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Alquézar B, Carmona L, Bennici S, Miranda MP, Bassanezi RB, Peña L. Cultural Management of Huanglongbing: Current Status and Ongoing Research. PHYTOPATHOLOGY 2022; 112:11-25. [PMID: 34645319 DOI: 10.1094/phyto-08-21-0358-ia] [Citation(s) in RCA: 15] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
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.
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Affiliation(s)
- Berta Alquézar
- Laboratório de Biotecnologia Vegetal, Pesquisa & Desenvolvimento, Fundo de Defesa da Citricultura (Fundecitrus), Vila Melhado, 14807-040 Araraquara, São Paulo, Brazil
- Instituto de Biología Molecular y Celular de Plantas (IBMCP), Consejo Superior de Investigaciones Científicas (CSIC) Universidad Politécnica de Valencia (UPV), 46022 Valencia, Spain
| | - Lourdes Carmona
- Instituto de Biología Molecular y Celular de Plantas (IBMCP), Consejo Superior de Investigaciones Científicas (CSIC) Universidad Politécnica de Valencia (UPV), 46022 Valencia, Spain
| | - Stefania Bennici
- Instituto de Biología Molecular y Celular de Plantas (IBMCP), Consejo Superior de Investigaciones Científicas (CSIC) Universidad Politécnica de Valencia (UPV), 46022 Valencia, Spain
| | - Marcelo P Miranda
- Instituto de Biología Molecular y Celular de Plantas (IBMCP), Consejo Superior de Investigaciones Científicas (CSIC) Universidad Politécnica de Valencia (UPV), 46022 Valencia, Spain
| | - Renato B Bassanezi
- Instituto de Biología Molecular y Celular de Plantas (IBMCP), Consejo Superior de Investigaciones Científicas (CSIC) Universidad Politécnica de Valencia (UPV), 46022 Valencia, Spain
| | - Leandro Peña
- Laboratório de Biotecnologia Vegetal, Pesquisa & Desenvolvimento, Fundo de Defesa da Citricultura (Fundecitrus), Vila Melhado, 14807-040 Araraquara, São Paulo, Brazil
- Instituto de Biología Molecular y Celular de Plantas (IBMCP), Consejo Superior de Investigaciones Científicas (CSIC) Universidad Politécnica de Valencia (UPV), 46022 Valencia, Spain
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Hu B, Rao MJ, Deng X, Pandey SS, Hendrich C, Ding F, Wang N, Xu Q. Molecular signatures between citrus and Candidatus Liberibacter asiaticus. PLoS Pathog 2021; 17:e1010071. [PMID: 34882744 PMCID: PMC8659345 DOI: 10.1371/journal.ppat.1010071] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Citrus Huanglongbing (HLB), also known as citrus greening, is one of the most devastating citrus diseases worldwide. Candidatus Liberibacter asiaticus (CLas) is the most prevalent strain associated with HLB, which is yet to be cultured in vitro. None of the commercial citrus cultivars are resistant to HLB. The pathosystem of Ca. Liberibacter is complex and remains a mystery. In this review, we focus on the recent progress in genomic research on the pathogen, the interaction of host and CLas, and the influence of CLas infection on the transcripts, proteins, and metabolism of the host. We have also focused on the identification of candidate genes for CLas pathogenicity or the improvements of HLB tolerance in citrus. In the end, we propose potentially promising areas for mechanistic studies of CLas pathogenicity, defense regulators, and genetic improvement for HLB tolerance/resistance in the future.
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Affiliation(s)
- Bin Hu
- Key Laboratory of Horticultural Plant Biology (Ministry of Education), Key Laboratory of Biology and Genetic Improvement of Horticultural Crops (Ministry of Agriculture), Huazhong Agricultural University, Wuhan, Hubei, China
| | - Muhammad Junaid Rao
- Key Laboratory of Horticultural Plant Biology (Ministry of Education), Key Laboratory of Biology and Genetic Improvement of Horticultural Crops (Ministry of Agriculture), Huazhong Agricultural University, Wuhan, Hubei, China
| | - Xiuxin Deng
- Key Laboratory of Horticultural Plant Biology (Ministry of Education), Key Laboratory of Biology and Genetic Improvement of Horticultural Crops (Ministry of Agriculture), Huazhong Agricultural University, Wuhan, Hubei, China
| | - Sheo Shankar Pandey
- Citrus Research and Education Center, Department of Microbiology and Cell Science, Institute of Food and Agricultural Sciences, University of Florida, Lake Alfred, Florida, United States of America
| | - Connor Hendrich
- Citrus Research and Education Center, Department of Microbiology and Cell Science, Institute of Food and Agricultural Sciences, University of Florida, Lake Alfred, Florida, United States of America
| | - Fang Ding
- Hubei Key Laboratory of Plant Pathology, Huazhong Agricultural University, Wuhan, Hubei, China
| | - Nian Wang
- Citrus Research and Education Center, Department of Microbiology and Cell Science, Institute of Food and Agricultural Sciences, University of Florida, Lake Alfred, Florida, United States of America
| | - Qiang Xu
- Key Laboratory of Horticultural Plant Biology (Ministry of Education), Key Laboratory of Biology and Genetic Improvement of Horticultural Crops (Ministry of Agriculture), Huazhong Agricultural University, Wuhan, Hubei, China
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Miranda MP, Eduardo WI, Tomaseto AF, Volpe HXL, Bachmann L. Frequency of processed kaolin application to prevent Diaphorina citri infestation and dispersal in flushing citrus orchards. PEST MANAGEMENT SCIENCE 2021; 77:5396-5406. [PMID: 34313389 DOI: 10.1002/ps.6579] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/01/2021] [Accepted: 07/27/2021] [Indexed: 06/13/2023]
Abstract
BACKGROUND Processed kaolin is a promising tactic that can be utilized for managing Diaphorina citri Kuwayama infestation. However, the frequency of kaolin application to protect citrus trees during flushing remains undetermined. The objective of this study was to ascertain the frequency of kaolin application (2%) required to reduce D. citri infestation and dispersal in flushing citrus orchards and to measure the spectral reflectance of kaolin-sprayed leaves. RESULTS Trees sprayed with kaolin at 7- and 14-day intervals showed an 80% psyllid reduction compared to untreated trees. In addition, there was lower psyllid dispersal in the kaolin-sprayed plots. Spectral measurements (wavelengths between 320 and 700 nm) showed an increased reflectance of 35.4% (adaxial leaf side) and 21.9% (abaxial leaf side) in mature leaves, and 9% (adaxial leaf side) and 2.2% (abaxial leaf side) in kaolin-sprayed immature leaves compared to untreated trees. CONCLUSION Application of kaolin (2%) at 7- and 14-day intervals can be an important and sustainable tool for reducing D. citri infestation and dispersal in flushing citrus orchards. The reduced D. citri population in plots with both kaolin application intervals may be related to the visual effect (whitish aspect) and increased light reflectance in citrus trees, which are probably the main mechanisms by which kaolin interferes on D. citri host finding behavior. © 2021 Society of Chemical Industry.
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Affiliation(s)
- Marcelo Pedreira Miranda
- Department of Research and Development, Fund for Citrus Protection - Fundecitrus, Araraquara, Brazil
| | - Wellington Ivo Eduardo
- Department of Research and Development, Fund for Citrus Protection - Fundecitrus, Araraquara, Brazil
| | - Arthur Fernando Tomaseto
- Department of Research and Development, Fund for Citrus Protection - Fundecitrus, Araraquara, Brazil
| | | | - Luciano Bachmann
- School of Philosophy, Sciences and Languages of Ribeirão Preto, University of São Paulo, Ribeirão Preto, Brazil
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Lopes SA, Cifuentes-Arenas JC. Protocol for Successful Transmission of ' Candidatus Liberibacter asiaticus' from Citrus to Citrus Using Diaphorina citri. PHYTOPATHOLOGY 2021; 111:2367-2374. [PMID: 33938771 DOI: 10.1094/phyto-02-21-0076-r] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
A protocol to successfully transmit the huanglongbing (HLB) pathogen, 'Candidatus Liberibacter asiaticus', between citrus plants by using the Asian citrus psyllid (ACP) and an alternative way to help growers control ACP are proposed. Best results were obtained when pathogen acquisition by adults reared on fully symptomatic 'Ca. Liberibacter asiaticus'-positive plants, latency, and inoculation occurred at ambient air temperatures ranging from 24 to 28°C and when a single infective adult ACP was confined for 7 days on soft, newly developing vegetative shoots (stages v2 to v4). No infection resulted from confinement of infective ACP adults on mature leaves (stage v6). Under the described conditions, single ACP adults could successfully transmit 'Ca. Liberibacter asiaticus' to an average of 56.5% (35 to 83%) of plantlets with v2 to v4 shoots growing in 0.3-liter tubes and to 80.5% (76 to 86%) of plants with v2 to v4 shoots growing in 4.7-liter pots. The use of single insects and plantlets reduces labor, space, and other resources necessary to undertake transmission tests. It also reduces time needed for transmission studies and should help accelerate research on HLB. The results were used to develop an index for favorability to infection (IFI) to determine orchard vulnerabilities to 'Ca. Liberibacter asiaticus'. The IFI is based on the heterogeneous population of new shoots that occurs on tree canopies and may offer alternative or complementary alternatives to the laborious and costly insect surveys currently used in most instances to determine threshold levels for insecticide applications.
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Ribeiro C, Xu J, Teper D, Lee D, Wang N. The transcriptome landscapes of citrus leaf in different developmental stages. PLANT MOLECULAR BIOLOGY 2021; 106:349-366. [PMID: 33871796 DOI: 10.1007/s11103-021-01154-8] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/22/2021] [Accepted: 04/12/2021] [Indexed: 06/12/2023]
Abstract
The temporal expression profiles of citrus leaves explain the sink-source transition of immature leaves to mature leaves and provide knowledge regarding the differential responses of mature and immature leaves to biotic stress such as citrus canker and Asian citrus psyllid (Diaphorina citri). Citrus is an important fruit crop worldwide. Different developmental stages of citrus leaves are associated with distinct features, such as differences in susceptibilities to pathogens and insects, as well as photosynthetic capacity. Here, we investigated the mechanisms underlying these distinctions by comparing the gene expression profiles of mature and immature citrus leaves. Immature (stages V3 and V4), transition (stage V5), and mature (stage V6) Citrus sinensis leaves were chosen for RNA-seq analyses. Carbohydrate biosynthesis, photosynthesis, starch biosynthesis, and disaccharide metabolic processes were enriched among the upregulated differentially expressed genes (DEGs) in the V5 and V6 stages compared with that in the V3 and V4 stages. Glucose level was found to be higher in V5 and V6 than in V3 and V4. Among the four stages, the largest number of DEGs between contiguous stages were identified between V5 and V4, consistent with a change from sink to source, as well as with the sucrose and starch quantification data. The differential expression profiles related to cell wall synthesis, secondary metabolites such as flavonoids and terpenoids, amino acid biosynthesis, and immunity between immature and mature leaves may contribute to their different responses to Asian citrus psyllid infestation. The expression data suggested that both the constitutive and induced gene expression of immunity-related genes plays important roles in the greater resistance of mature leaves against Xanthomonas citri compared with immature leaves. The gene expression profiles in the different stages can help identify stage-specific promoters for the manipulation of the expression of citrus traits according to the stage. The temporal expression profiles explain the sink-source transition of immature leaves to mature leaves and provide knowledge regarding the differential responses to biotic stress.
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Affiliation(s)
- Camila Ribeiro
- Citrus Research & Education Center, Department of Microbiology and Cell Science, Institute of Food and Agricultural Sciences (IFAS), University of Florida, Lake Alfred, FL, 33850, USA
| | - Jin Xu
- Citrus Research & Education Center, Department of Microbiology and Cell Science, Institute of Food and Agricultural Sciences (IFAS), University of Florida, Lake Alfred, FL, 33850, USA
| | - Doron Teper
- Citrus Research & Education Center, Department of Microbiology and Cell Science, Institute of Food and Agricultural Sciences (IFAS), University of Florida, Lake Alfred, FL, 33850, USA
| | - Donghwan Lee
- Citrus Research & Education Center, Department of Microbiology and Cell Science, Institute of Food and Agricultural Sciences (IFAS), University of Florida, Lake Alfred, FL, 33850, USA
| | - Nian Wang
- Citrus Research & Education Center, Department of Microbiology and Cell Science, Institute of Food and Agricultural Sciences (IFAS), University of Florida, Lake Alfred, FL, 33850, USA.
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Pandey SS, Nogales da Costa Vasconcelos F, Wang N. Spatiotemporal Dynamics of ' Candidatus Liberibacter asiaticus' Colonization Inside Citrus Plant and Huanglongbing Disease Development. PHYTOPATHOLOGY 2021; 111:921-928. [PMID: 33174821 DOI: 10.1094/phyto-09-20-0407-r] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
'Candidatus Liberibacter asiaticus' (CLas), the causal agent of citrus huanglongbing (HLB), colonizes inside the phloem and is naturally transmitted by the Asian citrus psyllid (ACP). Here, we investigated spatiotemporal CLas colonization in different tissues after ACP transmission. Of the nine plants successfully infected via ACP transmission, CLas was detected in the roots of all trees at 75 days postremoval of ACPs (DPR) but in the mature leaf of only one tree; this finding is consistent with the model that CLas moves passively from source to sink tissues. At 75 and 365 DPR, CLas was detected in 11.1 and 43.1% of mature leaves not fed on by ACPs during transmission, respectively, unveiling active movement to the source tissue. The difference in colonization timing of sink and source tissues indicates that CLas is capable of both passive and active movement, with passive movement being dominant. At 225 DPR, leaves fed on by ACPs during the young stage showed the highest ratio of HLB symptomatic leaves and the highest CLas titer, followed by leaves that emerged after ACP removal and mature leaves not fed on by ACPs. Importantly, our data showed that ACPs were unable to transmit CLas via feeding on mature leaves. It is estimated that it takes 3 years at most for CLas to infect the whole tree. Overall, spatiotemporal detection of CLas in different tissues after ACP transmission helps visualize the infection process of CLas in planta and subsequent HLB symptom development and provides evidence showing that young leaves should be the focus of HLB management.
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Affiliation(s)
- Sheo Shankar Pandey
- Citrus Research and Education Center, Department of Microbiology and Cell Science, University of Florida, Lake Alfred, FL 33850
| | | | - Nian Wang
- Citrus Research and Education Center, Department of Microbiology and Cell Science, University of Florida, Lake Alfred, FL 33850
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Root samples provide early and improved detection of Candidatus Liberibacter asiaticus in Citrus. Sci Rep 2020; 10:16982. [PMID: 33046775 PMCID: PMC7550583 DOI: 10.1038/s41598-020-74093-x] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2020] [Accepted: 09/23/2020] [Indexed: 11/08/2022] Open
Abstract
Huanglongbing (HLB), or Citrus Greening, is one of the most devastating diseases affecting agriculture today. Widespread throughout Citrus growing regions of the world, it has had severe economic consequences in all areas it has invaded. With no treatment available, management strategies focus on suppression and containment. Effective use of these costly control strategies relies on rapid and accurate identification of infected plants. Unfortunately, symptoms of the disease are slow to develop and indistinct from symptoms of other biotic/abiotic stressors. As a result, diagnosticians have focused on detecting the pathogen, Candidatus Liberibacter asiaticus, by DNA-based detection strategies utilizing leaf midribs for sampling. Recent work has shown that fibrous root decline occurs in HLB-affected trees before symptom development among leaves. Moreover, the pathogen, Ca. Liberibacter asiaticus, has been shown to be more evenly distributed within roots than within the canopy. Motivated by these observations, a longitudinal study of young asymptomatic trees was established to observe the spread of disease through time and test the relative effectiveness of leaf- and root-based detection strategies. Detection of the pathogen occurred earlier, more consistently, and more often in root samples than in leaf samples. Moreover, little influence of geography or host variety was found on the probability of detection.
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Andrade MO, Pang Z, Achor DS, Wang H, Yao T, Singer BH, Wang N. The flagella of 'Candidatus Liberibacter asiaticus' and its movement in planta. MOLECULAR PLANT PATHOLOGY 2020; 21:109-123. [PMID: 31721403 PMCID: PMC6913195 DOI: 10.1111/mpp.12884] [Citation(s) in RCA: 25] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
Citrus huanglongbing (HLB) is the most devastating citrus disease worldwide. 'Candidatus Liberibacter asiaticus' (Las) is the most prevalent HLB causal agent that is yet to be cultured. Here, we analysed the flagellar genes of Las and Rhizobiaceae and observed two characteristics unique to the flagellar proteins of Las: (i) a shorter primary structure of the rod capping protein FlgJ than other Rhizobiaceae bacteria and (ii) Las contains only one flagellin-encoding gene flaA (CLIBASIA_02090), whereas other Rhizobiaceae species carry at least three flagellin-encoding genes. Only flgJAtu but not flgJLas restored the swimming motility of Agrobacterium tumefaciens flgJ mutant. Pull-down assays demonstrated that FlgJLas interacts with FlgB but not with FliE. Ectopic expression of flaALas in A. tumefaciens mutants restored the swimming motility of ∆flaA mutant and ∆flaAD mutant, but not that of the null mutant ∆flaABCD. No flagellum was observed for Las in citrus and dodder. The expression of flagellar genes was higher in psyllids than in planta. In addition, western blotting using flagellin-specific antibody indicates that Las expresses flagellin protein in psyllids, but not in planta. The flagellar features of Las in planta suggest that Las movement in the phloem is not mediated by flagella. We also characterized the movement of Las after psyllid transmission into young flush. Our data support a model that Las remains inside young flush after psyllid transmission and before the flush matures. The delayed movement of Las out of young flush after psyllid transmission provides opportunities for targeted treatment of young flush for HLB control.
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Affiliation(s)
- Maxuel O. Andrade
- Citrus Research and Education CenterDepartment of Microbiology and Cell ScienceUniversity of Florida/Institute of Food and Agricultural SciencesLake AlfredFLUSA
| | - Zhiqian Pang
- Citrus Research and Education CenterDepartment of Microbiology and Cell ScienceUniversity of Florida/Institute of Food and Agricultural SciencesLake AlfredFLUSA
| | - Diann S. Achor
- Citrus Research and Education CenterDepartment of Microbiology and Cell ScienceUniversity of Florida/Institute of Food and Agricultural SciencesLake AlfredFLUSA
| | - Han Wang
- Citrus Research and Education CenterDepartment of Microbiology and Cell ScienceUniversity of Florida/Institute of Food and Agricultural SciencesLake AlfredFLUSA
| | - Tingshan Yao
- Citrus Research and Education CenterDepartment of Microbiology and Cell ScienceUniversity of Florida/Institute of Food and Agricultural SciencesLake AlfredFLUSA
- National Engineering Research Center for Citrus, Citrus Research Institute, Southwest UniversityChongqing400712People’s Republic of China
| | - Burton H. Singer
- Emerging Pathogens InstituteUniversity of FloridaGainesvilleFLUSA
| | - Nian Wang
- Citrus Research and Education CenterDepartment of Microbiology and Cell ScienceUniversity of Florida/Institute of Food and Agricultural SciencesLake AlfredFLUSA
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Cifuentes-Arenas JC, Beattie GAC, Peña L, Lopes SA. Murraya paniculata and Swinglea glutinosa as Short-Term Transient Hosts of ' Candidatus Liberibacter asiaticus' and Implications for the Spread of Huanglongbing. PHYTOPATHOLOGY 2019; 109:2064-2073. [PMID: 31425000 DOI: 10.1094/phyto-06-19-0216-r] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Murraya paniculata and Swinglea glutinosa are aurantioid hosts of the Asian citrus psyllid (ACP) Diaphorina citri, the principal vector of 'Candidatus Liberibacter asiaticus' (Las). Las is the pathogen associated with huanglongbing (HLB), the Asian form of which is the most devastating disease of Citrus species and cultivars (Rutaceae: Aurantioideae). M. paniculata is a common ornamental and S. glutinosa is grown as an ornamental, a citrus rootstock, and a hedgerow fence plant. Because of the uncertain status of these plants as reservoirs of Las, a series of cross-inoculation bioassays were carried out in different environments, using infected Valencia sweet orange (Citrus × aurantium) infected shoot tops as a source of inoculum and D. citri nymphs and adults reared on M. paniculata and S. glutinosa to inoculate pathogen-free Valencia orange plantlets. In contrast to sweet orange, Las was more unevenly distributed and reached much lower titers in M. paniculata and S. glutinosa. Infections in M. paniculata and S. glutinosa were also transient. Very few insects that successfully acquired Las from M. paniculata and S. glutinosa were able to transmit the pathogen to healthy citrus. Transmission rates were low from M. paniculata (1.0%) and S. glutinosa (2.0%) and occurred only in a controlled environment highly favorable to Las and ACP using 10-day-old adults that completed their life cycle on Las-positive plants. Our study showed that in HLB-endemic areas, M. paniculata and S. glutinosa can be deemed as epidemiologically dead-end hosts for Las and are not important alternative hosts of the pathogen for transmission to citrus. However, under a combination of conditions highly favorable to Las infection and transmission and in the absence of effective quarantine procedures, these plants could eventually serve as carriers of Las to regions currently free from HLB.
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Affiliation(s)
- Juan Camilo Cifuentes-Arenas
- School of Agricultural and Veterinarian Sciences, São Paulo State University, Jaboticabal, São Paulo, Brazil
- Departamento Científico, Fundecitrus, Araraquara, São Paulo, Brazil
| | | | - Leandro Peña
- Laboratório de Biotecnologia Vegetal, Pesquisa and Desenvolvimento, Fundecitrus, Araraquara, São Paulo, Brazil
- Instituto de Biología Molecular y Celular de Plantas, Consejo Superior de Investigaciones Científicas, Universidad Politécnica de Valencia, Valencia, España
| | - Silvio Aparecido Lopes
- School of Agricultural and Veterinarian Sciences, São Paulo State University, Jaboticabal, São Paulo, Brazil
- Departamento Científico, Fundecitrus, Araraquara, São Paulo, Brazil
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Andrade M, Wang N. The Tad Pilus Apparatus of ' Candidatus Liberibacter asiaticus' and Its Regulation by VisNR. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2019; 32:1175-1187. [PMID: 30925227 DOI: 10.1094/mpmi-02-19-0052-r] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Citrus huanglongbing (HLB) is one of the most destructive diseases affecting citrus plants. 'Candidatus Liberibacter asiaticus', an uncultivated α-proteobacteria, is the most widely spread causal agent of HLB and is transmitted by the Asian citrus psyllid Diaphorina citri. 'Ca. L. asiaticus' attachment to the psyllid midgut is believed to be critical to further infect other organs, including the salivary gland. In this study, the type IVc tight adherence (Tad) pilus locus encoded by 'Ca. L. asiaticus' was characterized. The Tad loci are conserved among members of Rhizobiaceae, including 'Ca. L. asiaticus' and Agrobacterium spp. Ectopic expression of the 'Ca. L. asiaticus' cpaF gene, an ATPase essential for the biogenesis and secretion of the Tad pilus, restored the adherence phenotype in cpaF mutant of A. tumefaciens, indicating CpaF of 'Ca. L. asiaticus' was functional and critical for bacterial adherence mediated by Tad pilus. Quantitative reverse transcription PCR (qRT-PCR) analysis revealed that 'Ca. L. asiaticus' Tad pilus-encoding genes and 'Ca. L. asiaticus' pilin gene flp3 were upregulated in psyllids compared with in planta. A bacterial one-hybrid assay showed that 'Ca. L. asiaticus' VisN and VisR, members of the LuxR transcriptional factor family, were bound to the flp3 promoter. VisNR regulate flp3. Negative regulation of the flp3 promoter by both VisN and VisR was demonstrated using a shuttle strategy, with analysis of the phenotypes and immunoblotting together with quantification of the expression of the flp3 promoter fused to the β-galactosidase reporter gene. Comparative expression analysis confirmed that 'Ca. L. asiaticus' visNR was less expressed in the psyllid than in the plant host. Further, motility and biofilm phenotypes of the visNR mutant of A. tumefaciens were fully complemented by expressing 'Ca. L. asiaticus' visNR together. The physical interaction between VisN and VisR was confirmed by pull-down and stability assays. The interaction of the flp3 promoter with VisR was verified by electrophoretic mobility shift assay. Taken together, the results revealed the contribution of the Tad pilus apparatus in the colonization of the insect vector by 'Ca. L. asiaticus' and shed light on the involvement of VisNR in regulation of the Tad locus.
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Affiliation(s)
- Maxuel Andrade
- Citrus Research and Education Center (CREC), Department of Microbiology and Cell Science, Institute of Food and Agricultural Sciences, University of Florida, Lake Alfred, FL 33850, U.S.A
| | - Nian Wang
- Citrus Research and Education Center (CREC), Department of Microbiology and Cell Science, Institute of Food and Agricultural Sciences, University of Florida, Lake Alfred, FL 33850, U.S.A
- China-USA Citrus Huanglongbing Joint Laboratory (A joint laboratory of the University of Florida Institute of Food and Agricultural Sciences and Gannan Normal University), National Navel Orange Engineering Research Center, Gannan Normal University, Ganzhou 341000, China
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The Probing Behavior Component of Disease Transmission in Insect-Transmitted Bacterial Plant Pathogens. INSECTS 2019; 10:insects10070212. [PMID: 31331012 PMCID: PMC6681269 DOI: 10.3390/insects10070212] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/22/2019] [Revised: 07/08/2019] [Accepted: 07/15/2019] [Indexed: 11/16/2022]
Abstract
Insects can be effective vectors of plant diseases and this may result in billions of dollars in lost agricultural productivity. New, emerging or introduced diseases will continue to cause extensive damage in afflicted areas. Understanding how the vector acquires the pathogen and inoculates new hosts is critical in developing effective management strategies. Management may be an insecticide applied to kill the vector or a host plant resistance mechanism to make the host plant less suitable for the vector. In either case, the tactic must act before the insect performs the key behavior(s) resulting in either acquisition or transmission. This requires knowledge of the timing of behaviors the insect uses to probe the plant and commence ingestion. These behaviors are visualized using electropenetrography (EPG), wherein the plant and insect become part of an electrical circuit. With the tools to define specific steps in the probing process, we can understand the timing of acquisition and inoculation. With that understanding comes the potential for more relevant testing of management strategies, through insecticides or host plant resistance. The primary example will be Candidatus Liberibacter asiaticus transmitted by Diaphorina citri Kuwayama in the citrus agroecosystem, with additional examples used as appropriate.
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Hall DG, Moulton KM. Transmission Rates of 'Candidatus Liberibacter asiaticus' to Greenhouse Seedlings by Laboratory Colonies of Asian Citrus Psyllid (Hemiptera: Liviidae). JOURNAL OF ECONOMIC ENTOMOLOGY 2018; 111:2546-2552. [PMID: 30124860 DOI: 10.1093/jee/toy240] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/10/2018] [Indexed: 05/27/2023]
Abstract
Asiatic huanglongbing (HLB), also known as citrus greening or yellow shoot disease, is a serious disease putatively caused by the bacterium 'Candidatus Liberibacter asiaticus' Jagoueix et al. (Rhizobiales: Rhizobiaceae) (CLas) transmitted by the Asian citrus psyllid (Diaphorina citri Kuwayama (Hemiptera: Liviidae)). Plant resistance to CLas holds promise as a strategy for reducing the economic impact of HLB; thus, citrus breeders are developing new varieties and cultivars and evaluating these for resistance/tolerance to CLas. A high-throughput inoculation program was established to expedite testing of germplasm. Colonies of Asian citrus psyllid maintained on CLas-infected plants are used for the inoculations. The primary inoculation step is to cage a healthy citrus seedling with new leaf growth for a 2-wk inoculation feeding period by 20 adult Asian citrus psyllids (no regard to sex or age) from these colonies. The adults are removed after the inoculation period, and the plants are then treated with a pesticide to eliminate any adults missed or infestation of immatures. The objective here was to evaluate inoculation rates under this procedure. Ten sets of 20 healthy citrus seedlings were subjected to the procedure, one set a month, and the percentage of seedlings successfully inoculated based on testing by quantitative polymerase chain reaction were determined 6 mo after each 2-wk inoculation period. The results indicated a 77% mean transmission rate (percent infected seedlings), with rates ranging from 40 to 100%. Transmission rates were positively correlated with the percentage of Asian citrus psyllid that tested positive for CLas but not correlated with titers of CLas in these psyllids. Possible reasons for variability in transmission rates are discussed.
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Affiliation(s)
- David G Hall
- U.S. Department of Agriculture, Agricultural Research Service, U.S. Horticultural Research Laboratory, Fort Pierce, FL
| | - Kathryn M Moulton
- U.S. Department of Agriculture, Agricultural Research Service, U.S. Horticultural Research Laboratory, Fort Pierce, FL
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Wu F, Huang J, Xu M, Fox EGP, Beattie GAC, Holford P, Cen Y, Deng X. Host and environmental factors influencing 'Candidatus Liberibacter asiaticus' acquisition in Diaphorina citri. PEST MANAGEMENT SCIENCE 2018; 74:2738-2746. [PMID: 29726075 DOI: 10.1002/ps.5060] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/15/2018] [Revised: 04/14/2018] [Accepted: 05/03/2018] [Indexed: 05/27/2023]
Abstract
BACKGROUND Diaphorina citri is a vector of 'Candidatus Liberibacter asiaticus' (CLas) associated with citrus Huanglongbing. In this study, the infection and titers of CLas in the psyllid, were monitored for life cycle stage, sex, host-plant CLas titer, host-plant genotype, and ambient temperature. RESULTS Acquisition efficiency of CLas by D. citri was highest in nymphs reared at 25 °C on a host plant with high CLas titers but was independent of the host genotypes assessed and of vector sex. We further observed that D. citri nymphs acquired CLas more rapidly than adults based on acquisition access periods (AAPs). CLas did not multiply in the alimentary canal, hemolymph, and salivary glands of adults for 18 days after a 3-day AAP as adult. However, CLas multiplication was detected in hemolymph and salivary gland of adults after the bacterium was acquired by nymphs. Eighty percent of salivary glands of adults contained CLas 18 days after a 3-day AAP as nymph compared to 10% 18 days after a 3-day AAP as adults. CONCLUSION Different factors tested herein influenced CLas acquisition efficiency of D. citri, CLas multiplication and spread inside the psyllid. These observations serve to better understand mechanisms of CLas infection in D. citri. © 2018 Society of Chemical Industry.
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Affiliation(s)
- Fengnian Wu
- Citrus Huanglongbing Research Laboratory/Laboratory of Insect Ecology, South China Agricultural University, Guangzhou, China
| | - Jiaquan Huang
- Citrus Huanglongbing Research Laboratory/Laboratory of Insect Ecology, South China Agricultural University, Guangzhou, China
| | - Meirong Xu
- Citrus Huanglongbing Research Laboratory/Laboratory of Insect Ecology, South China Agricultural University, Guangzhou, China
| | - Eduardo G P Fox
- Citrus Huanglongbing Research Laboratory/Laboratory of Insect Ecology, South China Agricultural University, Guangzhou, China
| | - G Andrew C Beattie
- School of Science and Health, Western Sydney University, Penrith, New South Wales, Australia
| | - Paul Holford
- School of Science and Health, Western Sydney University, Penrith, New South Wales, Australia
| | - Yijing Cen
- Citrus Huanglongbing Research Laboratory/Laboratory of Insect Ecology, South China Agricultural University, Guangzhou, China
| | - Xiaoling Deng
- Citrus Huanglongbing Research Laboratory/Laboratory of Insect Ecology, South China Agricultural University, Guangzhou, China
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Patt JM, Robbins PS, Niedz R, McCollum G, Alessandro R. Exogenous application of the plant signalers methyl jasmonate and salicylic acid induces changes in volatile emissions from citrus foliage and influences the aggregation behavior of Asian citrus psyllid (Diaphorina citri), vector of Huanglongbing. PLoS One 2018; 13:e0193724. [PMID: 29596451 PMCID: PMC5875780 DOI: 10.1371/journal.pone.0193724] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2017] [Accepted: 02/18/2018] [Indexed: 11/18/2022] Open
Abstract
Huanglongbing, also known as citrus greening, is a destructive disease that threatens citrus production worldwide. It is putatively caused by the phloem-limited bacterium Candidatus Liberibacter asiaticus (Las). Currently, the disease is untreatable and efforts focus on intensive insecticide use to control the vector, Asian citrus psyllid (Diaphorina citri). Emerging psyllid resistance to multiple insecticides has generated investigations into the use of exogenously applied signaling compounds to enhance citrus resistance to D. citri and Las. In the present study, we examined whether foliar applications of methyl jasmonate (MJ), a volatile signaling compound associated with the induced systemic resistance pathway, and salicylic acid, a constituent of the systemic acquired resistance pathway, would elicit the emission of defense-related volatiles in citrus foliage, and what effect this might have on the host-plant searching behavior of D. citri. Comparisons were made of volatiles emitted from growing shoots of uninfected and Las-infected 'Valencia' sweet orange (Citrus sinensis) trees over two consecutive sampling days. A settling behavioral assay was used to compare psyllid attraction to MJ-treated vs. Tween-treated citrus sprigs. All three main effects, Las infection status, plant signaler application, and sampling day, influenced the proportions of individual volatile compounds emitted in different treatment groups. MJ- and SA-treated trees had higher emission rates than Tween-treated trees. Methyl salicylate (MeSA) and β-caryophyllene were present in higher proportions in the volatiles collected from Las-infected + trees. On the other hand, Las-infected + MJ-treated trees emitted lower proportions of MeSA than did Las-infected + Tween-treated trees. Because MeSA is a key D. citri attractant, this result suggests that MJ application could suppress MeSA emission from Las-infected trees, an approach that could be used to discourage psyllid colonization during shoot growth. MJ application enhanced emission of E-β-ocimene, indole, volatiles attractive to many of the psyllid's natural enemies, indicating that MJ application could be used in an 'attract and reward' conservation biological control strategy. Volatile emissions in SA-treated trees were dominated by MeSA. MJ application elicited aggregation behavior in D. citri. Similar numbers of psyllids settled on MJ-treated versus Tween-treated sprigs, but a significantly greater percentage of the MJ-treated sprigs had aggregations of nine or more psyllids on them. Taken together, the results of this study indicate that exogenous applications of MJ or SA could be used to influence Asian citrus psyllid settling behavior and attract its natural enemies.
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Affiliation(s)
- Joseph M. Patt
- United States Department of Agriculture, Agricultural Research Service, U.S. Horticultural Research Laboratory, Fort Pierce, Florida, United States of America
- * E-mail:
| | - Paul S. Robbins
- United States Department of Agriculture, Agricultural Research Service, U.S. Horticultural Research Laboratory, Fort Pierce, Florida, United States of America
| | - Randy Niedz
- United States Department of Agriculture, Agricultural Research Service, U.S. Horticultural Research Laboratory, Fort Pierce, Florida, United States of America
| | - Greg McCollum
- United States Department of Agriculture, Agricultural Research Service, U.S. Horticultural Research Laboratory, Fort Pierce, Florida, United States of America
| | - Rocco Alessandro
- United States Department of Agriculture, Agricultural Research Service, U.S. Horticultural Research Laboratory, Fort Pierce, Florida, United States of America
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Sétamou M, Alabi OJ, Simpson CR, Jifon JL. Contrasting amino acid profiles among permissive and non-permissive hosts of Candidatus Liberibacter asiaticus, putative causal agent of Huanglongbing. PLoS One 2017; 12:e0187921. [PMID: 29236706 PMCID: PMC5728503 DOI: 10.1371/journal.pone.0187921] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2017] [Accepted: 10/27/2017] [Indexed: 12/13/2022] Open
Abstract
Huanglongbing is a devastating disease of citrus. In this study, a comprehensive profile of phloem sap amino acids (AA) in four permissive host plants of Candidatus Liberibacter asiaticus (CLas) and three non-permissive Rutaceae plants was conducted to gain a better understanding of host factors that may promote or suppress the bacterium. The AA profiles of Diaphorina citri nymphs and adults were similarly analyzed. A total of 38 unique AAs were detected in phloem sap of the various plants and D. citri samples, with phloem sap of young shoots containing more AAs and at higher concentrations than their mature counterparts. All AAs detected in phloem sap of non-permissive plants were also present in CLas -permissive hosts plus additional AAs in the latter class of plants. However, the relative composition of 18 commonly shared AAs varied between CLas -permissive hosts and non-permissive plants. Multivariate analysis with a partial least square discriminant methodology revealed a total of 12 AAs as major factors affecting CLas host status, of which seven were positively related to CLas tolerance/resistance and five positively associated with CLas susceptibility. Most of the AAs positively associated with CLas susceptibility were predominantly of the glutamate family, notably stressed-induced AAs such as arginine, GABA and proline. In contrast, AAs positively correlated with CLas tolerance/resistance were mainly of the serine family. Further analysis revealed that whereas the relative proportions of AAs positively associated with CLas susceptibility did not vary with host developmental stages, those associated with CLas tolerance/resistance increased with flush shoot maturity. Significantly, the proline-to-glycine ratio was determined to be an important discriminating factor for CLas permissivity with higher values characteristic of CLas -permissive hosts. This ratio could be exploited as a biomarker in HLB-resistance breeding programs.
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Affiliation(s)
- Mamoudou Sétamou
- Texas A&M University-Kingsville Citrus Center, Weslaco, United States of America
| | - Olufemi J. Alabi
- Department of Plant Pathology & Microbiology, Texas A&M AgriLife Research and Extension Center, Weslaco, TX, United States of America
| | - Catherine R. Simpson
- Texas A&M University-Kingsville Citrus Center, Weslaco, United States of America
| | - John L. Jifon
- Department of Horticultural Sciences, Texas A&M AgriLife Research and Extension Center, Weslaco, TX, United States of America
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George J, Ammar ED, Hall DG, Lapointe SL. Sclerenchymatous ring as a barrier to phloem feeding by Asian citrus psyllid: Evidence from electrical penetration graph and visualization of stylet pathways. PLoS One 2017; 12:e0173520. [PMID: 28278248 PMCID: PMC5344446 DOI: 10.1371/journal.pone.0173520] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2016] [Accepted: 02/21/2017] [Indexed: 12/30/2022] Open
Abstract
Asian citrus psyllid (Diaphorina citri) feeding behaviors play a significant role in the transmission of the phloem-limited Candidatus Liberibacter asiaticus (CLas) bacterium that causes the economically devastating citrus greening disease. Sustained phloem ingestion by D. citri on CLas infected plants is required for pathogen acquisition and transmission. Recent studies have shown a fibrous ring of thick-walled sclerenchyma around the phloem in mature, fully expanded citrus leaves that is more prominent on the abaxial compared with the adaxial side. The composition and thickness of this fibrous ring may have an important role in selection of feeding sites by D. citri based on leaf age and leaf surface, which in turn can affect pathogen acquisition and transmission. We measured feeding behavior using electrical penetration graph (EPG) recordings of individual D. citri adults placed on abaxial or adaxial surfaces of young or mature Valencia orange leaves to study the role of the sclerenchymatous ring in modifying D. citri feeding behavior. Feeding sites on the same leaf tissues were then sectioned and examined by epifluorescence microscopy. The duration of phloem ingestion (E2 waveform) by psyllids was significantly reduced on mature compared with young leaves, and on abaxial compared with adaxial leaf surfaces. The longest duration of phloem ingestion was observed from psyllids placed on the adaxial side of young leaves that had the least developed sclerenchyma. Bouts of phloem salivation (E1 waveform), however, were significantly longer on mature leaves compared with young leaves. D. citri adults made consecutive phloem feeding attempts (bouts) on the abaxial side of mature leaves and those bouts resulted in unsuccessful or shorter periods of phloem ingestion. Adults also made more frequent and longer bouts of xylem ingestion on mature leaves compared with adult psyllids placed on young leaves. Epifluorescence microscopy showed that the fibrous ring in young leaves was thinner and autofluoresced in red whereas the ring in mature leaves was thicker and autofluoresced in blue, indicating changes in structure and composition (e.g., lignification) of sclerenchyma correlated with leaf age. Our results support the hypothesis that the presence of a thick, well-developed fibrous ring around phloem tissues of mature leaves acts as a barrier to frequent or prolonged phloem ingestion by D. citri from citrus leaves. This may have an important role in limiting or preventing CLas acquisition and/or transmission by D. citri, and could be used for identification and development of resistant citrus cultivars.
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Affiliation(s)
- Justin George
- USDA-ARS, Subtropical Insects and Horticultural Research Unit, United States Horticultural Research Laboratory, Fort Pierce, Florida, United States of America
| | - El-Desouky Ammar
- USDA-ARS, Subtropical Insects and Horticultural Research Unit, United States Horticultural Research Laboratory, Fort Pierce, Florida, United States of America
- University of Florida, IFAS, Lake Alfred, Florida, United States of America
| | - David G. Hall
- USDA-ARS, Subtropical Insects and Horticultural Research Unit, United States Horticultural Research Laboratory, Fort Pierce, Florida, United States of America
| | - Stephen L. Lapointe
- USDA-ARS, Subtropical Insects and Horticultural Research Unit, United States Horticultural Research Laboratory, Fort Pierce, Florida, United States of America
- * E-mail:
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