Search Results (208)

Huanglongbing (HLB) is the main disease affecting citrus crops, and in the absence of resistant commercial cultivars, alternative management strategies are required. This study aimed to evaluate the effect of early application of tree regulators associated with foliar nutrition on tree development, fruit quality, tolerance to HLB in sweet orange trees and vascular tissue organizations. The experiment was conducted in a commercial Citrus sinensis “Lima Verde” orchard, with asymptomatic (PCR−) and symptomatic (PCR+) tree, distributed in a completely randomized design with eight replications per treatment. The following six treatments were evaluated: negative control (asymptomatic trees, PCR−); positive control (symptomatic trees, PCR+); foliar application of gibberellic acid; foliar application of 2,4-D; foliar spraying of nutrients solution; and a combination of nutrients solution with gibberellic acid and 2,4-D. The evaluations included disease severity, canopy growth, analysis of mineral nutrients by fruit, dry mass, fruit quality, and histopathological analysis of the phloem and xylem. The integrated treatment (foliar nutrition + growth regulators) significantly reduced HLB symptom severity, promoted canopy growth comparable to healthy trees, and decreased fruit drop by 62.7% relative to the untreated HLB control. Fruit yield increased from 9.89 to 22.50 kg tree⁻¹, representing a 127% increase, while harvested fruit number increased from 71.0 to 139.8 fruits tree⁻¹. The combined treatment also restored fruit diameter to values similar to healthy trees, increased total fruit dry matter from 14.5 to 24.2 g, and maintained soluble solids (9.56 °Brix) close to the healthy control (10.33 °Brix). Fruit zinc concentration increased by 48% compared with untreated HLB-infected trees. Histological analyses demonstrated enhanced cambial activity, larger phloem and xylem areas, reduced starch accumulation, and improved vascular integrity in treated trees. These findings highlight the potential of integrated tree regulators and nutritional approaches as a valuable alternative for improving tree performance and tolerance under HLB prevalent conditions. Full article

Huanglongbing (HLB), caused by Candidatus Liberibacter asiaticus (CLas) and vectored by Asian citrus psyllid (Diaphorina citri), remains a major constraint to sustainable citrus production. In Florida, individual protective covers (IPCs) have been adopted as an effective psyllid exclusion tool by shielding young trees from this vector of the phloem-dwelling bacterium CLas. Brassinosteroids (BRs), a class of plant steroid hormones, are being explored as a treatment to mitigate HLB and are approved for commercial use in the state. We investigated the effect of IPCs combined with homobrassinolide (HBr) applied as a foliar spray on CLas titer, canopy volume, tree growth, yield, fruit quality, and defense-related gene expression of the salicylic acid (SA) pathways in ‘Tango’ mandarin grafted on sour orange (SO) or US-942 rootstocks. After being covered with IPCs in the field for three years, trees were subjected to monthly foliar application of HBr upon IPC removal. The experiment included four treatment groups: trees with IPC and HBr spray (IPC HBr+), IPC without HBr (IPC HBr-), no-IPC with HBr (no-IPC HBr+), and no-IPC without HBr (no-IPC HBr-). IPCs effectively delayed bacterial infection for six to nine months after IPC removal, maintaining higher cycle threshold (Ct) values (lower CLas titers) than in no-IPC trees, confirming the protective effect of IPCs against early CLas colonization. The combination of IPCs and HBr spray significantly enhanced canopy volume, particularly in trees grafted on SO. This effect was sustained over one year and was consistently greater in IPC HBr+ trees than in IPC HBr- and no-IPC HBr+ or HBr- trees, suggesting a synergistic effect of the combined therapy on enhancing tree growth. The tree height and trunk diameter were primarily improved by IPC, regardless of HBr treatment. IPC-treated trees exhibited significantly greater height and trunk diameters (scion and rootstock) than no-IPC trees across one or both rootstocks, indicating that IPCs alone contribute to these horticultural growth improvements. IPC trees also showed reduced preharvest fruit drop compared to the no-IPCs trees, resulting in higher yields, with additional gains observed in IPC HBr+ trees on SO. Fruit quality attributes, including °Brix, titratable acidity, peel color, and size, did not differ significantly among treatments. Importantly, gene expression analysis revealed early and sustained upregulation of key SA pathway genes in IPC HBr+ trees, indicating that HBr effectively activated systemic acquired resistance (SAR), particularly on SO rootstock. This study highlights the complementary roles of IPCs and HBr in the management of HLB. While IPCs provided essential early protection against CLas and promoted long-term horticultural growth, HBr enhanced early canopy development, activated host defense mechanisms, and enhanced yield. The integration of both approaches offers a sustainable and effective strategy to protect young citrus trees, delay CLas infection, and improve tree health and productivity under endemic HLB. Full article

Thirteen mandarin and hybrid cultivars grafted onto the commercial rootstocks Rangpur Lime and Swingle Citrumelo were comparatively assessed for vegetative growth, fruit physicochemical attributes, and field incidence and severity of Altenaria Brown Spot (ABS) and Huanglongbing (HLB). The experiment was conducted from January 2015 to December 2018 under a randomized block design, with ten replicates per scion–rootstock combination. Plant height, canopy volume, fruit mass, juice yield, acidity, soluble solids, and disease assessments were performed. RL induced greater vegetative growth but was associated with higher HLB severity, particularly in the Dekopon IAC 2009 and TM × LP 358 varieties. SC resulted in less vigorous trees but improved fruit quality, with higher acidity and soluble solids. Regarding ABS, the Loose Jacket IAC 515 and Muscia varieties showed high susceptibility, while Ortanique IAC 554 and Rainha BRS exhibited tolerance to both ABS and HLB. These findings suggest that although RL promotes vigorous growth, it may increase disease susceptibility, whereas SC is associated with reduced disease severity and improved fruit quality. Ortanique IAC 554 and Rainha BRS showed consistently low severity of ABS and HLB, combined with stable vegetative development and fruit quality, underscoring the importance of rootstock choice for guiding cultivar deployment in orchards under high disease pressure. Full article

This study investigated the epidemiology and incidence of citrus Huanglongbing (HLB) disease in citron (Citrus medica L.) under varying field conditions. This research specifically aimed to quantify disease severity, assess populations of the primary vector, the Asian citrus psyllid (Diaphorina citri), and identify potential alternative host plants sustaining the vector and the pathogen. Field surveys were executed across three sites characterised by distinct elevations and management practices. Site-level soil nutrient profiles exhibited moderate acidity (pH 4.67–5.74) and significant differences in organic matter and nitrogen. These findings suggest that localised deficiencies in calcium and boron may exacerbate disease severity, contributing to the varied epidemiological patterns observed across sites. Analysis revealed that both HLB disease severity and D. citri population density were significantly influenced by altitude, field condition, and orchard management. The low-elevation site (860 m above sea level (ASL)), characterised by poor maintenance, exhibited the highest mean psyllid populations (averaging 13 individuals per sticky trap per day) and the most severe disease symptoms. Conversely, the high-elevation site (1674 m ASL) displayed significantly lower infection rates and healthier tree conditions. Symptomatic citron trees across all sites consistently exhibited characteristic HLB foliar and fruit symptoms (blotchy mottle and lopsided fruits). Quantitative Polymerase Chain Reaction (qPCR) successfully detected the causal agent, Candidatus Liberibacter asiaticus (CLas), in symptomatic citron samples from all locations, with the highest relative fold-change (2^−ΔΔCt = 4628.24). Crucially, multiple developmental stages of D. citri were observed infesting the common weed Bidens pilosa. Furthermore, qPCR confirmed the presence of CLas DNA within the B. pilosa tissue itself (2^−ΔΔCt = 210.84). This finding constitutes the first field-based evidence that B. pilosa can serve as a novel alternative host that supports both the D. citri vector and the CLas pathogen. These results establish citron as a highly susceptible host and identify B. pilosa as a new, critical epidemiological link in the HLB transmission cycle, thereby underscoring the necessity for integrated, landscape-level disease management strategies. Full article

Diaphorencyrtus aligarhensis parasitizes the Asian citrus psyllid (ACP), Diaphorina citri, the primary insect vector responsible for transmitting Huanglongbing (HLB), a severe citrus disease. Screening of appropriate reference genes is a critical prerequisite for reliable RT-qPCR analysis, which is essential for investigating the functions of target genes in D. aligarhensis across diverse experimental conditions. However, to date, no validated reference genes have been reported for this species. This study assessed seven housekeeping genes in D. aligarhensis under six conditions (developmental stage, body tissue, population, temperature, diet, and starvation) using five stability algorithms (geNorm, BestKeeper, NormFinder, RefFinder, and ∆Ct). The results identified the most suitable reference genes for specific experimental conditions: EIF5A and RPL32 for the developmental stage; RPL13 and H3 for population comparisons; RPS6 and GAPDH for different feeding diets; RPL32 and RPS6 for starvation; RPL7A and RPS6 for different body tissues (head, thorax, abdomen) and temperature gradients (5 °C, 15 °C, 25 °C, 35 °C). Furthermore, the expression profiles of HSP70 were markedly different when normalized to the most versus the least stable reference genes across body tissues, diets, starvation durations, and temperatures. Our findings establish the first set of RT-qPCR reference genes for D. aligarhensis, providing a useful foundation for functional genomics research on this biological control agent. Full article

Huanglongbing (HLB), a destructive citrus disease caused by Candidatus Liberibacter asiaticus (CLas), cannot be efficiently diagnosed at the early stage via conventional detection methods. Most current metabolomic studies on citrus HLB rely solely on the LC-MS platform and mainly focus on sweet orange, while integrated dual-platform metabolomic research targeting Orah mandarin, the dominant cultivated citrus variety, remains limited. In the present study, GC-MS and LC-MS were combined for the first time, alongside multivariate statistical analysis and pathway enrichment analysis, to systematically characterize metabolomic differences between healthy and HLB-infected Orah mandarin leaves. Suspected citrus leaf samples were collected from two major citrus-producing regions in Guangxi and further confirmed by qPCR detection. A large number of differentially accumulated metabolites were identified, which were primarily enriched in carbohydrate metabolism and amino acid metabolism pathways. Several candidate biomarkers applicable for early HLB diagnosis were also screened out. This study provides reliable scientific evidence and a theoretical foundation for elucidating the pathogenic mechanism of HLB and establishing field-based early diagnosis techniques. Full article

The global citrus industry is under severe threat from devastating diseases, including Huanglongbing (HLB), caused by Candidatus Liberibacter asiaticus (CLas), and Citrus tristeza disease, caused by Citrus tristeza virus (CTV). Establishing efficient pathogen elimination techniques is crucial for developing virus-free citrus nursery systems and helps facilitate the prevention and control of devastating diseases. This study systematically evaluated the multiple effects of hot water treatment and plant growth regulator application on bud germination, pathogen elimination, antioxidant enzyme activities, and CsWUS expression in citrus scion. The results showed that moderate hot-water treatment at 40 °C for 5 min promoted bud germination, while higher temperatures or extended durations were inhibitory. Both 6-benzylaminopurine (6-BA) and melatonin (MT) significantly enhanced germination, with 50 mg/L 6-BA and 100 μM MT being most effective. All treatments significantly enhanced pathogen elimination and increased the activities of antioxidant enzymes SOD, POD, and CAT, with melatonin concentrations of 100 μM and above reducing CLas and CTV titers by over 93.64% and 96.07%. Furthermore, hot-water treatment and MT, but not 6-BA, upregulated the expression of the virus-resistance-related gene CsWUS. A combined treatment of hot water and MT did not yield synergistic benefits. In conclusion, melatonin treatment, particularly at 100 μM, optimally balances high bud germination with effective pathogen elimination, likely through activating antioxidant defenses and CsWUS-mediated immunity. This study provides a practical and efficient strategy for citrus pathogen-free seedling production. Full article

Diaphorina citri (Kuwayama) is one of the primary vectors of Citrus Huanglongbing (HLB), which poses a danger to the long-term development of the citrus industry. In this work, the spatiotemporal expression processes of the genes encoding vitellogenin-3-like (Vg4) and vitellogenin receptor (VgR) in D. citri females during the 1- to 30-day developmental stage of ovarian development and oviposition behavior were investigated. Vg4 and VgR gene expression largely supports oocyte maturation in D. citri females at the 1- to 15-day developmental stage. During the 15- to 30-day developmental stage, the expression of the Vg4 and VgR genes predominantly promotes the progression of oviposition behavior. Comparisons of ovarian development and oviposition behavior revealed that in the 15- to 30-day developmental stage, female egg production accounted for 75–85% of total oviposition, while mature oocyte formation occurred largely after the 15th day of ovarian development. The findings of this study provide fresh theoretical support and insights into the use of RNA interference (RNAi) technology to reduce the damage caused by D. citri populations. Full article

Huanglongbing (HLB), primarily caused by ‘Candidatus Liberibacter asiaticus’ (CLas), threatens global citrus production. Deciphering the molecular interplay between citrus and CLas is crucial for successful control. This review synthesizes current understanding of the molecular mechanisms underlying citrus-CLas interactions, providing a comprehensive overview that spans immune signaling, hormonal and metabolic reprogramming, non-coding RNA-mediated regulation, pathogen effector biology, and emerging biotechnological interventions. We detail the hierarchical host response: initial immune recognition via pattern recognition receptors, triggering reactive oxygen species bursts and calcium signaling. Moreover, hormonal network reprogramming and their complex interplay in defense/susceptibility are examined. Transcriptomic studies have revealed key features of metabolic reprogramming, including suppression of photosynthesis and impairment of phloem function. Additionally, long-term strategies like cell wall reinforcement, accumulation of defensive compounds such as flavonoids and terpenoids, and roles of post-transcriptional regulation of microRNAs are discussed. Conversely, CLas counter-defense, notably effector-mediated immunity suppression and host metabolism manipulation, is also considered. Comparative transcriptomics between tolerant and susceptible varieties identifies tolerance or resistance genes/pathways for breeding and engineering. Despite this progress, critical knowledge gaps remain, particularly regarding the precise molecular mechanisms of CLas immune evasion and effector-mediated suppression, the genetic basis of natural tolerance, and the field-level efficacy of defense priming strategies. Future research directions should integrate single-cell omics, CRISPR/Cas9 editing, nano-enabled delivery, and microbiome engineering to bridge these gaps and accelerate HLB-tolerant/resistant citrus development. This review synthesizes how molecular profiling advances understanding of citrus defense mechanisms against HLB, and underscores the imperative for interdisciplinary research and global collaboration. Full article

Huanglongbing (HLB) is the most serious disease affecting citrus production worldwide, and its management relies on controlling its vector, Diaphorina citri. Although Tamarixia radiata (Waterston) is widely used in biological control programmes, Diaphorencyrtus aligarhensis (Shafee et al.) has been proposed as a complementary agent; both species were reported in Colombia in 2016, yet their interaction dynamics under local conditions remain poorly understood. This study evaluated the development, morphometry, and interaction patterns of both parasitoids under controlled rearing conditions using a shared host population. Three treatments were established: non-parasitised nymphs, nymphs exposed to D. aligarhensis, and nymphs exposed to T. radiata, with parasitoids allowed to oviposit for 24 h. Developmental duration and morphometric traits were recorded daily. T. radiata completed its life cycle in less time (~11.7 days) than D. aligarhensis (~14.4 days) and than non-parasitized nymphs (~17 days). Morphometric traits were consistent with previously reported ranges, and this study provides the first detailed characterisation of the immature stages of D. aligarhensis in Colombia. Particularly, events of multiparasitoidism and superparasitoidism were documented under standardised conditions, demonstrating that both species can exploit the same host simultaneously. These findings offer new insights into parasitoid interaction dynamics and establish a biological foundation for developing integrated biological control strategies against D. citri. Full article

Chronic crop diseases caused by uncultured, obligate, or host-dependent pathogens challenge traditional pathogen-centric paradigms that often interpret symptoms as direct outcomes of pathogen toxins, effectors, or tissue colonization. Here, we advance a host-centric immune framework that reframes disease as an emergent consequence of dysregulated host immune network activity, including prolonged activation, signaling miscoordination, and systemic physiological disruption. Using citrus huanglongbing (HLB) as a primary exemplar and canola clubroot as a parallel system, we synthesize evidence that persistent immune stimulation can drive self-damaging outputs, including sustained reactive oxygen species accumulation, chronic vascular and transport dysfunction, hormone imbalance, and growth–defense trade-offs. While many observations derive from transcriptomic, physiological, and genetic studies conducted under controlled experimental conditions, the available evidence collectively suggests that persistent immune activation may contribute substantially to disease-associated decline in these systems. We argue that pattern-triggered immunity (PTI) and effector-triggered immunity (ETI) operate as an integrated immune network whose feedback structure can become destabilized under chronic infection, generating immune states that are simultaneously harmful and often ineffective at pathogen clearance. We further discuss how panomic profiling, spatially resolved analyses, and network inference can diagnose host immune states at tissue and cell-type resolution, and how genome editing enables causal tests and rational immune tuning strategies that optimize defense amplitude, timing, and localization rather than indiscriminately amplifying resistance. By centering the host immune system as both a source of protection and pathology, this framework provides a conceptual and practical roadmap for understanding and engineering resilience in HLB, clubroot, and other chronic crop diseases in which pathogen biology remains experimentally opaque. Full article

Candidatus Liberibacter spp. can infect most citrus plants and rely entirely on phloem sieve tube cells of the host plant for survival. Candidatus Liberibacter primarily contains Ca. L. asiaticus (CLas), Ca. L. africanus (CLaf), and Ca. L. americanus (CLam). Among these, CLas is the most harmful and widely distributed and is the primary pathogen of the devastating citrus disease Huanglongbing (HLB). Effectors are among the core weapons secreted by pathogens into plant cells to attack the plant immune system. In this study, we focused on CLas-specific effectors and those that are highly expressed during the infection stage to identify essential virulence effectors. Using secretion signal peptide prediction analysis, 40 candidate effectors with potential secretory capabilities were identified. Transient expression of these candidate effectors in Nicotiana benthamiana revealed their impact on pattern-triggered immunity, including INF-induced cell death and microbial pattern-induced reactive oxygen species (ROS) bursts, and the resistance of N. benthamiana to the bacterial pathogen Pst DC3000. 10 candidate effectors capable of suppressing plant immunity were identified. The stable expression of these candidate effectors in Arabidopsis showed that several candidate effectors enhanced plant susceptibility to Pst DC3000 and inhibited flg22-induced ROS production and MAPK activation. Among the three candidate effectors that significantly suppressed ROS burst, one effector, E3 (CLIBASIA_03085), interacts with the plant NADPH oxidase RbohD, a key enzyme responsible for ROS production. This suggests that E3 likely inhibits ROS accumulation by directly targeting RbohD. Here, we identified multiple candidate effectors capable of suppressing microbial pattern-triggered immunity that may be essential virulence factors for CLas infection, enhancing our understanding of CLas pathogenesis. Full article

Antimicrobial resistance (AMR) is one of the major health threats of the 21st century and demands innovative sources of bioactive compounds. In 2019, infections caused by resistant bacteria directly accounted for 1.27 million deaths and contributed to an additional 4.95 million associated deaths, underscoring the urgency of exploring new strategies. Among emerging alternatives, specialized plant metabolites stand out, as their biosynthesis is enhanced under biotic or abiotic stress. These stimuli increase reactive oxygen species (ROS), activate cascades regulated by mitogen-activated protein kinases (MAPKs), and trigger defense-related hormonal pathways involving salicylic acid (SA), jasmonic acid (JA), ethylene (ET), and abscisic acid (ABA), which in turn regulate transcription factors and biosynthetic modules, promoting the accumulation of compounds with antimicrobial activity. In this review, we synthesize recent literature (2020–2025) with emphasis on studies that report quantitative activity metrics. We integrate evidence linking stress physiology and metabolite production, summarize mechanisms of action, and propose a conceptual multi-omics pipeline, synthesized from current best practices, that combines RNA sequencing and LC/GC-MS-based metabolomics with bioinformatic tools to prioritize candidates with antimicrobial potential. We discuss elicitation strategies and green extraction, highlight bryophytes (e.g., Pseudocrossidium replicatum) as a differentiated chemical source, and explore citrus Huanglongbing (HLB) as a translational case study. We conclude that integrating stress physiology, multi-omics, and functional validation can accelerate the transition of stress-induced metabolites toward more sustainable and scalable medical and agricultural applications. Full article

Citrus Huanglongbing (HLB) is one of the most destructive diseases in the global citrus industry; its pathogen is transmitted primarily by the Asian citrus psyllid (ACP), Diaphorina citri Kuwayama, making timely monitoring and control of ACP populations essential. Real-world ACP monitoring faces several challenges, including tiny targets easily confused with the background, noise amplification and spurious detections caused by textures, stains, and specular glare on yellow-boards, unstable localization due to minute shifts of small boxes, and strict constraints on parameters, computation, and model size for long-term edge deployment. To address these challenges, we focus on the yellow-board ACP monitoring scenario and create the ACP Yellow Sticky Trap Dataset (ACP-YSTD), which standardizes background and acquisition procedures, covering common interference sources. The dataset consists of 600 images with 3837 annotated ACP, serving as a unified basis for training and evaluation. On the modeling side, we propose TGSP-YOLO11, an improved YOLO11-based detector: the detection head is reconfigured to the two scales P2 + P3 to match tiny targets and reduce redundant paths; Guided Scalar Fusion (GSF) is introduced on the high-resolution branch to perform constrained, lightweight scalar fusion that suppresses noise amplification; ShapeIoU is adopted for bounding-box regression to enhance shape characterization and alignment robustness for small objects; and Network Slimming is employed for channel-level structured pruning, markedly reducing parameters, FLOPs, and model size to satisfy edge deployment, without degrading detection performance. Experiments show that on the ACP-YSTD test set, TGSP-YOLO11 achieves precision 92.4%, recall 95.5%, and F1 93.9, with 392,591 parameters, a model size of 1.4 MB, and 6.0 GFLOPs; relative to YOLO11n, recall increases by 4.6%, F1 by 2.4, and precision by 0.2%, while the parameter count, model size, and computation decrease by 84.8%, 74.5%, and 4.8%, respectively. Compared to representative detectors (SSD, RT-DETR, YOLOv7-tiny, YOLOv8n, YOLOv9-tiny, YOLOv10n, YOLOv12n, YOLOv13n), TGSP-YOLO11 improves recall by 33.9%, 19.0%, 8.5%, 10.1%, 6.3%, 4.6%, 6.9%, and 5.7%, respectively, and F1 by 19.9, 14.9, 5.1, 6.0, 2.6, 5.6, 3.6, and 3.9, respectively. Additionally, it reduces parameter count, model size, and computation by 84.0–98.8%, 74.5–97.9%, and 3.2–94.2%, respectively. Transfer evaluation indicates that on 20 independent yellow-board images not seen during training, the model attains precision 94.3%, recall 95.8%, F1 95.0, and 159.2 FPS. Full article

Huanglongbing (HLB) poses a severe threat to the sustainable citrus industry, causing significant alterations in the spectral reflectance and leaf chlorophyll content (LCC) of citrus leaves. This study investigates the quantitative relationship between spectral characteristics and LCC for the early detection of HLB in Mianju mandarin cultivars. We analyzed hyperspectral data from healthy and HLB-infected leaves, employing the least absolute shrinkage and selection operator (LASSO) method and spectral indices to select chlorophyll characteristic bands, and several machine learning models were used to estimate the LCC. The results indicate that: (1) HLB-infected leaves exhibit significantly different spectral reflectance, characterized by a distinct “blueshift of the red edge”; (2) a greater proportion of characteristic bands for HLB-infected leaves were located in the near-infrared region compared to healthy leaves; and (3) the LASSO-PLSR model demonstrated high predictive accuracy for LCC estimation—for healthy leaves (Rv² = 0.956, RMSEv = 0.675) and for HLB-infected leaves (Rv² = 0.816, RMSEv = 4.614)—with performance being notably superior for healthy leaves (Rv² difference of +0.146). This research establishes a systematic quantification between hyperspectral and chlorophyll content, suggesting that hyperspectral-based LCC estimation can serve as a reliable indirect indicator for the early detection of HLB, with substantial practical application potential. Full article