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Ibrahim YE, Al-Saleh MA, Widyawan A, El Komy MH, Al Dhafer HM, Brown JK. Identification and Distribution of the ' Candidatus Liberibacter asiaticus'-Asian Citrus Psyllid Pathosystem in Saudi Arabia. PLANT DISEASE 2024; 108:1083-1092. [PMID: 37953230 DOI: 10.1094/pdis-07-23-1460-re] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/14/2023]
Abstract
Citrus greening disease was first reported in Saudi Arabia during the 1970s when characteristic foliar and fruit symptoms were observed in commercial citrus groves. However, 'Candidatus Liberibacter asiaticus' (CLas) was not detected in symptomatic trees until 1981 to 1984 when CLas-like cells were observed by transmission electron microscopy in leaves collected from symptomatic citrus groves in southwestern Saudi Arabia. Despite the anticipated establishment of the CLas-Asian citrus psyllid (ACP) (Diaphorina citri Kuwayama) pathosystem, CLas presence has not been verified in suspect trees nor have ACP infestations been documented. Given the recent expansion of citrus production in Saudi Arabia, a systematic country-wide survey was carried out to determine the potential CLas distribution in the 13 citrus-growing regions of the country. Citrus trees were surveyed for the presence of CLas-psyllid vector(s) and characteristic disease symptoms in commercial and urban citrus trees. Adult psyllids collected from infested citrus trees were identified as ACP based on morphological characteristics. Real-time quantitative PCR amplification (qPCR) of the CLas β-subunit of the ribonucleotide reductase (RNR) gene from citrus leaf and fruit samples and/or ACP adults revealed that trees were positive for CLas detection in 10 of the 13 survey regions; however, CLas was undetectable in ACP adults. Phylogenetic and single nucleotide polymorphism (SNP) analyses of a PCR-amplified, cloned fragment of the CLas 16S rRNA gene (∼1.1 kbp) indicated Saudi Arabian isolates were most closely related to Florida, U.S.A., isolates. Analysis of climate variables indicated that the distribution of the ACP-CLas pathosystem observed in Saudi Arabia was consistent with published predictions of terrains most likely to support establishment.
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Affiliation(s)
- Yasser E Ibrahim
- Plant Protection Department, College of Food and Agriculture Sciences, King Saud University, Riyadh, Saudi Arabia
- Bacterial Diseases Research Department, Plant Pathology Research Institute, Agricultural Research Center, Giza, Egypt
| | - Mohammed A Al-Saleh
- Plant Protection Department, College of Food and Agriculture Sciences, King Saud University, Riyadh, Saudi Arabia
| | - Arya Widyawan
- Plant Protection Department, College of Food and Agriculture Sciences, King Saud University, Riyadh, Saudi Arabia
| | - Mahmoud H El Komy
- Plant Protection Department, College of Food and Agriculture Sciences, King Saud University, Riyadh, Saudi Arabia
| | - Hathal M Al Dhafer
- Plant Protection Department, College of Food and Agriculture Sciences, King Saud University, Riyadh, Saudi Arabia
| | - Judith K Brown
- School of Plant Sciences, The University of Arizona, Tucson, AZ 85721, U.S.A
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Higgins SA, Mann M, Heck M. Strain Tracking of ' Candidatus Liberibacter asiaticus', the Citrus Greening Pathogen, by High-Resolution Microbiome Analysis of Asian Citrus Psyllids. PHYTOPATHOLOGY 2022; 112:2273-2287. [PMID: 35678589 DOI: 10.1094/phyto-02-22-0067-r] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
The Asian citrus psyllid, Diaphorina citri, is an invasive insect and a vector of 'Candidatus Liberibacter asiaticus' (CLas), a bacterium whose growth in Citrus species results in huanglongbing (HLB), also known as citrus greening disease. Methods to enrich and sequence CLas from D. citri often rely on biased genome amplification and nevertheless contain significant quantities of host DNA. To overcome these hurdles, we developed a simple pretreatment DNase and filtration (PDF) protocol to remove host DNA and directly sequence CLas and the complete, primarily uncultivable microbiome from D. citri adults. The PDF protocol yielded CLas abundances upward of 60% and facilitated direct measurement of CLas and endosymbiont replication rates in psyllids. The PDF protocol confirmed our lab strains derived from a progenitor Florida CLas strain and accumulated 156 genetic variants, underscoring the utility of this method for bacterial strain tracking. CLas genetic polymorphisms arising in lab-reared psyllid populations included prophage-encoding regions with key functions in CLas pathogenesis, putative antibiotic resistance loci, and a single secreted effector. These variants suggest that laboratory propagation of CLas could result in different phenotypic trajectories among laboratories and could confound CLas physiology or therapeutic design and evaluation if these differences remain undocumented. Finally, we obtained genetic signatures affiliated with Citrus nuclear and organellar genomes, entomopathogenic fungal mitochondria, and commensal bacteria from laboratory-reared and field-collected D. citri adults. Hence, the PDF protocol can directly inform agricultural management strategies related to bacterial strain tracking, insect microbiome surveillance, and antibiotic resistance screening.
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Affiliation(s)
- Steven A Higgins
- Emerging Pests and Pathogens Research Unit, United States Department of Agriculture-Agricultural Research Service (USDA-ARS), Ithaca, NY 14853
| | - Marina Mann
- Plant Pathology and Plant Microbe Biology Department, Cornell University, Ithaca, NY 14853
| | - Michelle Heck
- Emerging Pests and Pathogens Research Unit, United States Department of Agriculture-Agricultural Research Service (USDA-ARS), Ithaca, NY 14853
- Plant Pathology and Plant Microbe Biology Department, Cornell University, Ithaca, NY 14853
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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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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: 4] [Impact Index Per Article: 1.3] [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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Raiol-Junior LL, Cifuentes-Arenas JC, de Carvalho EV, Girardi EA, Lopes SA. Evidence That ' Candidatus Liberibacter asiaticus' Moves Predominantly Toward New Tissue Growth in Citrus Plants. PLANT DISEASE 2021; 105:34-42. [PMID: 33201785 DOI: 10.1094/pdis-01-20-0158-re] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
'Candidatus Liberibacter asiaticus' (Las) is an unculturable, phloem-limited, insect-transmitted bacterium associated with the Asiatic form of huanglongbing (HLB), the most destructive citrus disease. In Asia and the Americas, it is transmitted by the Asian citrus psyllid (Diaphorina citri Kuwavama). Despite considerable research, little is known about the processes involved in plant infection and colonization by Las. This study was conducted to determine whether the basal portion (below girdling) of the plant is an important route for Las to move laterally from a point of inoculation on a branch to pathogen-free branches elsewhere in the canopy, and to quantify the influence of actively growing tissues on vertical upward (acropetally) or downward (basipetally) movement of Las. Nongirdled and fully or partially girdled stems of potted plants of 'Pera' sweet orange, graft-inoculated above or below girdling, were sampled in distinct regions and assessed by qPCR, 6 months postinoculation. Las invaded all regions of partially and nongirdled plants but remained restricted to the inoculated regions of fully girdled plants, evidence that in planta bacterium movement is limited to the phloem. In fully girdled plants, starch accumulated above the girdling site, probably because of changes in flow of phloem sap. To study the influence of actively growing tissues, inoculated 'Valencia' sweet orange plants were kept intact or were top- or root-pruned to force production of new tissues, and sampled at 15-day intervals. Las migrated rapidly and most predominantly toward newly developing root and leaf tissues. The rapid and predominant movement of Las to newly developed shoots and roots would explain failures of canopy heat treatments and pruning to cure HLB-affected trees, and reinforces the need to protect rapidly growing new shoots from feeding by D. citri in order to minimize transmission and spread of the pathogen by the vector within and between orchards.
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Affiliation(s)
| | | | | | - Eduardo A Girardi
- Empresa Brasileira de Pesquisa Agropecuária (EMBRAPA), Cruz das Almas BA, Brazil
| | - Silvio A Lopes
- Fundo de Defesa da Citricultura (Fundecitrus), Araraquara SP, Brazil
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Hilf ME, Luo W. Inoculation Period and Citrus Host Effect Establishment of New Infections of ' Candidatus Liberibacter asiaticus' Transmitted via Vegetative Grafting. PLANT DISEASE 2020; 104:1894-1899. [PMID: 32396053 DOI: 10.1094/pdis-09-19-2022-re] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Vegetative grafting is a common method of transmitting and propagating 'Candidatus Liberibacter asiaticus', the bacterial species accepted as the causal agent of the citrus disease huanglongbing (HLB). Generally, infected tissue that is grafted to a receptor tree remains in place indefinitely to ensure transmission. In this study, individual HLB-symptomatic leaves were grafted as 'Ca. L. asiaticus' inoculum sources to receptor trees of six citrus types and removed after an inoculation period (IP) of 21, 51, or 81 days. The goal was to assess the effect of varying IPs on transmission of bacteria to the receptor tree and on the successful establishment of a new infection. Survival analysis of data from three trials showed a significantly reduced proportion of infected trees with an IP of 21 days compared with IPs of 51 and 81 days but that there was no significant difference in the proportion of infected trees between IPs of 51 and 81 days. In addition, the time to first detection of pathogen DNA in an infected tree was delayed significantly for the 21-day IP when compared with the 51- and 81-day IPs. Survival analysis showed that the probability of infection of sweet orange trees was significantly higher than for trees of five other citrus types throughout the experiment. There was no significant difference between the infection probabilities of these latter five citrus types. The data from this study show that successful infection by grafting is dependent upon the time of exposure to the inoculum, that shorter IPs increase the time needed to establish a systemic infection, and that citrus types vary in their overall susceptibility to infection by 'Ca. L. asiaticus'.
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Affiliation(s)
- Mark E Hilf
- United States Department of Agriculture-Agricultural Research Service, 2001 South Rock Road, Fort Pierce, FL 34945, U.S.A
| | - Weiqi Luo
- United States Department of Agriculture-Agricultural Research Service, 2001 South Rock Road, Fort Pierce, FL 34945, U.S.A
- North Carolina State University, Center for Integrated Pest Management, Raleigh, NC 27606, U.S.A
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Hilf ME, Luo W. Dynamics of 'Candidatus Liberibacter asiaticus' Colonization of New Growth of Citrus. PHYTOPATHOLOGY 2018; 108:1165-1171. [PMID: 29757704 DOI: 10.1094/phyto-12-17-0408-r] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
'Candidatus Liberibacter asiaticus' is a phloem-colonizing intracellular bacterial pathogen of citrus associated with the disease huanglongbing. A study of patterns of colonization and bacterial population growth in new growth of different citrus types was conducted by pruning infected citron, sweet orange, sour orange, mandarin, citrange, and Citrus macrophylla trees to force the growth of axillary and adventitious shoots. The first three leaves on newly emerged shoots were collected at 30, 60, and 90 days to assess colonization and population growth of 'Ca. L. asiaticus' using real time PCR (qPCR). Single trials were conducted with mandarin and citron, two trials each for citrange, sour orange and sweet orange, and four trials for C. macrophylla. In citron the proportion of colonized leaves increased significantly over time, with 67, 85, and 96% of leaves colonized at 30, 60, and 90 days, respectively. For the other citrus types, the exact proportion of colonized leaves differed, but colonization exceeded 60% in mandarin, sour orange, and citrange, and exceeded 80% at 30 days in two trials with sweet orange and three trials with C. macrophylla, but there was no significant increase in the proportion of colonized leaves at 60 and 90 days. Bacteria were readily detected by 30 days in new leaves of all citrus types. Differences in the growth of the bacterial population between citrus types and at different times of the year were noted, but common trends were apparent. In general, bacterial titers peaked at 60 days, except in leaves of C. macrophylla where bacterial titers peaked at 30 days. The early and consistently high proportion of leaf colonization observed for new growth of sweet orange during two trials and for C. macrophylla during three trials indicates a near synchronous colonization of new leaves by 30 days.
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Affiliation(s)
- Mark E Hilf
- First author: U.S. Department of Agriculture-Agriculture Research Service (USDA-ARS), 2001 South Rock Road, Fort Pierce, FL 34945; and second author: USDA-ARS, Fort Pierce, Florida and North Carolina State University, Center for Integrated Pest Management, Raleigh 27606
| | - Weiqi Luo
- First author: U.S. Department of Agriculture-Agriculture Research Service (USDA-ARS), 2001 South Rock Road, Fort Pierce, FL 34945; and second author: USDA-ARS, Fort Pierce, Florida and North Carolina State University, Center for Integrated Pest Management, Raleigh 27606
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Lee H, Kim MK, Choi HS, Kang JH, Ju HJ, Seo JK. Efficient Transmission and Propagation of Tomato Chlorosis Virus by Simple Single-Leaflet Grafting. THE PLANT PATHOLOGY JOURNAL 2017; 33:345-349. [PMID: 28592953 PMCID: PMC5461053 DOI: 10.5423/ppj.nt.02.2017.0039] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/20/2017] [Revised: 03/05/2017] [Accepted: 03/06/2017] [Indexed: 06/07/2023]
Abstract
Tomato chlorosis virus (ToCV), a member of the genus Crinivirus, has caused an epidemic disease in tomato worldwide. ToCV is phloem-limited and transmitted by whiteflies in a semi-persistent manner, but not by mechanical inoculation. Experimental propagation of ToCV has been performed primarily by using whitefly-mediated inoculation. To develop a simple and convenient method for transmission of ToCV, we investigated grafting single-leaflets from tomato plants infected with ToCV to recipient tomato seedlings. Forty-one of 46 tomato seedlings tested were grafted successfully with single-leaflets infected with ToCV. Among them, 36 seedlings (87.8%) were systemically infected with ToCV and developed typical symptoms. Our results demonstrated that single-leaflet grafting could provide a sufficient amount of inoculum for the transmission of ToCV to the grafted seedlings.
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Affiliation(s)
- Huin Lee
- Crop Protection Division, National Institute of Agricultural Sciences, Rural Development Administration, Wanju 55365,
Korea
- Department of Agricultural Biology, Chonbuk National University, Jeonju 54896,
Korea
| | - Mi-Kyeong Kim
- Crop Protection Division, National Institute of Agricultural Sciences, Rural Development Administration, Wanju 55365,
Korea
| | - Hong-Soo Choi
- Crop Protection Division, National Institute of Agricultural Sciences, Rural Development Administration, Wanju 55365,
Korea
| | - Jin-Ho Kang
- Department of International Agricultural Technology and Institutes of Green Bio Science and Technology, Seoul National University, Pyeongchang 25354,
Korea
| | - Ho-Jong Ju
- Department of Agricultural Biology, Chonbuk National University, Jeonju 54896,
Korea
| | - Jang-Kyun Seo
- Department of International Agricultural Technology and Institutes of Green Bio Science and Technology, Seoul National University, Pyeongchang 25354,
Korea
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Tabay Zambon F, Plant K, Etxeberria E. Leaf-disc grafting for the transmission of Candidatus Liberibacter asiaticus in citrus ( Citrus sinensis; Rutaceae) seedlings. APPLICATIONS IN PLANT SCIENCES 2017; 5:apps.1600085. [PMID: 28090406 PMCID: PMC5231911 DOI: 10.3732/apps.1600085] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/18/2016] [Accepted: 12/06/2016] [Indexed: 06/06/2023]
Abstract
PREMISE OF THE STUDY The search for resistance/tolerance to the devastating citrus huanglongbing disease (syn. HLB or citrus greening) is generating an increasing number of new plants of diverse genetic makeup. As the increasing number of new plants require more space, resources, and time, the need for faster and more efficient HLB screening tests becomes crucial. METHODS AND RESULTS The leaf-disc grafting system described here consists in replacing a disc of leaf tissue with a similar disc from an infected plant. This can be performed in young seedlings not yet big enough to endure other types of grafting. Graft success and infection rates average approximately 80%. CONCLUSIONS We describe the successful adaptation of leaf-disc grafting as a powerful screening tool for HLB. The system requires minimal plant material and can be performed in seedlings at a very young age with increased efficiency in terms of time, space, and resources.
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Affiliation(s)
- Flavia Tabay Zambon
- Citrus Research and Education Center, University of Florida, 700 Experiment Station Road, Lake Alfred, Florida 33850 USA
| | - Karen Plant
- Citrus Research and Education Center, University of Florida, 700 Experiment Station Road, Lake Alfred, Florida 33850 USA
| | - Ed Etxeberria
- Citrus Research and Education Center, University of Florida, 700 Experiment Station Road, Lake Alfred, Florida 33850 USA
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