Citrus Bacterial Diseases Spread and Control Strategies in the World: Management and Molecular Approaches

A special issue of Agronomy (ISSN 2073-4395). This special issue belongs to the section "Pest and Disease Management".

Deadline for manuscript submissions: closed (26 September 2022) | Viewed by 5743

Special Issue Editor


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Guest Editor
Instituto Agronômico de Campinas, Cordeirópolis, São Paulo 13490-970, Brazil
Interests: citrus genomics and pathogens; functional genomics of citrus and their pathogens; genome editing

Special Issue Information

Dear Colleagues,

The genus Citrus belongs to the Rutaceae family and has many species of economical value. Citrus fruits comprise mandarins, sweet oranges, grapefruits, lemons, and limes, among others, and are produced worldwide. However, growing citrus fruits is becoming a challenge, particularly because of the diseases that the cultures face in the main production areas. Among these diseases, Citrus canker and Huanglongbing are two bacterial diseases that are difficult challenges for growers. Citrus canker is caused by Xanthomonas citri and leads to a reduction in fruit production, affects the marketability of the fruits and the access to export markets, and increases the cost of production. The dispersion of this bacterium occurs by natural factors such as wind and rain or by human activities. Huanglongbing is caused by Candidatus Liberibacter and is currently the most destructive disease for the citrus industry. Its bacteria are transmitted by psyllids and are present in the most important producing countries in the world, drastically affecting citrus fruit production. The fruits affected by this disease become economically worthless, displaying a poor size and quality. There is currently no cure for the disease.

This Special Issue will focus on the current status of these Citrus bacterial diseases and the recent advances in the strategies used for their control at different levels, from field management of the orchards to molecular studies of citrus fruits and their pathogens. We welcome reviews, original research articles, or short communications on the incidence of the diseases; nutritional aspects of the diseases; field management; plant–pathogen interactions; genetics, genomics, and molecular biology studies of Citrus, the bacteria, or the psyllid; new varieties including transformation and gene editing; and any innovative strategy for controlling these diseases.

We look forward to receiving your valuable contributions to this Special Issue.

Prof. Dr. Marco Aurélio Takita
Guest Editor

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Keywords

  • plant pathology
  • plant protection
  • integrated pest and disease management
  • breeding
  • nutrition
  • bacterial diseases
  • new breeding techniques

Published Papers (2 papers)

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Research

13 pages, 2825 KiB  
Article
Validation of Propidium Monoazide-qPCR for Assessing Treatment Effectiveness against ‘Candidatus Liberibacter asiaticus’ in Citrus
by Chuanyu Yang and Veronica Ancona
Agronomy 2022, 12(11), 2783; https://doi.org/10.3390/agronomy12112783 - 9 Nov 2022
Viewed by 2631
Abstract
Huanglongbing (HLB) is an important citrus disease associated with the phloem-limited, uncultured bacterium ‘Candidatus Liberibacter asiaticus’(CLas). Effective treatments against CLas have to be validated in the field, however, methods for the field assessment of treatment effectiveness are time-consuming, in part because DNA-based [...] Read more.
Huanglongbing (HLB) is an important citrus disease associated with the phloem-limited, uncultured bacterium ‘Candidatus Liberibacter asiaticus’(CLas). Effective treatments against CLas have to be validated in the field, however, methods for the field assessment of treatment effectiveness are time-consuming, in part because DNA-based assays, including quantitative PCR (qPCR), cannot differentiate between live and dead bacterial DNA. The aim of this study was to develop a method for rapid the evaluation of HLB therapies in field experiments. To this aim, a DNA extraction method from citrus leaf tissues with propidum monoazide (PMA), a dye that binds covalently to dsDNA making it unavailable for amplification in subsequent qPCR reactions, was optimized. The results indicated that the efficacy of PMA-qPCR was highly dependent on the primer set used. Primers targeting the 16S region of CLas showed a clear distinction between qPCR from PMA-treated and non-treated samples, while the RNR and LJ900 primers did not show significant differences between the DNA extraction methods. The PMA-qPCR viability analysis of CLas from citrus cuttings treated with different ampicillin (Amp) concentrations showed that all concentrations reduced CLas titers significantly starting 4 days after the initial treatment, unlike the water treatment, which did not show any change. This method was used for assessing the antibacterial activity of Amp, Streptomycin, Oxytetracycline (OTC), and a water control in field tests. The PMA-qPCR results indicated that Amp and OTC displayed significant antibacterial activity against CLas by 8 days post-injection, which was not detected in the non-PMA qPCR analysis. This method could allow the rapid validation of treatments against CLas in field experiments and facilitate the implementation of effective management strategies against HLB. Full article
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17 pages, 3270 KiB  
Article
Key Role of Heat Shock Protein Expression Induced by Ampicillin in Citrus Defense against Huanglongbing: A Transcriptomics Study
by Chuanyu Yang, Charles Powell, Yongping Duan, Xiongjie Lin, Goucheng Fan, Hanqing Hu and Muqing Zhang
Agronomy 2022, 12(6), 1356; https://doi.org/10.3390/agronomy12061356 - 2 Jun 2022
Cited by 2 | Viewed by 2659
Abstract
Citrus Huanglongbing (HLB) is a serious disease for the citrus industry. Earlier studies showed that ampicillin (Amp) can reduce titers of the pathogen which causes HLB and the bacteria Candidatus Liberibacter asiaticus (CLas) in HLB-affected citrus. CLas has not yet been cultured, so [...] Read more.
Citrus Huanglongbing (HLB) is a serious disease for the citrus industry. Earlier studies showed that ampicillin (Amp) can reduce titers of the pathogen which causes HLB and the bacteria Candidatus Liberibacter asiaticus (CLas) in HLB-affected citrus. CLas has not yet been cultured, so the mechanisms of Amp against CLas are unclear. Some chemicals were demonstrated to trigger citrus defense systems against CLas. Therefore, we hypothesize that Amp may induce citrus defenses against CLas. Here we applied three nano-formulations of varying droplet sizes to HLB-affected citrus to achieve different accumulated concentrations of Amp (high, medium, low) in the plants. We then used RNA-seq to analyze induction of gene expression of citrus defense systems against CLas in response to different concentrations of Amp. The results indicated that at all accumulated concentrations of Amp can significantly suppress CLas titer and mitigate HLB symptoms. Transcriptomic analyses showed that Amp treatment induced expression of heat shock proteins (Hsps) in HLB-affected citrus, and these Hsps were significantly related to several defense genes encoding R proteins, transcription factors, splicing factors, RNA-binding proteins, RNA-dependent RNA polymerase, Gibberellic acid methyltransferase 2, L-ascorbate peroxidase 2, and ferruginol synthase that confer tolerance to CLas in citrus plants. Taken together, these results suggest that Amp treatment of citrus plants can trigger expression of Hsps and related defense genes to respond to CLas infection. These findings are valuable for developing novel strategies to combat citrus HLB. Full article
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