Blue honeysuckle (Lonicera caerulea L.) is a deciduous shrub with perennial rootstock found in China. The objectives of this study were to explore the drought tolerance of blue honeysuckle, determine the effect of drought stress on two photosystems, and examine the mechanism of acquired drought tolerance. In this study, blue honeysuckle under four levels of simulated field capacity (100%, 85%, 75%, and 65% RH) was grown in split-root pots for drought stress treatment, for measuring the changes in chlorophyll content, photosynthetic characteristics, and leaf chlorophyll fluorescence parameters. The chlorophyll content of each increased under mild stress and decreased under moderate and severe stress. The net photosynthetic rate, transpiration rate, intercellular carbon dioxide concentration, and stomatal conductance of blue honeysuckle decreased with the increase in water stress. However, the water utilization rate and stomatal limit system increased under mild and moderate stress and decreased under severe stress. The maximum fluorescence (Fm), maximum photochemical efficiency, and quantum efficiency of photosystem II decreased with the decrease in soil water content, and the initial fluorescence increased significantly (p < 0.01). With the decrease in soil water content, the energy allocation ratio parameters decreased under severe drought stress. The main activity of the unit reaction center parameters first increased and then decreased. ABS/CSm, TRo/CSm, ETo/CSm, and REo/CSm gradually declined. After a comprehensive analysis, the highest scores were obtained under adequate irrigation (CK). Overall, we concluded that the water irrigation system of blue honeysuckle should be considered adequate.

This study investigated the impact of chitosan (CH, 1%) and aloe vera gel (AL, 30%) edible coatings on the preservation of blue honeysuckle quality during a 28-day storage at −1 °C. Coating with CH, AL, and CH+AL led to notable enhancements in several key attributes. These included increased firmness, total soluble solids, acidity, pH, and antioxidant capacity (measured through DPPH, ABTS, and FRAP assays), as well as the preservation of primary (ascorbic acid) and secondary metabolites (TPC, TAC, and TFC). The TAC and TFC levels were approximately increased by 280% and 17%, respectively, in coated blue honeysuckle after 28 d compared to uncoated blue honeysuckle. These coatings also resulted in reduced weight loss, respiration rate, color, abscisic acid, ethylene production, and malondialdehyde content. Notably, the CH+AL treatment excelled in preserving secondary metabolites and elevating FRAP-reducing power, demonstrating a remarkable 1.43-fold increase compared to the control after 28 days. Overall, CH+AL exhibited superior effects compared to CH or AL treatment alone, offering a promising strategy for extending the shelf life and preserving the quality of blue honeysuckle during storage.

Blue honeysuckle (Lonicera caerulea L.) is a perennial plant of the Caprifoliaceae family and Lonicera genus, the largest genus in the plant kingdom. Between September 2021 and September 2022, a le...

Blue honeysuckle (Lonicera caerulea L.) fruit is growing in popularity as a natural, functional 'super fruit', but its storage is challenged by pathogen infection. In June 2022, approximately 30% of 100 kg of blue honeysuckle fruits (cv. Lanjingling) obtained in Harbin, China (128.70°E, 44.87°N) showed postharvest fruit rot symptoms after 15 d of storage at 4°C, leading to whole fruit rotting with gray fungal growth (Fig.1 A). Small (1-2 mm) segments of infected tissue were obtained from 20 randomly selected fruits which were surface sterilized with 75% ethanol for 30 s and 5% sodium hypochlorite (NaOCl) for 3 min, rinsed three times with sterile distilled water, dried in paper towel, and plated in 9 cm Petri dishes containing potato dextrose agar (PDA). Five purified cultures were obtained and their front colonies were dark brown (Fig.1 C) on the PDA plates after 5 d at 25°C (Alam et al. 2019; Riquelme-Toledo et al. 2020). The conidia (n = 50) were single-celled, hyaline, either ellipsoid or ovoid, and measured 7.5-15.0 μm (11.7 μm average) × 6.0-11.4 μm (8.3 μm average). The conidiophores (Fig.1 E) were branched at the apex bearing bunches of conidia resembling grape clusters (Ellis 1971). For molecular confirmation, genomic DNA was extracted from a representative isolate LDGS-3 using the Ezup Column Fungi Genomic DNA Purification kit (Sangon Biotech, Shanghai, China). The internal transcribed spacer region (ITS, GenBank ON952502), heat shock protein (HSP60, GenBank OP039103), the second-largest subunit of RNA polymerase II (RPB2, GenBank OP186114) and glyceraldehyde 3-phosphate dehydrogenase (G3PDH, GenBank OQ658508) genes were partially amplified with the respective primers ITS1/ITS4, HSP60f/HSP60r, RPB2f/RPB2r, and G3PDH-F/G3PDH-R (Staats et al. 2005; White et al. 1990). BLAST analysis revealed that the sequences of the four genes showed 100% homology with the MH782039, MH796663, MN448501 and MH796662 sequences for isolates of Botrytis cinerea. Based on morphology and molecular characteristics, the isolate LDGS-3 was identified as B. cinerea. For pathogenicity, twenty healthy blue honeysuckle fruits (cv. Lanjingling) were superficially sterilized with 75% ethanol and washed with distilled water. Ten inoculated blue honeysuckle fruits, which were injected with 10 μL conidial suspension of isolate LDGS-3 (106 spores/mL) displayed fruit rot symptoms (Fig.1 B) inside 9 cm Petri dishes after 10 d at 4°C, while no symptoms were detected on ten fruits inoculated with sterile distilled water (Alam et al. 2019). The same isolate that was reisolated from infected fruits with the same morphological and molecular traits was also identified as B. cinerea, confirming Koch's postulates. B. cinerea was previously reported in Henan Province, China in hawthorn (Zhang et al. 2018). To our knowledge, this is the first report of postharvest fruit rot caused by B. cinerea on blue honeysuckle fruit in China, which will aid future management of this emerging postharvest disease.

Heilongjiang is the largest province with the small, cultivated fruit plant, blue honeysuckle (Lonicera caerulea L.), in China (Sun et al. 2024). Between September 2022 and September 2023, a leaf spot disease was observed on about 10 percent of blue honeysuckles of the 'Lanjingling' cultivar grown in a 6.66-ha field in Mudanjiang (129.38°E, 44.59°N), Heilongjiang Province, China. The typical symptoms include a few small brown sunken leaf spots (approximately 2 mm) in the fruiting stage that gradually expand into larger brown sunken lesions (approximately 10 mm) in the senescence stage (Fig. S1). Small 3-4-mm segments of infected tissue from 100 randomly selected leaf samples with typical symptoms were surface sterilized with 75% ethanol and 5% sodium hypochlorite, rinsed in sterile distilled water, and transferred to 9-cm Petri dishes containing potato dextrose agar (PDA) after drying. Finally, 10 isolated fungi were obtained through single-spore culture on PDA, and their conidia displayed a morphology consistent with Fusarium spp. (Zheng et al. 2023), and no other fungi were isolated. The fungal colonies on PDA were pink to dark red with fluffy aerial mycelium and pigmentation (Fig. S2). Microconidia were not observed, and the macroconidia of fungi had 2 to 6 septa, which were slender, sickle-shaped to nearly curved, with an average size of 38.83 (21.30 to 55.20) × 3.87 (2.70 to 6.60) μm (n = 50) on carnation leaf agar (Fig. S3). Genomic DNA was extracted from the representative isolate LD-245 for molecular verification, and PCR amplification was performed with ITS1/ITS4 (White et al. 1990), RPB2-5F2/RPB2-7CR (Liu et al. 1999), and EFl/EF2 (O'Donnell et al. 1998) primers. Sequences of LD-245 ITS (OR565903), RPB2 (OR584061), and TEF (PP965657) revealed 99 to 100% (494/494, 722/726, and 654/654) of identity with Fusarium asiaticum (MT322117, MH582121, and MT330257). Phylogenetic tree was constructed based on the concatenated sequences of ITS, RPB2, and TEF genes, and LD-245 was clustered with F. asiaticum (Fig. S4, Table S1). Therefore, based on the morphological characteristics and molecular phylogeny, LD-245 was identified as F. asiaticum. Six two-year-old healthy plants of the 'Lanjingling' cultivar were selected for a pathogenicity test. Three plants were inoculated with LD-245 conidial suspension (1 × 106 spores/ml) or with sterile water as an experimental control. All plants were cultured in a greenhouse (28℃, 75% relative humidity, 12 h light and dark cycle), and each experiment was replicated three times. Typical leaf spot symptoms were observed on inoculated leaves after 10 days (Fig. S5), whereas no symptoms were detected on water-treated leaves. The pathogens re-isolated from infected leaves displayed the same morphological and molecular traits as the initial isolate, and were again identified as F. asiaticum, confirming Koch's postulate. F. asiaticum was previously reported on giant elephant's ear (Alocasia macrorrhizos) (Zheng et al. 2023), causing leaf spot disease in China. This study is the first report of blue honeysuckle leaf spot disease caused by F. asiaticum in China. China has the largest blue honeysuckle cultivation area globally, and the production of blue honeysuckle with horticultural value is important for growers (Sun et al. 2024). Therefore, we hope researchers can develop efficient measures to manage emerging plant diseases in the future.

The impact of exogenous melatonin treatment on the postharvest quality and storability of blue honeysuckle fruit was investigated. Fruits were immersed in melatonin solutions at concentrations of 0 (control), 0.01, 0.05, and 0.25 mM for 5 min and subsequently stored at –1 °C for 63 d. Among all treatments, the combination of two-week storage without fruit puncturing and 0.05 mM melatonin application significantly delayed fruit softening and decay even at the initial stage of storage, while also increasing the concentration of phenolic compounds and enhancing antioxidant activity. During the later storage period (28–63 d), melatonin-treated fruits maintained higher levels of maltose, fructose, and sucrose, contributing to improved flavor retention. In contrast, both lower (0.01 mM) and higher (0.25 mM) concentrations were less effective or even detrimental to fruit quality. HPLC-ESI-QTOF-MS² analysis revealed that 0.05 mM melatonin effectively preserved several functional phenolics, including p-coumaroylquinic acid, caffeoyl glucose, 5-O-caffeoylquinic acid, 3-O-caffeoylquinic acid, luteolin-7-O-glucoside, and hydroxytyrosol. Thus, 0.05 mM melatonin is effective in delaying senescence and maintaining the postharvest quality of blue honeysuckle fruit.