scholarly journals Evidence That ‘Candidatus Liberibacter asiaticus’ Moves Predominantly Toward New Tissue Growth in Citrus Plants

Plant Disease ◽  
2021 ◽  
Vol 105 (1) ◽  
pp. 34-42 ◽  
Author(s):  
Laudecir L. Raiol-Junior ◽  
Juan C. Cifuentes-Arenas ◽  
Everton V. de Carvalho ◽  
Eduardo A. Girardi ◽  
Silvio A. Lopes
Keyword(s):  
Sweet Orange ◽  
Force Production ◽  
Tissue Growth ◽  
Candidatus Liberibacter Asiaticus ◽  
In Planta ◽  
Potted Plants ◽  
Candidatus Liberibacter ◽  
Leaf Tissues ◽  
Basal Portion ◽  
Liberibacter Asiaticus

‘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.

Census of Candidatus Liberibacter asiaticus population inside the phloem of citrus trees

2020 ◽  
Author(s):  
Fernanda N.C. Vasconcelos ◽  
Jinyun Li ◽  
zhiqian pang ◽  
Christopher Vincent ◽  
Nian Wang
Keyword(s):  
Population Size ◽  
Sweet Orange ◽  
Bacterial Pathogens ◽  
Candidatus Liberibacter Asiaticus ◽  
Metabolic Burden ◽  
Whole Plant ◽  
Candidatus Liberibacter ◽  
Leaf Tissues ◽  
Liberibacter Asiaticus ◽  
Orange Trees

Candidatus Liberibacter asiaticus (CLas) is the predominant causal agent of citrus huanglongbing (HLB). The pathogen population size in local tissues and the whole plant are critical for the development of disease symptoms via pathogenicity factors and causing metabolic burden to the host. However, the total population size of CLas in a whole plant and the ratio of CLas vs. citrus cells in local tissues have not been addressed previously. The total CLas population size for 2.5-year-old Valencia sweet orange trees was quantified using quantitative PCR to be approximately 1.74 x 109, whereas that of 7 and 20-year-old sweet orange trees were estimated to be 4.3 x 1010, and 6.0 x 1010, respectively. The majority of CLas cells were distributed in the leaf tissues (55.58%), followed by that in the branch tissues (36.78%), feeder roots (4.75%), trunk (2.39%), and structural root (0.51%) tissues. The ratios of citrus cells vs. CLas cells for branch, leaf, trunk, feeder root, and structural root samples were approximately 39, 44, 153, 191, and 561, respectively, representing the metabolic burden of CLas in different organs. Approximately 0.01% of the total citrus phloem volume was estimated to be occupied by CLas. The CLas titer inside the leaf was estimated to be approximately 1.64 x 106 cells/leaf or 9.2 x 104 cells cm-2 in leaves, approximately 104 times less than that of typical apoplastic bacterial pathogens. This study provides quantitative estimates of phloem colonization by bacterial pathogens and further understands the biology and virulence mechanism of CLas.

Probing the application of OmpA-derived peptides to disrupt the acquisition of ‘Candidatus Liberibacter asiaticus’ by Diaphorina citri

2021 ◽  
Author(s):  
Marcus Vinicius Merfa e Silva ◽  
Eduarda Regina Fischer ◽  
Mariana de Souza e Silva ◽  
Carolina Sardinha Francisco ◽  
Helvécio Coletta-Filho ◽  
...  
Keyword(s):  
Control Strategies ◽  
Insect Vector ◽  
Diaphorina Citri ◽  
Candidatus Liberibacter Asiaticus ◽  
In Planta ◽  
Host Interaction ◽  
Vector Population ◽  
Candidatus Liberibacter ◽  
Liberibacter Asiaticus ◽  
Bacterial Outer Membrane

Huanglongbing (HLB) is currently the most devastating disease of citrus worldwide. Both bacteria ‘Candidatus Liberibacter asiaticus’ (CLas) and ‘Ca. Liberibacter americanus’ (CLam) are associated with HLB in Brazil, but with a strong prevalence of CLas over CLam. Conventionally, HLB management focuses on controlling the insect vector population (Diaphorina citri; also known as Asian citrus psyllid – ACP) by spraying insecticides, an approach demonstrated to be mostly ineffective. Thus, development of novel more efficient HLB control strategies is required. The multifunctional bacterial outer membrane protein OmpA is involved in several molecular processes between bacteria and their hosts and has been suggested as a target for bacterial control. Curiously, OmpA is absent in CLam in comparison to CLas, suggesting a possible role on host-interaction. Therefore, in the current study, we have treated ACPs with different OmpA-derived peptides aiming to evaluate the acquisition of CLas by the insect vector. Treatment of psyllids with 5 µM of Pep1, Pep3, Pep5 and Pep6 in artificial diet significantly reduced the acquisition of CLas, while increasing the concentration of Pep5 and Pep6 to 50 µM abolished this process. In addition, in planta treatment with 50 µM of Pep6 also significantly decreased the acquisition of CLas and sweet orange plants stably absorbed and maintained this peptide for as long as three months post the final application. Together, our results demonstrate the promising use of OmpA-derived peptides as a novel biotechnological tool to control CLas.

scholarly journals The in Planta Effective Concentration of Oxytetracycline Against ‘Candidatus Liberibacter asiaticus’ for Suppression of Citrus Huanglongbing

2019 ◽  
Vol 109 (12) ◽  
pp. 2046-2054 ◽  
Author(s):  
Jinyun Li ◽  
Zhiqian Pang ◽  
Shuo Duan ◽  
Donghwan Lee ◽  
Vladimir G. Kolbasov ◽  
...  
Keyword(s):  
Field Experiments ◽  
Foliar Spray ◽  
Effective Control ◽  
Candidatus Liberibacter Asiaticus ◽  
In Planta ◽  
Fresh Tissue ◽  
Minimum Concentration ◽  
Candidatus Liberibacter ◽  
Liberibacter Asiaticus ◽  
Residue Levels

Huanglongbing (HLB) or greening currently is the most devastating citrus disease worldwide. The fastidious phloem-colonizing bacterium ‘Candidatus Liberibacter asiaticus’ (CLas) is the causal agent of citrus HLB in Florida. Bactericides containing the active ingredient oxytetracycline (OTC) have been used in foliar spray to control citrus HLB in Florida since 2016. However, the minimum concentration of OTC required to suppress CLas in planta remains unknown. We developed a new method for evaluating the effects of OTC treatment on CLas titers in infected plants and determined the relationship between OTC residue levels and control levels achieved for CLas using mathematical modeling in greenhouse and field experiments. In both greenhouse and field, OTC spray did not reduce the titers of CLas, and it produced undetectable or mild levels of OTC residue in leaves within 7 days post-application (DPA). In greenhouse, OTC injection at 0.05 g per tree decreased CLas titers to an undetectable level (cycle threshold value ≥ 36.0) from 7 to 30 DPA and produced a residue level of OTC at 0.68 to 0.73 µg/g of fresh tissue over this period. In the field, OTC injection at 0.50 g per tree resulted in the decline of CLas titers by 1.52 log reduction from 14 to 60 DPA, with residue levels of OTC at 0.27 to 0.33 µg/g of fresh tissue. In both trials, a first-order compart model of OTC residue dynamics in leaves of trunk-injected trees was specified for estimating the retention of effective concentrations. Furthermore, nonlinear modeling revealed significant positive correlations between OTC residue levels in leaves and the control levels for CLas achieved. The results suggested that the minimum concentrations of OTC required to suppress CLas populations in planta to below the detection limit are 0.68 and 0.86 µg/g and that the minimum concentrations of OTC required for initial inhibition of CLas growth in planta are ∼0.17 and ∼0.215 µg/g in leaf tissues under greenhouse and field conditions, respectively. This finding highlights that a minimum concentration of OTC should be guaranteed to be delivered to target CLas in infected plants for effective control of citrus HLB.

A Review of Huanglongbing (Citrus Greening) Management in Citrus Using Nutritional Approaches in China

2011 ◽  
Vol 12 (1) ◽  
pp. 24 ◽  
Author(s):  
Yulu Xia ◽  
Gecheng Ouyang ◽  
Ronald A. Sequeira ◽  
Yu Takeuchi ◽  
Ignacio Baez ◽  
...  
Keyword(s):  
Nutrient Management ◽  
Field Survey ◽  
Cultural Practices ◽  
Sweet Orange ◽  
Asian Citrus Psyllid ◽  
Diaphorina Citri ◽  
Candidatus Liberibacter Asiaticus ◽  
Candidatus Liberibacter ◽  
Citrus Maxima ◽  
Liberibacter Asiaticus

The Asian form of huanglongbing (HLB) is caused by ‘Candidatus Liberibacter asiaticus (Las),’ a phloem-limited bacterium transmitted by the Asian citrus psyllid, Diaphorina citri Kuwayama. Nutrient management, together with other cultural practices such as pruning and irrigation, for mitigation of the disease has been practiced in China for many years. Our literature review, field survey, and interviews with Chinese scientists and growers indicate that these cultural practices were generally ineffective for the disease management. However, a nutritional approach in conjunction with other cultural practices such as irrigation can maintain grove productivity for a certain time depending on the type of citrus species/cultivars, the age of the trees, the propagation method of the plants, the Asian citrus psyllid (ACP) (Diaphorina citri Kuwayama) population, and other factors. Symptomatic mature pommelo (Citrus maxima Merr) and sweet orange (C. sinensis L. Osbeck) plants can commonly survive and maintain a certain level of productivity for an additional 4 to 5 years, even longer assuming vigorous ACP control. Accepted for publication 27 June 2011. Published 3 October 2011.

scholarly journals Sec-Delivered Effector 1 (SDE1) of ‘Candidatus Liberibacter asiaticus’ Promotes Citrus Huanglongbing

2020 ◽  
Vol 33 (12) ◽  
pp. 1394-1404
Author(s):  
Kelley J. Clark ◽  
Zhiqian Pang ◽  
Jessica Trinh ◽  
Nian Wang ◽  
Wenbo Ma
Keyword(s):  
Cysteine Proteases ◽  
Citrus Paradisi ◽  
Candidatus Liberibacter Asiaticus ◽  
In Planta ◽  
Altered Expression ◽  
Model Plant Arabidopsis Thaliana ◽  
Candidatus Liberibacter ◽  
Liberibacter Asiaticus ◽  
Transgenic Citrus

Sec-delivered effector 1 (SDE1) from the huanglongbing (HLB)-associated bacterium ‘Candidatus Liberibacter asiaticus’ was previously characterized as an inhibitor of defense-related, papain-like cysteine proteases in vitro and in planta. Here, we investigated the contributions of SDE1 to HLB progression. We found that SDE1 expression in the model plant Arabidopsis thaliana caused severe yellowing in mature leaves, reminiscent of both ‘Ca. L. asiaticus’ infection symptoms and accelerated leaf senescence. Induction of senescence signatures was also observed in the SDE1-expressing A. thaliana lines. These signatures were apparent in older leaves but not in seedlings, suggesting an age-associated effect. Furthermore, independent lines of transgenic Citrus paradisi (L.) Macfadyen (Duncan grapefruit) that express SDE1 exhibited hypersusceptibility to ‘Ca. L. asiaticus’. Similar to A. thaliana, transgenic citrus expressing SDE1 showed altered expression of senescence-associated genes, but only after infection with ‘Ca. L. asiaticus’. These findings suggest that SDE1 is a virulence factor that contributes to HLB progression, likely by inducing premature or accelerated senescence in citrus. This work provides new insight into HLB pathogenesis. [Formula: see text] Copyright © 2020 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

scholarly journals In Planta Distribution of ‘Candidatus Liberibacter asiaticus’ as Revealed by Polymerase Chain Reaction (PCR) and Real-Time PCR

2008 ◽  
Vol 98 (5) ◽  
pp. 592-599 ◽  
Author(s):  
Satyanarayana Tatineni ◽  
Uma Shankar Sagaram ◽  
Siddarame Gowda ◽  
Cecile J. Robertson ◽  
William O. Dawson ◽  
...  
Keyword(s):  
Polymerase Chain Reaction ◽  
Real Time ◽  
Real Time Pcr ◽  
Citrus Tree ◽  
Candidatus Liberibacter Asiaticus ◽  
In Planta ◽  
Chain Reaction ◽  
Candidatus Liberibacter ◽  
Liberibacter Asiaticus ◽  
Polymerase Chain

Huanglongbing (HLB) is one of the most devastating diseases of citrus worldwide, and is caused by a phloem-limited fastidious prokaryotic α-proteobacterium that is yet to be cultured. In this study, a combination of traditional polymerase chain reaction (PCR) and real-time PCR targeting the putative DNA polymerase and 16S rDNA sequence of ‘Candidatus Liberibacter asiaticus,’ respectively, were used to examine the distribution and movement of the HLB pathogen in the infected citrus tree. We found that ‘Ca. Liberibacter asiaticus’ was distributed in bark tissue, leaf midrib, roots, and different floral and fruit parts, but not in endosperm and embryo, of infected citrus trees. Quantification analysis of the HLB bacterium indicated that it was distributed unevenly in planta and ranged from 14 to 137,031 cells/μg of total DNA in different tissues. A relatively high concentration of ‘Ca. Liberibacter asiaticus’ was observed in fruit peduncles. Our data from greenhouse-infected plants also indicated that ‘Ca. Liberibacter asiaticus’ was transmitted systemically from infection site to different parts of the plant. Understanding the distribution and movement of the HLB bacterium inside an individual citrus tree is critical for discerning its virulence mechanism and to develop management strategies for HLB.

scholarly journals Reaction of sweet orange cultivars expressing the attacin A gene to 'Candidatus Liberibacter asiaticus' infection

2013 ◽  
Vol 48 (11) ◽  
pp. 1440-1448 ◽  
Author(s):  
Rafaella Teles Arantes Felipe ◽  
Francisco de Assis Alves Mourão Filho ◽  
Silvio Aparecido Lopes ◽  
Beatriz Madalena Januzzi Mendes ◽  
Maurel Behling ◽  
...  
Keyword(s):  
Sweet Orange ◽  
Pcr Analysis ◽  
Candidatus Liberibacter Asiaticus ◽  
Randomized Design ◽  
Transgenic Lines ◽  
Candidatus Liberibacter ◽  
Liberibacter Asiaticus ◽  
Polymerase Chain ◽  
Attacin A ◽  
Leaf Symptoms

The objective of this work was to evaluate the reaction of four sweet orange cultivars expressing the attacin A gene to 'Candidatus Liberibacter asiaticus' (Las) infection, a bacterium associated to huanglongbing (HLB) disease. Transgenic sweet orange plants of Hamlin, Natal, Pêra, and Valência cultivars, as well as nontransgenic controls received inocula by grafting budwood sections of HLB-infected branches. Disease progression was evaluated through observations of leaf symptoms and by polymerase chain reaction (PCR) analysis, eight months after inoculation. A completely randomized design was used, with four experiments (one for each cultivar) performed simultaneously. Bacteria title was estimated by quantitative PCR (qPCR). HLB symptoms and Las titers were present in nontransgenic and transgenic plants expressing the attacin A gene of the four sweet orange cultivars, eight months after bacteria inoculation. Five transgenic lines (transformation events) of 'Pêra' sweet orange expressing the attacin A gene have significantly lower Las titers in comparison with nontransgenic plants of this cultivar.

Comparative iTRAQ proteome and transcriptome analyses of sweet orange infected by “Candidatus Liberibacter asiaticus”

2011 ◽  
Vol 143 (3) ◽  
pp. 235-245 ◽  
Author(s):  
Jing Fan ◽  
Chunxian Chen ◽  
Qibin Yu ◽  
Ronald H. Brlansky ◽  
Zheng-Guo Li ◽  
...  
Keyword(s):  
Sweet Orange ◽  
Candidatus Liberibacter Asiaticus ◽  
Candidatus Liberibacter ◽  
Liberibacter Asiaticus ◽  
Transcriptome Analyses

Spatiotemporal dynamics of Candidatus Liberibacter asiaticus colonization inside citrus plant and Huanglongbing disease development

2020 ◽  
Author(s):  
Sheo Shankar Pandey ◽  
Fernanda N.C. Vasconcelos ◽  
Nian Wang
Keyword(s):  
Passive Movement ◽  
Infection Process ◽  
Active Movement ◽  
Candidatus Liberibacter Asiaticus ◽  
In Planta ◽  
Mature Leaves ◽  
Young Leaves ◽  
Candidatus Liberibacter ◽  
Liberibacter Asiaticus ◽  
Different Tissues

Candidatus Liberibacter asiaticus (CLas), the causal agent of citrus huanglongbing, colonizes inside the phloem and is naturally transmitted by the Asian citrus psyllid (ACP). Here, we investigated the spatiotemporal CLas colonization in different tissues post ACP transmission. At 75 day-post-ACP-removal (DPR), CLas was detected in roots of all trees, but in the mature leaf of only one tree, of the nine plants that were successfully infected via ACP transmission, consistent with the model that CLas moves passively from the source to sink. CLas was detected in 11.1%, and 43.1% mature leaves, which were unfed by ACPs during transmission, at 75, and 365 DPR, respectively, unveiling active movement to the source tissue. The difference in colonization timing of sink and source tissues indicates CLas is capable of both passive and active movement with passive movement being dominant. At 225 DPR, leaves fed by ACPs during the young stage showed the highest ratio of HLB symptomatic leaves and highest CLas titer, followed by that of leaves emerged post ACP removal, and mature leaves not fed by ACPs. Importantly, our data showed that ACPs were unable to transmit CLas via feeding on mature leaves. It is estimated that it takes at most three years for CLas to infect the whole tree. Overall, the 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 the knowledge supporting that young leaves should be the focus of HLB management.

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