First Outbreak of Bacterial Leaf Spot Caused by Xanthomonas campestris on Canola in Argentina

Canola (Brassica napus) is an alternative crop to wheat in Argentina and ~16,000 ha are grown commercially in southern Buenos Aires Province. During 2003, experimental field plots of canola plants located at Agronomy Faculty, University of Buenos Aires, in Buenos Aires were severely damaged by a bacterial leaf spot. Average disease incidence across 25 2- to 5-month-old canola cultivars was 58% (range = 27 to 89%). During 2004, identical infection associated with blackened veins (8 to 12% of plants) were found in two commercial fields and experimental crops (rosette and flowering stages) in Tres Arroyos in southern Buenos Aires Province. Symptoms observed on adaxial surfaces consisted of v-shaped necrotic lesions on leaf margin surrounded by yellow halos. Yellow bacterial ooze was found on young lesions. The advanced phases of the disease included lesion enlargement, foliar chlorosis, and death of leaves. The disease developed from the lower leaves to the apex, resulting in complete leaf necrosis and defoliation. Ten samples (five plants per sample) with lesions were arbitrarily collected from 2003 to 2004 from commercial and experimental canola crops. Diseased leaf tissue was surface sterilized in 0.50% sodium hypochlorite for 30 s and rinsed in sterile distilled water (SDW). Leaf sections were macerated in SDW, and the extract was streaked onto nutrient agar. Plates were incubated at 28°C for 3 days. Resultant colonies were yellow, mucoid, and convex. Gram-negative, aerobic, and rod-shaped bacteria were obtained. Eight strains were biochemically characterized using API 20NE (BioMerieux, Marcy l'Etoile, France) and identified as Xanthomonas campestris (1). Strains hydrolyzed starch, gelatine, and aesculin and were positive for catalase and negative for oxidase, nitrate reduction, ureasa, and triptophanase. Strains were capable of utilizing D-glucose, D-mannose, D-maltose, malic acid, and N-acetyl-glucosamine. X. campestris. pv. campestris 8004 was used as a reference strain (2). Pathogenicity and host range for three isolates were completed by injecting a bacterial suspension (107 CFU/ml) into leaves of 2-week-old canola plants (cvs. Eclipse, Impulse, Master, and Mistral), cabbage (B. oleracea var. capitata), and cauliflower (B. oleracea var. botrytis) seedlings (two-leaf stage). The experiment (four inoculated and two control plants for each cultivar and each strain) was conducted in a greenhouse at 24°C and 75% relative humidity. Inoculated and control plants were enclosed in a plastic bag for 48 h after inoculation. Chlorotic patches on the leaves followed by a dry, brown necrosis spread beyond the initial injected area were observed in inoculated plants 8 days after inoculation. Enlarged spots caused death of leaves. The pathogen was successfully reisolated. Control plants, inoculated only with SDW, remained symptomless. The results suggest that the bacterium represents a potential threat to canola production in Argentina and indicate the need for further study to identify the pathovar involved in canola leaf spots. To our knowledge, this is the first report of an outbreak of X. campestris causing leaf spot of canola and in which the bacteria affecting canola commercial crops was biochemically characterized and host range was carried out in Argentina. References: (1) N. W. Schaad et al. Laboratory Guide for Identification of Plant Pathogenic Bacteria. 3rd ed. The American Phytopathological Society, St. Paul. MN, 2001. (2) P. Turner et al. Mol. Gen. Genet. 195:101, 1984.

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Report of Bacterial Leaf Spot on Collards and Turnip Leaves in Ohio

Plant Disease ◽

10.1094/pdis.2002.86.2.186a ◽

2002 ◽

Vol 86 (2) ◽

pp. 186-186 ◽

Cited By ~ 2

Author(s):

M. L. Lewis Ivey ◽

S. Wright ◽

S. A. Miller

Keyword(s):

Pseudomonas Syringae ◽

Leaf Spot ◽

Xanthomonas Campestris ◽

Similarity Index ◽

Acid Methyl Ester ◽

Bacterial Suspension ◽

Water Control ◽

Bacterial Leaf Spot ◽

Turnip Leaves ◽

Negative Controls

In 2000, circular water-soaked lesions typical of bacterial leaf spot were observed on leaves of collards (Brassica oleracea L. var. viridis) throughout commercial fields in northwest Ohio. Light brown, rectangular, water-soaked lesions were observed on turnip leaves (Brassica rapa L.). Bacterial streaming from lesions on both crops was observed microscopically. Cream colored, fluorescent colonies were isolated from diseased tissues on Pseudomonas F medium, and eight representative colonies (four from collards and four from turnip) were selected and purified. Fatty acid methyl ester analysis was performed on all of the isolates. Two from collards and two from turnip were identified as Pseudomonas syringae pv. maculicola (mean similarity index = 0.82 [MIDI Inc., Newark, DE]). DNA extracts from pure cultures of the P. syringae pv. maculicola strains were used as template in a polymerase chain reaction (PCR) assay with primers derived from the region of the coronatine gene cluster controlling synthesis of the coronafacic acid moiety found in P. syringae pv. tomato and P. syringae pv. maculicola (CorR and CorF2) (D. Cuppels, personal communication). DNA from P. syringae pv. tomato strain DC3000 and P. syringae pv. maculicola strain 88–10 (2) served as positive controls, while water and DNA from Xanthomonas campestris pv. vesicatoria strain Xcv 767 were used as negative controls. The expected 0.65-kb PCR product was amplified from three of four strains (two from turnip and one from collards) and the positive control DNA, but not from the negative controls. Pathogenicity tests were performed twice on 6-week-old turnip (‘Forage Star’, ‘Turnip Topper’, ‘Turnip Alamo’, ‘Turnip 7’), collard (‘Champion’) and mustard (Brassica juncea L. ‘Southern Giant Curl’) seedlings using the three PCR-positive strains. Premisted seedlings were spray-inoculated separately with each of the three strains (2 × 108 CFU/ml, 5 ml per plant) and a water control. Greenhouse temperatures were maintained at 20 ± 1°C. For both tests, all strains caused characteristic lesions on all of the crucifer cultivars within 5 days after inoculation; the control plants did not develop symptoms. To satisfy Koch's postulates, one of the turnip strains was reisolated from ‘Turnip Topper’ plants, and the collard strain was reisolated from ‘Champion’ plants. The three original and two reisolated strains induced a hypersensitive response in Mirabilis jalapa L. and Nicotiana tabacum L. var. xanthia plants 24 h after inoculation with a bacterial suspension (1 × 108 CFU/ml). The original and reisolated strains were compared using rep-PCR with the primer BOXA1R (1). The DNA fingerprints of the reisolated strains were identical to those of the original strains. To our knowledge, this is the first report of bacterial leaf spot on commercially grown collards and turnip greens in Ohio. References: (1) B. Martin et al. Nucleic Acids Res. 20:3479, 1992. (2) R. A. Moore et al. Can. J. Microbiol. 35:910, 1989.

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First Report of Bacterial Leaf Spot of Rieger Begonia Caused by Xanthomonas campestris pv. begoniae in China

Plant Disease ◽

10.1094/pdis-04-12-0391-pdn ◽

2013 ◽

Vol 97 (2) ◽

pp. 282-282 ◽

Cited By ~ 2

Author(s):

L. H. Zhou ◽

G. H. Ji

Keyword(s):

Leaf Spot ◽

Xanthomonas Campestris ◽

Infection Process ◽

Leaf Spot Disease ◽

Leaf Margin ◽

Bacterial Strains ◽

Bacterial Leaf Spot ◽

First Report ◽

Initial Symptoms ◽

Phosphate Buffered Saline

Rieger begonia are collectively referred to as a begonia hybrid group. Its global annual sales is 90,000,000 cutting seedlings. It is one of the top ten potted plants. In the summer of 2011, serious outbreaks of a suspected bacterial leaf spot disease were observed on five Rieger begonia cultivars (Dark Britt, Rebecca, Blitz, Barkos, and Borias). These plants were grown for potted cutting seedling production in commercial nurseries located in Shilin county of Yunnan Province, China. The initial symptoms of the disease were small circular or polygonal water-soaked needle spots on leaf margin that later these spots expanded and joined together, forming bigger inverted V-shaped necrotic specks (4). Yellow-pigmented bacterial colonies were consistently isolated from diseased leaves and stems on NA agar medium and incubated at 28°C. Twelve bacterial strains were isolated and used for further studies. All the isolates were Gram-negative, rod-shaped, motile, aerobic, and non-sporing. All of the bacterial strains isolated in the present study were identified as Xanthomonas campestris pv. begoniae (Xcb) based on biochemical and physiological identification (Biolog carbon source utilization analysis) and 16S rDNA sequences analysis and further pathogenicity determination (1). The results show that the sequence homology rate of HT1-1 (GenBank Accession No. JN648097) and X. euvesicatoria (syn. X. campestris pv vesicatoria) (GeneBank Accession No. AM039952) is 99%. This strongly suggests that the Rieger begonia isolates belong to X. campestris pv. begoniae (2). For Koch's postulates, 10 surface-disinfected young leaves from five susceptible Rieger begonia plants (cv. Dark Britt) were inoculated by spraying a phosphate-buffered saline suspension of each bacterial isolate (3.0 × 108 CFU/ml) onto the leaves (3). Controls were inoculated similarly with phosphate-buffered saline solution. All inoculated plants were covered with polyethylene bags for 24 h at 25°C and then put in the greenhouse. After inoculation, water-soaked and necrotic symptoms were observed on inoculated Rieger begonia leaves within 7 to 9 days. No symptoms were observed on controls. Bacteria were reisolated and confirmed to be identical to the original isolates by the methods described above. To our knowledge, this is the first report of Xcb causing leaf spot on Rieger begonia plants in China. The infection process of Xcb on Rieger begonia plants and rapid detection of this pathogen are underway. References: (1) M. R. Gillings et al. PNAS 12:102, 2005. (2) C. L. Oliver et al. Plant Dis. 4:96, 2012. (3) H. Ornek et al. New Dis. Rep. 13:40, 2006. (4) O. Pruvost et al. Plant Dis. 4:96, 2012.

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Role of Crop Debris and Weeds in the Epidemiology of Bacterial Leaf Spot of Lettuce in California

Plant Disease ◽

10.1094/pdis.2001.85.2.169 ◽

2001 ◽

Vol 85 (2) ◽

pp. 169-178 ◽

Cited By ~ 42

Author(s):

Jeri D. Barak ◽

Steven T. Koike ◽

Robert L. Gilbertson

Keyword(s):

Leaf Spot ◽

Xanthomonas Campestris ◽

Disease Incidence ◽

Polymerase Chain Reaction Primer ◽

Lettuce Seed ◽

Plant Debris ◽

Bacterial Leaf Spot ◽

Fallow Period ◽

Summer Fallow ◽

Winter Fallow

Bacterial leaf spot of lettuce (BLS), caused by Xanthomonas campestris pv. vitians, has increased in importance in California over the past 5 years. The pathogen can be seedborne, but it was not recovered from selected commercial lettuce seed lots planted during this time. Survival of X. campestris pv. vitians in association with plant debris was investigated in a 3-year field experiment in Salinas, CA. The initial lettuce spring crop was spray inoculated with X. campestris pv. vitians, which resulted in 100% disease incidence. Spring crops were followed by a 1-month summer fallow period, whereas fall crops were followed by a 5-month winter fallow period. High populations of X. campestris pv. vitians (up to 106 CFU/g) were recovered from lettuce plant debris after the 1-month summer fallow and BLS developed on all subsequent fall lettuce crops. During the winter fallow period, X. campestris pv. vitians populations associated with plant debris declined and, by 2 months after harvest, only small populations were detected. Spring crops also developed BLS, but at reduced levels. X. campestris pv. vitians was recovered from leaves of several symptomless weed species collected around commercial infested fields, but not from weeds collected around previously infested fields during fallow periods. During the course of this study, an X. campestris pv. vitians-specific polymerase chain reaction primer pair was developed.

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First Report of Xanthomonas fragariae Causing Angular Leaf Spot on Strawberry Plants in México

Plant Disease ◽

10.1094/pdis-07-13-0691-pdn ◽

2014 ◽

Vol 98 (5) ◽

pp. 682-682 ◽

Cited By ~ 3

Author(s):

S. P. Fernández-Pavía ◽

G. Rodríguez-Alvarado ◽

E. Garay-Serrano ◽

R. Cárdenas-Navarro

Keyword(s):

Leaf Spot ◽

Pathogenic Bacteria ◽

Disease Incidence ◽

Angular Leaf Spot ◽

Pcr Analysis ◽

Bacterial Suspension ◽

American Phytopathological Society ◽

First Report ◽

Leaf Surfaces ◽

Xanthomonas Fragariae

The state of Michoacán is the most important strawberry producer in México. During January 2007, field-grown strawberry plants cv. Aromas showing vein necrosis were observed in 3 ha in Zamora County, in fruit production fields. The average disease incidence in the field was 80%. Infected plants presented water-soaked lesions limited by veins on the lower leaf surfaces, which enlarged to form angular spots (1). Additionally, most affected plants presented severe necrosis in the main veins and reddish to necrotic lesions on the upper leaf surfaces. Gram-negative bacteria were consistently isolated from leaves with water-soaked lesions. Isolated bacteria produced mucoid, yellow colonies on YDC, grew on tween and nutrient agar (NA), but not on SX media. Strains produced non-fluorescent colonies on King's B media, were positive starch hydrolysis, negative esculin hydrolysis; and produced acid from fructose but not from arabinose, galactose, celobiose, and trehalose. Growth was inhibited by 2% NaCl (3). Indirect ELISA analysis (NEOGEN, Lansing, MI) was conducted using antibodies specific for Xanthomonas fragariae. Conventional PCR assay using the primer pairs 241A/241B was performed (2). The ELISA test was positive. The expected 300- and 550-bp bands were observed in the PCR analysis. The bacteria was identified as X. fragariae Kennedy and King. Pathogenicity tests were conducted twice in a greenhouse (24 ± 4°C) on a total of five strawberry cv. Aromas plants. The main vein of each of three leaves per plant were punctured using sterile needles. Pathogen inoculum was obtained from 6- to 8-day-old NA cultures. Bacteria were applied onto the wounds with a sterile cotton swab dipped into the bacterial suspension (105 CFU/ml). Inoculated plants were covered with plastic bags for 48 h. Symptoms resembling those seen in the field developed on all inoculated plants after 9 days. X. fragariae was re-isolated from the necrotic lesions and identified by PCR. Control plants were similarly inoculated with water but did not develop symptoms. To our knowledge, this is the first report of X. fragariae causing angular leaf spot in strawberry in Michoacán, México. References: (1) J. L. Maas, ed. Compendium of Strawberry Diseases. The American Phytopathological Society, St. Paul, MN, 1998. (2) M. R. Pooler et al. Appl. Environ. Microbiol. 62:3121, 1996. (3) N. W. Schaad et al. Laboratory Guide for Identification of Plant Pathogenic Bacteria. 3rd ed. The American Phytopathological Society, St. Paul, MN, 2001.

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Evaluating the Efficacy of Commercial Products for Management of Bacterial Leaf Spot on Lettuce

Plant Health Progress ◽

10.1094/php-2005-1121-01-rs ◽

2005 ◽

Vol 6 (1) ◽

pp. 3 ◽

Cited By ~ 9

Author(s):

Carolee T. Bull ◽

Steve T. Koike

Keyword(s):

Leaf Spot ◽

Management Strategy ◽

Xanthomonas Campestris ◽

Disease Incidence ◽

Leaf Spot Disease ◽

Bacterial Leaf Spot ◽

Disease Management Strategy ◽

Elemental Copper ◽

Lower Severity ◽

Fourth Experiment

The efficacy of Serenade, Maneb, Cuprofix, and mixtures of these products were evaluated for efficacy in reducing disease incidence and severity of bacterial leaf spot of lettuce caused by Xanthomonas campestris pv. vitians in six trials at two locations between 2001 and 2003. Additionally, Messenger, elemental copper, Quadris, and Actigard were evaluated in at least two of these trials. Mixtures of Serenade and Cuprofix reduced disease incidence in three of six experiments and reduced disease severity in a fourth experiment. Treatment with the Maneb and Cuprofix mixture was less effective but resulted in significantly less disease and lower severity in single experiments. These results indicate that a mixture of Serenade and Cuprofix may be a useful addition to an integrated bacterial leaf spot disease management strategy but this treatment may be too variable to justify it as a stand-alone treatment. Accepted for publication 21 October 2005. Published 21 November 2005.

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Bacterial Leaf Spot of Lettuce: Relationship of Temperature to Infection and Potential Host Range of Xanthomonas campestris pv. vitians

Plant Disease ◽

10.1094/pd-90-0465 ◽

2006 ◽

Vol 90 (4) ◽

pp. 465-470 ◽

Cited By ~ 11

Author(s):

P. E. Robinson ◽

J. B. Jones ◽

Ken Pernezny

Keyword(s):

Host Range ◽

Plant Species ◽

Leaf Spot ◽

Electrolyte Leakage ◽

Xanthomonas Campestris ◽

Optimum Temperature ◽

Fresh Market ◽

Bacterial Leaf Spot ◽

Causal Organism ◽

Potential Host

Epidemiological aspects, including optimum temperature for infection and host range of Xanthomonas campestris pv. vitians, causal organism of bacterial leaf spot (BLS) of lettuce, were investigated. The optimum temperature for infection was determined to be 22.7°C based on growth chamber studies. Internal populations were monitored over time in lettuce, tomato, pepper, parsley, cilantro, and beet. Each plant species was infiltrated with the bacterium at 105CFU/ml. Highest populations developed in lettuce (108CFU/cm2) followed by pepper with 106CFU/cm2, whereas the other plant species harbored much lower populations (105 to 103CFU/cm2). Infectivity titration endpoints were similar in pepper and lettuce (103 to 104CFU/ml). For other plant species tested, infectivity titration endpoints were 106 to 107 CFU/ml. Electrolyte leakage data and corresponding internal population data support the conclusion that fresh-market tomato is not a host of X. campestris pv. vitians but, instead, interacts in an incompatible response. Electrolyte leakage from cells of tomato plants inoculated with X. campestris pv. vitians or a pepper strain of X. axonopodis pv. vesicatoria peaked at 48 h, suggesting that tomato is not a host for the BLS pathogen. Both electrolyte leakage and population dynamics results point to pepper as a potential host of X. campestris pv. vitians.

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Development of Lettuce Breeding Lines Resistant to Bacterial Leaf Spot

HortScience ◽

10.21273/hortsci.40.4.1098a ◽

2005 ◽

Vol 40 (4) ◽

pp. 1098A-1098 ◽

Cited By ~ 1

Author(s):

Ryan J. Hayes ◽

Carolee T. Bull ◽

Polly H. Goldman ◽

Edward J. Ryder

Keyword(s):

Leaf Spot ◽

Xanthomonas Campestris ◽

Disease Incidence ◽

Field Trials ◽

Control Measures ◽

Bacterial Leaf Spot ◽

Sources Of Resistance ◽

Breeding Lines ◽

Overhead Irrigation ◽

Lettuce Breeding

Bacterial leaf spot of lettuce caused by Xanthomonas campestris pv. vitians (Xcv) is an important lettuce disease in California. No adequate control measures have been found, although resistance exists in several heirloom cultivars. Deployment of cultivars resistant to bacterial leaf spot will reduce these periodic and costly disease events. The objectives of this research were to 1) identify new sources of resistance within modern crisphead cultivars and 2) select for resistance in `Salad Crisp' × `Iceberg' progeny. Field plots were established and grown with overhead irrigation, and a three-strain mixture of Xcv was applied until runoff 1 week after thinning at 1 × 109 CFU/mL. Twenty-six crisphead cultivars were tested in unreplicated field trials and rated on a 1 (susceptible) to 4 (resistant) scale. Selection was carried out between and within families from the F2 to F4 generation. Sixteen F3 families were evaluated in unreplicated plots, and 12 F5 families were tested in replicated plots for disease incidence and severity. No usable levels of resistance were identified in the modern crisphead cultivars tested to date. All F3 families had resistance greater than `Iceberg', and 19 plants from eight families were selected for further breeding. Subsequently, 12 plants from two F4 families were selected. Replicated trials of 12 F5 families indicated that all lines have disease severity comparable to both parents. Breeding lines from crosses to `Salinas 88' are currently being developed.

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First Report of Bacterial Leaf Spot Caused by Xanthomonas campestris pv. olitorii on Jute Grown for Seed in India

Plant Disease ◽

10.1094/pdis-12-12-1196-pdn ◽

2013 ◽

Vol 97 (8) ◽

pp. 1109-1109

Author(s):

C. Biswas ◽

P. Dey ◽

A. Bera ◽

S. Satpathy ◽

B. S. Mahapatra

Keyword(s):

Bacterial Strain ◽

Leaf Spot ◽

Xanthomonas Campestris ◽

Disease Incidence ◽

Negative Control ◽

Nutrient Agar ◽

Distilled Water ◽

Bacterial Leaf Spot ◽

First Report ◽

Pure Cultures

Jute (Corchorus olitorius L.) is the second most important fiber crop after cotton in terms of global production (3). In November 2011, symptoms suggestive of bacterial infection were observed on a seed crop of jute at the CRIJAF research farm, Barrackpore, West Bengal, India. The disease appeared as small, brown, circular spots, usually less than 5 mm in diameter on the leaves and some of the spots were surrounded by a yellow halo. The lesions on the stems were elongated and in some cases were found to girdle the stem. In the later stages of disease, brown sunken spots were found on the green capsules. Disease incidence varied from about 20% to 90% of the total plants in different affected fields at the CRIJAF research farm. Bacterial leaf spot of jute with similar symptoms was reported in 1957 from Sudan (4). Five symptomatic and three asymptomatic leaf samples were collected from different jute fields. Bacterial colonies isolated on nutrient agar medium from infected young leaves were Xanthomonas-like and pale yellow cream in color. Total DNA was extracted from symptomatic as well as asymptomatic leaf samples by using an improved salt concentration and simple sodium acetate CTAB method (2). Single bacterial colonies were transferred to nutrient agar (NA) medium plates and incubated at 28°C for 48 h. Pure colonies from plates were used directly for DNA extraction using the QIAGEN DNeasy Blood and Tissue kit. PCR was carried out with Xanthomonas campestris specific primers NZ8F3/NZ85R3 (1), which generated an amplicon of 530 bp from all the symptomatic leaf samples as well as pure cultures of the isolated bacteria. No amplification was obtained from asymptomatic leaves. The amplicons from the five symptomatic samples collected from the field were sequenced and showed 100% identity with one another, and one sequence (strain JB-CO-13) was deposited in GenBank (Accession No. KC342185). The BLASTn analysis revealed that bacterial strain JB-CO-13 had 100% identity with X. campestris pv. olitorii (EU285213). Nucleotide span and ORF finder (NCBI) analysis indicated the 530-bp PCR amplicon coded part of a gyrase B gene that had 100% identity with a translated gene product (Protein ID: ABX84334). Three leaves of five 1-month-old jute plants (cv. JRO 204) in pot culture were infiltrated each with a separate bacterial strain using suspensions (1 × 105 CFU/ml) in distilled water. The negative control consisted of leaves infiltrated with sterile distilled water. The plants were kept in a greenhouse with mean maximum and minimum temperatures of 28.96 and 21.8°C, respectively. The plants were covered with plastic bags to maintain high relative humidity (>80%). Typical bacterial lesions were recorded on all the inoculated plants after 1 week. No lesions were seen on the negative control. To the best of our knowledge, this is the first report of bacterial leaf spot on C. olitorius caused by X. campestris pv. olitorii from India. References: (1) J. Adriko et al. Plant Pathol. 61:489, 2012. (2) C. Biswas, et al. Lett. Appl. Microbiol. 56:105, 2013. (3) Food and Agriculture Organization of the United Nations. Agricultural Commodities: Profiles and Relevant WTO Negotiating Issues. Online: http://www.fao.org/docrep/006/Y4343E/y4343e03.htm , 2003. (4) K. A. Sabet. Ann. Appl. Biol. 45:516, 1957.

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Genetic Diversity of Lettuce for Resistance to Bacterial Leaf Spot Caused by Xanthomonas campestris pv. vitians

Plant Health Progress ◽

10.1094/php-2007-0917-02-rs ◽

2007 ◽

Vol 8 (1) ◽

pp. 11 ◽

Cited By ~ 9

Author(s):

Carolee T. Bull ◽

Polly H. Goldman ◽

Ryan Hayes ◽

Laurence V. Madden ◽

Steven T. Koike ◽

...

Keyword(s):

Genetic Diversity ◽

Genetic Variation ◽

Disease Severity ◽

Strong Correlation ◽

Leaf Spot ◽

Xanthomonas Campestris ◽

Disease Incidence ◽

Bacterial Leaf Spot ◽

Severity Levels

Lettuce plants were artificially inoculated with three isolates of Xanthomonas campestris pv. vitians in field and greenhouse evaluations for genetic variation in resistance to bacterial leaf spot. The cultivar Little Gem had the least amount of disease, whether evaluated for disease severity or disease incidence. Disease severity levels for cultivar Batavia Reine des Glaces were not significantly different from those of Little Gem. Several cultivars including Vista Verde, Pybas 251, Pacific, Clemente, Salinas 88, and Sniper were highly susceptible. There was a strong correlation between results obtained in the greenhouse and those obtained in the field (r = 0.77, P = 0.009) indicating that greenhouse assays may be used to increase the number of cultivars evaluated and to speed breeding efforts. Accepted for publication 17 May 2007. Published 17 September 2007.

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First Report of Bacterial Leaf Spot of Lettuce (Lactuca sativa) Caused by Xanthomonas campestris pv. vitians in Saudi Arabia

Plant Disease ◽

10.1094/pdis-93-1-0107b ◽

2009 ◽

Vol 93 (1) ◽

pp. 107-107 ◽

Cited By ~ 5

Author(s):

M. Al-Saleh ◽

Y. Ibrahim

Keyword(s):

Saudi Arabia ◽

Lactuca Sativa ◽

Leaf Spot ◽

Xanthomonas Campestris ◽

Bacterial Suspension ◽

Strictly Aerobic ◽

Distilled Water ◽

Bacterial Leaf Spot ◽

Biochemical Tests ◽

First Report

In April of 2008, lettuce (Lactuca sativa L. cv. Darkland) plants grown in the Al-Ouunia Region of Saudi Arabia were observed with numerous lesions typical of bacterial leaf spot. Leaf lesions were irregular, small, pale green to black, and 2 to 5 mm in diameter. Bacteria were isolated from diseased leaf tissues by cutting leaves into small pieces (0.5 mm) and soaking them in 2 ml of sterile distilled water. The resulting suspension was streaked onto yeast dextrose calcium carbonate agar (YDC) (1) and plates were incubated at 28°C. Large, round, butyrus, bright yellow colonies typical of Xanthomonas spp. formed after 48 h and five strains were selected for further tests. A yellow, mucoid bacterium was consistently isolated from lettuce samples with typical bacterial leaf spot symptoms. All five strains tested in this study were gram negative, oxidase negative, nitrate reduction negative, catalase and esculin hydrolysis positive, motile, and strictly aerobic. All were slightly pectolytic but not amylolytic. All were identified as Xanthomonas campestris pv. vitians. The bacterium was identified with specific oligonucleotide primers (2). This primer pair directed the amplification of an approximately 700-bp DNA fragment from total genomic DNA of all X. campestris pv. vitians strains tested. Pathogenicity tests were performed by using bacterial cultures grown on YDC for 48 h at 28°C. Each strain was suspended in sterile distilled water and the bacterial concentration was adjusted to 106 CFU/ml. Leaves of 5-week-old lettuce plants (cv. Darkland) were sprayed with the bacterial suspension. The inoculated and sterile-water-sprayed control plants were covered with polyethylene bags for 48 h at 25°C, after which the bags were removed and plants were transferred to a greenhouse at 25 to 28°C (1). All strains were pathogenic on the lettuce cv. Darkland, causing typical bacterial leaf spot symptoms by 2 weeks after inoculation. All inoculated plants showed typical symptoms of bacterial leaf spot and symptoms similar to those observed on the samples collected. No symptoms developed on the control plants. The bacterium was reisolated from inoculated plants and identified as X. campestris pv. vitians by morphological, physiological, and biochemical tests as described above. To our knowledge, this is the first report of bacterial leaf spot of lettuce by X. campestris pv. vitians in Saudi Arabia. References: (1) F. Sahin and A. Miller. Plant Dis.81:1443, 1997. (2) J. D. Barak. Plant Dis.85:169, 2001.

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