First Report of Xanthomonas citri pv. citri Pathotype A Causing Asiatic Citrus Canker on Grapefruit and Mexican Lime in Senegal

In February 2010, grapefruit (Citrus paradisi) and Mexican lime (C. aurantifolia) leaves with erumpent callus-like lesions were collected in Senegal in the Sebikotane area between Dakar and Thies. Similar symptoms have been observed by local farmers since 2008, and lesions were morphologically similar to those of citrus canker caused by Xanthomonas citri pv. citri (Asiatic canker) and X. citri pv. aurantifolii (South American canker). Lesions were primarily reported from grapefruit (cv. Shambar), which is the most frequent citrus species produced in this area, and Mexican lime, which is also commonly grown. Both species are very susceptible to X. citri pv. citri pathotype A, and Mexican lime is susceptible to X. citri pv. citri pathotype A* and X. citri pv. aurantifolii (4). Fifteen Xanthomonas-like strains were isolated from disease samples using KC semiselective medium (3). PCR with primer pair 4/7 (2) revealed that all the Senegalese strains and the X. citri pv. citri strain CFBP 2525 from New Zealand, used as a positive control, generated the expected DNA fragment, whereas no fragment was observed for negative controls (distilled water instead of the template). Insertion sequence ligation-mediated (IS-LM)-PCR analysis (1) of X. citri pv. citri strains from Senegal and reference strains of X. citri pv. citri pathotypes A and A* (1), with MspI and four primer pairs (unlabelled MspI primer and four 5′-labelled insertion sequence-specific primers targeting three IS elements), indicated that the strains from Senegal were related to X. citri pv. citri but not to pv. aurantifolii. They were closely related to X. citri pv. citri pathotype A strains, with a broad host range, present in the Indian subcontinent and Mali (C. Vernière, unpublished data). Multilocus sequence analysis of four partial housekeeping gene sequences (atpD, dnaK, efp, and gyrB) confirmed that four Senegalese strains were not related to X. citri pv. aurantifolii and showed a full sequence identity to X. citri pv. citri sequence type ST3 (2), fully consistent with IS-LM-PCR. Using a detached leaf assay (4), Duncan grapefruit, Pineapple sweet orange, and Mexican lime leaves inoculated with all strains from Senegal developed typical erumpent, callus-like tissue at wound sites 2 weeks after the inoculations. Xanthomonas-like colonies were reisolated and PCR amplification with the primer pair 4/7 produced the same 468-nt DNA fragment. This represents the fourth outbreak of citrus canker reported from Africa within the last 5 years, the other documented reports were from Ethiopia (2007) and Mali and Somalia (2008). High disease prevalence was observed in Senegal with incidence exceeding 90% in the orchards where lime and grapefruit were infected for 3 years, indicating the suitability of environmental conditions in this region for the development of Asiatic citrus canker. The origin of the inoculum associated with the reported canker outbreak in Senegal is currently unknown and the precise distribution of the pathogen needs to be thoroughly assessed. To our knowledge, this is the first documented report of the presence of Asiatic citrus canker in Senegal and this occurrence increases the threat to citriculture in West Africa. References: (1) L. Bui Thi Ngoc et al. FEMS Microbiol. Lett. 288:33, 2008. (2) L. Bui Thi Ngoc et al. Int. J. Syst. Evol. Microbiol. 60:515, 2010. (3) O. Pruvost et al. J. Appl. Microbiol. 99:803, 2005. (4) C. Vernière et al. Eur. J. Plant Pathol. 104:477, 1998.

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Pathotype Identification of Xanthomonas citri pv. citri Strains Causing Citrus Canker in Vietnam

Plant Disease ◽

10.1094/pdis-93-6-0671a ◽

2009 ◽

Vol 93 (6) ◽

pp. 671-671 ◽

Cited By ~ 3

Author(s):

L. Bui Thi Ngoc ◽

C. Vernière ◽

C. Boyer ◽

K. Vital ◽

O. Pruvost ◽

...

Keyword(s):

Host Range ◽

Citrus Canker ◽

Pcr Analysis ◽

Aflp Analysis ◽

Bacterial Disease ◽

Citrus Paradisi ◽

Citrus Species ◽

Xanthomonas Citri ◽

Mexican Lime ◽

Wide Range

Asiatic citrus canker caused by Xanthomonas citri pv. citri is a bacterial disease of major economic importance in tropical and subtropical citrus-producing areas. It probably originated in Asia (2). X. citri pv. citri induces erumpent, callus-like lesions with a water-soaked margin on aerial organs of the plants. Severe attacks cause premature fruit drop and twig dieback. This pathogen has consequently been subjected to international quarantine regulation and eradication efforts. Two pathogenic variants of X. citri pv. citri can be separated by their host range. X. citri pv. citri pathotype A strains cause severe infection worldwide in a wide range of citrus species; grapefruit (Citrus paradisi) is particularly susceptible. More recently, another group of strains from different areas of West Asia has been designated as X. citri pv. citri pathotype A* (4). These A* strains are genetically related to X. citri pv. citri, but their host range is primarily restricted to Mexican lime (C. aurantifolia) and they do not infect grapefruit. Strains similar in host range were later reported in Florida, Thailand, and Cambodia (2). In this study, we investigated the distribution of X. citri pv. citri pathotypes in Southeast Asia. A large survey on citrus was conducted in 14 provinces in the north (Ha Noi, Hung Yen, Nghe Han, Ha Ting, and Phu Tho) and south (Can Tho, Long An, Dong Nai, Tien Giang, Vinh Long, Ben Tre, Dong Thap, Vung Tau, and Lam Dong) of Vietnam. We collected 557 X. citri pv. citri isolates, after cultivation on KC semiselective medium (3), from citrus species, including 60 strains from Mexican lime in eight provinces. Ligation mediated (IS-LM)-PCR analysis using primers targeting three insertion sequences (1) was done on all Vietnamese strains and on additional reference strains of X. citri pv. citri-A, -A*, and X. citri pv. aurantifolii. IS-LM-PCR indicated that all Vietnamese isolates were pathotype A and did not include any with a restricted host range (X. citri pv. citri-A* and X. citri pv. aurantifolii). Amplified fragment length polymorphism (AFLP) analysis was carried out on a subset of 84 X. citri pv. citri strains, including 22 strains from Mexican lime from seven provinces. AFLP was carried out using SacI/MspI and four primer pairs (unlabeled MspI +1 [A, C, T or G] primers and 5′-labeled – SacI + C primer for the selective amplification step) (2) and the data confirmed that all Vietnamese X. citri pv. citri strains were genetically related to pathotype A strains. Mexican lime and Duncan grapefruit or pineapple sweet orange leaves were inoculated with 25 strains from lime (representative of the genetic diversity) using a detached leaf assay (3) and they produced typical canker lesions on both host species. In spite of the presence of pathotype A* strains in neighboring countries (2), no strains genetically or pathogenically related to this pathotype were identified in this collection. A survey of commercial Mexican lime orchards, especially in Vietnamese provinces bordering Cambodia, should be undertaken to detect and eradicate A* strains because these are known to strongly impact lime production in other parts of Asia (e.g., Thailand). References: (1) L. Bui Thi Ngoc et al. Appl. Environ. Microbiol. 75:1173, 2009. (2) L. Bui Thi Ngoc et al. FEMS Microbiol. Lett. 288:33, 2008. (3) O. Pruvost et al. J. Appl. Microbiol. 99:803, 2005. (4) C. Vernière et al. Eur. J. Plant Pathol. 104:477, 1998.

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First report of Xanthomonas citri Subsp. Citri causing citrus canker on grape fruit (Citrus paradisi), washington naval (Citrus sinensis), kaghzi limon (Citrus aurantifolia Swingle), lemon (Citrus lim

The Pakistan Journal of Agricultural Sciences ◽

10.21162/pakjas/21.9701 ◽

2021 ◽

Vol 58 (04) ◽

pp. 1373-1377

Author(s):

Muhammad Shah Nawaz ul Rehman

Keyword(s):

Citrus Sinensis ◽

Sequence Similarity ◽

Citrus Canker ◽

Citrus Limon ◽

Evolutionary Analysis ◽

Citrus Paradisi ◽

Xanthomonas Citri ◽

Citrus Aurantifolia ◽

Grape Fruit ◽

Citrus Maxima

Citrus fruit production is largely affected by different bacterial and fungal pathogens. In Pakistan bacterial diseases like citrus bacterial canker (CBC) pose severe risk to citrus economy. Diagnoses of such diseases could be helpful to avoid the epidemics in nurseries or orchids. In 2011-12, citrus canker symptoms i.e., callus-like outgrowths on leaves and fruits of grape fruit (Citrus paradisi), Washington naval (Citrus sinensis), Kaghzi Limon (Citrus aurantifolia swingle), lemon (Citrus Limon) and pomelo (Citrus maxima) were noticed in Sargodha district of Punjab, Pakistan. Bacteria i.e., yellow mucoid, Xanthomonas- like isolates, were isolated from these lesions. Bacteria isolated from these lesions were cultured and total DNA was isolated. A diagnostic fragment of 581 bp based on rpf genes of Xanthomonas citri pv. citri was amplified, cloned and completely sequenced. BLAST and evolutionary analysis revealed that these isolates show 100% sequence similarity and group with Xanthomonas citri subsp. citri from Argentina (CP023285) and Reunion (CP018858), (CP018854). To our knowledge, this is the first formal report of X. campestris pv. citri pathotypes A on Citrus paradise, Citrus sinensis, Citrus maxima, Citrus Limon and Citrus aurantifolia swingle in Pakistan

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First Report of Xanthomonas citri pv. citri Causing Asiatic Citrus Canker in Burkina Faso

Plant Disease ◽

10.1094/pdis-06-13-0600-pdn ◽

2013 ◽

Vol 97 (12) ◽

pp. 1653-1653 ◽

Cited By ~ 3

Author(s):

C. C. Juhasz ◽

A. Leduc ◽

C. Boyer ◽

F. Guérin ◽

C. Vernière ◽

...

Keyword(s):

Burkina Faso ◽

Sweet Orange ◽

Citrus Canker ◽

Negative Control ◽

Citrus Species ◽

Xanthomonas Citri ◽

First Report ◽

Mexican Lime ◽

Volkamer Lemon ◽

Wide Range

Citrus canker, caused by Xanthomonas citri pv. citri, is a bacterial disease of economic importance in tropical and sub-tropical citrus-producing areas (EPPO-PQR online database). X. citri pv. citri causes severe infection in a wide range of citrus species, and induces erumpent, callus-like lesions with water-soaked margins leading to premature fruit drop and twig dieback. It has consequently been subjected to eradication efforts and international regulations. It was first described on the African continent in South Africa at the beginning of the 20th century, from which it was eventually eradicated. Since 2006, several outbreaks caused by phylogenetically diverse strains of X. citri pv. citri have been reported from several African countries (Ethiopia, Mali, Senegal, and Somalia). In July 2011, citrus canker in Burkina Faso was suspected in the area adjacent to the Sikassso Province of Mali where X. citri pv. citri has been confirmed. In November and December 2012, leaves of clementine (Citrus clementina), lemon (C. limon), Volkamer lemon (C. volkameriana), sweet orange (C. sinensis), tangelo (C. paradisi× C. reticulata), and mandarin (C. reticulata) were collected from orchards with trees showing symptoms of citrus canker in the Comoé, Houet, and Kénédougou provinces of Burkina Faso. Isolations performed using KC semi-selective medium (4) recovered 45 Xanthomonas-like strains. All Xanthomonas-like strains were tentatively identified as X. citri pv. citri by PCR (4/7 primers) using IAPAR 306 and sterile distilled water as the positive and negative controls, respectively (3). Among these, two strains (LK4-4 and LK4-5) produced a ‘fuscans’-like brown diffusible pigment, a phenotype never reported previously for X. citri pv. citri. MultiLocus Sequence Analysis targeting six housekeeping genes (atpD, dnaK, efp, gltA, gyrB, and lepA) (1,2) fully identified seven strains from Burkina Faso (LJ301-1, LJ303-1, LK1-1, LK2-6, LK4-3, LK4-4, and LK4-5) as X. citri pv. citri (and not to any other Xanthomonas pathovars pathogenic to citrus or host range-restricted pathotypes of pathovar citri), and more specifically as sequence type ST2 which is composed mostly of pathotype A strains of X. citri pv. citri (2). The same seven strains were inoculated to at least four leaves of each of grapefruit cv. Henderson, Mexican lime SRA 140 (C. aurantifolia), Tahiti lime SRA 58 (C. latifolia), and sweet orange cv. Washington Navel, using a detached leaf assay (2). All strains developed typical erumpent, callus-like tissue at wound sites on all citrus species inoculated. No lesions developed on the negative control (sterile 10 mM tris buffer). Koch's postulate was fulfilled after reisolation of Xanthomonas-like yellow colonies from symptoms on Mexican lime produced by the seven strains. Boiled bacterial suspensions were assayed by PCR with 4/7 primers (3) and produced the expected 468-bp amplicon in contrast with the PCR negative control. To our knowledge, this is the first report of X. citri pv. citri in Burkina Faso. Citrus canker-free nurseries and grove sanitation should be implemented for reducing the prevalence of Asiatic canker in Burkina Faso and a thorough survey of citrus nurseries and groves in the region should be conducted. References: (1) N. F. Almeida et al. Phytopathology 100:208, 2010. (2) L. Bui Thi Ngoc et al. Int. J. Syst. Evol. Microbiol. 60:515, 2010. (3) J. S. Hartung et al. Phytopathology 86:95, 1996. (4) O. Pruvost et al. J. Appl. Microbiol. 99:803, 2005.

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Complete Genome Sequences of Six Copper-Resistant Xanthomonas citri pv. citri Strains Causing Asiatic Citrus Canker, Obtained Using Long-Read Technology

Genome Announcements ◽

10.1128/genomea.00010-17 ◽

2017 ◽

Vol 5 (12) ◽

Cited By ~ 3

Author(s):

Damien Richard ◽

Claudine Boyer ◽

Christian Vernière ◽

Blanca I. Canteros ◽

Pierre Lefeuvre ◽

...

Keyword(s):

Citrus Canker ◽

Economic Losses ◽

Broad Host Range ◽

Citrus Species ◽

Xanthomonas Citri ◽

Genome Sequences ◽

Content Type ◽

Complete Genomes ◽

Long Read ◽

Resistant Strains

ABSTRACT The gammaproteobacterium Xanthomonas citri pv. citri causes Asiatic citrus canker. Pathotype A strains have a broad host range, which includes most commercial citrus species, and they cause important economic losses worldwide. Control often relies on frequent copper sprays. We present here the complete genomes of six X. citri pv. citri copper-resistant strains.

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First Report of Xanthomonas citri pv. citri-A* Causing Citrus Canker on Lime in Ethiopia

Plant Disease ◽

10.1094/pdis-93-2-0203b ◽

2009 ◽

Vol 93 (2) ◽

pp. 203-203 ◽

Cited By ~ 9

Author(s):

E. Derso ◽

C. Vernière ◽

O. Pruvost

Keyword(s):

Host Range ◽

Rift Valley ◽

Disease Incidence ◽

Citrus Canker ◽

Aflp Analysis ◽

Xanthomonas Citri ◽

First Report ◽

Mexican Lime ◽

Wide Range ◽

Citrus Production

Asiatic citrus canker caused by Xanthomonas citri pv. citri hinders national citrus markets in tropical and subtropical areas and international trade. The bacterium induces erumpent, callus-like lesions causing defoliation, premature fruit drop, and twig dieback. Because of the damage caused by infection and reduced marketability of fruit, several countries have undergone eradication. Strains with different host ranges have been described. Pathotype A strains are the most widespread and produce canker in a wide range of citrus species. Pathotype A* strains with a host range restricted to Mexican lime (Citrus aurantifolia), Tahiti lime (C. latifolia), and alemow (C. macrophylla), but not infecting the susceptible species grapefruit (C. paradisi), were described in different areas of Asia (4). Reemergence of X. citri pv. citri pathotype A was recently described in Africa as affecting citrus production in Mali and Somalia. Canker-like infected citrus trees with symptoms on leaves, fruits, and stems were first observed in 2004 in Ethiopia in the Rift Valley Region. After a survey conducted in 2008, the disease was recorded in different areas of the Rift Valley located in the lowlands (altitude <1300 m, daily mean temperatures 24 to 29°C) and confirmed to only affect Mexican lime orchards with disease incidence as much as 80%. Ten canker-like infected leaves were collected during this survey from eight different orchards distributed along the infected area. Isolations were performed using KC semiselective medium (3), and Xanthomonas-like isolates were further characterized. PCR was used to check the identity of these isolates by using X. citri pv. citri strain CFBP 2525 from New Zealand as the positive control and distilled water as the template for the negative control. The DNA fragment typical of X. citri pv. citri was obtained from all the bacterial isolates using the diagnostic primer pair 4/7 (2). Amplified fragment length polymorphism (AFLP) analysis of the 80 Ethiopian isolates and additional reference isolates from X. citri pv. citri-A, -A*, and pv. aurantifolii using SacI/MspI and four primer pairs (unlabeled MspI + 1 [A, C, T, or G] primers and 5′-labeled-SacI + C primer for the selective amplification step) (1) grouped all the Ethiopian isolates in a cluster that was comprised of only X. citri pv. citri pathotype A* strains. On the basis of the AFLP, Ethiopian isolates were only distantly related to X. citri pv. aurantifolii. When inoculated to Mexican lime and Duncan grapefruit by a detached leaf assay (4), all of the Ethiopian strains produced canker on lime only. This confirms the larger geographical distribution of pathotype A*, and to our knowledge, is the first report of its presence on the African continent. This could allow studying the epidemiology of pathotype A* strains in a unique situation where they do not compete with pathotype A strains. The molecular characterization of Ethiopian strains suggests that this introduction event is not related to the recent introduction of citrus canker in neighboring Somalia where X. citri pv. citri pathotype A was identified. Ethiopia will have to prevent the introduction of this wide host range pathotype to avoid further negative impacts on citrus production. References: (1) N. Ah-You et al. Phytopathology 97:1568, 2007. (2) J. S. Hartung et al. Phytopathology 86:95, 1996. (3) O. Pruvost et al. J. Appl. Microbiol. 99:803, 2005. (4) C. Vernière et al. Eur. J. Plant Pathol. 104:477, 1998.

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Foliar Application of Biofilm Formation–Inhibiting Compounds Enhances Control of Citrus Canker Caused by Xanthomonas citri subsp. citri

Phytopathology ◽

10.1094/phyto-04-13-0100-r ◽

2014 ◽

Vol 104 (2) ◽

pp. 134-142 ◽

Cited By ~ 42

Author(s):

Jinyun Li ◽

Nian Wang

Keyword(s):

Biofilm Formation ◽

Foliar Application ◽

Citrus Canker ◽

Pcr Analysis ◽

Xanthomonas Citri ◽

Bacterial Populations ◽

Canker Disease ◽

Abiotic Surfaces ◽

Polymerase Chain ◽

Important Disease

Citrus canker caused by the bacterium Xanthomonas citri subsp. citri is an economically important disease of citrus worldwide. Biofilm formation plays an important role in early infection of X. citri subsp. citri on host leaves. In this study, we assessed the hypothesis that small molecules inhibiting biofilm formation reduce X. citri subsp. citri infection and enhance the control of citrus canker disease. D-leucine and 3-indolylacetonitrile (IAN) were found to prevent biofilm formation by X. citri subsp. citri on different abiotic surfaces and host leaves at a concentration lower than the minimum inhibitory concentration (MIC). Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) analysis indicated that IAN repressed expression of chemotaxis/motility-related genes in X. citri subsp. citri. In laboratory experiments, planktonic and biofilm cells of X. citri subsp. citri treated with D-leucine and IAN, either alone or in combination, were more susceptible to copper (CuSO4) than those untreated. In greenhouse assays, D-leucine and IAN applied alone or combined with copper reduced both the number of canker lesions and bacterial populations of X. citri subsp. citri on citrus host leaves. This study provides the basis for the use of foliar-applied biofilm inhibitors for the control of citrus canker alone or combined with copper-based bactericides.

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First Report of Citrus Canker Caused by Xanthomonas citri in Somalia

Plant Disease ◽

10.1094/pdis-92-6-0981c ◽

2008 ◽

Vol 92 (6) ◽

pp. 981-981 ◽

Cited By ~ 6

Author(s):

G. M. Balestra ◽

A. Sechler ◽

E. Schuenzel ◽

N. W. Schaad

Keyword(s):

Pathogenic Bacteria ◽

Science Research ◽

Citrus Canker ◽

Research Unit ◽

Citrus Paradisi ◽

Xanthomonas Citri ◽

First Report ◽

Plant Pathogenic Bacteria ◽

Pathogenicity Tests ◽

Phenotypic Tests

Xanthomonas citri (synonym = Xanthomonas axonopodis pv. citri) (3) has been reported in several countries in Africa (1) but not Somalia. During 2006 and 2007, hyperplasia-type lesions, often surrounded by a water-soaked margin and yellow halo, typical of citrus canker caused by X. citri were found on 8- to 10-year-old lime (Citrus limetta) and grapefruit (Citrus × paradisi Macfed.) trees in northern and southern Somalia, respectively. Ten leaf samples diagnosed presumptively as citrus canker by Xac ImmunoStrip test kits (Agdia, Elkhart, IN) were mailed to the USDA Foreign Disease-Weed Science Research Unit at Ft. Detrick, MD. To confirm the identification of X. citri, isolations were made from several lesions from each sample onto yeast-dextrose-CaCO3 (YDC) agar (2). Yellow, xanthomonad-like mucoid, convex colonies were purified and stored on YDC slants. Phenotypic tests were done as described (2), and real-time PCR assays were done using primers XCit8F and XCit5R with probe XCitP2 (N. W. Schaad, unpublished). For pathogenicity tests, cultures were grown overnight in liquid nutrient broth-yeast (4) medium adjusted to contain 1 × 105 CFU/ml and inoculated into leaves of lime seedlings with the blunt end of a 2-ml syringe. After 21 to 30 days in a lighted dew chamber (Model I-60DLM; Percival Scientific, Inc. Perry, IA) at 30/23°C day/night, symptoms were recorded. Cultures of sample S-1 (northern Somalia) from lime were phenotypically atypical of X. citri, PCR negative, and nonpathogenic. However, cultures of samples 3 to 7 (southern Somalia) from grapefruit were typical of X. citri and PCR positive; cultures 3 and 4 were tested for pathogenicity and produced erumpent lesions on lime. Isolations onto YDC agar resulted in typical mucoid, convex, yellow, PCR-positive colonies. To our knowledge, this is the first report of X. citri on citrus plants in Somalia. Strains S3 and S4 have been deposited in ICPB at Ft. Detrick, MD as ICPB 11650 and 11651, respectively. References: (1) J. F. Bradbury. Guide to Plant Pathogenic Bacteria. CAB International, Egham, UK, 1986. (2) N. W. Schaad et al. Xanthomonas. Page 175 in: Laboratory Guide for Identification of Plant Pathogenic Bacteria. 3rd ed. N. W. Schaad et al. eds. American Phytopathological Society, St. Paul. MN. 2001. (3) N. W. Schaad et al. Syst. Appl. Microbiol. 29:690, 2006. (4) A. K. Vidaver. Appl. Microbiol. 15:1523, 1967.

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First Report of Xanthomonas citri pv. citri-A* Causing Citrus Canker on Lime in Cambodia

Plant Disease ◽

10.1094/pdis-92-11-1588a ◽

2008 ◽

Vol 92 (11) ◽

pp. 1588-1588 ◽

Cited By ~ 5

Author(s):

L. Bui Thi Ngoc ◽

C. Vernière ◽

O. Pruvost ◽

T. So ◽

G. I. Johnson

Keyword(s):

Host Range ◽

Large Scale ◽

Severe Infection ◽

Citrus Canker ◽

Aflp Analysis ◽

Citrus Species ◽

Bacterial Strains ◽

Xanthomonas Citri ◽

Mexican Lime ◽

Wide Host Range

Asiatic citrus canker caused by Xanthomonas citri pv. citri (X. citri pv. citri-A) is detrimental to citrus production in tropical and subtropical areas. The bacterium can cause severe infection on many citrus species, initially causing water-soaked leaf lesions that become erumpent and necrotic, often with a chlorotic halo. Severe infection causes premature fruit drop and twig dieback. X. citri pv. citri-A has consequently been subject to eradication and international quarantine regulations. In the 1990s, strains with a host range restricted to Mexican lime (Citrus aurantifolia), but not infecting grapefruit (C. paradisi), were described in different areas of Southwest Asia (4). This variant was designated X. citri pv. citri-A* because of its phenotypic and genetic similarities with X. citri pv. citri. Lime leaves with canker lesions were collected in 2007 from a citrus nursery in Kandal Province, Cambodia and isolations were performed with KC semiselective medium (3). Four Xanthomonas-like strains were further characterized by PCR alongside positive control strain CFBP 2525 from New Zealand. The expected DNA fragment was obtained using primer pair 4/7 (2) from the bacterial strains but not when distilled water was used as a template. Amplified fragment length polymorphism (AFLP) analysis of the four X. citri pv. citri strains from Cambodia and reference strains X. citri pv. citri-A (CFBP 2525, CFBP 2900, LMG 9322), -A* (CFBP 2911, JF90-2, JK2-10, JK143-1, JM47-2), and X. citri pv. aurantifolii (CFBP 2866, CFBP 2868, CFBP 2901) using SacI/MspI and four primer pairs (1) separated the Cambodian strains into two distinct haplotypes (i.e., AFLP fingerprint patterns). One haplotype was closely related (evolutionary genome divergences [EGD] ≤0.006 [1]) to X. citri pv. citri-A strains with a wide host range and the other was most genetically related to a strain of X. citri pv. citri-A* from Thailand (EGD of 0.003). On the basis of AFLP, the Cambodian isolates were not related to X. citri pv. aurantifolii (EGD values of >0.060). When inoculated to Mexican lime and Duncan grapefruit using a detached leaf assay in which inoculum droplets containing ∼1 × 106 CFU were deposited on wounds (4), the strains genetically related to X. citri pv. citri-A produced typical canker lesions on both citrus species a week after inoculation, whereas the Cambodian strains related to X. citri pv. citri-A* by AFLP analysis only produced canker lesions on lime. Our finding extended the geographical distribution of pathotype A*. Identification of both pathotypes from a few samples collected in a nursery suggests a potential for large-scale distribution of these strains within the citrus orchards in Cambodia, where the most important citrus crop is sweet orange, suggesting that the occurrence of X. citri pv. citri-A* is of moderate economic significance, in contrast with X. citri pv. citri-A strains with a wide host range. Diseased citrus nursery plants are a major source of primary inoculum in developing countries. Sanitation of citrus nurseries against citrus canker in Cambodia is a prerequisite for improved management of the disease. References: (1) N. Ah-You et al. Phytopathology 97:1568, 2007. (2) J. S. Hartung et al. Phytopathology 86:95, 1996. (3) O. Pruvost et al. J. Appl. Microbiol. 99:803, 2005. (4) C. Vernière et al. Eur. J. Plant Pathol. 104:477, 1998.

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Occurrence of a Citrus Canker Strain With Limited Host Specificity in South Texas

Plant Health Progress ◽

10.1094/php-06-17-0037-rs ◽

2017 ◽

Vol 18 (4) ◽

pp. 196-203 ◽

Cited By ~ 1

Author(s):

John V. da Graça ◽

Madhurababu Kunta ◽

Jong-Won Park ◽

Marissa Gonzalez ◽

Gem Santillana ◽

...

Keyword(s):

Host Range ◽

Citrus Canker ◽

South Texas ◽

Pcr Analysis ◽

Leaf Extracts ◽

Mexican Lime ◽

Molecular Tests ◽

Citrus Varieties ◽

Stem Lesions ◽

Infiltration Method

In October 2015, a Mexican lime exhibiting citrus canker symptoms was found by the USDA APHIS PPQ in a residential property in Rancho Viejo, Cameron County, Texas. Real-time PCR analysis detected the presence of Xanthomonas citri subsp. citri; USDA APHIS PPQ in Beltsville, MD confirmed this diagnosis. A delimiting survey was initiated and suspect leaf samples were collected and sent to the PPQ Beltsville lab for analysis. By October 2017, leaf samples from 197 trees were confirmed positive for citrus canker, all within a 5-mile radius; in addition, a further 59 symptomatic trees were found and all 256 infected trees (254 Mexican lime, one makrut lime, and one Ponderosa lemon) were removed. Survey data collected on stem lesions suggested the oldest lesions to be between 4 to 6 years old. A host-range study using 12 citrus varieties, including the major commercial varieties grown in Texas, were inoculated with crude leaf extracts from symptomatic leaves by leaf infiltration method. Mexican limes and alemow were the only citrus plants that developed definitive canker lesions. A combination of host range, serological, and molecular tests suggested that this isolate was different from the typical Asiatic strain and more similar to X. citri subsp. citri AW which was only previously reported from Florida on Mexican lime and alemow.

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