Melatonin is a secondary messenger in plants that is involved in the regulation of abiotic stress responses, but it is unclear whether it enhances the adaptive capacity of blueberries to cope with salinity stress. The effects of exogenous application of melatonin (100, 200, and 300 μmol·L⁻¹) on the growth, photosynthetic characteristics, leaf anatomy, and physiological and biochemical properties of blueberry plants under mixed salt stress (90 mmol·L⁻¹: 30 mmol·L⁻¹ Na₂CO₃ + 60 mmol·L⁻¹ NaCl) were investigated. The results showed that blueberries under 90 mmol·L⁻¹ mixed salt stress had significant salt damage symptoms, with reduced blueberry biomass, reduced chlorophyll content, and photosynthesis inhibition. In contrast, melatonin-treated blueberries showed significantly reduced salt damage symptoms compared with stressed blueberry plants, with the optimum effect at 200 μmol·L⁻¹, along with increased chlorophyll content, improved photosynthetic capacity, and increased leaf thickness under stress. Melatonin treatment resulted in reduced malondialdehyde (MDA) content and relative electrolyte leakage (EL), increased K⁺ content, and decreased Na⁺ content in blueberry roots, stems and leaves, thereby reducing the toxic effects of mixed salts on blueberries. The results indicate that melatonin can mitigate the effects of mixed salt stress on blueberries and that foliar spraying of melatonin could alleviate mixed salt-induced damage to blueberries, with the optimum effect at 200 μmol·L⁻¹ treatment. This study provided a valuable basis for exploring the mechanism of exogenous melatonin action in blueberries in saline environments.

In order to clarify the relationship between mineral nutrients and rhizosphere microorganisms at different growth and development stages of blueberry (Vaccinium spp.), this work studied the dynamic changes in element content and microbial quantity in different parts of blueberry plants. The test material was a 12-year-old half-highbush blueberry variety (‘Beilu’). The changes in the mineral nutrient elements in leaves, branches and the soil of blueberry plants were studied at the full bloom stage (T1), green fruit stage (T2), mature stage (T3) and late mature stage (T4), and the correlations of the average contents of mineral elements in the four periods were studied. The bacterial community in the rhizosphere soil was determined and analyzed using 16S rRNA high-throughput sequencing technology. The results showed that the changes in other mineral elements in various parts of blueberry plants varied in different periods. Nitrogen (N) showed a downward trend in branches, leaves and soil, especially in leaves (p < 0.05). The N contents in T2, T3 and T4 decreased by 9.9%, 26.4% and 29.9%, respectively. The N contents in the leaves and branches showed a downward trend at different growth stages, especially in leaves. The phosphorus (P) content in leaves showed a trend of increasing first and then decreasing, while it continued to increase in branches. The content of potassium (K) in leaves changed significantly, where it increased first and then decreased. The content of calcium (Ca) in leaves decreased first and then increased, while the content of magnesium (Mg) in branches and leaves decreased first and then increased, and the relative change was significant. The contents of iron (Fe) and zinc (Zn) in leaves decreased first and then increased, while the contents of manganese (Mn) and copper (Cu) were relatively stable. Cu decreased first and then increased in leaves and soil, and it increased first and then decreased in branches. The mineral nutrients in different growth stages of blueberry showed significant correlation in leaves, branches and soil. Mn in leaves was significantly positively correlated with P, Ca, Mg, Mn, Cu and Zn in soil (p < 0.01). Nitrogen and calcium in leaves were significantly correlated with manganese and phosphorus in soil, respectively. Ca in branches was significantly positively correlated with N and K in soil and was significantly positively correlated with Zn in soil (p < 0.01). Magnesium was significantly negatively correlated with iron in soil. The bacterial community structure of the blueberry rhizosphere soil changed significantly over time (p < 0.05), and the relative abundance showed the following trend: T4 > T2 > T3 > T1. At the phylum level, Proteobacteria, Acidobacteria, Actinobacteria, Chloroflexi and Verrucomicrobia were the dominant bacteria in different periods. Candidatus solibacter and Bryobacter were significantly higher in T1 and T3 than in T1 and T4. Bradyrhizobium flora increased significantly at T3. Sphingomonas increased significantly at T1 (p < 0.05).

Blueberries are highly prone to postharvest decay, resulting in significant nutrient loss and economic damage. Current research on the postharvest storage of blueberries primarily focuses on storage techniques, while the underlying mechanisms remain insufficiently explored. To further explore the role of exogenous melatonin (MT) in delaying the senescence of blueberry fruit, this study treated fruits with sterile water (control) and 300 μmol·L⁻¹ MT during the pink fruit stage. After maturation, the fruits were stored at 4 °C for 30 days, and we investigated the effects of exogenous MT on postharvest blueberry quality, reactive oxygen species (ROS) metabolism, antioxidant enzyme activities, and the expression of related genes. The results showed that, compared to the control, 300 μmol·L⁻¹ MT effectively delayed the increase in fruit decay rate and the decline in firmness, while enhancing the total soluble solids (TSS) content and ascorbic acid (AsA) levels. It also reduced the accumulation of malondialdehyde (MDA), hydrogen peroxide (H₂O₂), and the production rate of superoxide anion (O₂⁻), while maintaining higher activities of ascorbate peroxidase (APX), superoxide dismutase (SOD), and catalase (CAT). Furthermore, MT treatment upregulated the expression of antioxidant enzyme-related genes VcSOD1, VcSOD2, and VcAPX3. These findings indicate that treating blueberries with 300 μmol·L⁻¹ MT at the pink fruit stage improves postharvest quality, alleviates oxidative damage, and delays senescence. This study provides a theoretical foundation and practical reference for blueberry storage and preservation, laying the groundwork for further understanding the regulatory mechanisms of exogenous MT in postharvest fruit senescence.

These days, one of the main issues preventing agricultural development is salinized soils. Potassium fulvic acid (PFA) not only regulates plant growth, but also improves the soil nutrient content and physical structure, which makes it a soil conditioner worth promoting. Nevertheless, the research conducted thus far on the subject of PFA with regard to plant growth and inter-root microbial communities remains somewhat limited in scope. In this study, a pot experiment was conducted to simulate both the normal environment and salt stress environment. The objective of this experiment was to verify the effect of PFA on the growth of blueberry (Vaccinium corymbosum L.) as well as its effect on the soil physical and chemical indices and the soil microbial community structure. The findings demonstrated that the implementation of potassium fulvic acids exhibited a minimal impact on the growth of blueberry plants under standard environmental conditions. However, it was observed to exert a substantial effect on enhancing various physiological parameters, including plant height, root activity, and chlorophyll synthesis, particularly in response to salt stress. PFA led to a substantial augmentation in the soil organic matter content, alongside a notable rise in the alkali-hydrolyzable nitrogen (AN) and available potassium (AK) content. Concurrently, PFA caused a notable escalation in the activities of soil urease, sucrase, acid phosphatase, and catalase (p < 0.05) in the salt-stressed environment. PFA increased the abundance of Acidobacteria, Myxococcota, Ascomycota, and Fungi_phy_Incertae_sedis under salt stress, which was mainly related to the decrease in electrical conductivity (EC) values and increase in soil acid phosphatase (S-ACP) activity. It is evident that the implementation of PFA is advantageous in enhancing the saline environment, mitigating the impact of salt damage on blueberries and establishing a foundation for the expansion of cultivated areas and the sustainable cultivation of blueberries.

Due to its thin, juicy skin and high physiological activity, blueberries are easily susceptible to damage by pathogenic bacteria during storage and transportation after harvest. However, there are relatively few studies on the mechanisms by which blueberries resist rot disease. Therefore, in this study, the blueberry cultivar ‘Northland’ was used as the experimental material. Using a combination of single spore isolation, morphological analysis, and molecular biology methods, the types of pathogenic bacteria responsible for postharvest decay of blueberries were investigated, as well as the mechanisms by which EBR influences disease resistance and quality control. The results indicated that the pathogen responsible for blueberry fruit rot was Talaromyces amestolkiae , and treatment with 2,4-epibrassinolide (EBR) could significantly reduce both the fruit rot rate and the disease index. Among the treatments, 0.4 mg/L EBR showed the most pronounced effect, effectively maintaining fruit firmness, titratable acidity, and soluble solids content, while reducing weight loss, decreasing the extent of membrane lipid peroxidation, and enhancing the activities of antioxidant enzymes such as superoxide dismutase (SOD) and peroxidase (POD) by 251.46% and 208.18%, respectively. Additionally, the activity of pathogenesis-related proteins, including chitinase, increased, and the stability of antioxidants, such as total phenols, was preserved. EBR improved the disease resistance of blueberry fruit through multi-pathway synergy and delayed the deterioration of postharvest quality. The findings of this study can offer theoretical support for the eco-friendly prevention and management of postharvest diseases in blueberries.

The degree of soil salinization is still on the rise. In saline environments, NaCl is the main substance that causes plant salt damage, with the toxicity of ions under salt stress primarily involving sodium (Na⁺) or chloride (Cl⁻). However, fewer studies have focused on Cl⁻ stress. This study investigated the differences in the growth and physiology of five blueberry varieties under Cl⁻ stress, aiming to understand the mechanisms of Cl⁻ tolerance and the physiological responses to Cl⁻ stress in these varieties. Five blueberry varieties (‘Northland’, ‘PL19’, ‘Duke’, ‘Reka’, and ‘Bonnie’) were used as test materials. This study examined the changes in growth and physiological indices of blueberry plants under different concentrations of Cl⁻ (A1–A6: 50, 100, 150, 200, 250, and 300 mmol/L) treatments. A control treatment (CK) was included to serve as a baseline for comparison. We comprehensively evaluated the Cl⁻ tolerance of these five varieties to screen for chlorine-tolerant varieties. This study examined the concentration-dependent changes in growth and physiological indices of blueberry plants, including plant height, leaf area, chlorophyll content, electrical conductivity, levels of soluble sugar (SS), malondialdehyde (MDA), proline (Pro), and soluble protein (SP), as well as the activities of superoxide dismutase (SOD) and catalase (CAT). The results revealed that as the Cl⁻ concentration increased, the growth of all blueberry varieties was inhibited; plant height, leaf area, and chlorophyll content consistently declined, whereas electrical conductivity showed a steady increase. SS and MDA content exhibited a biphasic response, with an increase at lower Cl⁻ concentrations followed by a decrease at higher concentrations. The activities of SOD and CAT in ‘Duke’ consistently increased with rising Cl⁻ levels. In ‘PL19’ and ‘Reka’, chlorophyll content decreased with increasing Cl⁻, while their proline content rose initially and then declined. In contrast, the other varieties generally showed an increasing trend in proline content. Similarly, the soluble protein content of ‘Northland’ and ‘PL19’ increased at lower Cl⁻ levels and decreased at higher concentrations, whereas ‘Bonnie’, ‘Duke’, and ‘Reka’ displayed an overall declining trend. Principal component analysis indicated that the Cl⁻ tolerance of the blueberry varieties ranked as follows: ‘Duke’ > ‘Bonnie’ > ‘Reka’ > ‘PL19’ > ‘Northland’. These findings lay a foundation for blueberry cultivation in saline–alkaline soils and support the selection and development of new, chlorine-tolerant varieties.