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Angular leaf spot of cucurbits is generally considered to be caused by Pseudomonas syringae pv. lachrymans. It has a worldwide distribution and has been observed to emerge sporadically under humid and wet conditions. Reports of multiple P. syringae pathovars associated with the disease and lack of molecular analysis has left the true diversity of populations in the United States unclear. In this study, we collected 27 P. syringae strains causing foliar lesions and blighting on watermelon, cantaloupe, and squash in Florida, Georgia, and California over several years. Strains were fluorescent on King’s medium B agar and displayed the typical phenotypic and biochemical characteristics of P. syringae. P. syringae pv. lachrymans is a member of genomospecies 2. However, the genetic profiles obtained through both MLSA (gyrB, rpoD, gapA, and gltA) and BOX-PCR (BOXA1R) identified 26 of the P. syringae strains to be distributed among three clades within genomospecies 1, and phylogenetically distinct from genomospecies 2 member P. syringae pv. lachrymans. A novel MLSA haplotype of the pathogen common to all states and cucurbit hosts was identified. Considerable genetic diversity among P. syringae strains infecting cucurbits is associated with the same disease, and reflects the larger ecological diversity of P. syringae populations from genomospecies 1.

During a 4-week period in May through June 1996, 15% of 50 mature lisianthus (Eustoma grandiflorum) ‘Maurine Blue’ and ‘Maurine White’ plants exhibited stem blight in a landscape planting in west-central Florida. Initial disease symptoms included stem necrosis at the soil line, and yellowing and tan discoloration of leaves. As blighting of the stem progressed, infected plants wilted and died. Posted 6 June 2000.

In 1998, a new disease was detected on 3-week-old commercial broccolini (Brassica oleracea L. var. botrytis × B. alboglabra) transplants in a Salinas Valley, Monterey County, CA greenhouse. Initial symptoms were small (2 to 4 mm diameter) circular to angular, water-soaked spots. As the disease progressed, spots remained relatively small, but turned tan to brown. When diseased tissues were macerated and streaked on King's medium B, a blue-green fluorescent pseudomonad was consistently isolated. Strains were levan positive, oxidase negative, and arginine dihydrolase negative. Strains did not rot potato slices, but induced a hypersensitive reaction on tobacco (Nicotiana tabacum L. ‘Turk’). Fatty acid methyl ester analysis (MIS-TSBA, version 4.10, MIDI Inc., Newark, DE) indicated that strains had a high similarity index (0.82 or higher) to Pseudomonas syringae, and GN (version 3.50, Biolog, Inc., Hayward, CA) profiles also identified strains as P. syringae. The bacterium associated with the disease, therefore, was identified as P. syringae van Hall. Pathogenicity was demonstrated by growing inoculum in nutrient broth shake cultures for 48 h, misting the broth cultures (1×106 CFU/ml) onto broccolini (cv. Aspabrock), and subjecting the plants to 48 h of high humidity. Control plants were misted with sterile nutrient broth. After 4 to 5 days in a greenhouse, leaf spot symptoms developed on all inoculated broccolini plants, and reisolated strains were characterized and found to be P. syringae. Control plants remained symptomless. The results of two sets of pathogenicity tests were the same. Repetitive sequence-based polymerase chain reaction using the BOXA1R primer resulted in identical banding patterns for the broccolini pathogen and for known isolates of P. syringae pv. maculicola from crucifers. In host range testing, P. syringae pv. maculicolawas pathogenic to broccolini plants. The broccolini isolates and P. syringae pv. maculicola isolates had the same pathogenicity results when crucifers and tomatoes were tested as hosts; broccoli and cauliflower (B. oleracea var. botrytis) were infected, and tomato results were variable. These tests suggest that the broccolini pathogen is the bacterial leaf spot pathogen, Pseudomonas syringae pv. maculicola, that occurs on broccoli and cauliflower transplants (1). To our knowledge, this is the first report of this pathogen causing a disease on commercially grown broccolini. Reference: (1) S. T. Koike et al. Plant Dis. 82:727, 1998.

A postharvest discoloration of the cultivated mushroom Agaricus bisporus in Pennsylvania was associated with three pathotypes of fluorescent pseudomonads. Pathotype A strains caused pitted, dark-brown blotches on mushroom caps, formed precipitates in agar ('white line' reactions) with Pseudomonas tolaasii strain ATCC 14340 (reclassified as P. 'reactans'), were phenotypically like P. fluorescens biovar V, and fit descriptions of P. tolaasii. Pathotype B strains caused pitted, yellow- brown, sometimes slimy lesions on mushrooms, formed no 'white line' reactions, were phenotypically like P. fluorescens biovars III and V, and fit descriptions of P. 'gingeri'. Pathotype C strains caused mild, lightbrown discoloration on mushrooms with little tissue collapse, formed 'white line' reactions with P. tolaasii ATTC 33618 (type strain), had P. fluorescens biovar III and V phenotypes, and fit descriptions of P. 'reactans'. Isolations from mushroom casing material yielded all pathotypes including both pathogenic and nonpathogenic strains of P. 'reactans' with distinguishing phenotypic or chemical characteristics. Cellular fatty acid analysis suggested pathogenic strains of P. 'reactans' were more similar to P. tolaasii and P. 'gingeri' than to saprophytic strains of P. fluorescens, and nonpathogenic strains were more similar to saprophytic P. fluorescens than to P. tolaasii or P. 'gingeri'.

Strains of Xanthomonas campestris pv. vesicatoria were isolated from several tomato fields in Florida that differed from tomato race 1 (T1) strains commonly found in Florida. The strains produced a compatible reaction on tomato genotype Hawaii 7998 (H7998), were amylolytic and pectolytic, and were classified originally as T2 strains. However, these strains produced a rapid hypersensitive response when infiltrated into the tomato genotypes Hawaii 7981 (H7981), PI 126932, and PI 128216, whereas T2 strains produced a compatible reaction. In an experiment where electrolyte leakage was determined in leaflets of tomato cv. Bonny Best (compatible with all tomato strains), H7998 (resistant to T1 strains), and the two PIs, a member of these new strains induced a rapid hypersensitive response in the three tomato genotypes, whereas a T2 strain did not. After low concentrations of bacteria were infiltrated into the mesophyll of leaflets of PI 126932, PI 128216, H7998, and cv. Walter (compatible with all tomato strains), internal populations of the amylolytic, pectolytic Florida strain were reduced when tested in the first two genotypes but not in the latter two genotypes. Populations of the T1 strain were reduced only in H7998. These new strains are designated tomato race 3 (T3). When the T3 strains were compared with a representative group of T1 and T2 strains by fatty acid analysis and carbon substrate utilization patterns, the new T3 strains clustered distinctly from representative T1 and T2 strains. The evidence suggests the T3 strain is a recent introduction to Florida. An amylolytic, pectolytic strain isolated from seed grown in Thailand reacted similarly to the T3 strains on the tomato differentials. It also clustered with the T3 strains in the fatty acid and carbon substrate utilization dendrograms

Silver staining of sodium dodecyl sulfate-lysed cells of Xanthomonas campestris pv. vesicatoria electrophoretically separated in polyacrylamide gel revealed broad, dark gray bands in the low molecular weight region. The molecular weight of these bands was characteristic for each of the two major phenotypic groups identified in our X. c. vesicatoria collection. A 32- to 35-kDa band, designated a, was present in 192 of 197 tomato race 1 strains; whereas, a 25- to 27-kDa band, designated β, was present in all 55 strains of tomato race 2. Race 1 strains expressing an a band were unable to hydrolyze starch (Amy - ), and very few degraded pectate (Pec - ). In contrast, most race 2 strains were Amy + and Pec + [...]

Xanthomonas campestris pv. vesicatoria strains from a worldwide collection were assigned to the A or B group by testing for amylolytic activity and the presence of the α or β protein band. Cluster analyses of serological, carbon substrate utilization, and fatty acid composition data resulted in dendrograms with interspersed clusters of A and B strains, suggesting that the strain populations within each group are heterogeneous. However, further analysis of the data identified features unique to members of each group. Two monoclonal antibodies reacted only with group A strains, and two reacted only with group B strains. Reactivity patterns further subdivided each group into three serovars [...]

We report on the cloning of DNA involved in expression of two epitopes associated with lipopolysaccharide (LPS) in Xanthomonas campestris pv, vesicatoria and on the use of part of this region for differentiating A (nonpectolytic/amylolytic) and B strains (pectolytic/amylolytic) of this pathogen. From a genomic library of A-strain 75-3 that expresses two epitopes, two recombinant cosmids conferred expression of two epitopes in 87-13, an A strain that does not express the two epitopes. One of the two overlapping clones, pEC79S, contained a 27-kb insert and was used for further analysis. Immunoblots revealed that the epitopes are components of LPS in 75-3 [...]

Pathogenic and nonpathogenic strains of Agrobacterium tumefaciens (i.e., biovar 1), A. rhixogenes (i.e., biovar 2), A. vitis (i.e., biovar 3), and A. rubi were tested for their ability to utilize 95 different carbon sources available in the GN Microplate system and analyzed for fatty acid content using the MIDI gas-liquid chromatography system. Several carbon sources were identified as being of diagnostic value. With the exception of the A, rubi strain, hydroxy-L-proline and i-erythritol were exclusively metabolized by A. tumefaciens and A. rhizogenes, respectively. Analysis of fatty acid composition confirmed that cis-vaccenic acid (18:1 ω cis) is the predominant acid in all the Agrobacterium strains [...]