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There is limited information on the distribution of blueberry viruses in the U.S. or around the world other than where the viruses were first discovered and characterized. A survey for blueberry viruses was carried out in the U.S. in 2015–2017. Most blueberry viruses have been characterized to the point that sensitive diagnostic assays have been developed. These assays are based on ELISA or variations of PCR, which were employed here to determine the presence of blueberry viruses in major blueberry production and nursery areas of the U.S. The viruses included in this study were: blueberry fruit drop (BFDaV), blueberry latent (BlLV), blueberry leaf mottle (BLMoV), blueberry mosaic (BlMaV), blueberry red ringspot (BRRV), blueberry scorch (BlScV), blueberry shock (BlShV), blueberry shoestring (BlSSV), blueberry virus A (BVA), peach rosette mosaic (PRMV), tobacco ringspot (TRSV), and tomato ringspot (ToRSV). In the Pacific Northwest BlShV was the most widespread virus, with BlScV and ToRSV detected in a limited number of fields in Oregon and Washington, but BlScV was widespread in British Columbia. In the upper midwest, the nematode-borne (ToRSV, TRSV), aphid-transmitted (BlSSV and BVA) and pollen-borne (BLMoV) viruses were most widespread. In the northeast, TRSV, ToRSV, and BlScV, were detected most frequently. In the southeast, BRRV and BNRBV were the most widespread viruses. BlLV, a cryptic virus with no known symptoms or effect on plant growth or yield was present in all regions. There are other viruses present at low levels in each of the areas, but with the lower incidence they pose minimal threat to nursery systems or fruit production. These results indicate that there are hotspots for individual virus groups that normally coincide with the presence of the vectors. The information presented highlights the high risk viruses for nursery and fruit production each pose a different challenge for control.

Background Blueberry ( Vaccinium spp. ) celebrated for its rich nutritional content and significant health benefits, was referred to as the ‘Queen of Fruits’ and the ‘King of Berries’. The development of blueberry fruits is closely related to plant hormones. Glycosylation mediated by UDP-glycosyltransferases (UGTs) is a key step in plant hormones homeostasis. However, the UGT members has not been reported in blueberry to date. Results A total of 361 VcUGT genes were identified and classified into 11 groups. Whole-genome and segmental duplications drove VcUGT expansion, with structural analysis revealing conservation within subgroups but divergence among them. Group G members were associated with cytokinin glycosylation, particularly dihydrozeatin, which promotes fruit enlargement. RT-qPCR suggested VcUGTs involvement in fruit development, while functional validation confirmed VcUGT160 localization to the nucleus and cell membrane, likely mediating dihydrozeatin glycosylation. Conclusions The results of this study identified and characterized the UGT gene family in Blueberry. VcUGT160 may function in mediating dihydrozeatin glycosylation. Moreover, these findings enhance our understanding of VcUGTs evolution and function in blueberry.

Soil salinity poses a significant environmental challenge for the growth and development of blueberries. However, the specific mechanisms by which blueberries respond to salt stress are still not fully understood. Here, we employed a comprehensive approach integrating physiological, metabolomic, and transcriptomic analyses to identify key metabolic pathways in blueberries under salt stress. Our findings indicate that blueberries primarily adapt to salt stress by modulating pathways associated with carbohydrate metabolism, organic acid metabolism, amino acid metabolism, and various organic compounds. Key metabolites involved in this response include sucrose, propionic acid, and palmitic acid. A total of 241 transcription factors were differentially expressed, with significant involvement from families such as AP2, Dof, GATA, WRKY, and TCP. Notably, the galactose metabolism pathway was associated with 5 DAMs and 24 DEGs, while the starch and sucrose metabolism pathway contained 5 DAMs and 23 DEGs, highlighting their crucial roles in mitigating salt stress. Overexpression of VcGolS3 in transgenic Arabidopsis conferred tolerance to salt and drought stresses, primarily evidenced by a significant increase in GolS enzyme activity and reduced ROS accumulation. This study provides valuable insights into the molecular mechanisms underlying the blueberry response to salt stress and lays the groundwork for breeding salt- and drought-tolerant blueberry varieties. Key message The key gene VcGolS3 involved in blueberry stress resistance was screened through a combined analysis of transcriptomics and metabolomics, and it was confirmed that the gene plays an important role in plant resistance to salt and drought stresses.

Highbush blueberry (Vaccinium corymbosum) fruits contain substantial quantities of flavonoids, which are implicated in a wide range of health benefits. Although the flavonoid constituents of ripe blueberries are known, the molecular genetics underlying their biosynthesis, localization, and changes that occur during development have not been investigated. Two expressed sequence tag libraries from ripening blueberry fruit were constructed as a resource for gene identification and quantitative realtime reverse transcription-polymerase chain reaction primer design. Gene expression profiling by quantitative real-time reverse transcription-polymerase chain reaction showed that flavonoid biosynthetic transcript abundance followed a tightly regulated biphasic pattern, and transcript profiles were consistent with the abundance of the three major classes of flavonoids.Proanthocyanidins (PAs) and corresponding biosynthetic transcripts encoding anthocyanidin reducíase and leucoanthocyanidin reducíase were most concentrated in young fruit and localized predominantly to the inner fruit tissue containing the seeds and placentae. Mean PA polymer length was seven to 8.5 subunits, linked predominantly via B-type linkages, and was relatively constant throughout development. Flavonol accumulation and localization patterns were similar to those of the PAs, and the B-ring hydroxylation pattern of both was correlated with flavonoid-3'-hydroxylase transcript abundance. By contrast, anthocyanins accumulated late in maturation, which coincided with a peak in flavonoid-3-O-glycosyltransferase and flavonoid-3' 5'-hydroxylase transcripts. Transcripts of VcMYBPAl, which likely encodes an R2R3-MYB transcriptional regulator of PA synthesis, were prominent in both phases of development. Furthermore, the initiation of ripening was accompanied by a substantial rise in abscisic acid, a growth regulator that may be an important component of the ripening process and contribute to the regulation of blueberry flavonoid biosynthesis.

Background Blueberry fruit exhibit atypical climacteric ripening with a non-auto-catalytic increase in ethylene coincident with initiation of ripening. Further, application of ethephon, an ethylene-releasing plant growth regulator, accelerates ripening by increasing the proportion of ripe (blue) fruit as compared to the control treatment. To investigate the mechanistic role of ethylene in regulating blueberry ripening, we performed transcriptome analysis on fruit treated with ethephon, an ethylene-releasing plant growth regulator. Results RNA-Sequencing was performed on two sets of rabbiteye blueberry (‘Powderblue’) fruit: (1) fruit from divergent developmental stages; and (2) fruit treated with ethephon, an ethylene-releasing compound. Differentially expressed genes (DEGs) from divergent developmental stages clustered into nine groups, among which cluster 1 displayed reduction in expression during ripening initiation and was enriched with photosynthesis related genes, while cluster 7 displayed increased expression during ripening and was enriched with aromatic-amino acid family catabolism genes, suggesting stimulation of anthocyanin biosynthesis. More DEGs were apparent at 1 day after ethephon treatment suggesting its early influence during ripening initiation. Overall, a higher number of genes were downregulated in response to ethylene. Many of these overlapped with cluster 1 genes, indicating that ethylene-mediated downregulation of photosynthesis is an important developmental event during the ripening transition. Analyses of DEGs in response to ethylene also indicated interplay among phytohormones. Ethylene positively regulated abscisic acid (ABA), negatively regulated jasmonates (JAs), and influenced auxin (IAA) metabolism and signaling genes. Phytohormone quantification supported these effects of ethylene, indicating coordination of blueberry fruit ripening by ethylene. Conclusion This study provides insights into the role of ethylene in blueberry fruit ripening. Ethylene initiates blueberry ripening by downregulating photosynthesis-related genes. Also, ethylene regulates phytohormone-metabolism and signaling related genes, increases ABA, and decreases JA concentrations. Together, these results indicate that interplay among multiple phytohormones regulates the progression of ripening, and that ethylene is an important coordinator of such interactions during blueberry fruit ripening.

The northern highbush blueberry variety ‘Duke’ was used as the test material, and different concentrations of 2,4-Epibrassinolide (EBR) (0, 0.2, 0.4, 0.6, and 0.8 mg·L -1 ) were applied during the bud expansion stage, with a second application administered at one-day intervals following the first. Samples were collected at the bud, flower, and fruit stages and subsequently treated with artificial low temperatures (2°C) after sampling. The effects of various concentrations of exogenous EBR on the physiological indices of cold resistance and the expression of the cold resistance gene VcCBF3 in blueberry buds, flowers, and young fruits were investigated through comprehensive evaluation and correlation analysis. The objective was to identify the optimal concentration of EBR to enhance the cold resistance of blueberries. The results indicate that: (1) Under low temperature stress, the contents of soluble sugar, soluble protein and proline increased, along with the activities of superoxide dismutase, peroxidase, and catalase. The expression of the VcCBF3 gene expression and the ascorbate-glutathione cycling system were up-regulated, and with the increase of EBR concentration, the expression of the VcCBF3 gene initially rose and then declined. The content of malondialdehyde and the production rate of superoxide anion radicals decreased, and with the increase of EBR concentration, the content of malondialdehyde first decreased and then increased. (2) Overall low temperature resistance, flowers > buds > young fruits. (3) Appropriate concentrations of exogenous EBR can effectively mitigate freezing damage in blueberries caused by low temperatures. A comprehensive evaluation and correlation analysis of each cold tolerance index and the expression of the VcCBF3 gene revealed that a treatment concentration of 0.4 mg·L -1 had the most significant mitigating effect among the sprayed EBR concentrations of 0, 0.2, 0.4, 0.6, and 0.8 mg·L -1 .

Environmental factors play an important role in anthocyanin biosynthesis, and potassium, an essential nutrient for blueberry growth, can act as an enzyme activator. However, few reports exist on the transcriptional and anthocyanin metabolic changes in blueberries regulated by potassium. The results indicated that potassium treatment significantly increased the contents of malvidin, petunidin, and delphinidin in blueberry fruits and accelerated early color development, particularly favoring the accumulation of darker pigments such as malvidin, petunidin, and delphinidin when applied at the young fruit stage. Transcriptome analysis identified 102 glucose metabolism-related genes and 12 differential potassium transport genes potentially involved in potassium-mediated anthocyanin synthesis and accumulation, with AKT1 and KUP potassium transporters being upregulated under potassium fertilization. In the anthocyanin biosynthesis pathway, 13 genes, including UFGT , F3H , CHI , HCT , C12RT1 , DFR , and F3’5’H , were closely linked to flavonoid and anthocyanin metabolite synthesis regulated by potassium. Furthermore, potassium treatment markedly enhanced the activities of key enzymes, F3H, F3’5’H, and UFGT, in the anthocyanin synthesis pathway of blueberry fruits. Overall, these findings elucidate the influence of potassium application timing on anthocyanin synthesis and provide valuable insights into the molecular mechanisms governing anthocyanin biosynthesis in blueberries.

Although they are staple foods in cuisines globally, many commercial fruit varieties have become progressively less flavorful over time. Due to the cost and difficulty associated with flavor phenotyping, breeding programs have long been challenged in selecting for this complex trait. To address this issue, we leveraged targeted metabolomics of diverse tomato and blueberry accessions and their corresponding consumer panel ratings to create statistical and machine learning models that can predict sensory perceptions of fruit flavor. Using these models, a breeding program can assess flavor ratings for a large number of genotypes, previously limited by the low throughput of consumer sensory panels. The ability to predict consumer ratings of liking, sweet, sour, umami, and flavor intensity was evaluated by a 10-fold cross-validation, and the accuracies of 18 different models were assessed. The prediction accuracies were high for most attributes and ranged from 0.87 for sourness intensity in blueberry using XGBoost to 0.46 for overall liking in tomato using linear regression. Further, the best-performing models were used to infer the flavor compounds (sugars, acids, and volatiles) that contribute most to each flavor attribute. We found that the variance decomposition of overall liking score estimates that 42% and 56% of the variance was explained by volatile organic compounds in tomato and blueberry, respectively. We expect that these models will enable an earlier incorporation of flavor as breeding targets and encourage selection and release of more flavorful fruit varieties.

Background Blueberry ( Vaccinium section Cyanococcus) is a commercially important fruit crop. Its cultivation is challenging due to specific climate and soil requirements, with even minor temperature fluctuations potentially affecting growth and fruit yield. Heat stress impairs growth and photosynthesis by causing damage to the photosystem II (PSII) complex. Hence, identifying genomic regions influencing the maximum quantum efficiency of PSII and the overall photosynthetic capacity of plants under heat stress is crucial. Results In this study, we exposed 266 interspecific cross derivatives of blueberry plants to heat stress in controlled conditions for two consecutive years and evaluated their responses through phenotypic, chlorophyll fluorescence, and vegetation indices measurements. We observed continuous and significant variation for all the measured traits, indicating their quantitative nature. Genome-wide association studies (GWAS) using 126,816 single-nucleotide polymorphisms revealed several candidate genes encoding molecular chaperones, serine-threonine kinases, and DEAD-box proteins, which play critical roles in heat stress responses in plants. Additionally, we identified 10,393 differentially expressed genes (DEGs) from the transcriptomic analysis of V. corymbosum and V. darrowii plants subjected to 6 and 9 hours of heat stress. RNA-Seq data were further confirmed by quantitative real-time PCR analysis of randomly selected genes. Functional characterization through Gene Ontology and pathway analysis of 325 genes commonly expressed in all four comparison groups indicated that DEGs were mainly enriched in protein processing in the endoplasmic reticulum. Through GWAS and transcriptomic analysis, we uncovered 23 genes on chromosomes 1, 2, 3, 4, 5, 7, 8, 9, 10, and 12 associated with chlorophyll fluorescence parameters and vegetation indices under heat stress. Conclusions This study provides a deeper understanding of the genetic basis of chlorophyll fluorescence under heat stress in blueberries, offering valuable information for breeding strategies to develop blueberry cultivars with enhanced photosynthetic efficiency.

Summary Colour change is an important event during fruit ripening in blueberry. It is well known that miR156/SPLs act as regulatory modules mediating anthocyanin biosynthesis and ethylene plays critical roles during colour change, but the intrinsic connections between the two pathways remain poorly understood. Previously, we demonstrated that blueberry VcMIR156a/VcSPL12 affects the accumulation of anthocyanins and chlorophylls in tomato and Arabidopsis. In this study, we first showed that VcMIR156a overexpression in blueberry led to enhanced anthocyanin biosynthesis, decreased chlorophyll accumulation, and, intriguingly, concomitant elevation in the expression of ethylene biosynthesis genes and the level of the ethylene precursor ACC. Conversely, VcSPL12 enhanced chlorophyll accumulation and suppressed anthocyanin biosynthesis and ACC synthesis in fruits. Moreover, the treatment with ethylene substitutes and inhibitors attenuated the effects of VcMIR156a and VcSPL12 on pigment accumulation. Protein‐DNA interaction assays indicated that VcSPL12 could specifically bind to the promoters and inhibit the activities of the ethylene biosynthetic genes VcACS1 and VcACO6. Collectively, our results show that VcMIR156a/VcSPL12 alters ethylene production through targeting VcACS1 and VcACO6, therefore governing fruit colour change. Additionally, VcSPL12 may directly interact with the promoter region of the chlorophyll biosynthetic gene VcDVR, thereby activating its expression. These findings established an intrinsic connection between the miR156/SPL regulatory module and ethylene pathway.