Abstract
Severe outbreaks of leaf spot disease of leafy vegetable brassica crops have occurred from early spring to late fall for at least the past 7 years in Lexington County, South Carolina, the major growing region for leafy greens in the state. Significant economic losses to this disease totaling $1.7 million have been incurred by large and small growers. In 2005, Pseudomonas syringae pv. maculicola was reported as one of the causal organisms of leaf spot disease in South Carolina (2). Investigations during 2006 and 2007 have led to the isolation of another bacterium causing leaf spotting of brassica crops. Symptoms in the field were nearly identical to symptoms caused by P syringae pv. maculicola, i.e., small, brown necrotic spots, often with chlorotic halos that expand and coalesce to cover the leaves. Colonies recovered from diseased tissues were xanthomonad like, nonfluorescent on Pseudomonas Agar F, mucoid on yeast extract dextrose chalk medium, grew at 35°C, hydrolyzed starch, positive for protein digestion, alkaline in litmus milk, and produce acid from arabinose. Sequence data from the 16S rDNA and fatty acid methyl ester analysis gave the best homology to Xanthomonas campestris pv. campestris with a similarity score index of >0.98 and >0.70, respectively, confirming genus and species. Excised-cotyledon assays, used to differentiate between pathovars campestris and armoraciae, confirmed the pathovar as campestris (1). Pathogenicity assays with spray inoculations (1 × 10 7 CFU/ml) (3) on eight plants each of ‘Topper’ and ‘Alamo’ turnip, ‘Early Jersey Wakefield’ cabbage, and ‘Money maker’ tomato produced leaf-spot symptoms within 10 days in the greenhouse and growth chamber on the turnip and cabbage plants, but not the tomato. X. campestris pv. campestris, which is common throughout the world, also is the causal agent of black rot in brassica. Typical black rot symptoms are seen often in Lexington County fields in summer and are quite different from the leaf spot symptoms observed. Leaf-spotting X. campestris pv. campestris (LS) strains and black rot (BR) strains, recovered from black rot-symptomatic plants lacking leaf spots, from the same fields were compared in greenhouse pathogenicity assays on six plants each of ‘Topper’ turnip and ‘Early Jersey Wakefield’ cabbage. Spray inoculations with 20 individual LS strains and 10 individual BR strains, collected from 2005 to 2007, produced symptoms unique to each group. These symptoms included chlorotic ‘V’-shaped lesions initiating from the leaf margins with black veining when plants were inoculated with BR strains, versus rapid and severe leaf spotting followed by chlorotic ‘V’-shaped lesions typically lacking black-veining 10 to 16 days postinoculation associated with LS strains. Additional inoculation tests gave similar results. To our knowledge, this is the first report of a severe leaf spotting disease of field-grown brassica leafy greens caused by X. campestris pv. campestris in South Carolina. These findings may have importance in differentiation of bacterial leaf spot pathogens in brassica crops. References: (1) A. M. Alvarez et al. Phytopathology 84:1449, 1994. (2) A. P. Keinath et al. Plant Dis. 90:683, 2006. (3) W. P. Wechter et al. Hortic Sci. 42:1140, 2007.
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Claims 11
Claim · model-written summary
Severe leaf spot outbreaks affected leafy brassicas in Lexington County across seasons for at least seven years.
- Outcome
- Severe outbreaks of leaf spot diseasee0
- Value
- past 7 yearse0
- Setting
- Lexington County, South Carolinae0
BrassicaOrganisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Severe outbreaks of leaf spot disease of leafy vegetable brassica crops have occurred from early spring to late fall for at least the past 7 years in Lexington County, South Carolina”
Claim · model-written summary
The leaf spot outbreaks caused $1.7 million in grower losses.
Verbatim
e0“Significant economic losses to this disease totaling $1.7 million have been incurred by large and small growers.”
t0“Leafy Brassica Greens”
Claim · model-written summary
Investigators isolated another bacterium causing brassica leaf spotting.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Investigations during 2006 and 2007 have led to the isolation of another bacterium causing leaf spotting of brassica crops.”
Claim · model-written summary
Diseased brassicas had small brown necrotic leaf spots, often with chlorotic halos that expanded and merged.
Verbatim
e0“small, brown necrotic spots, often with chlorotic halos that expand and coalesce to cover the leaves.”
t0“Leafy Brassica Greens”
Claim · model-written summary
Sequence and fatty acid analyses identified the bacterium as Xanthomonas campestris pv. campestris.
- Taxon
- Leafy Brassica Greenst0
- Interactor
- Xanthomonas campestris pv. campestris
Xanthomonas campestris pv. campestrise0pathogen - Outcome
- Xanthomonas campestris pv. campestrise0
- Value
- >0.98 and >0.70e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Sequence data from the 16S rDNA and fatty acid methyl ester analysis gave the best homology to Xanthomonas campestris pv. campestris with a similarity score index of >0.98 and >0.70, respectively, confirming genus and species.”
t0“Leafy Brassica Greens”
Claim · model-written summary
Excised cotyledon assays confirmed pathovar campestris.
Verbatim
e0“Excised-cotyledon assays, used to differentiate between pathovars campestris and armoraciae, confirmed the pathovar as campestris”
t0“Leafy Brassica Greens”
Claim · model-written summary
Spray inoculation produced leaf spots on turnip and cabbage within 10 days.
- Taxon
- turnip
.jpg?width=60)
Brassica rapa subsp. rapae0 - Treatment
- Spray inoculationse0
- Outcome
- leaf-spot symptomse0
- Value
- 10 dayse0
Not reportedInteractorComparatorDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
.jpg?width=500)
Verbatim
e0“Spray inoculations (1 × 10 7 CFU/ml) (3) on eight plants each of ‘Topper’ and ‘Alamo’ turnip, ‘Early Jersey Wakefield’ cabbage, and ‘Money maker’ tomato produced leaf-spot symptoms within 10 days in the greenhouse and growth chamber on the turnip and cabbage plants, but not the tomato.”
Claim · model-written summary
The same spray inoculations produced leaf spots on cabbage within 10 days.
- Taxon
- cabbage
Brassica oleracea var. capitatae0 - Treatment
- Spray inoculationse0
- Outcome
- leaf-spot symptomse0
- Value
- 10 dayse0
Not reportedComparatorDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Spray inoculations (1 × 10 7 CFU/ml) (3) on eight plants each of ‘Topper’ and ‘Alamo’ turnip, ‘Early Jersey Wakefield’ cabbage, and ‘Money maker’ tomato produced leaf-spot symptoms within 10 days in the greenhouse and growth chamber on the turnip and cabbage plants, but not the tomato.”
Claim · model-written summary
Tomato did not develop leaf spots after spray inoculation.
- Taxon
- tomato
Solanum lycopersicume0 - Treatment
- Spray inoculationse0
- Outcome
- not the tomatoe0
Not reportedComparatorDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Spray inoculations (1 × 10 7 CFU/ml) (3) on eight plants each of ‘Topper’ and ‘Alamo’ turnip, ‘Early Jersey Wakefield’ cabbage, and ‘Money maker’ tomato produced leaf-spot symptoms within 10 days in the greenhouse and growth chamber on the turnip and cabbage plants, but not the tomato.”
Claim · model-written summary
Black rot strains caused chlorotic V-shaped lesions with black veins.
- Taxon
- Leafy Brassica Greenst0
- Treatment
- inoculated with BR strainse0
- Interactor
- BR strainse0pathogen
- Outcome
- chlorotic ‘V’-shaped lesionse0
Not reportedComparatorDirection
Verbatim
e0“chlorotic ‘V’-shaped lesions initiating from the leaf margins with black veining when plants were inoculated with BR strains”
t0“Leafy Brassica Greens”
Claim · model-written summary
Leaf spotting strains caused severe leaf spots followed by V-shaped lesions usually without black veins.
- Taxon
- Leafy Brassica Greenst0
- Treatment
- LS strainse0
- Interactor
- LS strainse0pathogen
- Outcome
- rapid and severe leaf spottinge0
Not reportedComparatorDirection
Verbatim
e0“rapid and severe leaf spotting followed by chlorotic ‘V’-shaped lesions typically lacking black-veining 10 to 16 days postinoculation associated with LS strains”
t0“Leafy Brassica Greens”
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