Recent iocv_journalcitruspathology items

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

Sat, 2 May 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...

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...

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.

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.

Construction and application of infectious citrus viroids for biological indexing

Mon, 20 Nov 2017 00:00:00 +0000

Viroid species identified in citrus induce a range of symptoms in this host as well as in non-citrus hosts. Currently, 7 citrus viroid species are recognized including Citrus bent leaf viroid (CBLVd), Hop stunt viroid (HSVd), Citrus dwarfing viroid (CDVd), Citrus bark cracking viroid (CBCVd), Citrus viroid V (CVd-V), Citrus viroid VI (CVd-VI) and Citrus exocortis viroid (CEVd). Cachexia-inducing variants of HSVd and CEVd, which causes exocortis, are considered severe pathogens of citrus, whereas other viroid species induce less severe symptoms such as stunting, either singly or in combination. Some viroid species, such as CDVd, have previously been used to deliberately induce stunting for high density planting of citrus, but studies on the effects of commercial orchards are limited. Research on the effect of viroid species requires the isolation of single viroid species. Biological isolation of single species from...

Huanglongbing solutions and the need for anti-conventional thought

Fri, 3 Nov 2017 00:00:00 +0000

Citrus huanglongbing (HLB) has been recognized for a century yet control and management remain elusive despite over 90 years of intensive research. The bacterial pathogen is an insect endosymbiont that was most likely inadvertently introduced into citrus where it found a compatible environment for growth in citrus phloem cells and therefore jumped from the animal to plant kingdom. Because the genus citrus did not coevolve with the bacteria it has no resistance and little tolerance to it and the resulting vascular disease is severe. The winged insect vector of the bacteria, the Asian citrus psyllid (ACP), is an exotic introduced species in its own right, prolific, and difficult to control even on a regional spatial scale. The resulting disease has a long latent period prior to symptom expression and a challenging cryptic period during which detection by convention PCR and other methods can be elusive. The result is an unusually rapid increase and spread of the resulting disease....

Interaction between Phytophthora nicotianae and Candidatus Liberibacter asiaticus damage to citrus fibrous roots

Mon, 24 Jul 2017 00:00:00 +0000

Huanglongbing (HLB) is associated with the phloem-limited bacterium, Candidatus Liberibacter asiaticus (Las). Phytophthora nicotianae (P.n.) causes root rot of citrus, which reduces water and nutrient uptake by citrus fibrous roots. The discovery that Las damage to fibrous roots occurs before tree canopy symptoms develop led to the prediction that Las root infection directly damages roots and may interact with soil-borne pathogens to cause further damage. Hence, comparison of root damage by Las and P.n. alone or in combination was carried out on seedlings of Cleopatra mandarin (Citrus reticulata Blanco) rootstock to evaluate the possible interaction of Las and P.n. and their relative contribution to fibrous root loss. The results demonstrated that i) roots of seedlings have a similar level of damage when inoculated with Las or P.n., and coinoculation causes comparable damage as each pathogen alone; and ii) Las infection increases and decreases P.n. infection incidence overtime...

Keynote Summary: Black swans, dragons and the phoenix: rebuilding citrus after HLB

Tue, 6 Jun 2017 00:00:00 +0000

Keynote Summary: Black swans, dragons and the phoenix: rebuilding citrus after HLB

Keynote Summary: The social side of pest and disease biosecurity: reflections from Australia

Wed, 24 May 2017 00:00:00 +0000

Keynote Summary: The social side of pest and disease biosecurity: reflections from Australia

Tribute to Prof. Joseph Bové

Thu, 11 May 2017 00:00:00 +0000

Tribute to Prof. Joseph Bové

Joseph (Josy) M. Bové - Selected Photos

Thu, 11 May 2017 00:00:00 +0000

Joseph (Josy) M. Bové - Selected Photos

Program of the 5th International Research Conference on Huanglongbing (IRCHLB-V), March 14-17, 2017, Orlando, Florida, U.S.A.

Tue, 9 May 2017 00:00:00 +0000

Program of the 5th International Research Conference on Huanglongbing (IRCHLB-V), March 14-17, 2017, Orlando, Florida, U.S.A.

Joseph (Josy) M. Bové Dedication

Tue, 9 May 2017 00:00:00 +0000

Joseph (Josy) M. Bové Dedication

Abstracts of Presentations at the 5th International Research Conference on Huanglongbing

Fri, 28 Apr 2017 00:00:00 +0000

Abstracts of Presentations at the 5th International Research Conference on Huanglongbing

IOCV-XX-Abstracts of Presentations at the 20th Conference of the International Organization of Citrus Virologists, China, 2016

Thu, 15 Sep 2016 00:00:00 +0000

IOCV-XX-Abstracts of Presentations at the 20th Conference of the International Organization of Citrus Virologists, China, 2016

The past and present status of Citrus tristeza virus in Florida

Thu, 8 Sep 2016 00:00:00 +0000

The Citrus tristeza virus (CTV) strains present in an area can determine the type and severity of disease produced. Using real time RT-qPCR, we screened a series of representative samples collected throughout Florida from 1964 to 2002 for CTV strain presence. We found that contrary to previous reports, the historical samples were infected with both the T30 and T36 strains, the latter often at low titer. The VT strain was rare, with a scattered distribution. We compared this to samples collected in 2014 and 2015, and found that T30 and T36 are prevalent in nearly all commercial groves; VT strain incidence has increased markedly. With changing cultural practices, such as an increase in sour orange rootstock use, tristeza disease continues to be a significant threat to the Florida citrus industry.

Bacillus subtilis QST 713, copper hydroxide, and their tank mixes for control of bacterial citrus canker in Saudi Arabia

Sat, 21 May 2016 00:00:00 +0000

Citrus Bacterial Canker (CBC) is a serious disease that affects production of almost all commercial citrus cultivars in subtropical citrus growing regions worldwide. In this study, the effectiveness of monthly foliar sprays of wettable powder formulation Serenade MAX of Bacillus subtilis QST 713, alone or as tank mixes with copper hydroxide on CBC disease development was evaluated under greenhouse and uncovered nursery conditions. The QST 713 as a tank mix with copper hydroxide reduced significantly the disease severity and incidence, followed by the copper hydroxide treatment, compared to the control. The disease incidence on leaves of inoculated trees treated with a combination of copper with QST 713 was never higher than 19%, whereas, the disease incidence reached 43% for non-sprayed trees. It was possible to reduce the number of copper sprays up to 6 sprays per season when it was mixed with the bio-fungicide QST 713 to effectively control CBC compared with 8 sprays...

Keynote Summary: Half a century on huanglongbing: learning about the disease, trying to control it

Mon, 2 May 2016 00:00:00 +0000

Keynote Summary: Half a century on huanglongbing: learning about the disease, trying to control it

Comparison of gene expression changes in susceptible, tolerant and resistant hosts in response to infection with Citrus tristeza virus and huanglongbing

Wed, 23 Mar 2016 00:00:00 +0000

The pathogens Candidatus Liberibacter asiaticus (Las) and Citrus tristeza virus (CTV) are both phloem limited and have significant economic impact on citrus production wherever they are found. Studies of host resistance have indicated that Poncirus trifoliata has tolerance or resistance to both pathogens, suggesting that there may be some common factors in the 2 kinds of resistance. We have conducted studies of host gene expression changes that occur in response to infection to gain further insight. Controlled inoculation by grafting infected budwood was used to infect potted greenhouse plants of Cleopatra mandarin (Citrus reticulata), US-897 (C. reticulata x P. trifoliata), and US-942 (C. reticulata x P. trifoliata) with CTV and with Las, the pathogen associated with the disease huanglongbing (HLB). Stem and leaf tissue was collected at 10, 20, and 30 weeks after inoculation, DNA and RNA were extracted and subjected to qPCR...

IRCHLB-IV-Abstracts of Presentations at the 4th International Research Conference on Huanglongbing

Mon, 29 Feb 2016 00:00:00 +0000

IRCHLB-IV-Abstracts of Presentations at the 4th International Research Conference on Huanglongbing

Mapping sequences involved in induction of decline by Citrus tristeza virus T36 on the sour orange rootstock.

Mon, 9 Nov 2015 00:00:00 +0000

Historically, decline (or tristeza) has been a devastating disease of citrus caused by Citrus tristeza virus (CTV). Decline is a man-made disease based largely on propagation of sweet orange, grapefruit, and mandarins on the sour orange rootstock. In Florida, the major problem caused by CTV has been decline, since severe stem-pitting isolates are absent. Although this disease can be controlled by using alternative rootstocks, there are soils in which all other rootstock choices are less desirable in terms of fruit quality and yield. A major goal has been to develop measures that allow growers to use the sour orange rootstock in the presence of CTV. Florida has 2 predominant strains of CTV, a decline (T36) strain and a non-decline strain (T30). A first step was to map the viral determinant that induces decline. This was done by creating hybrids with T30 sequences substituted into T36 to identify sequences correlated with loss of decline symptoms. This project was delayed...

The psorosis disease of citrus: a pale light at the end of the tunnel

Mon, 5 Oct 2015 00:00:00 +0000

Abstract First reported in 1896, psorosis was the first citrus disease proven to be graft transmissible and also the first for which eradication and budwood certification programs were launched to prevent its economic damage. For many years psorosis etiology remained elusive and only in 1986 it was associated with the presence of virus-like particles in infected plants. However, in the last two decades a virus with unusual morphology (Citrus psorosis virus, CPsV) was characterized and closely associated with psorosis disease as previously defined by field symptoms and by biological indexing in sensitive indicator plants. With a tripartite, negative-sense, RNA genome and a ~48 kDa coat protein, CPsV, the presumed causal agent of psorosis, is the type member of the genus Ophiovirus, within the new family Ophioviridae. Availability of the complete genomic sequence of two CPsV isolates and partial sequences of many others has enabled i) setting up rapid...

A historical note on two unreported obstacles for cross-protecting mature citrus trees against severe Citrus tristeza virus isolates.

Fri, 28 Aug 2015 00:00:00 +0000

A historical note on two unreported obstacles for cross-protecting mature citrus trees against severe Citrus tristeza virus isolates.

Within-orchard edge effects of the azimuth of the sun on Diaphorina citri adults in mature orchards.

Fri, 28 Aug 2015 00:00:00 +0000

Huanglongbing (HLB) is considered the most devastating disease of citrus. The bacterium and vector associated with HLB in Florida are Candidatus Liberibacter asiaticus and Diaphorina citri (Asian citrus psyllid), respectively. D. citri is positively phototropic, and higher populations have been found along edges of orchards exposed to the sun. A survey was designed to determine if D. citri adult populations along edges of orchards varied according to time-of-day and time-of-year in relation to the azimuth of the sun. The survey was conducted twice. Citrus orchards, each divided into 9 sampling areas, were surveyed for D. citri via stem-tap sampling. Orchards were sampled 3 times per day (near sunrise, solar noon, and sunset) and 4 times per year (near the summer solstice, autumnal equinox, winter solstice, and vernal equinox). Time-of-year and sampling area significantly affected psyllid counts (P =...

Where have all the flowers gone? Postbloom fruit drop of citrus in the Americas.

Tue, 28 Jul 2015 00:00:00 +0000

Postbloom fruit drop (PFD), caused primarily by Colletotrichum acutatum, is a serious disease annually in the humid tropical citrus areas of the Americas and occurs more sporadically in the humid subtropics. The fungus infects flowers of all citrus species producing orange-brown lesions on petals that result in abscission of the fruitlets leaving the persistent calyx and floral disk attached to the twigs. C. acutatum also causes Key lime anthracnose and is morphologically identical to PFD, but the strains can be differentiated by molecular means and pathogenicity tests. C. acutatum produces abundant conidia on infected petals that are dispersed primarily by rain splash. After the bloom season, the fungus persists as appressoria on persistent calyces and other vegetative plant parts. Those appressoria are stimulated to germinate by flower extracts and produce secondary conidia to initiate a new disease cycle. Some cultural measures are useful in reducing disease severity, but control...

First report on citrus dry rot in sour orange rootstock in Texas

Tue, 30 Jun 2015 00:00:00 +0000

A grapefruit tree on sour orange rootstock in a residential property in Mission, TX was suspected to have citrus dry root rot disease based on symptoms. The causal organism was isolated from the infected root samples and based on fungal cultural and microscopic morphology and PCR, it was confirmed to be Fusarium solani (Martius) Appel & Wollenweber emend. Snyder & Hansen. A total of 10 healthy sour orange rootstock seedlings were inoculated using conidial suspension of the fungus by the standard root-dip method. After 9 month post inoculation, the inoculated fungus was re-isolated from root and stem sections of these plants. Plants were smaller in size and displayed the classical symptoms of dry rot. The fungal colonies were confirmed to be F. solani based on fungal morphology and PCR. This is the first report of F. solani infecting sour orange rootstock plants in Texas.

Huanglongbing in Texas: Report on the first detections in commercial citrus

Thu, 25 Jun 2015 00:00:00 +0000

Huanglongbing (HLB), also known as citrus greening, is a destructive citrus disease associated with 3 α-proteobacteria species of Candidatus Liberibacter. The first report of HLB in the USA was from Florida in 2005 and Ca. L. asiaticus (Las) is the only species currently confirmed in the USA. In January 2012, a Valencia sweet orange tree in a commercial orchard in San Juan, Texas, tested positive for Las by real-time and conventional PCR assays and by the sequence of its partial 16S rRNA gene. The sample tested negative for Ca. L. americanus and Ca. L. africanus. All 4 Valencia sweet orange seedlings that were graft-inoculated using budwood from the first Texas HLB-infected tree showed typical HLB symptoms 3 months post-inoculation and tested positive for the pathogen. Such HLB typical symptoms as leaf blotchy mottle, twig die-back, veinal chlorosis, lopsided and greening fruits were observed on the Las-positive tree in the orchard, which immediately...

Announcement of the International Citrus Microbiome (Phytobiome) Consortium.

Thu, 25 Jun 2015 00:00:00 +0000

Announcement of the International Citrus Microbiome (Phytobiome) Consortium.

Citrus tristeza virus strains present in New Zealand and the South Pacific.

Tue, 26 May 2015 00:00:00 +0000

Citrus are an important subsistence and commercial crop across the South and Central Pacific. Unfortunately, the spread of plant material has contributed to the spread of citrus pathogens, such as Citrus tristeza virus (CTV). In this study, we examined the incidence and diversity of CTV strains present in both New Zealand, and island nations of the South and Central Pacific, and found that all presently described strains are present, and exist and complex mixtures of strains. Phylogenetic analysis suggests little difference in strain diversity between locations, suggesting extensive movement of infected planting material occurred in the past.

Xyloporosis: A history of the emergence and eradication of a citrus viroid disease

Mon, 27 Apr 2015 00:00:00 +0000

The etiology of xyloporosis, a disease that has severe effects on citrus trees grafted onto certain citrus rootstocks, was enigmatic for a long time. Symptoms on test hosts following transmission through grafting suggested that it was synonymous with citrus cachexia, a disease that mainly affects mandarin trees. Recent molecular studies have confirmed that certain Hop stunt viroid (HSVd) isolates induce cachexia and xyloporosis symptoms in disease-sensitive citrus hosts. These HSVd infections are mostly symptomless in numerous Near East and Western Mediterranean fruit trees and grapevines; including plants widely cultivated in those regions for several millennia, long before the emergence of xyloporosis and cachexia as diseases of citrus trees. The present review tracks historical changes in citrus propagation practices and the pathological consequences of those changes that contributed to the emergence of xyloporosis as an economically significant disease of citrus trees grafted...

Citrus phytophthora diseases: Management challenges and successes

Mon, 27 Apr 2015 00:00:00 +0000

Phytophthora spp. are present in nearly all citrus groves in Florida and Brazil and phytophthora-induced diseases, especially foot and root rot, have the potential to cause economically important crop losses. Disease-related losses due to root rot are difficult to estimate because fibrous root damage and yield loss are not always directly proportional. Challenges from phytophthora diseases have been addressed in both countries by enacting phytosanitary requirements for production of pathogen-free nursery trees in enclosed structures, propagated from indexed and certified pathogen-free sources, in conjunction with several other cultural management practices. In Florida groves, a statewide soil sampling program provides growers with soil propagule counts to estimate the damage that Phytophthora spp. are causing to fibrous roots. The results can be used along with rootstock tolerance, soils, topography, irrigation, and drainage to make a decision for the need to treat with fungicides...

Sunn hemp, a major source-plant of the phytoplasma associated with huanglongbing symptoms of sweet orange in São Paulo State, Brazil

Wed, 22 Apr 2015 00:00:00 +0000

In São Paulo State (SPS), sweet orange (Citrus sinensis) trees with huanglongbing (HLB) symptoms are infected with Candidatus (Ca.) Liberibacter (L.) asiaticus (Las) or Ca. L. americanus (Lam). However, in 2007, 3 years after HLB was first reported in SPS, some trees with characteristic HLB symptoms were found free of liberibacters, but infected with a phytoplasma of 16Sr group IX. This phytoplasma was further characterized by PCR amplification of ribosomal protein genes rpsC-rplV-rpsS and amplicon sequencing. A qPCR test to detect the phytoplasma in plants and insects was also developed on the basis of the ribosomal protein genes. The phytoplasma was transmitted from citrus-to-citrus by grafting. The 16Sr group IX phytoplasma associated with HLB symptoms in sweet orange in SPS and characterized by the above techniques was named “HLB-phytoplasma”. Although the HLB-phytoplasma is widely distributed in many municipalities of central, northern, and northwestern SPS, the number of...

Cell Penetrating Peptides as an Alternative Transformation Method in Citrus

Tue, 23 Dec 2014 00:00:00 +0000

Huanlongbing (HLB) has caused the loss of thousands of trees in Florida’s multi-billion dollar citrus industry. An effective, long-term strategy to controlling this disease will be by the incorporation of genetic resistance into commercial genotypes. Because conventional breeding is limited by the lack of natural resistance in citrus to HLB, genetic engineering is now considered a significant alternative to incorporating such characteristics. In fact, despite general concerns from the public against genetically modified organisms (GMOs), one National Academy report¹ stated that genetic engineering will be the way to fully exterminate HLB, while growers’ support of a transgenic approach for disease resistant traits also continues to rise. The primary transformation method of citrus typically uses Agrobacterium, in which explants are suspended with the bacterium and subsequently placed on selection media. After treatment, the explants produce shoots that...

Mandarin and mandarin hybrid genetic transformation for resistance to Candidatus Liberibacter asiaticus

Tue, 23 Dec 2014 00:00:00 +0000

Brazil is one of the largest producers and exporters of citrus. Currently, Huanglongbing disease (HLB) associated to Candidatus Liberibacter asiaticus (CLas) is the main threat to the citrus industry. The aim of this work is to study the genetic transformation of mandarin/mandarin hybrid 'Thomas' (Citrus reticulata Blanco) and 'Fremont' (C. clementina hort. ex Tanaka x C. reticulata Blanco) with the gene that encodes an attacin antibacterial peptide (attA) driven by phloem-specific promoters. The genetic transformation experiments were performed with epicotyl segments, via Agrobacterium tumefaciens (EHA 105), with the gene constructs pCAtSUC2/attA and pCAtPP2/attA, containing the attA gene controlled by AtSUC2 and AtPP2 promoters. Transgenic plants were identified by PCR analysis and acclimatized to greenhouse conditions. The plants will be propagated and evaluated for resistance to CLas.

A Tomato Detached Leaf Assay for Chemical Genomics of an HLB Model System

Tue, 23 Dec 2014 00:00:00 +0000

To better understand plant-pathogen interactions in Huanglongbing disease and develop control strategies we investigated a novel approach known as chemical genomics with Tomato “Psyllid Yellows”, caused by Candidatus Liberibacter psyllaurous (CLps), as a model of HLB. Chemical genomics involves three key stages starting with designing and performing high-throughput chemical screening, identifying chemicals inducing desired effects and dissecting the genetic targets of the candidate chemical. Our study has been focused on developing a high throughput chemical screen assay using model plants such as tomato and Arabidopsis that can be infected by Candidatus Liberibacter psyllaurous (Clps). The key objective is to identify chemicals that induce plant defense against CLps infection or its transmission via psyllids. We evaluated Arabidopsis thaliana and tomato in different media such as MS sterile media and hydroponic culture, however qPCR results...

One-for-all: a monoclonal antibody specific to different recombinant proteins in transgenic citrus plants

Tue, 23 Dec 2014 00:00:00 +0000

The easy and rapid identification of a recombinant protein in transgenic plants is becoming increasingly relevant as more transgenic plants are used for research and commercial applications. Tagging recombinant proteins with a small peptide (epitope) can perform such a task using a variety of immunological methods. Epitope tags are short, hydrophilic peptide sequences recognized by specific antibodies. Compared with larger protein fusions, the small size of epitope tags makes them less likely to interfere with protein folding and function.

We describe herein the detection of the c-myc epitope using different immunological methods in citrus transgenic plants. A c-myc tag sequence (N-EQKLISEEDL-C, corresponding to the C-terminal amino acids (410-419) of human c-myc protein) was added to the DNA sequence by PCR and the resulting proteins are being tested at the CREC. Our experiments with a genetically altered endogenous citrus gene modified to produce a protein with the...

Evidence that ‘flying dragon’ trifoliate orange delays HLB symptom expression for four sweet orange cultivars, Tahiti lime and Okitsu mandarin

Tue, 23 Dec 2014 00:00:00 +0000

Huanglongbing (HLB), caused by Candidatus Liberibacter asiaticus and vectored by Diaphorina citri, was first reported in 2004 in Brazil and is currently widespread in São Paulo State. Brazil is the world’s largest sweet orange producer and has 49,000 ha cultivated with ‘Tahiti’ lime acid lime. Mandarin cultivation represents 5.5% of total citrus production in the country. In 2001, three experiments were planted in the Citrus Experimental Station (EECB), Bebedouro, Northern São Paulo State, where the first HLB symptomatic tree was detected in 2006. The initial objective was to evaluate the performance of ‘Folha Murcha’ sweet orange, ‘Tahiti’ acid lime and ‘Okitsu’ mandarin grafted on twelve rootstocks including Rangpur lime, Swingle citrumelo, Rubidoux and Flying Dragon (FD) trifoliate oranges. Cumulative HLB incidence (CI) was calculated in 2009. Folha Murcha and Tahiti lime trees on FD had lower CI values (6.7 and 10%) than trees on Rangpur lime (33.3 and...

Breaking citrus juvenility by modulating endogenous miR156 and miR172 levels

Tue, 23 Dec 2014 00:00:00 +0000

The ability to either transform mature citrus directly or to transform juvenile citrus and also induce it to flower and set fruit within a few years is critical for evaluation of fruit quality, quantity and of horticultural performance of any transgenic trees. In plants, the transition from juvenile to adult stage is regulated by the sequential and complementary action of microRNAs miR156 and miR172. miR156 suppresses the expression of specific transcriptional factors that would otherwise promote the juvenile to adult phase transition, including factors that activate miR172, which directly promotes the transition. Here, we created a target mimic for miR156 to attempt to sequester miR156 and reduce its levels in juvenile citrus. We cloned the nonprotein coding gene IPS1 from Arabidopsis and replaced its native microRNA target with the predicted citrus target of citrus miR156, resulting in a citrus miR156 mimic gene, cMIM156. Five sweet orange (Hamlin)...

Preliminary Evidence for Rootstock Effects on HLB Infection Frequency and Disease Severity in Sweet Orange and ‘SugarBelle’ Trees