Bacterial Streaming Research Articles

First Report of Bacterial Leaf Spot on Leafy Brassica Greens Caused by Pseudomonas syringae pv. maculicola in South Carolina.

As of 2001, South Carolina ranked second in the United States in acreage of turnip greens (Brassica rapa) and collard (B. oleracea) and third in acreage of mustard (B. juncea). In June 2001, a leaf disease was found on turnip greens (cv. Alamo), mustard (cvs. Southern Giant Curled and Florida Broadleaf), and rape salad greens (B. napus var. napus cv. Essex) on a commercial farm in Lexington County, South Carolina. Symptoms appeared after a heavy rainstorm that included blowing sand. The disease was found in May and June 2002 on three additional farms in the same county on turnip greens cv. Topper and Royal Crown and collard cv. Top Bunch. Symptoms included small tan spots, water soaking, yellowing, and brown necrosis of leaves after spots coalesced on the lower halves of plants. Yellowing was more prevalent on older than on younger leaves. Leaf samples were collected in 2001 and 2002 from the affected hosts on the four farms. Bacterial streaming was evident from these samples and 27 strains were isolated on nutrient agar or King's medium B (KMB). All strains were gram negative and fluoresced bluegreen or yellow under UV light after 48-h growth at 28°C on Pseudomonas agar F (PAF). On the basis of LOPAT tests, the strains were identified as P. syringae (2). All 27 strains were tested for pathogenicity to rape salad greens cv. Essex and then to turnip greens cv. Topper. Plants were grown in peat-vermiculite potting mix in 10-cm-diameter pots in a greenhouse. P. syringae pv. maculicola F41, isolated from turnip in Oklahoma, and P. syringae pv. tomato F33, isolated from tomato in Oklahoma, were included as positive and negative controls along with a noninoculated control. Bacteria were grown on KMB for 48 h at 24°C, and bacterial suspensions were prepared and adjusted to 0.1 optical density at 600 nm. Three-week-old plants were held at 95 to 100% relative humidity (RH) for 48 h before they were sprayed just to runoff with inoculum and then held at 95 to 100% RH for 48 h after inoculation (4). After an additional 5 to 8 days in a greenhouse, nine strains and F41 caused symptoms on both Topper and Essex similar to symptoms observed in the field. No symptoms were observed on noninoculated plants or plants inoculated with F33. On the basis of repetitive sequence-based polymerase chain reactions with the BOXA1R primer, the DNA fingerprint of each of the nine pathogenic strains from South Carolina was nearly identical to that of F41. Bacteria isolated from inoculated, symptomatic turnip leaves had identical LOPAT and BOXA1R profiles to the corresponding original strains. Pathogenic strains had bluegreen fluorescence on PAF, whereas nonpathogenic strains fluoresced yellow. Five pathogenic strains, as well as F41, were further identified to species and pathovar with fatty acid methyl ester profiles as P. syringae pv. maculicola. To our knowledge, this is the first report of P. syringae pv. maculicola from South Carolina. Over the past 10 years, P. syringae pv. maculicola has been found in Oklahoma (4), California (1), and Ohio (3). Bacterial leaf spot has occurred yearly in South Carolina since the initial outbreaks. Currently, it is the disease that causes the greatest yield losses of leafy brassica greens in the state.

First Report of Bacterial Wilt of Annual Bluegrass Caused by Xanthomonas translucens pv. poae in Montana.

During August 2003, a golf course putting green sample composed of Poa annua from the Buffalo Hill Country Club in Kalispell, MT exhibiting symptoms of general decline, wilting, and necrosis was submitted to the University of Rhode Island Turfgrass Disease Diagnostic Laboratory. No pathogenic fungi were observed or cultured from affected plants. Bacterial streaming was observed from cut leaves. Cut leaves were surface disinfested for 5 min in a 0.6% sodium hypochlorite solution and plated on yeast dextrose calcium carbonate (YDC) agar media. A single yellow, mucoid colony type composed of rod-shaped bacteria was isolated from all leaves. Bacteria were gram negative, lacked anaerobic growth, did not fluorescence on King's medium B, and were able to grow at 33°C on YDC. Colonies were transferred to YDC for 10 days, DNA was extracted and a 2,190-bp region encompassing the 16S rRNA, ITS, and 5' end of the 23S rRNA was amplified via polymerase chain reaction (PCR) using previously published protocols (1). Sequence comparisons of the resulting 2,190-bp PCR product revealed a 99.7% sequence similarity with X. translucens pv. poae (American Type Culture Collection [ATCC] no. 33804) and a 99.8% sequence similarity with X. translucens pv. poae M-1 (Torrington, CT). No higher sequence similarity could be identified from a BLAST search. The Montana isolate and the previously described M-1 isolate were inoculated onto four replicates of 5-month-old P. annua var. annua plants by dipping cut leaves into a bacterial suspension adjusted to 109 CFU/ml in 0.9% NaCl. Control plants were dipped into 0.9% NaCl without the presence of the bacteria. All plants were placed in the greenhouse at an average daytime temperature of approximately 24°C and 12 h of sunlight. After 8 weeks, the plants were assessed for disease and checked for bacterial streaming. This experiment was repeated once. The Montana isolate caused approximately 68 and 70% leaf death and the M-1 isolate caused 21 and 25% leaf death in the two experiments. Bacterial streaming was observed in approximately 50 and 80% of the examined leaves inoculated with the M-1 and Montana isolates, respectively. Control plants showed no leaf mortality or bacterial streaming. Although this pathogen was originally identified in the United States in Michigan (2) and has been prevalent in the northeastern United States for the past 10 to 15 years, to our knowledge, this is the first report of the disease in the northwestern United States.

An Outbreak of a Leaf Spot Disease of Cabbage in Southern Florida Caused by Xanthomonas campestris pv. armoraciae.

From October to December 2001, a leaf spot disease was observed in numerous commercial fields of red and green cabbage (Brassica oleracea var. capitata L.) in the Everglades Agricultural Area, south and east of Lake Okeechobee and in the environs of Immokalee in southwestern Florida. Discrete water-soaked to greasy appearing spots were observed in the leaf blades with no evidence of marginal V-shaped lesions characteristic of black rot caused by Xanthomonas campestris pv. campestris. Profuse bacterial streaming was observed when cut leaf sections were examined microscopically. A bacterium that formed yellow colonies on nutrient agar was consistently isolated from these lesions. Ten bacteria were isolated, purified, and characterized. All strains were aerobic, gram-negative rods. Strains were positive for esculin hydrolysis, proteolysis in litmus milk, and gelatin liquefaction. Strains were negative for urease production, nitrate reduction, oxidase, and utilization of asparagine as a sole source of carbon and nitrogen. Fatty acid methyl ester analysis indicated a match with Florida library strains of X. campestris pv. raphani (similarity indices 0.605-0.738). Suspensions (2 × 107 CFU/ml in phosphate-buffered saline) of two Oklahoma strains identified as X. campestris pv. armoraciae provided by J. P. Damicone (3) and four representative Florida strains were applied to plants using a hand-held sprayer. Pathogenicity of the strains was tested on three replicate greenhouse-grown plants of the following: green cabbage cv. Market Early; red cabbage cv. Salad Delight; radish cv. Red Silk; tomato cv. Sunny; sweet bell pepper cv. Jupiter; and fresh horseradish roots purchased from a retail grocery chain. A strain of X. campestris pv. campestris originally isolated from Homestead, FL was also included in pathogenicity tests. All Florida and Oklahoma strains produced leaf spots, but no V-shaped lesions, on leaves of green cabbage, red cabbage, radish, tomato, and horseradish. Typical black rot symptoms were observed only in radish and green and red cabbage inoculated with the X. campestris pv. campestris strain. On the basis of these results, we identify the Florida strains as X. campestris pv. armoraciae (1,2,3), recognizing the precedent of X. campestris pv. armoraciae over X. campestris pv. raphani based on extensive genetic and serological data (1). Our strains appear to be more similar to those causing outbreaks on crucifers in Oklahoma (3) than those in Ohio (2), because Florida strains were pathogenic on tomato.

First Report of Bacterial Fruit Blotch of Watermelon Caused by Acidovorax avenae subsp. citrulli in Illinois.

In August 2001, symptomatic mature fruit of watermelon (Citrullus lanatus) cvs. Crimson Sweet and Royal Sweet were collected from six fields (48 ha) in Iroquois, Kankakee, and Mason counties in Illinois. The fruit surface had dark green, water-soaked lesions, and the rind's epidermis was cracked. Sections of infected rind were examined with a light microscope, and bacterial streaming was observed. Rind tissue was disinfested by rubbing the fruit surface with a paper towel moistened with 70% ethanol. Pieces of rind from the margins of lesions were placed in a test tube containing sterile-distilled water. The tube was shaken, and the suspension was streaked on King's medium B agar in petri plates. The plates were incubated at 26°C for 3 days. A nonfluorescent, gramnegative, anaerobic, oxidase-positive, rod-shaped bacterium was isolated that produced creamy white colonies on nutrient agar. The bacterium was identified as Acidovorax avenae subsp. citrulli based on an enzyme-linked immunosorbent assay test specific for A. avenae subsp. citrulli (kit PSA 14,800; Agdia Inc., Elkhart, IN). The disease was diagnosed as bacterial fruit blotch (1,2). The occurrence of bacterial fruit blotch of watermelon in Illinois is important because (i) watermelon is widely grown in Illinois, (ii) the pathogen also infects melons and pumpkins, and (iii) Illinois grows approximately 1,000 ha of melons and 8,000 ha of pumpkins.

Xanthomonas Leaf Spot and Stem Canker on Blueberry in Nurseries in Florida.

In June and July 1998, in nurseries in south Florida, lesions were observed on the foliage and stems of three southern high-bush cultivars of blueberry hybrids (Vaccinium coryumbosum). Plants were approximately 1.5 to 2 years of age (0.6 to 1 m high). Disease incidence ranged from 95 to 50%, depending on cultivar. Lesions on leaves were roughly round, 5 to 20 mm in diameter, reddish brown surrounded by a yellow halo, and frequently coalesced to form large blighted areas. Stem cankers were soft, dark brown-to-black, and often resulted in the death of the entire branch. Microscopic examination of free-hand sections through lesion margins revealed bacterial streaming. Isolation of bacteria on nutrient agar consistently recovered mucoid, yellow bacteria typical of a xanthomonad. A pure culture of the bacteria was gram negative, oxidase negative, nonfluorescent, and proteolytic and produced a hypersensitive reaction on tobacco. Strains had fatty acid profiles with 88.5% similarity to Xanthomonas campestris pv. maniotis and 84.6% similarity to X. campestris pv. fici. Koch's postulates were fulfilled by spray-inoculation of 18-month-old blueberry cv. Sharpblue with a bacterial suspension (1 × 108 CFU/ml) in sterile water. Control plants were sprayed with sterile distilled water. Plants were covered with plastic for 24 h and kept in a growth chamber at 25°C with a 12-h photoperiod. Symptoms were reproduced on inoculated plants, and bacteria were reisolated from lesions. Control plants were asymptomatic. The disease was controlled by applications of copper compounds, increased plant spacing, rouging of infected plants, reduction of leaf wetness, and elimination of overhead irrigation.

Occurrence of Bacterial Leaf Spot of Escarole Caused by Pseudomonas cichorii in the Everglades Agricultural Area of Southern Florida.

In the fall of 1997, 1998, and 2000, a leaf spot disease of escarole (Cichorium endivia L.) was widespread among commercial plantings in the Everglades Agricultural Area (EAA), south and east of Lake Okeechobee, FL. Symptoms consisted of dry, dark gray-to-black lesions that expanded to ≈4 cm in diameter. Concentric rings were often observed in mature lesions. Growers and scouts in the area consistently identified this disease as Alternaria leaf spot, because the symptoms closely resembled Alternaria leaf spots seen on a number of other vegetables. Prolific bacterial streaming occurred when cut portions of lesions were observed microscopically. A fluorescent bacterium was consistently isolated when a sterile inoculation needle was pushed through lesions. Eight bacterial strains were isolated, restreaked to obtain pure cultures, and characterized. All strains were aerobic, gram-negative rods that were oxidase positive and arginine dihydrolase negative. Negative reactions were recorded for levan formation and rotting of potato slices. All strains utilized glucose, mannitol, and m-tartrate and were negative for sucrose, sorbitol, benzoate, d-arabinose, l-rhamnose, and cellobiose. Results for utilization of D-aspartate were variable. Based on these results, the causal agent of bacterial leaf spot of escarole was identified as Pseudomonas cichorii. Greenhouse-grown plants of escarole, cv. Full Heart, and Cos lettuce, cv. Tall Guzmaine, were mistinoculated with a suspension (107 CFU/ml) of each test strain from escarole and P. cichorii strain Pc28, originally isolated from celery (1). Plants were bagged for 3 days after inoculation. Symptoms characteristic of this disease were evident on escarole inoculated with all test strains and Pc28 6 days after inoculation. Pure cultures of P. cichorii were recovered from lesions on King's B medium. Three test strains produced mild leaf spot symptoms in Cos lettuce, but the symptoms were distinctly different from those associated with the common bacterial leaf spot of lettuce in Florida caused by Xanthomonas campestris pv. vitians (2). To our knowledge, this is the first report of P. cichorii causing this unusual target spot symptom on escarole in the EAA.

Bacterial Leaf Stripe Caused by Xanthomonas translucens pv. cerealis on Intermediate Wheatgrass in Idaho.

Intermediate wheatgrass (Thinopyrum intermedium [Host] Barkworth & D.R. Dewey) (synonyms: Agropyron intermedium [Host] Beauv.; Elytrigia intermedia [Host] Nevski) is widely grown as a forage crop and is also used to control soil erosion. In a seed production field of cv. Rush in Washington County, ID, more than 80% of the plants were found affected by a disease with leaf stripe symptoms. The lesions were initially elongated, water-soaked, and translucent, later developing into brown, necrotic, interveinal stripes that often coalesced. Frequently, yellowish, dried, granular, or flaky exudate was present on the lesion surfaces. Microscopic examination of cut pieces of symptomatic tissue showed profuse bacterial streaming. Isolations on nutrient agar and King's medium B agar consistently yielded smooth, circular, butyrous, yellow, raised bacterial colonies. The bacterium was rod-shaped, Gram-negative, oxidase-negative, aerobic, and did not reduce nitrate. Substrate utilization profiles (Biolog Inc.), and cellular fatty acid analysis (Analytical Services Inc.) identified the bacterium as a pathovar of Xanthomonas translucens (syn: X. campestris pv. translucens). For pathogenicity tests, 3- to 5-week-old greenhouse-grown seedlings were injected in the whorl with a water suspension of 24-h-old culture (approximately 107 cfu/ml) of the bacterium. Control plants were injected with sterile distilled water. The plants were incubated at 25 to 28°C and observations were recorded after 6 to 10 days. The bacterium was pathogenic (causing water-soaked lesions, often with bacterial exudate) to T. intermedium cvs. Rush, Tegmar, PI 547316, and PI 380636; wheat cvs. Stephens, Vandal, FF 301, and FFR 525; barley cvs. Galena, Lud, and Steptoe; oat cvs. Boone, Clinton, Erban, Marion, Mohawk, Nemaha, Olena, and Tama; rye cvs. Florida 401, Hazel, Musketeer, Oklon, Rymin, Wintermore, and Wrens 96; Agropyron cristatum cv. Ephraim; A. cristatum × desertorum cv. Hycrest; Bromus arvensis; B. briziformis; B. catharticus; B. inermisssp. inermis; B. inermis ssp. pumpellianus; B. japonicus; B. marginatus; B. popovii; B. rigidus; B. tomentellus; Dactylis glomerata cvs. Paiute and Potomac; Elymus repens; Leymus mollis; L. angustus cv. Prairieland; Lolium arundinaceum cv. Fawn; L. perenne cv. Zero Nui; and Psathyrostachys juncea cv. Bozoisky. It was only weakly pathogenic (with small, chlorotic or water-soaked lesions and no exudation) to Phleum pratense cv. Climax and Pseudoroegneria spicata ssp. spicata cv. Goldar. It was not pathogenic to Andropogon gerardii cv. Pawnee; Festuca ovina; Oryza sativa cvs. Cypress, Newbonnet, and M201; or Schizachyrium scoparium cv. Camper. Based on the pathogen's natural host and its wide host range among cereals and grasses as verified by inoculation, the bacterium was identified as X. translucens pv. cerealis. This is the first report of natural occurrence of this pathogen on T. intermedium. A sample (105 g) of seed used for planting the affected field was found contaminated with 7.5 × 104 cfu/g of the pathogen, and seed to seedling transmission was observed in greenhouse tests. Contaminated seed, thus, may serve as a source of primary inoculum to intermediate wheatgrass, which in turn may serve as an inoculum source to other susceptible cereals and grasses growing in the vicinity.

Xanthomonas Blight of Onion in South Africa.

During April 1999, a foliar blight of onion (Allium cepa L. 'Granex 33') was reported in an early commercial planting under center pivot irrigation in the Limpopo Valley of the Northern Province of South Africa. Regular fungicide sprays failed to inhibit the progress of the disease. Foliar symptoms started as water-soaked lesions that elongated and turned chlorotic followed by tissue collapse in some leaves. Leaves often collapsed at the point of infection. Bulb size was severely reduced and premature leaf death caused irregular maturation and bulb size in the field. The symptoms were similar to those of Xanthomonas blight, described on the same cultivar in Hawaii (1). Microscopic examination of hand cut sections trough lesion margins showed bacterial streaming. Isolation on semi-selective diagnostic milk Tween agar (2) yielded almost pure cultures of a typical xanthomonad. The mucoid, yellow pigmented bacterium was rod shaped, gram negative, catalase positive, oxidase negative, utilized glucose oxidatively, and was lypolytic (Tween 80), proteolytic (skimmed milk), and amolytic. Biolog GN Microplate profiles as read by the MicroLog database release 3.50 (Biolog, Hayward, CA) were similar to those of a pathovar (similarity indices of 0.29 to 0.71). Symptoms were successfully reproduced on glasshouse grown Granex 33 seedlings at the five-leaf stage by spray and syringe inoculations (1) and the pathogen reisolated as described above. Ten seedlings were used in the pathogenicity test, of which five served as controls. After inoculation, seedlings were covered overnight with plastic bags, after which bags were removed and seedlings grown in the greenhouse at 24 to 30°C and natural light until symptom development. Attempts to isolate the pathogen from the seed lot used to plant the affected field were unsuccessful. The disease re-occurred in early plantings of Granex 33 on the same farm in April 2000 toward the end of an unusually wet summer rainy season. Damage caused by the disease was so severe in one early planting that it was plowed under. High temperatures and humid conditions combined with overhead irrigation could have enhanced disease development and spread during the early growth of the crop. No further spread was observed during cooler and drier weather later in the season.

First Report of Bacterial Leaf Spot of Basil Caused by Pseudomonas viridiflava in Argentina.

In June 1998, during a cool, humid period, typical bacterial spot symptoms were observed on basil plantlets (Ocimun basilicum L. 'Royal Louis' and 'Zaes') in a commercial greenhouse in La Plata, Argentina. Affected plants had dark brown to black lesions on cotyledons. Spots on leaves were first water soaked, then became necrotic and progressed inward from the margins. Disease incidence approached 30%. Symptoms were similar to those reported by Little et al. (2) on basil affected by Pseudomonas viridiflava. No pathogenic fungi or viruses were associated with symptomatic plants. Bacterial streaming was observed from lesion margins. Bacteria consistently isolated from leaf lesions formed cream-colored, glistening, convex colonies on sucrose peptone agar and a green fluorescent pigment on King's medium B. Bacterial growth produced a distinctive olive green pigment on glycerol agar medium and a pink pigment on T-5 medium (1). Four isolates selected for further study were aerobic, Gram-negative, non-spore-forming rods. In LOPAT (levan-oxidase-potato rot-arginine dihydrolase-tobacco hypersensitivity) tests, all induced a hypersensitive response in tobacco plants, caused soft rot of potato tubers, and were negative for levan, oxidase, and arginine dihydrolase. In addition, strains rotted onion slices and produced a reddish sunken lesion on bean pods. Acid was produced aerobically from D-glucose, mannitol, mesoinositol and sorbitol, but not from D-arabinose, L-rhamnose, melibiose, amygdalin, or sucrose. Bacteria used D-tartrate, pyruvate, and citrate, but not benzoate. The strains did not hydrolyze starch, exhibited an oxidative metabolism of glucose, and did not reduce nitrates to nitrites or accumulate poly-β-hydroxybutyrate inclusions. Negative reactions were obtained with indole, ornithine, and D-tryptophan. Isolates hydrolyzed gelatine, used Tween 80, were positive for catalase, and were unable to grow in the presence of 5% NaCl. Colonies developed at 4°C but not 37°C. Reactions were identical to those of reference strains ICMP 5776 and 12363, which were included in all tests for comparison. Pathogenicity was verified on 35-day-old basil plants by both spraying and infiltration inoculations with bacterial suspensions (108 and 105 cells per ml, respectively). Carborundum was included in the inoculum used for a set of plants inoculated by spraying. Controls were injected or sprayed (with and without Carborundum) with sterile, distilled water. In addition, bean (Phaseolus vulgaris cv. Nag12 INTA) and lettuce (Lactuca sativa cv. criolla), both reported as host plants, were inoculated by spraying with bacterial suspensions of 107 cells per ml plus Carborundum. After 48 h in a humid chamber, inoculated plants and controls were maintained at 23 ± 3°C. Symptoms on basil plants inoculated by injection or spraying with Carborundum were identical to those observed on basil in the field. Symptoms on bean and lettuce were similar to those described for P. viridiflava. The bacterium was reisolated from lesions of all species tested, fulfilling Koch's postulates. No lesions were observed on controls or on plants sprayed without Carborundum, suggesting that bacteria gain entry through wounds. The microorganism was identified by physiological tests and polymerase chain reaction as P. viridiflava. This is the first report of bacterial leaf spot of basil in Argentina.

Pseudomonas syringae Leaf Blight, a New Disease of Kalmia latifolia.

In spring and fall of 1997, and in February 1998, Kalmia latifolia cv. Olympic Fire plants with severe leaf blight symptoms were submitted to the Oregon State University Plant Clinic from a commercial nursery. The primary symptom was a dark purple leaf blight, often associated with the leaf mid-rib. Disease progressed down the petioles and into twigs, causing blackening of affected tissues and leaf drop. Abundant bacterial streaming was observed oozing from the margins of affected tissue when examined at ×100. Isolations from affected tissues were made onto King's medium B (KB). A fluorescent bacterium was recovered and identified as Pseudomonas syringae by the Biolog system of identification. Identity was confirmed by fatty acid methyl ester analysis performed by Larry Barnes (Texas A&M University, College Station). Attempts to determine the pathovar were unsuccessful. A single colony isolate of the bacterium was raised on KB. Koch's postulates were completed by the following procedures. A bacterial suspension was made from a 24-h-old agar culture of this isolate with phosphate buffer with 0.2% gelatin (PBG). The concentration of the suspension was adjusted to 8 × 107 cells per ml by direct enumeration. Five milliliters of the suspension was atomized onto young leaves on six twigs of Kalmia latifolia. Controls consisted of young leaves on four twigs atomized with 5 ml of PBG. Twigs receiving the inoculum or the PBG were enclosed in plastic bags and maintained at room temperature near a north-facing window. Symptoms appeared 6 days later: dark purple spots on the margins of inoculated leaves and blight symptoms near the leaf mid-rib. Symptoms did not appear on PBG-sprayed leaves. Pseudomonas syringae was successfully reisolated from surface-disinfested inoculated leaves but not from leaves sprayed with PBG. This is the first report of Pseudomonas syringae causing a leaf blight of Kalmia.

First Report of Bacterial Fruit Blotch of Watermelon in Oregon.

Most of the watermelons, Citrullus lanatus (Thunb.) Matsum. & Nakai, consumed in the Pacific Northwest during the summer months are grown in the southern Columbia Basin under dry (<5 cm rainfall), low relative humidity (46 to 57%), and high temperature (29 to 41°C) conditions, using transplants, plastic mulch, and drip irrigation. During May 1996, irregularly shaped, water-soaked lesions were observed on cotyledons and first true leaves of watermelon cv. Sangria transplants growing in a greenhouse. Similar lesions were observed later on older leaves in a commercial field of cv. Millionaire. Microscopic examination of symptomatic tissue revealed bacterial streaming, and isolation on nutrient agar consistently yielded numerous creamy to off-white bacterial colonies. Bacteria from purified, single colonies were Gram negative and rod shaped. Physiological characterization by the Biolog GN Bacterial Identification System (version 3.5) showed a similarity of 0.971 to the Biolog description for Acidovorax avenae subsp. citrulli. Pathogenicity of two strains was confirmed in three separate tests by hypodermic needle infiltration of cotyledons or by stab inoculation into hypocotyls of 12 to 24 21-day-old cv. Crimson Sweet seedlings with aqueous suspensions of bacteria containing approximately 6.0 × 108 CFU/ml. Inoculum was prepared from 48-h-old nutrient agar cultures. Test plants were incubated in the greenhouse at 21°C, under a 16-h photoperiod. Hypocotyl and cotyledon inoculations produced water-soaked lesions within 24 to 48 h on both the hypocotyl and cotyledons or just the cotyledon, respectively, on plants inoculated by either method. No symptoms developed on control plants infiltrated or stabbed with sterile water only. Isolations from three symptomatic seedlings yielded colonies similar in morphology to those used for inoculation. Tests of two purified cultures by Biolog indicated the bacteria were A. avenae subsp. citrulli. The symptomatic test plants were transplanted to fields, and the maturing melons developed large, dark green, water-soaked lesions with irregular margins. Similar fruit symptoms were seen in commercial fields. Labels on seed used in commercial production and in our tests warned of risks related to fruit blotch. This is the first report of bacterial fruit blotch of watermelon in Oregon. This disease may have a significant impact on watermelon production in the Columbia Basin.

Xanthomonas campestris pv. graminis . [Descriptions of Fungi and Bacteria

Abstract A description is provided for Xanthomonas campestris pv. graminis . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: Lolium italicum, L. multiflorum, L. perenne, Dactylis glomerata, Festuca pratensis , and Trisetum flavescens . Single cases of natural infection of Agropyron repens, Phalaris arundinacea and Phleum pratense are also recorded (62, 241), but their status in the natural host range is unknown. In inoculation tests (Egli et al. , 1975; Egli &amp; Schmidt, 1982) the following were highly susceptible: Alopecurus pratensis, Dactylis glomerata, Festuca arundinacea, F. pratensis, F. rubra, Lolium loliaceum, L. multiforum, L . parabolicae, L. perenne, L. remotum, L. temulentum, Phleum arenarium and P. bertolonii . Showing much less susceptibility were Agrostis alba, Arrhenatherum elatius, Phleum alpinum, P. phleoides, P. pratense, Poa annua, P. compressa, P. fertilis, P. memoralis, P. pratensis and P. trivialis . Leyns et al. (61, 6162) found that Agrosas tenuis and Festuca ovina were moderately susceptible when inoculated. Egli et al. (1975) recorded doubtful symptoms on Hordeum vulgare and Triacum aestivam on inoculation, but consider that they are unlikely to be naturally infected. DISEASE: Bacterial wilt of forage grasses. Symptoms usually first noticed at the heading stage, when young leaves curl and wither, and shoots remain stunted or may die. Other plants will continue to make poor growth and produce small, distorted inflorescences. Chlorotic and necrotic zones form on the older leaves along long stretches of vascular bundles, often extending into the sheaths. Bacterial streaming may be seen under the microscope from the cut ends of vascular bundles of infected tissue mounted in water. GEOGRAPHICAL DISTRIBUTION: CMI Map 533, ed. 1, 1979 lists France, Germany, Switzerland and Wales, to which must be added Scotland (63, 2925), Belgium (61, 4199), Netherlands, Norway (62, 241), and New Zealand (62, 241). Possibly in USA (IL; 61, 5045) though this disease is currently attributed to a Rickettsia- like organism. TRANSMISSION: Within the crop transmission is presumed to be by the blades of mowing machines.

Xanthomonas campestris pv. poae . [Descriptions of Fungi and Bacteria

Abstract A description is provided for Xanthomonas campestris pv. poae . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: Naturally infects Poa trivialis . By artificial inoculation Poafertilis and P. nemoralis are both moderately susceptible, P. annua rather less susceptible, and P. pratensis and P. compressa little or not at all affected. DISEASE: Bacterial wilt of rough stalked meadow grass ( Poa trivialis ). The symptoms are the same as those produced by X. campestris pv. graminis on other forage grasses. At the heading stage young leaves are seen to curl and wither, and shoots remain stunted or die. Some plants produce small, distorted inflorescences. Chlorotic and necrotic areas form along the vascular bundles of older leaves and often extend into their sheaths. Bacterial streaming is usually visible under the microscope. GEOGRAPHICAL DISTRIBUTION: Switzerland. Probably present but unrecognised in some other european countries. TRANSMISSION: Within the crop the main means of transmission is probably mowing machinery.

Xanthomonas campestris pv. arrhenatheri . [Descriptions of Fungi and Bacteria

Abstract A description is provided for Xanthomonas campestris pv. arrhenatheri . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: Arrhenatherum elatius . By inoculation strain 705 gave much less severe symptoms on Alopecuruspratensis and Dactylis glomerata , but other grasses tested were not diseased (Egli et al. , 1975) Three other strains (711, 719, and 725) gave mild symptoms on Lolium multiflorum , and one (730) gave a slight reaction on Phleum pratense . The reactions on Festuca pratensis and Poa trivialis were negative or negligible (Egli &amp; Schmidt 1982). It is unlikely that the above inoculated hosts would be infected naturally. DISEASE: Bacterial wilt of tall oat grass. The symptoms are identical to those caused by X. campestris pv. graminis on other forage grasses. They are first seen at the heading stage when young leaves curl and wither and shoots remain stunted or may die. In some plants poor growth continues and small distorted inflorescences are produced. Chlorotic and necrotic zones form on older leaves along the vascular bundles, often extending into the sheaths. Bacterial streaming may be seen under the microscope from cut ends of vascular bundles of infected tissue mounted in water. GEOGRAPHICAL DISTRIBUTION: Switzerland. All of Egli's isolates came from that country and the pathogen has not yet been reported from elsewhere. TRANSMISSION: As with X. campestris pv. graminis transmission within the crop is thought to be mainly by mowing machinery.

Xanthomonas campestris pv. phlei . [Descriptions of Fungi and Bacteria

Abstract A description is provided for Xanthomonas campestris pv. phlei . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: Phleumpratense . In inoculation tests Egli &amp; Schmidt (1982) found that Phleum alpinum, P. arenarium, P . bertolonii (2 cvs.), P. phleoides and P. pratense (2 cvs.) were all highly susceptible. Lolium multiflorum showed mild symptoms in this test, but none in another. Other grasses, including Festuca pratensis, Arrhenatherum elatius and Poa trivalis showed little or, more often, no symptom development. DISEASE: Bacterial wilt of timothy grass. The symptoms are the same as those caused by X. campestris pv. graminis on other forage grasses. Young leaves curl and wither and shoots remain stunted or die. In some plants growth continues poorly and small, distorted inflorescences are produced. Chlorotic and necrotic zones form along the vascular bundles of older leaves, often extending to the sheaths. Bacterial streaming is often visible under the microscope from the cut edges of infected tissue. GEOGRAPHICAL DISTRIBUTION: Norway (Egli &amp; Schmidt, 1982) and Belgium (61, 6162) are the only reports so far, but the disease is probably more widespread in Europe than this would suggest. TRANSMISSION: As for X. campestris pv. graminis transmission within the crop is thought to be mainly by mowing machinery. The possibility of seed transmission should not be overlooked, although this has not been proved.