Spread Of Huanglongbing Research Articles

ZnO quantum dots reduce acquisition of huanglongbing pathogen by Diaphorina citri.

Diaphorina citri Kuwayama is the main vector of the Huanglongbing (HLB) pathogen Candidatus Liberibacter asiaticus (CLas). Therefore, reducing CLas acquisition by D. citri is crucial for controlling the spread of HLB. This study aimed to investigate the effect of ZnO quantum dots (ZnO QDs) on CLas acquisition by D. citri. The results showed that ZnO QDs were absorbed by citrus plants and D. citri, inducing reactive oxygen species generation in the intestine and causing intestinal cell apoptosis. The uptake rate of CLas was reduced to 75% and 22.3% after treatment with 2 and 5 mg ∙ mL-1 ZnO QDs, respectively, compared with 100% in the control group. Transcription analysis showed significant changes in the expression of D. citri genes related to apoptosis, oxidative stress, and DNA replication and repair. The results suggested that ZnO QDs could efficiently reduce CLas acquisition by D. citri, providing a safe and reliable tool for HLB prevention and control. © 2024 Society of Chemical Industry.

Confirmation of Candidatus Liberibacter asiaticus in Asian Citrus Psyllids and Detection of Asian Citrus Psyllids in Commercial Citrus in Georgia (U.S.A.).

The Asian citrus psyllid (ACP) is the vector of Candidatus Liberibacter asiaticus (CLas), the causal agent of citrus greening or Huanglongbing (HLB), one of the most devastating citrus diseases worldwide. The citrus industry in Georgia (U.S.A.) is in the process of a rapid expansion, and based on experiences with HLB in Florida, there is great concern about the potential impacts of HLB on this emerging industry. Prior to 2023, ACP had been identified in residential citrus trees in isolated Georgia counties but little to no testing of psyllids for CLas had occurred. However, in 2023, one individual psyllid collected from Chatham County was confirmed positive for CLas by PCR and sequencing. Furthermore, during 2023, ACP adults and nymphs were identified for the first time in a Georgia commercial citrus grove. The finding of ACP in a commercial planting represents a significant risk for CLas dissemination, and thereby has the potential to stall the rapid expansion of Georgia's citrus industry. In the coming years, surveillance and testing of ACP from commercial groves will be essential for the early detection and management of HLB and its vector to reduce HLB spread within Georgia's commercial groves.

Modeling the Transmission Dynamics and Optimal Control Strategy for Huanglongbing

Huanglongbing (HLB), also known as citrus greening disease, represents a severe and imminent threat to the global citrus industry. With no complete cure currently available, effective control strategies are crucial. This article presents a transmission model of HLB, both with and without nutrient injection, to explore methods for controlling disease spread. By calculating the basic reproduction number (R0) and analyzing threshold dynamics, we demonstrate that the system remains globally stable when R0<1, but persists when R0>1. Sensitivity analyses reveal factors that significantly impact HLB spread on both global and local scales. We also propose a comprehensive optimal control model using the pontryagin minimum principle and validate its feasibility through numerical simulations. Results show that while removing infected trees and spraying insecticides can significantly reduce disease spread, a combination of measures, including the production of disease-free budwood and nursery trees, nutrient solution injection, removal of infected trees, and insecticide application, provides superior control and meets the desired control targets. These findings offer valuable insights for policymakers in understanding and managing HLB outbreaks.

Climate change mitigation and seasonal infestation patterns of citrus psyllid Diaphorina citri: implications for managing huanglongbing (HLB) disease in tangerine citrus

The citrus psyllid, Diaphorina citri, is a recognized vector of the devastating Huanglongbing (HLB) disease in citrus plants, posing a significant threat to global citrus production. As climate change continues to influence agroecological conditions, comprehending the population dynamics of this vector is imperative for effective disease management. This study delved into the relationship between climate variations and D. citri infestation patterns in tangerine citrus orchards from January to December 2018. Leveraging a dataset of 12 monthly observation sets, we comprehensively analyzed the abundance of the citrus psyllid population. Our investigation unveiled a clear association between climate variability and the incidence of citrus psyllid infestations and HLB occurrences. Importantly, our findings revealed that D. citri infestations were confined to the budding phase. Contrary to expectations, rainfall and temperature did not correlate positively with the development of the D. citri population or the prevalence of HLB disease in tangerine citrus. These results suggest other factors significantly affect HLB spread, impacting disease management. Further research is needed to identify and understand these factors, providing valuable insights for mitigating climate change’s impact on citrus cultivation.

Decoding Huanglongbing: Understanding the Origins, Impacts, and Remedies for Citrus Greening

Citrus cultivation is a vital component of the agricultural sector, offering significant nutritional and economic benefits. However, citrus plants face numerous disorders, including Huanglongbing (HLB), also known as citrus greening disease. HLB is a devastating disease caused by the bacterial species Candidatus Liberibacter asiaticus (Las), primarily transmitted by the citrus psyllid and grafting. Investigating the distribution and molecular characterization of HLB in various citrus varieties and psyllid populations is crucial. Molecular techniques and iodine starch staining have been used to detect HLB symptoms. Several studies have been designed to determine the incidence and severity of HLB symptoms in different citrus varieties and locations and estimate the psyllid population density in different citrus varieties. Furthermore, these studies established a correlation between the population of psyllids and the incidence and severity of HLB in different locations and these findings suggest a potential link between psyllid infestation and the prevalence of HLB. This study highlights the prevalence of HLB in various locations and varieties, providing insights into the distribution, severity, and correlation between psyllid populations and HLB incidence. The reliability of PCR testing for Las infection confirms its effectiveness. Such findings suggest implementing integrated pest management strategies, including monitoring and controlling psyllid populations, removing infected plants, and using certified disease-free planting materials to prevent HLB spread.

Possible economic losses on the oranges production chain of Peru due to introduction of Huanglongbing (HLB): Simulation of prospective scenarios to 2045

Huanglongbing (HLB) is a citrus disease known for causing significant production losses, and its potential introduction into Peru looms on the horizon. The aim of this study was to assess the potential economic losses within the Central Jungle's orange production chain, specifically in the Region Junín. This assessment involved simulating the spread of HLB under prospective scenarios spanning from 2026 to 2045, aiming to estimate the cost-benefit of preventing these losses through the implementation of a national phytosanitary program (PNF). The methodology employed in this study comprised administering questionnaires to local growers and estimating economic losses across three scenarios. The first scenario assumed a baseline production trend without HLB presence, while the second scenario considered an epidemiological situation with HLB but without the implementation of a PNF. The third scenario factored in HLB with varying degrees of adoption among PNF-affiliated growers. The findings highlight several risk factors contributing to the potential spread of HLB in Junín. The epidemiological model reveals that HLB can swiftly render young trees unproductive. Cumulatively, economic losses from 2026 to 2045 could reach a staggering US$ 371,146 thousand if no intervention takes place. However, this figure could be significantly reduced to US$ 44,890 thousand if 100% of growers embrace the PNF. Such public policy measures would not only prevent production losses but also generate substantial social benefits. These scenarios underscore the stark negative impacts HLB could inflict on the local orange production chain. The implementation of the PNF proves to be a critical intervention, preventing production losses, preserving jobs, and safeguarding related economic activities. Without timely public intervention, the economic losses at stake could render the agribusiness sector unsustainable.

Gene silencing of cathepsins B and L using CTV-based, plant-mediated RNAi interferes with ovarial development in Asian citrus psyllid (ACP), Diaphorina citri.

Diaphorina citri Kuwayama (Hemiptera: Liviidae) is a vector of the bacteria Candidatus Liberibacter americanus (CLam) and Candidatus Liberibacter asiaticus (CLas), which are phloem-restricted and associated with the most important and destructive worldwide citrus disease, Huanglongbing (HLB). Currently, no cure for HLB has been described. Therefore, measures have focused on reducing D. citri populations. In these insects, cathepsin B (DCcathB) and L (DCcathL) enzymes play an important role in digestion, and are involved in embryogenesis, immune defense, and ecdysis. In this study, we used a CTV-based vector to deliver dsRNA (CTV-dsRNA) into Citrus macrophylla plants targeting DCcathB and DCcathL genes in D. citri that fed on the phloem of these CTV-RNAi infected plants. Subsequently, we evaluated expression of DCcathB and DCcathL genes as well as the Vitellogenin (Vg) gene by RT-qPCR in D. citri fed on CTV-dsRNA occurring in plant phloem. It was found that a defective phenotype in D. citri females as a result of knockdown of DCcathB and DCcathL genes mediated by CTV dsRNA. These results showed that Psyllids fed on plants treated with the CTV-dsRNA exhibited downregulation of the Vg gene, one of the most important genes associated with embryogenic and female development, which was associated with dsRNA-mediated silencing of the two cathepsin genes. Based on our findings, a CTV-based strategy for delivering RNAi via plants that targets DCcathB and DCcathL genes may represent a suitable avenue for development of dsRNA-based tools to manage D. citri that limits the spread of HLB.

CsTPS21 encodes a jasmonate-responsive monoterpene synthase producing β-ocimene in citrus against Asian citrus psyllid

Huanglongbing (HLB), spread by the Asian citrus psyllid (ACP), is a widespread, devastating disease that causes significant losses in citrus production. Therefore, controlling the ACP infestation and HLB infection is very important for citrus production. The aim of our study was to identify any citrus volatile which could be used as a repellent or less attractant towards ACP, and to envisage the potential of this strategy to control HLB spread. The present study identified a terpene synthase (TPS)-encoding gene CsTPS21 in citrus plants, and this gene was predicted to encode a monoterpene synthase and had an amino acid sequence similar to β-ocimene synthase. CsTPS21 was significantly upregulated by ACP infestation and methyl jasmonic acid (MeJA) treatment but downregulated by salicylic acid (SA). Further heterologous gene expression studies in yeast cells and tobacco plants indicated that the protein catalyzed the formation of β-ocimene, which acted as an ACP repellent. Detailed analysis of tobacco overexpressing CsTPS21 showed that CsTPS21 synthesizing β-ocimene regulated jasmonic acid (JA)-associated pathways by increasing the JA accumulation and inducing the JA biosynthetic gene expression to defend against insect infestation. These findings provide a basis to plan strategies to manage HLB in the field using β-ocimene and CsTPS21 as candidates.

Silencing of V-ATPase-E gene causes midgut apoptosis of Diaphorina citri and affects its acquisition of Huanglongbing pathogen.

The Asian citrus psyllid, Diaphorina citri Kuwayama, is among the most important pests of citrus. It is the main vector of the Huanglongbing (HLB) pathogen Candidatus Liberibacter asiaticus (CLas), which causes severe losses in citrus crops. Control of D. citri is therefore of paramount importance to reduce the spread of HLB. In this regard, using RNA interference (RNAi) to silence target genes is a useful strategy to control psyllids. In this study, using RNAi, we examined the biological functions of the V-ATPase subunit E (V-ATP-E) gene of D. citri, including its effect on acquisition of CLas. The amino acid sequence of V-ATP-E from D. citri had high homology with proteins from other insects. V-ATP-E was expressed at all D. citri life stages analyzed, and the expression level in mature adults was higher than that of teneral adults. Silencing of V-ATP-E resulted in a significant increase in mortality, reduced body weight, and induced cell apoptosis of the D. citri midgut. The reduced expression of V-ATP-E was indicated to inhibit CLas passing through the midgut and into the hemolymph, leading to a majority of CLas being confined to the midgut. In addition, double-stranded RNA of D. citri V-ATP-E was safe to non-target parasitic wasps. These results suggest that V-ATP-E is an effective RNAi target that can be used in D. citri control to block CLas infection.

An Improved Recombinase Polymerase Amplification Coupled with Lateral Flow Assay for Rapid Field Detection of 'Candidatus Liberibacter asiaticus'.

Huanglongbing (HLB) is a destructive citrus disease that affects citrus production worldwide. 'Candidatus Liberibacter asiaticus' (CLas), a phloem-limited bacterium, is the associated causal agent of HLB. The current standard for detection of CLas is real-time quantitative polymerase chain reaction (qPCR) using either the CLas 16S rRNA gene or the ribonucleotide reductase (RNR) gene-specific primers/probe. qPCR requires well-equipped laboratories and trained personnel, which is not convenient for rapid field detection of CLas-infected trees. Recombinase polymerase amplification (RPA) assay is a fast, portable alternative to PCR-based diagnostic methods. In this study, an RPA assay was developed to detect CLas in crude citrus extracts utilizing isothermal amplification, without the need for DNA purification. Primers were designed to amplify a region of the CLas RNR gene, and a fluorescent labeled probe allowed for detection of the amplicon in real-time within 8 mins at 39°C. The assay was specific to CLas, and the sensitivity was comparable to qPCR, with a detection limit cycle threshold of 34. Additionally, the RPA assay was combined with a lateral flow device for a point-of-use assay that is field deployable. Both assays were 100% accurate in detecting CLas in fresh citrus crude extracts from leaf midribs and roots from five California strains of CLas tested in the Contained Research Facility in Davis, California. This assay will be important for distinguishing CLas-infected trees in California from those infected by other pathogens that cause similar disease symptoms and can help control HLB spread.

Kaolin particle films disrupt landing, settling behavior and feeding of Trioza erytrae on lemon plants.

The citrus greening disease or Huanglongbing (HLB) is the most devastating disease of citrus crops. Trioza erytreae is a vector of HLB. Since its introduction in Europe, the insect reached the northern region of Spain and the southern region of Portugal, threatening relevant citrus production areas. Limiting the spread of HLB vectors is mandatory to prevent this disease. In this work, we assessed the effect of kaolin, a white mineral clay, on the landing, settling behavior and feeding behavior of Trioza erytreae on lemon plants. After kaolin application, the number of plants on which the insect was found was significantly lower than on untreated plants in the laboratory and in the field. Moreover, there were significantly fewer T.erytreae and a shorter duration of phloem-related events on kaolin-treated than untreated plants. The use of kaolin could be a suitable and efficient tool for inclusion into integrated pest management programs or organic production to reduce populations of T.erytreae and subsequently limit the spread of HLB in citrus crops. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Entomopathogenic fungus disrupts the phloem-probing behavior of Diaphorina citri and may be an important biological control tool in citrus

Citrus is among the most important fruit crops worldwide; however, numerous pests and diseases affect the orchards, increasing production costs. The psyllid Diaphorina citri, is a vector of the phloem-limited bacteria ‘Candidatus Liberibacter spp.’, the causal agent of Huanglongbing (HLB) disease. The lack of a cure for HLB requires management of the vector, mainly by intensive use of chemical insecticides, leading to the selection of resistant populations. Our study determined the effects of the entomopathogenic fungus Cordyceps fumosorosea on the probing behavior of D. citri at different time points after the fungus was applied by spraying. The electrical penetration graph technique was used to monitor the stylet activities of D. citri after application of the microbiological product. The effects were more pronounced between 30 and 96 h after the insects were sprayed, with significant disruption of the stylet activities related to the phloem and directly associated with the transmission of HLB. Our study indicated that the microbiological product Challenger®, with the active ingredient C. fumosorosea fungus, can significantly change the probing behavior of D. citri, may be helpful in more-sustainable management of the vector, and can be used to reduce the spread of HLB.

Global dynamics and bifurcation analysis of an insect-borne plant disease model with two transmission routes

Huanglongbing (HLB) is a plant disease mainly spread by the insect-borne citrus psyllid. It is the most destructive citrus pathosystem worldwide. To understand the impact of sexual transmission on HLB dynamics, we propose a host–vector–HLB compartment model incorporating two transmission routes. The basic reproduction number [Formula: see text] is derived. Various interventions of the disease are assessed. We also investigate the effect of different incidence functions to simulate sexual transmission. For the case of sublinear incidence functions, the disease-free equilibrium is globally asymptotically stable (GAS) provided [Formula: see text]. For mass action incidence of sexual transmission, the endemic equilibrium is GAS provided [Formula: see text]. However, under nonlinear incidence, it is proved that the model may exhibit backward bifurcation. Theoretical and numerical studies reveal that (i) different forces of infection between heterosexual psyllids in the model may have a distinct impact on disease dynamics; (ii) sensitivity analysis shows that for [Formula: see text], the transmission rate between host and vector is more sensitive parameter than that between heterosexual psyllids; (iii) if the sexual transmission is ignored, the disease burden is likely to be underestimated in comparison with realistic scenarios; (iv) in the absence of chemical insecticides, the combined use of yellow sticky traps and injection of nutrient solutions can be more effective in suppressing the spread of HLB. These findings provide valuable insights for public policymakers to determine the long-term viability of implemented HLB management strategies and highlight the urgency of finding sustainable HLB solutions.

Ubiquitin-proteasome pathway annotation in Diaphorina citri canreveal potential targets for RNAi-based pest management.

Ubiquitination is an ATP-dependent process that targets proteins for degradation by the proteasome. Here, we annotated 15 genes from the ubiquitin-proteasome pathway in the Asian citrus psyllid, Diaphorina citri. This psyllid vector has come to prominence in the last decade owing to its role in the transmission of the devastating bacterial pathogen, Candidatus Liberibacter asiaticus (CLas). Infection of citrus crops by this pathogen causes Huanglongbing (HLB), or citrus greening disease, and results in the eventual death of citrus trees. The identification and correct annotation of these genes in D.citri will be useful for functional genomic studies to aid the development of RNAi-based management strategies aimed at reducing the spread of HLB. Investigating the effects of CLas infection on the expression of ubiquitin-proteasome pathway genes may provide new information about the role these genes play in the acquisition and transmission of CLas by D.citri.

Osmotic stress induces long-term biofilm survival in Liberibacter crescens

Citrus greening, also known as Huanglongbing (HLB), is a devastating citrus plant disease caused predominantly by Liberibacter asiaticus. While nearly all Liberibacter species remain uncultured, here we used the culturable L. crescens BT-1 as a model to examine physiological changes in response to the variable osmotic conditions and nutrient availability encountered within the citrus host. Similarly, physiological responses to changes in growth temperature and dimethyl sulfoxide concentrations were also examined, due to their use in many of the currently employed therapies to control the spread of HLB. Sublethal heat stress was found to induce the expression of genes related to tryptophan biosynthesis, while repressing the expression of ribosomal proteins. Osmotic stress induces expression of transcriptional regulators involved in expression of extracellular structures, while repressing the biosynthesis of fatty acids and aromatic amino acids. The effects of osmotic stress were further evaluated by quantifying biofilm formation of L. crescens in presence of increasing sucrose concentrations at different stages of biofilm formation, where sucrose-induced osmotic stress delayed initial cell attachment while enhancing long-term biofilm viability. Our findings revealed that exposure to osmotic stress is a significant contributing factor to the long term survival of L. crescens and, possibly, to the pathogenicity of other Liberibacter species.

Genomic identification, annotation, and comparative analysis of Vacuolar-type ATP synthase subunits in Diaphorinacitri.

The hemipteran insect Diaphorina citri, or Asian citrus psyllid, is a vector for Candidatus Liberibacter asiaticus (CLas), the bacterium causing citrus greening disease, or Huanglongbing (HLB). Millions of citrus trees have been destroyed, and every grove in Florida, USA, has been directly affected by this disease. In eukaryotes, vacuolar-type ATP synthase (V-ATPase) is an abundant heterodimeric enzyme that serves the cell with essential compartment acidification through the active processes that transport protons across the membrane. Fifteen putative V-ATPase genes in the D. citri genome were manually curated. Comparative genomic analysis revealed that D. citri V-ATPase subunits share domains and motifs with other insects, including the V-ATPase-A superfamily domain. Phylogenetic analysis separates D. citri V-ATPase subunits into expected clades with orthologous sequences. Annotation of the D. citri genome is a critical step towards developing directed pest management strategies to reduce the spread of HLB throughout the citrus industry.

Modelling and stationary distribution of a stochastic citrus greening epidemic model with resistance

Citrus greening disease (also known as Huanglongbing (HLB)) is an insect-borne disease worldwide, and it is the greatest threat to the global citrus industry, with no resistant commercial citrus varieties and no curable chemicals. In this paper, a stochastic SEII-SI compartmental model for the spread of HLB between its vector (psyllids) and host (citrus trees) was considered. The effects of incubation and infectious periods and insecticides resistance were involved in the model. The existence of a unique global positive solution was discussed. Sufficient criteria were analyzed and established for the persistence and extinction in the mean. By using suitable Lyapunov functions, a unique stationary distribution was proven to exist, for the stochastic model. Model analysis indicated that increasing the intensity of the noises could benefit and accelerate the extinction of disease. However, insecticide resistance could increase the risk of epidemic prevalence and be detrimental to disease control. Some numerical simulations were presented to validate the theoretical analysis.

Cultural Management of Huanglongbing: Current Status and Ongoing Research.

Huanglongbing (HLB), formerly known as greening, is a bacterial disease restricted to some Asian and African regions until two decades ago. Nowadays, associated bacteria and their vectors have spread to almost all citrus-producing regions, and it is currently considered the most devastating citrus disease. HLB management can be approached in terms of prevention, limiting or avoiding pathogen and associated vectors to reach an area, or in terms of control, trying to reduce the impact of the disease by adopting different cultural strategies depending on infestation/infection levels. In both cases, control of psyllid populations is currently the best way to stop HLB spread. Best cultural actions (CHMAs, TPS system) to attain this goal and, thus, able to limit HLB spread, and ongoing research in this regard is summarized in this review.

Controlling Citrus Huanglongbing: Green Sustainable Development Route Is the Future.

Huanglongbing (HLB) is the most severe bacterial disease of citrus crops caused by Candidatus Liberibacter spp. It causes a reduction in fruit yield, poor fruit quality, and even plants death. Due to the lack of effective medicine, HLB is also called citrus “AIDS.” Currently, it is essential for the prevention and control of HLB to use antibiotics and pesticides while reducing the spread of HLB by cultivating pathogen-free seedlings, removing disease trees, and killing Asian citrus psyllid (ACP). New compounds [e.g., antimicrobial peptides (AMPs) and nanoemulsions] with higher effectiveness and less toxicity were also found and they have made significant achievements. However, further evaluation is required before these new antimicrobial agents can be used commercially. In this review, we mainly introduced the current strategies from the aspects of physical, chemical, and biological and discussed their environmental impacts. We also proposed a green and ecological strategy for controlling HLB basing on the existing methods and previous research results.

Citrus Huanglongbing (HLB) and the Brazilian Efforts to Overcome the Disease

Recorded in Brazil since 2004, Huanglongbing (HLB), or simply Greening, is the most impacting disease in citrus production worldwide. It induces qualitative and quantitative losses in production, but also can be lethal to the infected citrus plant. The disease is caused by phloem-limited bacteria with three identified species, Candidatus Liberibacter asiaticus (CLas), Ca. L. africanus (CLaf), and Ca. L. americanus (CLam). CLas and CLam are reported in Brazil, being vectored by the Asian citrus psyllid Diaphorina citri. HLB-infected citrus exhibit blotchy mottling with green islands on leaves, and small and lopsided fruits. As the infection progresses, excessive fruit drop and dead branches are frequently observed, shortening the trees' lifespan and reducing fruit yield and quality. HLB occurrence is restricted to the States of São Paulo, Minas Gerais, Mato Grosso do Sul and Paraná, which corresponds to more than 85% of citrus production in Brazil. Although citrus production is concentrated in these states, commercial citrus groves are present in 85% of the microregions of Brazil, reinforcing the economic and social importance of citrus for the country. Thus, in addition to the economic damage already caused to the national citrus industry, the spread of HLB to other regions of Brazil represents a great risk to the economic and food security of these non-affected regions. For this reason, the management of HLB is supported by legislative force, both at the federal and state levels. In 2008, based on scientific knowledge at the time, the Brazilian Ministry of Agriculture published a Normative Instruction 53 (IN53) which established criteria related to HLB surveillance and control, imposing the obligation to carry out periodic phytosanitary inspections, eradication of symptomatic hosts and planting HLB-free nursery trees. The implementation of IN53 has already resulted in the eradication of 55.5 million HLB-infected citrus plants in the State of São Paulo alone in the period from 2007 to 2019. In May 2021, IN53 was revoked and Portaria 317 was published. This new policy establishes the National Programme for HLB Prevention and Control. It addresses the problem according to the HLB status in each State, with or without the disease, and sets the general guidelines for local control actions.<br/> In view of the economic importance and complexity of this pathosystem, the disease has required concerted mobilization of the research community and inter-institutional cooperation, which has been working intensively to understand all the components directly and indirectly involved with the pathosystem. Also, a major cooperation effort is needed to gather all the information to develop and/or improve technologies and cultural practices to fight the disease better and reduce its impacts as much as possible. Here we present some of these efforts which are being carried out to develop short, medium and long term solutions for HLB control and management in areas of occurrence, as well as for surveillance and risk mitigation in non-affected areas.