Recent ucr_plantpathmicro_iocv items

History and evolution of the citrus budwood and seed scheme in Australia

Mon, 20 Jul 2026 00:00:00 +0000

The Australian citrus budwood and seed scheme is one of the oldest in the world and has been instrumental in maintaining the health, productivity, and uniformity of Australian citrus plantings. The scheme is run as a non-profit company under the trading name of Auscitrus, with most facilities at Dareton in far southwest New South Wales (NSW). In this paper, we provide a brief history of the citrus industry in Australia, including key events that led to the creation of a seed and budwood scheme in NSW in 1928. The emergence of plant diseases such as Phytophthora gummosis, citrus tristeza and exocortis compelled the industry to adopt new propagation and cultural practices. Industry and government continue to support and strengthen Auscitrus and Australian citrus biosecurity in the areas of diagnostics and surveillance, germplasm management, public education, policy and strategy. Auscitrus is a key component for the Australian citrus industry to manage endemic and respond to exotic...

Direct tissue print blotting followed by RT-qPCR for the detection of viroids in citrus germplasm

Wed, 15 Jul 2026 00:00:00 +0000

Citrus viroids are widespread and can impact tree health by causing bark scaling, stunting, gumming, and browning of phloem tissues, resulting in tree decline and yield reduction. Citrus viroids can be readily transmitted via mechanical injuries, grafting, pruning/cutting tools, and from tree propagation using infected, symptomless budwood. Due to their pathogenic potential and ease of transmission, laboratory testing of therapied budwood source plants is required for producing and preserving viroid-free propagative materials in citrus germplasm programs. Tissue-print blotting for nucleic acid isolation followed by reverse transcription (RT)-qPCR has been shown to be cost efficient and enable higher throughput testing capacity than traditional tissue grinding and nucleic acid purification methods for the detection of citrus bacteria and viruses (e.g., ‘ Candidatus Liberibacter sp.’ and citrus tristeza virus). However, this method has not been tested for citrus viroid detection....

Update on ‘Candidatus Liberibacter asiaticus’ incidence in five districts of the Punjab province of Pakistan

Sat, 2 May 2026 00:00:00 +0000

‘Candidatus Liberibacter asiaticus’ (CLas) is a devastating pathogen of citrus associated with Huanglongbing (HLB, citrus greening disease). HLB is economically significant in Asia and has destroyed millions of citrus trees worldwide during the last century. Since 2007, when the first molecular evidence for the presence of CLas in North-West Frontier Province of Pakistan (Khyber Pakhtunkhwa) were presented, there have been a limited number of studies reporting the pathogen in different citrus growing districts of the Punjab Province, one of the major citrus producing areas of the country. In this study, a small-scale survey was conducted in citrus groves exhibiting HLB-like symptoms in different districts of Punjab Province. The aim was to obtain current information on the incidence of CLas in the area and complement the previous studies. Conventional and real time quantitative polymerase chain reaction (PCR and qPCR) assays were used for the detection of CLas in the...

California Statewide Action Plan for Asian Citrus Psyllid and Huanglongbing

Fri, 19 Dec 2025 00:00:00 +0000

This document sets forth the California Department of Food and Agriculture (CDFA), Citrus Pest and Disease Prevention Division’s (CPDPD) statewide Action Plan for Asian citrus psyllid (ACP) and huanglongbing (HLB). This document details the program implemented by CPDPD to sustain and protect California’s commercial citrus production, residential citrus plantings, and naturalresources.

Abstracts 2025 IOCV XXIII

Fri, 19 Dec 2025 00:00:00 +0000

This publication contains the abstracts of the oral and poster presentations of the 23rd Conference of the International Organization of Citrus Virologists (IOCV), held in Mildura, Australia, March 16-20, 2025.

Program of the 23th Conference of International Organization of Citrus Virologists, Australia, 2025

Fri, 19 Dec 2025 00:00:00 +0000

This is the program of the 23rd Conference of the International Organization of Citrus Virologists (IOCV), held in Mildura, Australia, March 16-20, 2025.

A case study on the risk of spread of citrus huanglongbing in family farming in São Paulo and Minas Gerais States, Brazil

Tue, 16 Dec 2025 00:00:00 +0000

Since its detection in Brazil in 2004, huanglongbin g (HLB) has caused expressive damage to the citrus belt in São Paulo, Minas Gerais and Paraná states. The disease incidence is higher in small groves mainly related to family farming. A risk analysis was performed in citrus regions in São Paulo and Minas Gerais with the objective of identifying the main factors associated with the introduction and spread of HLB in this farm profile. A structured questionnaire was applied comprising 27 closed questions with binary answers (0 or 1 as no or yes ) to 39 citrus growers along 12 municipalities. The regions were selected according to the HLB incidence and relevance of citrus family farming, and farms were assessed by non-probabilistic and convenience sampling. The Analytic Hierarchy Process (AHP) was used to prioritize and weigh specific criteria related to the factors evaluated. Based on the answers, each farm was classified into four risk classes: low (0 to 0.25), intermediate...

Program of the 2022 Online Webinars Conference of IOCV XXII

Sun, 9 Mar 2025 00:00:00 +0000

This is the program of the online webinars of the 22nd Conference of the International Organization of Citrus Virologists (IOCV), September 7, 14, 21, and 28, 2022

Abstracts 2022 IOCV XXII

Sun, 9 Mar 2025 00:00:00 +0000

This article contains the abstracts presented at the online webinars of the 22nd Conference of the International Organization of Citrus Virologists (IOCV), September 7, 14, 21, and 28, 2022

Further investigation on citrus phantom disorders of unconfirmed viral etiology

Tue, 18 Jun 2024 00:00:00 +0000

This brief report expands upon the original review article published in Journal of Citrus Pathology in 2023 on citrus “phantom” disorders of presumed virus and virus-like etiology and addresses five additional disorders: citrus seed-borne virus disorder in New Zealand, bergamot vein yellowing in Greece, bergamot gummosis in Italy, bud knot in Italy, and a disorder resembling citrus crinkly leaf in Cuba. Each disorder is characterized by distinct symptoms and transmission patterns yet remains unresolved in terms of causative agents or conditions. By providing comprehensive information on these phantom citrus disorders, this report aims to serve as an additional reference for the citrus research community, industry stakeholders, and regulatory offices.

Manipulating the structure of citrus tristeza virus populations

Thu, 16 May 2024 00:00:00 +0000

Interaction between viruses is one of the major factors that determines viral population structure or equilibrium, which is a determinant of virus pathogenesis. If we could manipulate virus interactions, we could potentially limit the effects of disease. Using citrus tristeza virus (CTV) as a model, we examined if we could alter the equilibrium of a population by adding different CTV genotypes or other citrus pathogens. We found that population structure could be altered through the addition of specific CTV genotypes, disrupting existing interactions and selectively changing the titer of specific genotypes, while the addition of other citrus viruses or viroids did not have an effect.

Program of the 2024 IRCHLB VII

Wed, 15 May 2024 00:00:00 +0000

Program of the 2024 IRCHLB VII

Abstracts 2024 IRCHLB VII

Wed, 15 May 2024 00:00:00 +0000

Abstracts 2024 IRCHLB VII

Applying volumetric electron microscopy to visualize xylem tissue impacted by citrus tristeza virus-induced stem pitting

Mon, 1 Jan 2024 00:00:00 +0000

Citrus tristeza virus (CTV) causes several disease syndromes in different citrus hosts: quick decline, seedling yellows and stem pitting. CTV-induced stem pitting leads to substantial economic losses in sensitive citrus varieties, including grapefruit. The formation of stem pits has previously been linked to the ability of the virus to colonize xylem tissue outside of its typical phloem limitation, thereby disrupting normal xylem development. The nature of this compromised tissue has not been fully elucidated. In this study, stem pits were characterized at the molecular anatomical level using a combination of techniques to better understand the characteristics of the xylem and phloem tissues impacted by severe pitting. Biological staining was used to visualize CTV-induced stem pitting and was complemented with a novel technology that has not previously been used to study CTV-induced stem pitting, namely serial block-face scanning electron microscopy (SBF-SEM). This proof-of-concept...

Two distinct viral suppressors of RNA silencing encoded by citrus tatter leaf virus

Mon, 1 Jan 2024 00:00:00 +0000

Two proteins of the citrus tatter leaf virus (CTLV), a strain of the apple stem grooving virus (ASGV), capable of inducing citrus bud union disorders on commercially important trifoliate and citrange rootstocks, were identified as viral suppressors of RNA silencing (VSR). Both the coat protein (CP) and the movement protein (MP) suppressed RNA silencing in GFP-transgenic Nicotiana benthamiana 16c plants in agrobacterium-mediated co-infiltration assays; the MP acted as a local VSR, while the CP acted as a systemic VSR. When the potato virus X (PVX) infectious vector harbored either the CTLV CP or MP gene, viral infection and symptom development were promoted in N. benthamiana . Deletions of amino acids in the CP sequence or the MP sequence resulted in failure to promote PVX infections as well as suppression of silencing in agrobacterium-mediated co-infiltration assays. Mass spectrometry-based immunoprecipitation proteomics showed that neither the CTLV CP nor the MP interacts...

Whole genome analysis of spontaneous antimicrobial resistance in Liberibacter crescens suggests long-term efficacy for antimicrobial treatment of citrus greening disease

Mon, 1 Jan 2024 00:00:00 +0000

Currently, oxytetracycline and streptomycin are being applied to citrus groves in Florida for the control of citrus greening disease caused by the unculturable bacterium Candidatus Liberibacter asiaticus. Here, the closest cultured relative, L. crescens , was used to estimate the frequency of spontaneous antimicrobial resistance of Liberibacter spp. Results yielded thirteen streptomycin and zero oxytetracycline mutants after exposing 13 billion cells to the antimicrobials. These low rates, alongside the restrictive habitats of the vector and pathogen, suggest resistance may develop very slowly, if at all. Thus, the treatments will likely remain useful long enough before pathogen-resistant or -tolerant genotypes are deployed.

Citrus Phantom Disorders of Presumed Virus and Virus-like Origin: What Have We Learned in the Past Twenty Years?

Tue, 23 May 2023 00:00:00 +0000

In the process of recording and studying citrus diseases in the 20th century, citrus pathologists reported several suspected graft-transmissible disorders that were thought to be of virus or virus-like origin. While later work clarified and characterized most of these disorders, others were left unaddressed beyond their initial reports, and their status has remained unresolved for decades. For this reason, and for lack of a better term, such disorders are considered “phantoms”. In this work, our group performed an extensive literature review and communicated with renowned citrus pathologists and members of the International Organization of Citrus Virologists from around the world. Here we summarize and present in an organized manner the most up to date information for multiple phantom disorders, including disorders that have been subsequently characterized as a result of research efforts of the past 20 years. This review article could act as a reference point for citrus pathologists,...

Citrus Bent Leaf Viroid Present in Citrus in South Africa

Fri, 31 Mar 2023 00:00:00 +0000

Currently six viroid species are recognised which infect the genera Citrus and Poncirus, with an additional tentative new species reported. Citrus bent leaf viroid (CBLVd) has been reported from various citrus growing regions world-wide, but has not been formally documented from South Africa. CBLVd was detected in field samples in various citrus growing regions in South Africa during routine diagnostic analyses conducted since 2011. The detection and sequence verification of CBLVd from field samples is reported in this study. Biological confirmation of CLBVd could be done for one sample that was shown to contain a single viroid infection. Bent-leaf symptom expression was observed after slash inoculation of sample RNA to the ‘Etrog’ citron indicator host. This study was a retrospective analysis, of previously identified CLBVd-positive samples, to document the long-standing presence of CBLVd in South Africa.

High throughput sequencing of a stem pitting citrus tristeza virus isolate from Hunan Province P.R. China

Sun, 1 Jan 2023 00:00:00 +0000

A stem-pitting isolate of citrus tristeza virus (CTV), spreading in Hunan province of China (HU-PSTS), was sequenced and indexed on indicator plants. Biological assays showed that HU-PSTS is a highly aggressive stem pitting isolate belonging to biogroup 5. Viral small RNAs (18-26 nt) of the isolate were deep sequenced by Illumina technology to gain genomic information on the CTV strain infecting the source plant. The reads mapping with 17 CTV reference genomes enabled us to re-assemble the genomes of VT, T68, T30 and T3 strains. Among the VT, the highest number of mapped reads (47-41%) was with SG29, T318A, CT11A, Nuaga and AT-1 genomes, whereas T68, T30 and T3 genomes were less represented (28-20%). Alignments with genomes belonging to T36 and RB strains revealed percentage of mapped reads ranging from 10 to 12%. This is the first sequenced genome of a CTV isolate from Hunan province. According to the results, further sequencing and bioindexing need to be developed to...

Survey estimates of the incidence and diversity of Citrus tristeza virus in California

Sun, 1 Jan 2023 00:00:00 +0000

Surveys were conducted to assess Citrus tristeza virus (CTV) in California. Orchard surveys in central California during 2009 to 2013 estimated CTV incidence from 0.05% to 2.9%. Similar surveys in Ventura, Riverside, San Bernardino, and San Diego Counties in 2020-22 estimated CTV incidence from 6.3% to 34.9% while CTV was rarely found in the other five counties surveyed. T30 comprised over 95% of CTV detected alone or in mixtures with other strains in southern California and constituted 59% of 550 CTV accessions maintained in Tulare, California. VT, RB, and S1 genotypes were also found but T36 was rarely detected. No evidence of CTV-induced economic damage was noted except for occasional CTV quick decline on sour orange rootstock.

Structural changes in Florida citrus production, 1980-2021 and associated consequences of weather events and disease.

Sun, 1 Jan 2023 00:00:00 +0000

Florida citrus production from 1980-2021 was examined and modeled to determine the impacts associated with weather events and disease introductions. Specifically, the study examined the effects of North Atlantic hurricanes, freezes events and two disease introductions -- Asiatic citrus canker (ACC), and Huanglongbing (HLB) -- on productions levels and on the structure of the Florida citrus industry. The models estimated quantified the effects on production associated with the weather events and disease introductions. Using the deterministic model generated, forecasts were generated to identify future implications of HLB on Florida citrus production. Theses generated forecasts were compared to actual production levels and the USDA Crop forecast to test and validate the model. Whereas testing indicated a significant structural change in the Florida citrus industry resulting from adverse weather events and disease introductions, published economic...

First report of citrus virus A in Australia

Tue, 3 May 2022 00:00:00 +0000

Citrus virus A (CiVA) was detected for the first time in Australia in a living pathogen collection. Buds were originally collected from a Washington navel field tree prior to 1970 and graft-inoculated onto a Symons sweet orange indicator plant. The virus was detected using conventional and quantitative reverse transcription polymerase chain reactions and high-throughput sequencing. This variant shares 96.3% (RNA1) and 96.7% (RNA2) nucleotide identity with isolates of CiVA from South Africa and China, respectively. Foliar symptoms of leaf flecking and oak leaf patterns, consistent with detections of CiVA in other regions, were observed on the foliage of the original accession and inoculated indicator plants. Subsequent surveys of an Australian citrus variety collection detected a different CiVA sequence variant in two accessions of Pera sweet orange; this variant had 97% similarity to the other Australian variant.

Economic Impact of California’s Citrus Industry in 2020

Thu, 10 Feb 2022 00:00:00 +0000

The value of California citrus production in the 2020-21 marketing year was $3.63 billion. The total economic impact of the industry on California’s economy in 2020-21 was $7.6 billion. The California citrus industry added $1.9 billion to California’s state GDP in 2020. Estimated full time equivalent jobs in the California citrus industry in 2020-21 totaled 24,247. Estimated wages paid by the California citrus industry income in 2020-21 totaled $759 million. A 20% reduction in California citrus acreage would cause a loss of 8,213 jobs, $214 million in employee income, and reduce state GDP by $569 million.

First Report of Citrus Bent Leaf Viroid and Citrus Dwarfing Viroid in Argentina

Sat, 1 Jan 2022 00:00:00 +0000

Samples collected from citrus trees with viroid-like symptoms in citrus orchards in Tucumán, Salta, and Jujuy provinces(northwestern Argentina) were initially indexed on citron (Citrus medica) and then analysed by s-PAGE. These samples werefound to be infected with different viroid species, among them, CEVd and HSVd have been already identified. In order todetermine the presence of other viroids, we performed a RT-PCR assay using specific primers for CBLVd, CDVd, Citrus barkcracking viroid (CBCVd) and Citrus viroid V (CVd-V).

Forty-two samples including 15 lemons, 15 oranges, 8 grapefruits, 2 citrumelos and 2 Cleopatra mandarins were analysed.On the basis of amplification of the appropriately sized DNA, CDVd was detected in thirty-eight samples and CBLVd in allgrapefruit samples. CBCVd and CVd-V were not found in any samples to date. Analysis of the amplicon sequences revealed96% and 97% identity with CBLVd GenBank reference sequences, and 96% to 98% with CDVd GenBank...

Investigating the Impact of Huanglongbing in Citrus in Southern Lao PDR

Sat, 1 Jan 2022 00:00:00 +0000

Citrus has been promoted in the Lao People’s Democratic Republic (Lao PDR) as a poverty reduction strategy for at least two decades. However, citrus trees have been in widespread decline for no less than ten years. Since 2010, the authors have observed symptoms on citrus trees consistent with the bacterial disease huanglongbing (HLB). These symptoms included asymmetric leaf mottle, small lopsided fruit, poor fruit production and tree decline. The authors then initiated a long-term study on the occurrence of HLB in southern Lao PDR. Samples of leaf mid-ribs were collected from citrus trees in orchards, nurseries, and backyards across four provinces: Champasak, Sekong, Salavan, and Savannakhet. The presence of ‘Candidatus Liberibacter asiaticus’, the putative causal agent of the Asiatic form of HLB, was confirmed in 59 of 109 samples collected in all four provinces. The Asian citrus psyllid, the vector of ‘Ca. L. asiaticus’, was also observed on citrus trees...

Huanglongbing in Bangladesh: A Pilot Study for Disease Incidence, Pathogen Detection, and its Genetic Diversity

Sat, 1 Jan 2022 00:00:00 +0000

Huanglongbing (HLB), also known as citrus greening, is the most serious disease affecting citrus production in Asia, Africa, the Americas, and the Arabian Peninsula. HLB is associated with the α-Proteobacteria “CandidatusLiberibacter asiaticus” (CLas), “Ca. L. africanus” (CLaf), and “Ca. L. americanus” (CLam). The Bangladesh citrus industry comprises mandarins, sweet oranges, pummelos, limes, and lemons. In 2017-2018, a survey was conducted for two consecutive years in 18 sweet orange growing areas of Bangladesh, and the presence of CLas in these areas was confirmed by polymerase chain reaction. HLB incidence and severity were assessed based on leaf symptoms. The results unveiled a widespread prevalence of HLB with incidence ranging between 0.08 and 56% and severity between 1.80 and 28.33. Information on the genetic diversity of CLas Bangladeshi isolates was obtained based on the presence or absence of...

Vegetative shoot flush dynamics of ‘Pera’ sweet orange on three rootstock cultivars

Sat, 1 Jan 2022 00:00:00 +0000

The dynamics and intensity of new shoot flushes of ‘Pera’ sweet orange scions [Citrus × sinensis (L.) Osbeck] grafted onto ‘Rough’ lemon (Citrus × limonia var. jambhiri Lush.), ‘Swingle’ citrumelo [Citrus × aurantium var. paradisi x Poncirus trifoliata (L.) Raf.] and ‘Sunki’ mandarin (Citrus reticulata ‘Sunki’) rootstocks were evaluated in the field at a citrus farm located in a northern region of the state of Sao Paulo, Brazil. Every 20 days for 16 months, new shoots were counted within a square frame of 0.25 m² set on the central portion of the canopy and classified based on their phenological stages. Trees on ‘Swingle’ rootstock produced a lower area under the flush shoot dynamics curve (AUFSD) and mean number of new shoots than trees on ‘Rough’ lemon or ‘Sunki’ mandarin. For trees on all three rootstocks, new shoot intensities varied...

Citrus Bud Certification in Arizona

Mon, 20 Dec 2021 00:00:00 +0000

Citrus Bud Certification in Arizona

Program of the 3rd International Research Conference on Huanglongbing (IRCHLB-III), Feb. 4-8, 2013, Orlando, Florida, U.S.A.

Fri, 5 Nov 2021 00:00:00 +0000

Program of the 3rd International Research Conference on Huanglongbing (IRCHLB-III), Feb. 4-8, 2013, Orlando, Florida, U.S.A.

Fifty Years of IOCV, 1957 to 2007: From Graft-Transmitted Citrus Agents to Viroids, Viruses and Endogenous Bacteria

Tue, 12 Oct 2021 00:00:00 +0000

Fifty Years of IOCV, 1957 to 2007: From Graft-Transmitted Citrus Agents to Viroids, Viruses and Endogenous Bacteria

In situ localization of citrus exocortis viroid RNA using an optimized RNAscope™ assay

Fri, 14 May 2021 00:00:00 +0000

Due to their small size, locating pathogenic RNAs, such as viroids, in plant tissue and cell organelles has been difficult. Viroids are small circular single-stranded RNA plant pathogens that reduce plant growth, vigor, and yield in economically important crops such as potato, tomato, hops and citrus. Viroid infections in plants are largely diagnosed by dot blot hybridization, polyacrylamide gel electrophoresis (PAGE) or gels, or real-time quantitative polymerase chain reaction (qPCR). Because traditional plant in situ hybridization studies for viroids are often limited by the lack of signal amplification and binding specificity due to the small target sequence, we examined the use of RNAscope™ (Advanced Cell Diagnostics Inc., Newark, CA). This in situ hybridization method increases the detection by amplifying the signal of a single target, to detect the cellular distribution of citrus exocortis viroid (CEVd) with higher sensitivity and specificity. We found...

Citrus Rootstocks: Their characters and reactions (an unpublished manuscript)

Sat, 24 Apr 2021 00:00:00 +0000

IOCV is pleased to present “Citrus Rootstocks: Their Characters and Reactions”, an unpublished manuscript by the late Prof. W.P. Bitters, University of California, Riverside. Based upon Prof. Bitters research and many other sources, this work was compiled between the late 1960’s and 1986 (additional information in preface). It represents a comprehensive (for that era) treatment of many facets of citrus rootstock physiology, horticulture, and pathology. Rootstocks serve as both conduits for citrus disease development and potential disease management tools, as well as tools in dealing with abiotic stresses. The history of the use of rootstocks for citrus has largely been determined by these factors, and they continue to greatly influence citrus rootstock research and usage. Although many advances in knowledge regarding citrus rootstocks have been made since 1986, the basic information presented remains important for all citriculturists. We hope that this Special Topic in IOCV’s...

Program of the 20th Conference of International Organization of Citrus Virologists, China, 2016

Fri, 12 Feb 2021 00:00:00 +0000

Program of the 20th Conference of International Organization of Citrus Virologists, China, 2016

First comprehensive sanitary report of citrus-infecting viruses and viroids in Uruguay

Fri, 1 Jan 2021 00:00:00 +0000

Citrus is the highest-value fruit crop in terms of international trade. However, citrus species are susceptible to several diseases caused by different pathogens which directly cause a decrease in production leading to economic losses. In the last half-century, the citrus industry in Uruguay has had a strong socio-economic impact and is also constantly evolving to stay competitive in world markets, by introduction of new varieties and improvement of production practices to obtain high yielding orchards. Nevertheless, despite the existence since 2014 of the Uruguayan National Citrus Sanitary and Certification Program, scarce information is available regarding the virus and viroid status of commercial citrus in Uruguay. The incidence of citrus tristeza virus (CTV), citrus psorosis virus (CPsV), satsuma dwarf virus (SDV), citrus exocortis viroid (CEVd), hop stunt viroid (HSVd), citrus dwarfing viroid (CDVd), citrus bark cracking viroid (CBCVd) and citrus bent leaf viroid (CBLVd)...

First report of citrus virus A in citrus in South Africa

Fri, 1 Jan 2021 00:00:00 +0000

High-throughput sequencing (HTS) of citrus indicator hosts, originally inoculated from field samples and showing transient chlorotic flecking or oak leaf patterns, revealed the presence of the first South African variant of citrus virus A (CiVA). This virus was first identified in citrus in Italy and was classified as a member of the second species (Coguvirus eburi) of the genus Coguvirus within the order Bunyavirales. The South African sequence variants of CiVA share 95.26-95.55% (RNA1) and 94.82-97.85% (RNA2) nucleotide sequence identity with the CiVA sequences from the Italian isolate. The discovery of CiVA in South African citrus orchards indicates a wide distribution of CiVA and further investigations are required to determine the association of CiVA with citrus disease symptoms.

Evaluating high-resolution computed tomography to study citrus tristeza virus-induced stem pitting

Fri, 1 Jan 2021 00:00:00 +0000

Citrus tristeza virus (CTV) is the most important viral pathogen of citrus. CTV-induced stem pitting negatively impacts grapefruit and sweet orange production. The mechanisms of stem pitting development in CTV-infected citrus remain unclear. This study evaluated the utility of high-resolution CT scanning as a tool to study stem pitting in live citrus material. CT scans were used to easily identify pits based on differences in tissue density. Stem pits were also mapped and modelled three-dimensionally along the length of the stem. Nano-CT scanning proved to be a potentially valuable, non-destructive method for stem pitting characterization in citrus.

Why we should care about culturing the Huanglongbing associated bacterium ‘Candidatus Liberibacter asiaticus’: the importance of terms and interpretations

Fri, 16 Oct 2020 00:00:00 +0000

Having bacteria grown in pure culture has been the foundation of bacteriology, by allowing a wide range of microbiological studies towards understanding the functionality of a specific bacterium. However, most bacteria have not been axenically cultured to date, thus hindering the understanding of their role in the context of their host or environment. One of these unculturable bacteria are the recently emergent plant pathogens ‘Candidatus Liberibacter spp.’. This group is comprised by dynamic psyllid-vectored, phloem-limited plant pathogens and endophytes that harm a wide range of economically important crops worldwide. ‘Candidatus Liberibacter asiaticus’ (CLas) is associated with Huanglongbing (HLB) in most of the main citrus-producing areas globally, a disease causing severe economic damages. Although the establishment of axenic cultures of CLas remains a major scientific challenge, many research groups have devoted efforts to culture this bacterium to aid...

IOCV-IX-Abstracts of Presentations at the 19th Conference of the International Organization of Citrus Virologists, South Africa, 2013

Wed, 14 Oct 2020 00:00:00 +0000

IOCV-IX-Abstracts of Presentations at the 19th Conference of the International Organization of Citrus Virologists, South Africa, 2013

Managing biosecurity risks to Australian citrus

Wed, 14 Oct 2020 00:00:00 +0000

The high health status of Australian citrus germplasm has been maintained largely due to a successful quarantine system and propagation scheme. Most endemic graft transmissible diseases are rarely observed in Australian orchards due to the use of high health status propagation material supplied by Auscitrus. Citrus tristeza virus is present throughout the citrus growing areas although mild strain cross protection has been effectively managing grapefruit stem pitting in white grapefruit varieties for over 40 years. However, diseases like huanglongbing and canker are ever present threats to the biosecurity of the Australian citrus industry. The introduction of mandatory nursery registration and compulsory use of pathogen tested propagation material would provide greater security to the industry in the face of increasing biosecurity threats.

Program of the 19th Conference of International Organization of Citrus Virologists, South Africa, 2013

Wed, 14 Oct 2020 00:00:00 +0000

Program of the 19th Conference of International Organization of Citrus Virologists, South Africa, 2013

Action Plan for Asian Citrus Psyllid and Huanglongbing (Citrus Greening) in California

Thu, 23 Jul 2020 00:00:00 +0000

This document sets forth the California Department of Food and Agriculture (CDFA), Citrus Pest and Disease Prevention Division (CPDPD) statewide Action Plan for Asian citrus psyllid (ACP) and Huanglongbing (HLB). This document details the program implemented by CPDPD to sustain and protect California’s commercial citrus production, residential citrus plantings, and natural resources.

Inability of the brown citrus aphid (Toxoptera citricida) to transmit citrus psorosis virus under controlled conditions

Wed, 1 Jan 2020 00:00:00 +0000

Might Toxoptera citricida (BrCA) be a citrus psorosis virus (CPsV) vector? We examined CPsV transmission by the BrCA throughout two experiments. In experiment 1, 4 CPsV-infected plants bearing BrCA colonies were introduced in separated cages with 12 healthy 'Madame Vinous' sweet orange (MV) seedlings in each one (48 in total). In experiment 2, 5 BrCAs collected from each CPsV-infected plant were transferred into 3 MV seedlings for each one (12 in total) and left for a 72-h inoculation period. Both experiments were replicated once. No psorosis symptoms or CPsV detection evidences a BrCA inability for CPsV transmission under our controlled conditions.

Citrus dwarfing viroid reduces canopy volume by affecting shoot apical growth of navel orange trees grown on trifoliate orange rootstock

Wed, 1 Jan 2020 00:00:00 +0000

Citrus dwarfing viroid (CDVd) infection of navel orange trees (Citrus sinensis (L.) Osb.) on ‘Rich 16-6’ trifoliate orange (Poncirus trifoliata (L.) Raf.) rootstock has been previously reported to reduce canopy volume by approximately 50%. We demonstrated that the reduction in tree size of CDVd-infected citrus resulted from a >20% reduction in the apical growth of individual shoots within the tree canopy. We also demonstrated that the reduced canopy volume of the CDVd-infected trees is a long lasting phenotype comparable to that of ‘Flying Dragon’ rootstock, which is known to reduce citrus tree size.

Biography of Stephen M Garnsey

Mon, 21 Oct 2019 00:00:00 +0000

Biography of Stephen M Garnsey

Program of the 2019 Joint Conference of IOCV XXI and IRCHLB VI

Thu, 3 Oct 2019 00:00:00 +0000

Program of the 2019 Joint Conference of IOCV XXI and IRCHLB VI

Abstracts 2019 Joint IOCV XXI and IRCHLB VI

Thu, 3 Oct 2019 00:00:00 +0000

Abstracts 2019 Joint IOCV XXI and IRCHLB VI

From spinach chloroplasts to endogenous bacteria causing diseases in citrus: an autobiography of Joseph Marie Bové

Mon, 9 Sep 2019 00:00:00 +0000

From spinach chloroplasts to endogenous bacteria causing diseases in citrus: an autobiography of Joseph Marie Bové

Changes in host microRNA expression during citrus tristeza virus induced disease

Tue, 1 Jan 2019 00:00:00 +0000

The physical effects of disease induced by Citrus tristeza virus (CTV) on its citrus host have long been known, but not how disease is induced either by the virus, or its effects on the host at the genetic level. In this study we aimed to examine the latter, by deliberate inoculation of Citrus macrophylla with a mutant T36-based infectious clone known to induce stem pitting and other growth abnormalities. The microRNA populations of disease-expressing plants were compared with plants infected with asymptomatic, wild-type T36, and with un-inoculated controls. We found that while virus infection induced change in expression of a large number of miRNAs, the onset of disease correlated with the downregulation of miR164, a miRNA associated with vascular differentiation. This is the first evidence of specific host miRNAs associated with the induction of a CTV disease syndrome.

A survey of Florida citrus viruses and viroids

Tue, 21 Aug 2018 00:00:00 +0000

Efficient disease management is critical in the production of citrus; a crop that is susceptible to several plant pathogens. The ongoing battle with citrus greening has led to a shift in cultural practices, which could lead to a resurgence of previously controlled diseases. Here we investigated the presence of several common citrus-infecting viruses and viroids (Citrus leaf blotch virus, Apple stem grooving virus (synonym: Citrus tatter leaf virus), Citrus exocortis viroid, Hop stunt viroid (synonym: Citrus viroid II), and Citrus dwarfing viroid (synonym: Citrus viroid III) in Florida citrus groves. All five viruses and viroids are still present, with varying incidence. It would be prudent to take them into consideration when developing citrus disease management strategies.

Overexpression of the Arabidopsis NPR1 protein in citrus confers tolerance to Huanglongbing

Sun, 6 May 2018 00:00:00 +0000

Huanglongbing (HLB), also known as citrus greening, is one of the most destructive diseases of citrus worldwide. It is caused by unculturable phloem-limited bacteria that belong to the Candidatus Liberibacter genus including Ca. L. asiaticus (CLas), Ca. L. africanus, and Ca. L. americanus. Currently, there is no effective control strategy for HLB and no known cure for the disease. We have previously generated transgenic ‘Duncan’ grapefruit and ‘Hamlin’ sweet orange expressing the Arabidopsis NPR1 (AtNPR1) gene, which encodes a master regulator of systemic acquired resistance. Characterization of the transgenic lines indicated that overexpression of AtNPR1 confers resistance to citrus canker, another serious bacterial disease in citrus. In this study, we intensively screened these transgenic lines for resistance or tolerance to HLB under greenhouse conditions. Three independent transgenic lines (one...

Graft-transmissible citrus diseases in P. R. China-research developments

Tue, 24 Apr 2018 00:00:00 +0000

In the P.R. China, ten graft-transmissible pathogens have been identified towards citrus, including Candidatus Liberibacter asiaticus, Citrus tristeza virus (CTV), Citrus tatter-leaf virus (CTLV), Citrus exocortis viroid (CEVd), Citrus yellow vein clearing virus (CYVCV),Satsuma dwarf virus (SDV), Citrus vein enation virus (CVED), Citrus psorosis virus (CPsV), Citrus cachexia viroid (CCaVd) and Citrus chlorotic dwarf virus (CCDV). Of these pathogens, the first five cause damage in field citrus trees, whereas the latter five were occasionally detected from the imported citrus materials or field trees. The research progresses about HLB, CTV, CYVCV etc. within recent three years have briefly been reviewed.

Citrus Greening Disease and the Greening Bacterium