermore, novel_Chr17_18081 was negatively correlated with MdMFP2 and was involved in the regulation of the fatty acid degradation. Our research indicated that mdm-miR408c, novel_Chr17_18081, and their target genes (MdfabDs, MdfabG, and MdMFP2) were collectively involved in 'Binzi' aroma production.

We used 256 apple germplasm resources for a thorough examination of the genetic diversity associated with 26 phenotypic traits (i.e., genetic diversity analysis, cluster analysis, correlation analysis, principal component analysis, and membership function). The average coefficient of variation for 12 morphological traits was 66.39% (21.10–201.5%). The coefficient of variation was highest and lowest for the fruit arris and the width of the eye basin, respectively. Additionally, the diversity index ranged from 0.54 to 1.33. Moreover, the coefficient of variation for 14 numerical traits varied from 5.37% to 50%. The titratable acid content had the highest coefficient of variation, with a diversity index ranging from 2.01 to 2.08 (average of 2.045). A cluster analysis categorized 256 germplasms into four groups, among which Group I included germplasms with large fruits and the best comprehensive performance. Of the top 10 principal components revealed by the principal component analysis, principal component 1 was mainly related to fruit size and flavor. The top 10 germplasms were selected on the basis of comprehensive scores using the membership function method. Furthermore, a stepwise regression analysis identified 15 key traits for identifying apple germplasms, including the vegetative growth day, fruit weight, and the firmness of the fruit without skin. These results can serve as the foundation for future analyses of the phenotypic diversity of apple germplasms, while also providing a theoretical basis for screening, characterizing, and further improving excellent apple germplasms.

China is the largest center of genetic diversity of apple (Malus Mill.), with rich germplasm resources. In the process of evolution and domestication, a large number of apple landraces appeared, and they played a very important role before the introduction of modern cultivated apple varieties to China. However, the habitat of Malus landraces is under serious threat. In this study, 19 pairs of polymorphic simple sequence repeat primers were used to analyze the genetic structure and genetic relationships of Malus landraces and the potential distribution was predicted according to eight environmental variables using MaxEnt modeling. The results showed that the genetic variation of Malus landraces was high (Ho = 0.728 and He = 0.884), and the genetic differentiation was mainly distributed within respective populations and with almost no differentiation among populations. The five population groups were ranked, from highest genetic diversity level to lowest, as follows: Malus domestica subsp. chinensis > Malus prunifolia > Malus robusta > Malus asiatica > Malus micromalus. The 216 germplasms were divided into five groups based on Nei's genetic distance, whereas the Bayesian structure analysis categorized them into two groups. Population structure and principal coordinate analyses showed that Malus domestica subsp. chinensis, Malus asiatica and Malus prunifolia may be derived from similar genetic sources. In the modeling analysis, the cumulative contribution of temperature to the distribution of Malus landraces in suitable growth areas reached 66.1 %, and BIO4 (temperature seasonality) was identified as the major factor influencing the distribution of Malus landraces. Under four future emission scenarios, the potential distribution range of Malus landraces basically unchanged, but the total potential distribution area is projected to grow greatly over time and will tend to shift to higher latitudes.

Glomerella leaf spot (GLS), caused by the fungus Colletotrichum fructicola, is considered one of the most destructive diseases affecting apples. The VQ-WRKY complex plays a crucial role in the response of plants to biotic stresses. However, our understanding of the defensive role of the VQ-WRKY complex on woody plants, particularly apples, under biotic stress, remains limited. In this study, we elucidated the molecular mechanisms underlying the defensive role of the apple MdVQ37-MdWRKY100 module in response to GLS infection. The overexpression of MdWRKY100 enhanced resistance to C. fructicola, whereas MdWRKY100 RNA interference in apple plants reduced resistance to C. fructicola by affecting salicylic acid (SA) content and the expression level of the CC-NBS-LRR resistance gene MdRPM1. DAP-seq, Y1H, EMSA, and RT-qPCR assays indicated that MdWRKY100 inhibited the expression of MdWRKY17, a positive regulatory factor gene of SA degradation, upregulated the expression of MdPAL1, a key enzyme gene of SA biosynthesis, and promoted MdRPM1 expression by directly binding to their promotors. Transient overexpression and silencing experiments showed that MdPAL1 and MdRPM1 positively regulated GLS resistance in apples. Furthermore, the overexpression of MdVQ37 increased the susceptibility to C. fructicola by reducing the SA content and expression level of MdRPM1. Additionally, MdVQ37 interacted with MdWRKY100, which repressed the transcriptional activity of MdWRKY100. In summary, these results revealed the molecular mechanism through which the apple MdVQ37-MdWRKY100 module responds to GLS infection by regulating SA content and MdRPM1 expression, providing novel insights into the involvement of the VQ-WRKY complex in plant pathogen defence responses.