scholarly journals First Report of Bacterial Head Rot of Broccoli Caused by Pseudomonas fluorescens in China

Plant Disease ◽  
2009 ◽  
Vol 93 (11) ◽  
pp. 1219-1219 ◽  
Author(s):  
B. Li ◽  
G. L. Wang ◽  
Z. Y. Wu ◽  
W. Qiu ◽  
Q. M. Tang ◽  
...  
Keyword(s):  
Fatty Acid ◽  
Pseudomonas Fluorescens ◽  
Pathogenic Bacteria ◽  
Disease Incidence ◽  
Identification System ◽  
Rrna Gene ◽  
First Report ◽  
Microbial Identification ◽  
Microbial Identification System ◽  
Head Rot

During warm and humid periods in the winters from 2005 to 2008, head rot symptoms on broccoli (cv. Sijilv) (Brassica oleracea L. var italica Planch) were observed in commercial fields in Ningbo, Zhejiang Province, China. In agreement with the report of Cui and Harling (1), water-soaked lesions developed on the buds and then progressed into a brown-black soft rot. Longitudinal sections of the symptomatic inflorescences showed brown discoloration and rotting of the internal tissues. Broccoli production is hampered by the disease, with disease incidence ranging from 65 to 81%. Bacteria were isolated by streaking on nutrient agar (3) and individual colonies formed after 2 to 3 days of incubation at 28°C. Fifteen of thirty isolates induced hypersensitive reactions (HR) on tobacco leaves (Nicotiana tabacum cv. Samsun) within 48 h. All the HR-positive strains were fluorescent on King's medium B and the colonies were smooth, convex, entire, and round. Classical bacteriological tests indicated that the fluorescent strains were gram negative, obligate aerobes, arginine dihydrolase positive, and oxidase positive. Also, the fluorescent strains were positive for the production of levan from sucrose. Five representative strains were further characterized by the Biolog Microbial Identification System, version 4.2 (Biolog Inc., Hayward, CA) and gas chromatography of fatty acid methyl esters (FAME) using the Microbial Identification System (MIDI Inc., Newark, DE) with the aerobic bacterial library (TSBA50). The five strains were identified as Pseudomonas fluorescens with Biolog and FAME similarity indexes of 0.61 to 0.68 and 0.52 to 0.58, respectively. The 16S rRNA gene sequence of broccoli strain PFB-01 (GenBank Accession No. GQ352649) was determined according to Li et al. (2). A subsequent GenBank search showed that this sequence had 98% nucleotide identity with the type strain of P. fluorescens (ATCC 17386T, GenBank Accession No. AF094726). Koch's postulates were completed by the inoculation of broccoli heads (cv. Sijilv) with cell suspensions (107 CFU/ml) of the above five strains by spraying on the surface of subcorymbs. Each treatment had five replicates. All strains induced head rot symptoms similar to those observed in natural infections. No symptoms were noted on the control plants inoculated with sterile water. Bacteria were successfully reisolated from symptomatic heads and confirmed by the cellular fatty acid composition. To our knowledge, this is the first report in China that P. fluorescens is the causal pathogen of bacterial head rot of broccoli. References: (1) X. Cui and R. Harling. Phytopathology 96:408, 2006. (2) B. Li et al. J. Phytopathol. 154:711, 2006. (3) N. W. Schaad et al. Laboratory Guide for Identification of Plant Pathogenic Bacteria. 3rd ed. The American Phytopathological Society. St. Paul, MN, 2001.

scholarly journals First Report of Pear Blossom Blast Caused by Pseudomonas syringae pv. syringae in China

Plant Disease ◽  
2008 ◽  
Vol 92 (5) ◽  
pp. 832-832 ◽  
Author(s):  
L. H. Xu ◽  
G. L. Xie ◽  
B. Li ◽  
B. Zhu ◽  
F. S. Xu ◽  
...  
Keyword(s):  
Pseudomonas Syringae ◽  
Similarity Index ◽  
Nutrient Agar ◽  
Identification System ◽  
Pyrus Pyrifolia ◽  
Rrna Gene ◽  
Bacterial Disease ◽  
First Report ◽  
Microbial Identification ◽  
Microbial Identification System

In the spring of 2006, a new bacterial disease was noted in pear orchards near Hangzhou, Zhejiang Province, China. The disease caused severe blossom blast on pears (Pyrus pyrifolia; cv. Cuiguan). Early symptoms of the disease included blackening of the calyx end of developing fruit, blackening of blossom clusters while leaves of affected blossom clusters appeared normal, or death of clusters consisting of both blossoms and leaves. Later, tips of twigs turned dark brown and died. No bacterial ooze was observed. Twelve bacterial isolates were recovered from ten samples of buds and blossoms. Six isolates were selected for identification. They were similar to those of the reference strains of Pseudomonas syringae pv. syringae LMG5570 and LMG 2230 from Belgium in phenotypic tests on the basis of the Biolog Microbial Identification System (version 4.2; Biolog Inc., Hayward, CA), pathogenicity tests, gas chromatographic analysis of fatty acid methyl esters (FAMEs) using the Microbial Identification System (MIDI Inc., Newark, DE) with aerobic bacterial library (TABA50), and electron microscopy (TEM, KYKY-1000B, Japan). All isolates tested were gram-negative, aerobic rods measuring 1.5 to 2.4 × 0.5 to 0.6 μm with 2 to 4 polar flagella. Fluorescent green diffusible pigment was produced on King's Medium B. Colonies were gray-white and slightly raised with smooth margins on nutrient agar. They produced levan on sucrose nutrient agar. A hypersensitive reaction was observed on tobacco cv. Benshi 24 h after inoculation. All isolates were identified as P. syringae pv. syringae with Biolog similarity index of 0.57 to 0.86 and FAME similarity index of 0.58 to 0.81. Identification as P. syringae pv. syringae was confirmed using 16S rDNA universal primers (2,3): 5′-AGA GTT TGA TCA TGG CTC AG-3′ forward primer, 5′-ACG GTT ACC TTG TTA CGA CTT-3′ reverse primer. The PCR fragments of the three isolates were sequenced and compared with sequences in GenBank. They had 99% similiarity with P. syringae pv. syringae 16S rRNA gene strain NCPPB 3869. Koch's postulates were conducted on buds of the original pear cultivar growing in pots and detached pear blossoms in flasks by spray inoculation with cell suspensions containing 108 CFU/ml of the six isolates at 18 to 22°C with two replications. The bacteria induced symptoms on buds and blossoms similar to those observed in the field. The bacterium was reisolated from symptomatic pear buds and internal ovary tissues. P. syringae pv. syringae was first reported in England as the cause of pear blossom blast in 1914 (1). After searching all the Chinese agricultural databases and major journals (National Knowledge Infrastructure database, Vip Chinese periodical database, Chinese wanfang database, China InfoBank, Scientia Agricultura Sinica, Acta Phytopathologica Sinica, Acta Phytophylacica Sinica, and Journal of Fruit Science), to our knowledge, this is the first report of pear blossom blast caused by P. syringae pv. syringae in China. The disease cycle on pear trees and the control strategies in the regions are being further studied. References: (1) B. P. Barker et al. Ann. Appl. Biol. 1:85, 1914. (2) U. Edward et al. Nucleic Acids Res. 17:7843,1989. (3) B. Li et al. J. Phytopathol. 34:141, 2006.

scholarly journals First Report of Head Rot of Brassica oleracea convar. botrytis var. italica Caused by Pseudomonas fluorescens in Southern Italy

Plant Disease ◽  
2007 ◽  
Vol 91 (5) ◽  
pp. 638-638 ◽  
Author(s):  
P. Lo Cantore ◽  
N. S. Iacobellis
Keyword(s):  
Pseudomonas Fluorescens ◽  
Brassica Oleracea ◽  
Pathogenic Bacteria ◽  
Southern Italy ◽  
Similarity Index ◽  
Identification System ◽  
Bacterial Strains ◽  
First Report ◽  
Pectolytic Activity ◽  
Head Rot

During the winter of 2004, symptoms were observed in commercial cauliflower (Brassica oleracea L. convar. botrytis (L.) Alef. var. italica) fields of “romanesco” type (cv. Navona) in Apulia, southern Italy. These symptoms were noted on inflorescences that were almost ready for harvest, and a bacterial etiology was suspected. In particular, the corymbs showed water-soaked and brown discolored areas which then rotted. The above alterations involved the whole inflorescences, or in some cases, only a few florets. Longitudinal sections of the symptomatic inflorescences or the single floret showed brown discoloration and rotting of the internal tissues. The disease caused severe crop losses (approximately 100% either in the field or after harvest). Bacteria were isolated from water-soaked and soft-rotted cauliflower heads on King's medium B (KB). The strains were purified on nutrient agar and assayed for pathogenicity on subcorymbs from freshly harvested cauliflower heads. Bacterial suspensions containing approximately 108 CFU/ml were then sprayed on the surface of subcorymbs (3 subcorymbs per strain). Furthermore, in other pathogenicity assays, the florets were dipped in 108 CFU/ml bacterial suspensions or small aliquots of inoculum were injected into the peduncle of subcorymbs with a sterile syringe. Cauliflower heads treated with sterile distilled water were used as controls. After inoculation, the subcorymbs were maintained at 25°C and approximately 100% relative humidity for 48 h. All bacterial strains either applied to cauliflower subcorymbs by spray inoculation or dipping reproduced the disease symptoms. Intensity of symptoms varied with the inoculation method. Injection of bacteria caused water soaking and soft rot of cauliflower internal tissues. No symptoms were observed in negative control subcorymbs inoculated with sterile water. All bacterial strains were gram negative and fluorescent on KB. Isolates (17 of 18) showed the LOPAT characters of group Vb (++−+−) fluorescent pseudomonads, and only strain USB1237 showed characters of group IVb (−+++−) (3). The pectolytic activity of the latter strain was confirmed by the pectinase plate assay (4). The identity of representative strains was confirmed by the nutritional profile obtained with the Biolog Identification System (MicroLogTM System Release 4.2; Biolog, Inc., Hayward, CA). Strains USB1224, USB1226, USB1228, USB1231, USB1235, USB1236, USB1238, and USB1239 were identified as Pseudomonas fluorescens with similarity indices of 0.86, 0.52, 0.73, 0.81, 0.73, 0.74, 0.69, and 0.85, respectively. The pectolytic strain USB1237 was identified as a Pseudomonas spp. that is closely related to P. putida (similarity index = 0.45). In conclusion, the above results indicate that P. fluorescens is responsible for head rot of cauliflower. A similar disease has been previously reported on broccoli in different areas (1,2), but to our knowledge, this is the first report of head rot of cauliflower caused by P. fluorescens. References: (1) C. H. Canaday et al. Phytopathology 77:1712, 1987. (2) P. D. Hildebrand. Can. J. Plant Pathol. 8:350, 1986. (3) R. A. Lelliott and D. E. Stead. Methods for the diagnosis of bacterial diseases of plants. In: Methods in Plant Pathology. Vol. 2, T. F. Preece, ed. Blackwell Scientific Publications, Oxford, UK, 1987. (4) N. W. Schaad et al. Laboratory Guide for Identification of Plant Pathogenic Bacteria. The American Phytopathological Society, St. Paul, MN, 2001.

scholarly journals First Report of Pseudomonas cichorii Causing Leaf Spot of Vegetable Sponge Gourd in China

Plant Disease ◽  
2014 ◽  
Vol 98 (1) ◽  
pp. 153-153 ◽  
Author(s):  
B. J. Li ◽  
H. L. Li ◽  
Y. X. Shi ◽  
X. W. Xie
Keyword(s):  
Leaf Spot ◽  
Pathogenic Bacteria ◽  
Identification System ◽  
Pathogenicity Test ◽  
Distilled Water ◽  
Pseudomonas Cichorii ◽  
First Report ◽  
Microbial Identification ◽  
Pectolytic Activity ◽  
Sponge Gourd

A suspect bacterial leaf spot on vegetable sponge gourd (Luffa cylindrical (L.) Roem.) was found in a commercial greenhouse in Pi County, Chengdu City, Sichuan Province, China, in February 2011. Approximately 20 to 30% of plants were affected, causing serious economic loss. Symptoms occurred only on seedlings and consisted of water-soaked, irregularly shaped, black lesions on the surface and margins of cotyledons. A bacterium was consistently isolated on nutrient agar from diseased leaf tissues that had been surface disinfected in 70% ethyl alcohol for 30 s. The bacterium produced small gray colonies with smooth margins, was gram negative, fluoresced on King's B medium, and showed pectolytic activity when inoculated on potato slices. The partial sequences of 16SrRNA gene (1,377 bp) of the bacterium (GenBank Accession No. KC762217), amplified by using universal PCR primers 16SF (5′-AGAGTTTGATCCTGGCTCAG-3′) and 16SR (5′-GGTTACCTTGTTACGACTT-3′), shared 100% similarity with that of Pseudomonas cichorii (GenBank Accession No. HM190228). The vegetable sponge gourd isolate was also identified by using the Biolog Microbial Identification System (version 4.2, Biolog Inc., Hayward, CA) as P. cichorii with the following characteristics (1): negative for arginine dihydrolase, gelatin liquefaction, and N2 production. Positive reactions were obtained in tests for catalase, oxidase, potato rot, utilization of melibiose, and mannitol. Tests were negative for utilization of sucrose, trehalose, D-arabinose, raffinose, cellobiose, and rhamnose. A pathogenicity test was conducted on 4-week-old vegetable sponge gourd plants by spray-inoculation with 108 CFU/ml sterile distilled water on the leaves of 15 vegetable sponge gourd plants and by needle puncture on the stems of 15 other plants with P. cichorii, respectively. Control plants were misted with sterile distilled water or punctured on the stem with a clean needle. Plants were placed in a greenhouse maintained at 28 ± 2°C with relative humidity of 80 to 85%. Symptoms, the same as seen on the original diseased plants, developed after 7 to 10 days on inoculated plants. Control plants remained healthy. The bacterium was readily re-isolated from inoculated plants and identified as P. cichorii using P. cichorii-specific primer hrpla/hrp2a (1). To our knowledge, this is the first report of P. cichorii causing disease on commercially grown vegetable sponge gourd in China. This new finding will provide the basis for developing resources for diagnostics and management, including screening varieties for resistance. References: (1) S. Mazurier et al. J. FEMS Microbiol. Ecol. 49:455, 2004. (2) N. W. Schaad et al., eds. Laboratory Guide for Identification of Plant Pathogenic Bacteria, 3rd ed. APS Press, St. Paul, MN, 2001.

scholarly journals First Report of Leaf Spot and Blight Caused by Ralstonia pickettii on Bird of Paradise Tree in Italy

Plant Disease ◽  
2008 ◽  
Vol 92 (5) ◽  
pp. 835-835 ◽  
Author(s):  
G. Polizzi ◽  
M. Dimartino ◽  
P. Bella ◽  
V. Catara
Keyword(s):  
Leaf Spot ◽  
Pathogenic Bacteria ◽  
Disease Incidence ◽  
Similarity Index ◽  
Nutrient Agar ◽  
23S Rrna ◽  
Identification System ◽  
Rrna Gene ◽  
Small Subunit Rrna ◽  
Ralstonia Pickettii

Bird of Paradise tree (Strelitzia alba (L. f.) Skeels) is an ornamental perennial tropical plant grown in southern Italy. In the summer of 2006 and 2007, a widespread, severe leaf disease was observed on seedlings and 1- to 2-year-old plants in two glasshouses located in eastern Sicily. Disease incidence ranged from 10 to 25%. Symptoms on the leaves consisted of dark brown-to-black stripes of varying length and found between the lateral veins. Lesions sometimes coalesced into a large area of necrotic tissue. Symptomatic tissues were ground in a drop of sterile distilled water (SDW) with a scalpel. Suspensions were streaked on King's medium B (KB), nutrient agar, and yeast extract nutrient agar (2). Isolated strains were gram negative and oxidase positive, non-levan, negative in tobacco hypersensitivity test, white and nonmucoid on yeast dextrose calcium carbonate agar, did not produce fluorescent pigments on KB, and utilized glucose, mannitol, trehalose, arabinose, mannose, and N-acetylglucosamine. Bacterial strains were identified as Ralstonia pickettii by using the Biolog Identification System (MicroLogTM System Release 4.2; Biolog, Inc., Hayward, CA) with a similarity index ranging from 0.52 to 0.67. For an additional confirmation of identity, the small subunit rRNA gene (SSUrDNA) was amplified with primers 530F and Uni 1492R (1). The resulting nucleotide sequence was compared with sequences deposited in GenBank and showed the highest identity (99%) to sequences of R. pickettii strains. Pathogenicity tests were performed on 20 cm tall potted plants. Four S. alba plants were inoculated by infiltrating leaf veins with bacterial suspensions for each of the four isolates (107 CFU ml–1 in SDW) with a 25-gauge needle and syringe. Plants were placed in polyethylene bags 1 day before inoculation and maintained there for 3 days after inoculation. Four control plants were inoculated with SDW. Water-soaked areas in the lateral veins of leaves were observed in all inoculated plants 4 days after inoculation. Within 10 days, dark brown-to-black stripes that coalesced into dark necrotic areas were observed. All isolates induced similar symptoms. Control plants did not show any symptoms. The pathogen was reisolated from symptomatic tissue and identified as R. pickettii by Biolog. A similar disease on S. reginae caused by a Pseudomonas sp. was previously reported from Florida (3). To our knowledge, this is the first record in the world of leaf spot and blight caused by R. pickettii. References: (1) D. J. Lane. 16S/23S rRNA sequencing. Page 115 in: Nucleic Acid Techniques in Bacterial Systematics. E. Stackebrandt and M. Goodfellow, eds. John Wiley and Sons, NY, 1991. (2) N. W. Schaad et al. Laboratory Guide for Identification of Plant Pathogenic Bacteria. The American Phytopathological Society, St. Paul, MN, 2001. (3) C. Wehlburg. Plant Dis. Rep. 55:447, 1971.

scholarly journals First Report of a Field Outbreak of a Bacterial Leaf Spot of Cantaloupe and Squash Caused by Pseudomonas syringae pv. syringae in Georgia

Plant Disease ◽  
2003 ◽  
Vol 87 (5) ◽  
pp. 600-600 ◽  
Author(s):  
D. B. Langston ◽  
F. H. Sanders ◽  
J. H. Brock ◽  
R. D. Gitaitis ◽  
J. T. Flanders ◽  
...  
Keyword(s):  
Pseudomonas Syringae ◽  
Leaf Spot ◽  
Tap Water ◽  
Acid Methyl Ester ◽  
Economic Damage ◽  
Identification System ◽  
First Report ◽  
Microbial Identification ◽  
Microbial Identification System ◽  
Physiological Tests

In March 2000, a leaf spot was reported affecting yellow summer squash (Cucurbita pepo) and cantaloupe (Cucumis melo) in commercial fields in Colquitt, Echols, and Grady counties in Georgia. All of the crops affected were reported within a 10-day period, and average temperatures during that time were 8 to 22.5°C, which is very close to the 50-year normal temperatures for these areas located in southwest Georgia. Incidence in affected fields was 100%. Lesions on squash leaves appeared irregularly shaped, dark, water soaked, somewhat vein restricted, and were 5 to 10 mm in diameter. Lesions on cantaloupe were angular, light tan, and necrotic with a lesion diameter of 2 to 5 mm. A general chlorosis was observed around lesions of both crops. Leaf distortion was observed on squash. Four isolates collected were used in biochemical, pathogenicity, and physiological tests. Gram-negative, rod-shaped bacteria were isolated from diseased tissue from squash and cantaloupes. Bacteria were aerobic, catalase-positive, fluorescent on King's medium B (1), oxidase-negative, nonpectolytic on potato, arginine dihydrolase-negative, utilized sucrose as a carbon source, produced levan, and gave a hypersensitivity response on tobacco (HR). Analysis of fatty acid methyl ester (FAME) profiles using the Microbial identification system (Sherlock version 3.1, Microbial identification system, Newark, DE) characterized representative strains as Pseudomonas syringae (similarity indices 0.65 to 0.80). Upon further characterization, the strains were negative for l (+)-tartarate utilization but utilized l-lactate and betaine and also exhibited ice nucleation activity. These characteristics are consistent with those of Pseudomonas syringae pv. syringae. Squash and cantaloupes were grown in a greenhouse for 4 weeks. Bacteria were grown in nutrient broth, resuspended in sterile tap water, and standardized using a spectrophotometer. Plants were inoculated by infiltrating leaves with 1 ml of bacterial suspensions (1 × 107 CFU/ml) using sterile syringes. Sterile water was used as a negative control, and 1 ml was infiltrated into leaves of squash and cantaloupes. Water-soaked lesions developed in 4 to 6 days on squash and cantaloupes inoculated with bacterial suspensions, and Pseudomonas syringae pv. syringae was isolated from diseased tissue. No symptoms developed on squash and cantaloupes used as negative controls. This outbreak of Pseudomonas syringae pv. syringae did not cause significant economic damage to either crop as symptoms subsided once daily high temperatures reached 28 to 32°C. This disease has been isolated from several cucurbit transplants reared in greenhouses, but to our knowledge, this is the first report of this disease occurring in the field. Reference: (1) E. O. King et al. J. Lab. Clin. Med. 44:301, 1954.

scholarly journals First Report of a Leaf Blight of Onion Caused by Xanthomonas spp. in Georgia

Plant Disease ◽  
2003 ◽  
Vol 87 (6) ◽  
pp. 749-749 ◽  
Author(s):  
F. H. Sanders ◽  
D. B. Langston ◽  
J. H. Brock ◽  
R. D. Gitaitis ◽  
D. E. Curry ◽  
...  
Keyword(s):  
Disease Incidence ◽  
Methyl Esters ◽  
Economic Loss ◽  
Leaf Blight ◽  
Identification System ◽  
Sterile Water ◽  
Disease Symptoms ◽  
First Report ◽  
Microbial Identification ◽  
Dry Conditions

In October of 2001 and 2002, a leaf blight was reported affecting Vidalia onion (Allium cepa) cvs. Pegasus and Sweet Vidalia, respectively, in one field each. Lesions on onion seedlings began as a water-soaked, tip dieback that gradually blighted the entire leaf. Symptoms on onion transplants appeared as elongated, water-soaked lesions that typically collapsed at the point of initial infection. In both cases, disease was very severe on seedlings, and disease incidence was 50% or more in both fields. Warm temperatures combined with overhead irrigation and above average rainfall likely enhanced the severity and spread of disease. Disease was not detected on more mature onions once cool, dry conditions occurred later in the season, and no significant economic loss occurred. Seed was tested from seed lots of the aforementioned cultivars and Xanthomonas spp. were not found. Diseased tissue was macerated in sterile, phosphate-buffered saline, and 10 μl of the resulting suspension was streaked on nutrient agar plates. Yellow-pigmented, gram-negative, rod-shaped bacteria were isolated routinely from diseased tissue. Bacteria were catalase-positive, cellulolytic, oxidase-negative, amylolytic, proteolytic, and utilized glucose in an oxidative manner. Analysis of whole cell, fatty acid methyl esters (FAME) using the Microbial Identification System (MIS, Sherlock version 3.1; MIDI, Inc., Newark, DE) identified four representative strains of the bacterium as a pathovar of Xanthomonas axonopodis (similarity indices 0.75 to 0.83). Known Xanthomonas spp. from onion from Colorado and Texas (1,2) had similar FAME profiles when analyzed by the MIDI system. Onion plants were grown under greenhouse conditions for 2 months and inoculated by injecting the base of a quill with 1.0 ml of bacterial suspensions (1 × 107 CFU ml-1) of the Xanthomonas sp. isolated from Georgia, and negative controls were inoculated with 1 ml of sterile water. Disease symptoms developed on plants inoculated with bacterial suspensions in 4 to 7 days and Xanthomonas sp. was isolated from the lesions produced. Disease symptoms occurred when the same suspension was sprayed on onion foliage. No symptoms occurred on plants inoculated with 1 ml of sterile water. To our knowledge, this is the first report of Xanthomonas spp. affecting Vidalia onions. References: (1) T. Isakeit et al. Plant Dis. 84:201, 2000. (2) H. F. Schwartz and K. Otto. Plant Dis. 84:922, 2000.

scholarly journals First Report of Bacterial Soft Rot on Vanda Orchids Caused by Dickeya chrysanthemi (Erwinia chrysanthemi) in the United States

Plant Disease ◽  
2008 ◽  
Vol 92 (6) ◽  
pp. 977-977 ◽  
Author(s):  
R. A. Cating ◽  
J. C. Hong ◽  
A. J. Palmateer ◽  
C. M. Stiles ◽  
E. R. Dickstein
Keyword(s):  
Pathogenic Bacteria ◽  
Soft Rot ◽  
The United States ◽  
Erwinia Chrysanthemi ◽  
Disease Spread ◽  
Rrna Gene ◽  
Bacterial Disease ◽  
Water Control ◽  
First Report ◽  
Microbial Identification

Vanda orchids are epiphytes grown for their attractive flowers by commercial producers and hobbyists throughout Florida. In August 2007, five Vanda hybrids, with an economic value of $150 each, were found at a nursery in central Florida with leaves that were macerated, brown, and water soaked. According to the growers, the plants were normal the previous day but symptoms developed rapidly. The plants were immediately removed from the greenhouse to prevent potential disease spread. Bacteria were isolated according to the method of Schaad et al. (1). Isolated bacteria grew at 37°C, were gram negative, degraded pectate, and produced phosphatase. MIDI (Sherlock version TSBA 4.10; Microbial Identification 16 System, Newark, DE) (SIM 0.906) identified the bacteria as Erwinia chrysanthemi (Dickeya chrysanthemi Burkholder et al. 1953) Samson et al. 2005. PCR was performed on the 16S rRNA gene (GenBank Accession No. EU526397) with primers 27f (5′-GAGAGTTTGATCCTG GCTCAG-3′) and 1495r (5′-TACGGCTACCTTGTTACGA-3′) (2). Subsequent DNA sequencing and GenBank search showed the isolated strain is 99% identical to that of Dickeya chrysanthemi. Four leaves each of six Vanda hybrids were inoculated by injecting approximately 150 μl of a bacteria suspension at 1 × 108 CFU/ml into each leaf. One plant was inoculated with water in each of four leaves. Plants were enclosed in plastic bags and returned to the greenhouse under 50% shade at 29°C day and 17°C night temperatures. Within 24 h, soft rot symptoms appeared on inoculated leaves. The water control appeared normal. D. chrysanthemi was reisolated and identified with the above method, thus Koch's postulates were fulfilled. To our knowledge, this is the first report of a soft rot caused by D. chrysanthemi on Vanda hybrids. Because of the popularity and high value of Vanda orchids, proper identification of this rapidly progressing bacterial disease is of great importance for the commercial producer and homeowner alike. References: (1) N. W. Schaad et al. Erwinia soft rot group. Page 56 in: Laboratory Guide for Identification of Plant Pathogenic Bacteria. 3rd ed. N. W. Schaad et al., eds. American Phytopathological Society. St. Paul, MN, 2001. (2) W. G. Weisburg. J. Bacteriol. 173:697, 1991.

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