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Citrus canker is a disease caused by the gram-negative bacterium Xanthomonas citri subp. citri (X. citri), which affects all commercially important varieties of citrus and can lead to significant losses. Fruit sanitization with products such as chlorine-based ones can reduce the spread of the disease. While effective, their use raises concerns about safety of the workers. This work proposes essential oils (EOs) as viable alternatives for fruit sanitization. EOs from Cymbopogon species were evaluated as to their antibacterial activity, their effect on the bacterial membrane, and their ability to sanitize citrus fruit. The in vitro assays revealed that the EOs from C. schoenanthus and C. citratus had a lower bactericidal concentration at 312 mg L−1, followed by 625 mg L−1 for C. martini and C. winterianus. Microscopy assay revealed that the bacterial cell membranes were disrupted after 15 min of contact with all EOs tested. Regarding the sanitizing potential, the EOs with higher proportions of geraniol were more effective in sanitizing acid limes. Fruit treated with C. shoenanthus and C. martini showed a reduction of ∼68% in the recovery of viable bacterial cells. Therefore, these EOs can be used as viable natural alternatives in citrus fruit disinfection. [ABSTRACT FROM AUTHOR]

Aims Citrus canker caused by Xanthomonas citri subsp. citri (X. citri) is a disease of economic importance. Control of this disease includes the use of metallic copper, which is harmful to the environment and human health. Previous studies showed that the crude extract from the fungus Pseudogymnoascus sp. LAMAI 2784 isolated from Antarctic soil had in vitro antibacterial action against X. citri. The aim of the present study was to expand the applications of this extract. Methods and results In greenhouse assays, the crude extract was able to reduce bacterial infection on citrus leaves from 1.55 lesions/cm2 (untreated plants) to 0.04 lesions/cm2. Bisdechlorogeodin was identified as the main compound of the bioactive fraction produced by Pseudogymnoascus sp. LAMAI 2784, which inhibited bacterial growth in vitro (IC90 ≈ 156 µg ml−1) and permeated 80% of X. citri cells, indicating that the membrane is the primary target. Conclusion The present results showed that the bioactive fraction of the extract is mainly composed of the compound bisdechlorogeodin, which is likely responsible for the biological activity against X. citri , and the main mechanism of action is the targeting of the cell membrane. This study indicates that bisdechlorogeodin has valuable potential for the control of X. citri. [ABSTRACT FROM AUTHOR]

Virus-induced gene silencing (VIGS) is a powerful technology for molecular characterization of gene functions in plants and has the potential to prevent and control plant diseases. Unfortunately, VIGS in many woody perennials such as citrus are severely hindered because they have a long juvenile period and are recalcitrant to infection compared to herbaceous plants. Here, we report the development of a simple and effective VIGS system based on citrus leaf blotch virus (CLBV), a virus endemic in most citrus-producing countries but showing no symptoms in most citrus varieties. By Agrobacterium-mediated vacuum-infiltration (AVI), pCLBV201-su245 and pCLBV201-pds391 triggered efficient gene silencing (85%) and silencing phenotypes began to appear at 30 days post infiltration/inoculation (dpi), a similar period for achieving that on herbaceous plants. Moreover, the silencing phenotypes could still be observed four years post inoculation. Further, pCLBV201-lob369 was constructed to silence the gene lateral organ boundaries1 (lob1), encoding a key factor for susceptibility to citrus canker that caused by Xanthomonas citri ssp. citri (Xcc). The resistance evaluation results showed that the lesion area, disease index, and bacterial content in the pCLBV201-lob369 treatment group were decreased by 64%, 14%, and 67%, respectively. This work provides a simple and effective VIGS system for citrus which has the potential to be used for diseases control. [ABSTRACT FROM AUTHOR]

Citrus canker is an infectious bacterial disease and one of the major threats to the orange juice industry, a multibillion-dollar market that generates hundreds of thousands of jobs worldwide. This disease is caused by the Gram-negative bacterium Xanthomonas citri subsp. citri. In Brazil, the largest producer and exporter of concentrate orange juice, the control of citrus canker is exerted by integrated management practices, in which cupric solutions are intensively used in the orchards to refrain bacterial spreading. Copper ions accumulate and are as heavy metals toxic to the environment. Therefore, the aim of the present work was to evaluate bifunctional fusion proteins (BiFuProts) as novel and bio-/peptide-based alternatives to copper formulations to control citrus canker. BiFuProts are composed of an anchor peptide able to bind to citrus leaves, and an antimicrobial "killer" peptide to protect against bacterial infections of plants. The selected BiFuProt (Mel-CgDEF) was bactericidal against X. citri at 125 μg mL−1, targeting the bacterial cytoplasmic membrane within the first minutes of contact. The results in the greenhouse assays proved that Mel-CgDEF at 250 μg mL−1 provided protection against X. citri infection on the leaves, significantly reducing the number of lesions by area when compared with the controls. Overall, the present work showed that the BiFuProt Mel-CgDEF is a biobased and biodegradable possible alternative for substitute cupric formulations. Key points: • The bifunctional fusion protein Mel-CgDEF was effective against Xanthomonas citri. • Mel-CgDEF action mechanism was the disruption of the cytoplasmic membrane. • Mel-CgDEF protected citrus leaves against citrus canker disease. [ABSTRACT FROM AUTHOR]

Citrus canker, caused by the bacterium Xanthomonas citri (Xcc), is one of the most devastating diseases for the citrus industry. Xylose is a constituent of the cell wall of plants, and the ability of Xcc to use this carbohydrate may play a role in virulence. Xcc has two genes codifying for xylose isomerase (XI), a bifunctional enzyme that interconverts D-xylose into D-xylulose and D-glucose into D-fructose. The aim of this work was to investigate the functional role of the two putative XI ORFs, XAC1776 (xylA1) and XAC4225 (xylA2), in Xcc pathogenicity. XI-coding genes of Xcc were deleted, and the single mutants (XccΔxylA1 or XccΔxylA2) or the double mutant (XccΔxylA1ΔxylA2) remained viable. The deletion of one or both XI genes (xylA1 and/or xylA2) increased the aggressiveness of the mutants, causing disease symptoms. RT-qPCR analysis of wild strain and xylA deletion mutants grown in vivo and in vitro revealed that the highest expression level of hrpX and xylR was observed in vivo for the double mutant. The results indicate that XI depletion increases the expression of the hrp regulatory genes in Xcc. We concluded that the intracellular accumulation of xylose enhances Xcc virulence. [ABSTRACT FROM AUTHOR]

Citrus canker, caused by the bacterium Xanthomonas citri subsp. citri (Xcc), is a disease that causes serious problems to the global citrus industry. Matrix-Assisted Laser Desorption/Ionization Time-of-Flight (MALDI-TOF) Mass Spectrometry (MS) has been used in human medicine to diagnose various diseases caused by both fungi and bacteria. In agriculture, this technique has potential for the diagnosis of diseases due to the low cost of large-scale analysis and quickness. This study showed that MALDI-TOF MS combined with chemometric analysis was effective for differentiating the macromolecule profile of orange leaves with canker lesions, healthy leaves, and leaves with phytotoxicity symptoms, proving that this technique may be used for the rapid diagnosis of citrus canker. [ABSTRACT FROM AUTHOR]

The genus Xanthomonas comprises several cosmopolitan plant‐pathogenic bacteria that affect more than 400 plant species, most of which are of economic interest. Citrus canker is a bacterial disease that affects citrus species, reducing fruit yield and quality, and is caused by the bacterium Xanthomonas citri subsp. citri (Xac). The Xac3819 gene, which has previously been reported to be important for citrus canker infection, encodes an uncharacterized glutathione S‐transferase (GST) of 207 amino‐acid residues in length (XacGST). Bacterial GSTs are implicated in a variety of metabolic processes such as protection against chemical and oxidative stresses. XacGST shares high sequence identity (45%) with the GstB dehalogenase from Escherichia coli O6:H1 strain CFT073 (EcGstB). Here, XacGST is reported to be able to conjugate glutathione (GSH) with bromoacetate with a Km of 6.67 ± 0.77 mM, a kcat of 42.69 ± 0.32 s−1 and a kcat/Km of 6.40 ± 0.72 mM−1 s−1 under a saturated GSH concentration (3.6 mM). These values are comparable to those previously reported for EcGstB. In addition, crystal structures of XacGST were determined in the apo form (PDB entry 6nxv) and in a GSH‐bound complex (PDB entry 6nv6). XacGST has a canonical GST‐like fold with a conserved serine residue (Ser12) at the GSH‐binding site near the N‐terminus, indicating XacGST to be a serine‐type GST that probably belongs to the theta‐class GSTs. GSH binding stabilizes a loop of about 20 residues containing a helix that is disordered in the apo XacGST structure. [ABSTRACT FROM AUTHOR]

Citrus canker is one of the most devastating disease of citrus crop. It is a worldwide disease, caused by bacterium Xanthomonas axonopodis pv. citri. Citrus canker incidence has been observed on most of the citrus varieties. Severe infection of the bacterium produces a variety of effects including defoliation, dieback, severely blemished fruit, reduced fruit quality and premature fruit drop. Present study was conducted at Citrus Research Institute, Sargodha during the years 2016-18 on ten years old kinnow plants. There were ten treatments including control with four replications. Spray was done four times in a year during the months of March, April, August, and September. The efficacy of different treatments was compared to control the disease incidence on leaves and fruits. It was concluded that Bordeaux mixture was the most suitable chemical to control the canker on kinnow plant and it also improved the quality of fruit in terms of fruit weight, fruit size and juice weight. Besides, copper hydroxide and onion extract were also found efficacious to control the disease. In future, these chemicals and plant extracts could be used in different combinations to control canker on different citrus varieties. [ABSTRACT FROM AUTHOR]

Citrus canker type A is a serious disease caused by Xanthomonas citri subsp. citri (X. citri), which is responsible for severe losses to growers and to the citrus industry worldwide. To date, no canker-resistant citrus genotypes are available, and there is limited information regarding the molecular and genetic mechanisms involved in the early stages of the citrus canker development. Here, we present the CitrusKB knowledge base. This is the first in vivo interactome database for different citrus cultivars, and it was produced to provide a valuable resource of information on citrus and their interaction with the citrus canker bacterium X. citri. CitrusKB provides tools for a user-friendly web interface to let users search and analyse a large amount of information regarding eight citrus cultivars with distinct levels of susceptibility to the disease, with controls and infected plants at different stages of infection by the citrus canker bacterium X. citri. Currently, CitrusKB comprises a reference citrus genome and its transcriptome, expressed transcripts, pseudogenes and predicted genomic variations (SNPs and SSRs). The updating process will continue over time by the incorporation of novel annotations and analysis tools. We expect that CitrusKB may substantially contribute to the field of citrus genomics. CitrusKB is accessible at http://bioinfo.deinfo.uepg.br/citrus. Users can download all the generated raw sequences and generated datasets by this study from the CitrusKB website. [ABSTRACT FROM AUTHOR]