Characterization of bacterial knot disease caused by Pseudomonas savastanoi pv. savastanoi on pomegranate (Punica granatum L.) trees: a new host of the pathogen.

UNLABELLED: This study aimed to isolate and identify the causal organism causing hyperplastic outgrowths (knots) on stems and branches of pomegranate trees in the Eastern Mediterranean region of Turkey. Bacterial colonies were isolated from young knots on plates containing selective nutrient media. Biochemical tests, fatty acid analysis and PCR were performed to identify possible causal disease agent. Representative isolates were identified as Pseudomonas.pv.savastanoi (Psv) using biochemical tests, fatty acid profiling and PCR. Following inoculation of pomegranate plants (cv. hicaz) with bacterial suspensions, 25 of 54 bacterial isolates caused typical knots at the site of inoculation. PCR analysis, using specific primer for Psv, generated a single amplicon from all isolates. The similarity of the sequence of Turkish pomegranate isolate was 99% similar to the corresponding gene sequences of Psv in the databases. Based on symptoms, biochemical, molecular, pathogenicity tests and sequence analyses, the disease agent of knots observed on the pomegranate trees is Psv. To the best of our knowledge, this research has revealed pomegranate as a natural host of Psv, which extends the list of host plant species affected by the pathogen in the world and Turkey. SIGNIFICANCE AND IMPACT OF THE STUDY: Pomegranate trees were affected by the disease with outgrowths (galls or knot) disease. Currently, there is no published study on disease agent(s) causing the galls or knots on pomegranate trees in worldwide. Bacterial colonies were isolated from young knots. The causal agent of the knot Pseudomonas savastanoi pv.savastanoi (Psv) was identified based on symptoms, biochemical, molecular methods, pathogenicity tests and sequence analysis. To the best of our knowledge, this is the first report of Psv on pomegranate as a natural host, which extends the growing list of plant species affected by this bacterium in the world and Turkey.

Satellite Remote Sensing of Wheat Infected by Wheat streak mosaic virus.

The prevalence of wheat streak mosaic, caused by Wheat streak mosaic virus, was assessed using Landsat 5 Thematic Mapper (TM) images in two counties of the Texas Panhandle during the 2005-2006 and 2007-2008 crop years. In both crop years, wheat streak mosaic was widely distributed in the counties studied. Healthy and diseased wheat were separated on the images using the maximum likelihood classifier. The overall classification accuracies were between 89.47 and 99.07% for disease detection when compared to "ground truth" field observations. Omission errors (i.e., pixels incorrectly excluded from a particular class and assigned to other classes) varied between 0 and 12.50%. Commission errors (i.e., pixels incorrectly assigned to a particular class that actually belong to other classes) ranged from 0 to 23.81%. There were substantial differences between planted wheat acreage reported by the United States Department of Agriculture-National Agricultural Statistics Service (USDA-NASS) and that detected by image analyses. However, harvested wheat acreage reported by USDA-NASS and that detected by image classifications were closely matched. These results indicate that the TM image can be used to accurately detect and quantify incidence of wheat streak mosaic over large areas. This method appears to be one of the best currently available for identification and mapping disease incidence over large and remote areas by offering a repeatable, inexpensive, and synoptic strategy during the course of a growing season.

First Report of Bacterial Leaf Spot Caused by Pseudomonas cichorii on Schefflera arboricola in Turkey.

In late winter and spring of 2006 and 2008, leaf spots with yellow halos were observed on dwarf schefflera (Schefflera arboricola cvs. Gold Capella, Trinette, and Green Gold) that were grown as potted plants in two commercial ornamental greenhouses in Adana and Mersin, Turkey. Average disease incidence was assessed as 10% during the term of the study. Isolations were made from leaf spots symptoms on King's medium B. Bacteria consistently isolated from diseased tissues formed green fluorescent colonies on the medium. Ten representative bacterial strains were examined and found to be gram negative, rod shaped, and aerobic, levan, pectolytic, and arginine dihydrolase negative, and oxidase positive. They all induced a hypersensitive response in tobacco (Nicotiana tabacum cv. Samsun). All strains were identified as Pseudomonas cichorii with similarity indices of 79 to 99% based on fatty acid methyl ester (FAME) profiles determined by Sherlock Microbial Identification System software (TSBA 6 v. 6.00; Microbial ID, Newark, DE). Pathogenicity of the strains was confirmed on five dwarf schefflera plants by leaf tissue infiltration with bacterial suspensions (107 CFU ml-1) in sterile distilled water. P. cichorii NCPPB 3802 and sterile water were used as positive and negative controls, respectively. The same symptoms as those observed in the commercial greenhouses were observed on dwarf schefflera leaves within 12 to 15 days after inoculation. The bacteria were reisolated from the inoculated plants and identified as the same as the original strain by conventional tests and FAME analysis. Negative control plants remained disease free. Occurrence of bacterial leaf spot caused by P. cichorii on vegetable crops in Turkey (1,3) and dwarf schefflera in other countries (2) has been reported previously, but to our knowledge, this is the first report of the observation of P. cichorii on dwarf schefflera in Turkey. References: (1) Y. Aysan et al. Plant Pathol. 52:782. 2003. (2) A. R. Chase and D. D. Brunk. Plant Dis. 68:73, 1984. (3) F. Sahin et al. Acta Hortic. 695:93, 2005.

First Outbreak of Bacterial Black Rot on Cabbage, Broccoli, and Brussels Sprouts Caused by Xanthomonas campestris pv. campestris in the Mediterranean Region of Turkey.

During warm and humid periods in the winters of 2004 to 2006, severe leaf necrosis and vein rot symptoms were observed on cabbage (Brassica oleracea var. capitata L.), broccoli (Brassica oleracea var. italica Plenck.), and Brussels sprouts (Brassica oleracea var. gemmifera D.C.) in the Mediterranean Region of Turkey. Symptoms were characterized by yellow, V-shaped areas of the leaf margin, with the internal tissue turning from brown to black. Infected seedlings were also observed in commercial nurseries in Adana with a disease incidence of nearly 10 to 25%. Isolations made from leaves and veins of the affected plants on yeast dextrose calcium carbonate agar yielded yellow, mucoid, and convex colonies. Twenty isolates recovered from diseased leaf samples were selected at random to identify the causal organism. All isolates were nonspore forming, gram negative, rod shaped, motile, aerobic, oxidase-negative, catalase-positive, and amylolytic-positive (3). All isolates induced hypersensitive responses on tobacco (Nicotiana tabacum cv. Samsun). The isolates were identified as Xanthomonas campestris pv. campestris on the basis of fatty acid methyl ester (FAME) profiles determined by Sherlock Microbial Identification System software (Microbial ID, Newark, DE) and indirect ELISA. The similarity indices for the FAME analysis ranged from 80 to 94% (2). Indirect ELISA with a polyclonal antibody (Agdia, Elkhart IN; BRA 97000/0500) further confirmed the identity of the pathogen in both pure culture and infected plant. The mean absorbance values for three replications of indirect ELISA tests ranged from 1.411 to 3.508 at a wavelength of A405 (1). Pathogenicity of the isolates was tested on 5-week-old cabbage plants by spray inoculation using bacterial suspensions (107 CFU/ml) prepared in saline buffer (0.85% NaCl). Sterile saline buffer was sprayed on negative control plants. Inoculated and control plants were maintained for 5 days at 25°C and 70% relative humidity to observe symptom development. No symptoms developed on negative control plants. The bacterium was reisolated from inoculated cabbage plants and identified as X. campestris pv. campestris by FAME and an ELISA test. To our knowledge, this is the first report of the occurrence and outbreak of X. campestris pv. campestris in the Mediterranean Region of Turkey. References: (1) A. M. Alvarez et al. Phytopathology 84:1449, 1994. (2) A. R. Chase et al. Phytopathology 82:754, 1992. (3) 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.

Occurrence of Bacterial Fruit Blotch of Watermelon Caused by Acidovorax avenae subsp. citrulli in the Eastern Mediterranean Region of Turkey.

Turkey has the second highest production level of watermelon (Citrullus lanatus L.) in the world, with 3.8 million tons produced in 2005. In the spring of 2005, a severe outbreak of a disease resembling bacterial fruit blotch was observed on watermelon cv. Crispy growing in a production area of 35,000 ha in Adana Province in the eastern Mediterranean Region of Turkey. In 13 commercial watermelon fields surveyed in this study, incidence of symptomatic fruit ranged from 30 to 45%. Characteristic symptoms were dark, gray-green stains or blotches on the surface of fruits. Cracks developed in the rind and released an amber-colored substance. Bacteria were consistently isolated from affected fruits and they formed nonfluorescent colonies on King's medium B. Identification of isolated bacterial strains was based on the methods described by Schaad et al. (2). All strains were oxidase positive, gram negative, arginine dyhydrolase negative, and produced a hypersensitive response on tobacco leaves (Nicotiana tabacum cv. Samsun). Strains were identified as Acidovorax avenae subsp. citrulli (1,2) on the basis of the results of biochemical tests (1,2) and sole carbon substrate utilization (BIOLOG GN; Biolog Inc., Hayward, CA) with 75 to 93% similarity indices. A pathogenicity test was performed for nine identified strains by injecting a bacterial suspension (108 CFU/ml of saline) under the rind of three harvested watermelon (cv. Diyarbakir) fruits and into the stems of three seedlings. Saline was used as the negative control. The fruits and seedlings inoculated with each strain were incubated in polyethylene bags for 48 h at 25°C. Dark green water-soaked lesions developed on inoculated fruits and water-soaking and stem necrosis were observed on the seedlings 3 to 5 days after inoculation. The bacterium was readily reisolated from inoculated fruits and seedlings and identified as A. avenae subsp. citruli on the basis of BIOLOG GN. In 1995, bacterial fruit blotch of watermelon has been observed and eradicated in the Marmara Region of western Turkey (1). Therefore, to our knowledge, this is the first outbreak of bacterial fruit blotch on watermelon in the eastern Mediterranean Region of Turkey. References: (1) G. Demir. J. Turk. Phytopathol. 25:43, 1996. (2) N. W. Schaad et al. Laboratory Guide for Identification of Plant Pathogenic Bacteria. The American Phytopathological Society, St Paul, MN, 2001.

An Outbreak of Bacterial Stem Rot of Dieffenbachia amoena Caused by Erwinia carotovora subsp. carotovora in the Eastern Mediterranean Region of Turkey.

Severe outbreaks of bacterial stem rot disease occurred on dieffenbachia plants (Dieffenbachia amoena cv. Tropic Snow) during the autumn and spring seasons of 2002 and 2003 in two commercial glasshouses (3.5 ha) near Adana and Mersin in the Eastern Mediterranean Region of Turkey. Characteristic symptoms of the disease were wilting of the lower leaves, darkening and water soaking of the leaves and stem at or below the soil level, and browning in the vessel and pith of the diseased plants. Eventually, the stem and leaves completely rotted, and the plants collapsed. Nearly 30 and 40% (2002 and 2003, respectively) of the 20,000 potted plants in the glasshouses were destroyed because of the disease. Cuttings often developed a typical soft rot during propagation. Disease incidence was estimated at approximately 50% on propagating material during 2003. Isolations were made from rotted stems, leaves, and discolored vessels of the dieffenbachia plants on King's medium B. Bacteria consistently isolated from the diseased tissues formed white-to-cream colonies on the medium. Bacteria from purified colonies were gram, oxidase, and arginine dyhidrolase negative, catalase positive, and facultative anaerobic. Ten representative strains all fermented glucose and reduced nitrates to nitrites. The strains caused soft rot of potato slices within 24 h at 25°C. All strains were resistant to erythromycin in an antibiotic disk (15 µg) assay. Negative results were obtained from utilization of α-methyl glycoside, reducing substance from sucrose, and indole production from tryptophane and phosphathase activity. Positive results were obtained from pectate, aesculin, and gelatine liquefaction for all strains. Acid was produced from glucose, sucrose, mannitol, mannose, lactose, raffinose, melibiose, trehalose, and L(+)-arabinose but not Darabinose, sorbitol, inulin, and maltose. Pathogenicity was confirmed by needle-stab inoculation at the stem on three plants each of dieffenbachia and tomato plants (5-week-old cv. H-2274). Sterile distilled water was used as a negative control. All plants were covered with polyethylene bags for 48 h at 25°C. Within 72 h after inoculation, water-soaking and soft-rot symptoms were observed on dieffenbachia and tomato plants. All of the bacterial strains isolated in the present study were identified as Erwinia carotovora subsp. carotovora (Jones) based on fatty acid methyl ester analysis with similarity indices ranging from 80 to 94%. Furthermore, Biolog GN (Department of Plant Protection, Faculty of Agriculture, Ataturk University, Erzurum, Turkey) profiles identified them as the same pathovar with similarity values of 67 to 72%. All of the test results were similar to those of reference strain GSPB 435 (Gottinger Sammlung phytopathogener Bakterien, Georg-August University, Gottingen, Germany) of E. carotovora subsp. carotovora used in this study. To our knowledge, this is the first report of the occurrence and outbreak of a bacterial rot disease on dieffenbachia grown in the Eastern Mediterranean Region of Turkey. Contaminated cuttings may be the primary source of inoculum within and between glasshouses.

Watermelon as a New Host of Pseudomonas viridiflava, Causal Agent of Leaf and Stem Necrosis, Discovered in Turkey.

Severe leaf and stem necrosis symptoms were observed on watermelon seedlings (Citrullus lanatus cv. Euroca) in Adana, Turkey during a warm and humid period in January 2004. Streak-plate isolations were made from leaf and stem lesions on King's medium B. A fluorescent, yellowish mucoid, gram-negative, and oxidase-, levan- and arginin dihydrolase-negative bacterium was consistently isolated from diseased plant samples. All seven representative strains isolated were pectolytic on potato slices and hypersensitive reaction positive on tobacco leaves. The result of LOPAT tests and morphology of the strains were different from Pseudomonas syringae pathovars. The strains produced acid from sorbitol, fructose, glucose, L (+) arabinose, D (+) xylose, D (-) mannitol, but not from D (+) sucrose, trehalose, maltose, melibiose, lactose, and D (-) arabinose. Utilization of D (-) tartrate was positive. Incubation was at 28°C, and the results of the tests were evaluated 7 days after inoculation. Fatty acid analysis (Ataturk University, Erzurum, Turkey) confirmed the bacterial strains as P. viridiflava with a similarity index of 83 to 86% (3). The strains were pathogenic on watermelon, melon, and tomato plants with needle inoculation of bacterial suspensions containing 108CFU ml-1 in a 0.85% saline. Water-soaking and stem necrosis symptoms were observed on the inoculated plants 5 to 7 days after inoculation. The bacterium was readily reisolated from inoculated plants and identified as strains of P. viridiflava, which has been previously reported as a pathogen of melon grown in Turkey (1) and Greece (2). To our knowledge, this is the first study demonstrating the occurrence and outbreak of leaf and stem necrosis disease caused by P. viridiflava on watermelon in the world. References: (1) A. Aysan et al. Plant Pathol. 52:800, 2003. (2) D. E. Goumans and A. K. Chatzaki. Eur. J. Plant Pathol. 104:181, 1998. (3) J. D. Janse et al. Syst. Appl. Microbiol. 15:538, 1992.