bluuebunny/crossref_metadata_2025 huggingface dataset:
Responses of Barley Cultivars and Lines to Isolates of Pyrenophora teres
Authors: Douiyssi A. , Rasmusson D. C. , Roelfs A. P.
Published: May 2007

Net blotch, caused by Pyrenophora teres, is among the most damaging foliar diseases of barley worldwide. A knowledge of the reaction of local cultivars, putative resistant lines, and variability in the net blotch pathogen is necessary to develop a successful resistance breeding program. Disease responses of 38 barley lines to 15 P. teres isolates were studied at the seedling and adult plant stages in the glasshouse, and field responses to net blotch were evaluated at three Moroccan locations. No tested barley was resistant to all isolates, and resistance was apparently of the specific type. Pathogenic variability was great, as none of the 15 isolates were identical. For each isolate tested, a specific high level of resistance was found in one or more host lines. Seedling and adults plants often differed in response to the same isolate. Adult plant resistance was commonly observed in response to isolate I-1, and seedling resistance was more common to isolate I-14. Adult plant resistance of nine lines was undetected in seedling evaluations using isolate I-1. The seedling glasshouse and field responses of the barley lines varied considerably, limiting the value of seedling testing for resistance. Field reactions of resistant and moderately resistant were consistent across the three locations for the lines Heartland, Minn 7, CI 2333, and CI 2549. The variability observed in P. teres and failure to find lines with resistance to all isolates suggests that breeding for resistance should emphasize pyramiding of resistance genes.
First Report of Early Rot of Cranberry Caused by Phyllosticta vaccinii in Wisconsin
Authors: McManus P. S.
Published: May 2007

Phyllosticta vaccinii Earle causes early rot of cranberry (Vaccinium macrocarpon Aiton) and previously was reported in fruit and leaves from Massachusetts and New Jersey, but not Wisconsin or Washington (2). This fungus previously was introduced into Wisconsin, apparently on planting stock, but did not persist in the field (2). In the present study, rotted fruit were collected in central Wisconsin in September 1997 from research plots adjacent to a commercial planting that had been started from field cuttings from New Jersey. P. vaccinii was isolated from 12 of 31 symptomatic berries, and its identity was verified by cultural and morphological characteristics (3). P. vaccinii was not isolated from rotted fruit from five other sites in central and northern Wisconsin. In three separate experiments, 10 to 25 cv. Stevens or Searles cranberry fruit were punctured with a needle, inoculated with 2 to 4 × 105 conidia from sporulating cultures of P. vaccinii, and incubated at 28°C in a moist chamber. After 5 to 14 days, soft, watery spots developed at the inoculation point on 8 to 22% of the fruit in different experiments, and P. vaccinii was reisolated from the lesions. Fruit that were punctured but not inoculated neither developed symptoms nor yielded P. vaccinii. Previous attempts at fulfilling Koch's postulates by inoculating mature fruit were unsuccessful (1). P. vaccinii is one of approximately 15 species of fungi involved in the cranberry fruit rot complex in the eastern U.S. where fungicides are applied to greater than 95% of cranberry acreage, usually three times per year, primarily to control preharvest fruit rots. In Wisconsin, however, preharvest fruit rots are insignificant; less than 25% of the acreage is treated with fungicides. The occurrence of early rot in Wisconsin and the threat of introducing pathogens on cranberry cuttings are troublesome in light of the Food Quality Protection Act of 1996, which threatens registration of fungicides used to control cranberry fruit rots.

References: (1) D. M. Boone. Pages 35-36 in: Compendium of Blueberry and Cranberry Diseases. F. L. Caruso and D. C. Ramsdell, eds. American Phytopathological Society, 1995. (2) G. J. Weidemann and D. M. Boone. Plant Dis. 67:1090, 1983. (3) G. J. Weidemann et al. Mycologia 74:59, 1982.
Natural Infection of Citronmelon with Acidovorax avenae subsp. citrulli
Authors: Isakeit T. , Black M. C. , Jones J. B.
Published: May 2007

Citronmelon fruits (Citrullus lanatus var. citroides (Bailey) Mansf.) with lesions were collected from a cowpea field in Frio County, TX, in July 1997. The lesions were circular, necrotic, or water-soaked, approximately 3 mm in diameter, and did not extend into the flesh of the fruit. Nonfluorescent, gram-negative bacteria were consistently isolated from lesions. Six representative strains were identified as Acidovorax avenae subsp. citrulli (Aac), using Biolog GN MicroPlates and the MicroLog data base release 3.50 (0.533 to 0.813 similarity). Aac causes leaf and fruit lesions (bacterial fruit blotch, BFB) on watermelon (C. lanatus (Thunb.) Matsum. & Nakai). Strains were tested for pathogenicity on watermelon seedlings (cv. Royal Sweet) by daubing bacterial suspensions (approximately 108 CFU/ml) onto cotyledons of 1-week-old seedlings. Water soaking of cotyledons, followed by necrosis and seedling death, occurred within 5 days. These symptoms were indistinguishable from those caused by watermelon strains of Aac. Bacteria were reisolated from symptomatic seedlings. The source of the infection is not known. Watermelons had been grown in this field in 1996, but no BFB symptoms were observed. Citron fruit infected with Aac were found in nearby watermelon fields where BFB was present; the closest field was 50 m from the cowpea field. These observations suggest that citronmelon, a common weed in south Texas, has the potential to perpetuate Aac. This is the first documentation of a naturally occurring infection of citronmelon with Aac.
Effect of Copper Bactericides on Copper-Resistant and -Sensitive Strains ofPseudomonas syringaepv.syringae
Authors: Scheck Heather J. , Pscheidt Jay W.
Published: May 2007

Fourteen formulations of copper-based bactericides were evaluated for their efficacy in reducing populations of copper-resistant and -sensitive strains of Pseudomonas syringae pv. syringae growing on tissue-cultured lilac and of copper-sensitive strains of this pathogen on field-grown lilac. The amount of free cupric ions (Cu2+) in solution was the only predictor of formulation efficacy, but this variable could not be estimated from the metallic copper content of the product. Relative to nontreated controls, all copper-based bactericides reduced the population size of copper-sensitive strains by 50%, but only cupric hydroxide mixed with mancozeb or ferric chloride reduced the population size of copper-resistant strains by an equivalent amount. Several noncopper bactericides, including streptomycin-sulfate, caused only small reductions in bacterial populations on tissue-cultured or field-grown lilacs. In the field, two applications of cupric hydroxide (wettable powder) when plant growth stages were at dormant (mid-February) and delayed dormant (late February) provided better control than either one or no treatments.
The Role of Colletotrichum spp. in Postharvest Anthracnose of Citrus and Survival of C. acutatum on Fruit
Authors: Timmer L. W. , Brown G. E. , Zitko S. E.
Published: May 2007

Colletotrichum gloeosporioides causes postharvest anthracnose of citrus fruit and is a common saprobe in citrus groves, whereas C. acutatum infects flower petals and causes postbloom fruit drop (PFD). The purpose of this study was to determine whether C. acutatum caused anthracnose, survived as quiescent infections on fruit, and represented a threat for introduction of the PFD pathogen to disease-free areas. When Robinson tangerine fruit were artificially inoculated with both species and exposed to high levels of ethylene, only fruit inoculated with C. gloeosporioides developed postharvest anthracnose. However, C. acutatum was readily reisolated from inoculation sites on asymptomatic fruit. Navel oranges harvested from groves with severe PFD the previous spring developed low levels of anthracnose, but only C. gloeosporioi-des was isolated from lesions. Valencia orange fruit harvested at bloom during a PFD outbreak had high surface populations of C. acutatum which declined rapidly during 2 to 3 weeks of storage. Quiescent infections formed on artificially inoculated and naturally exposed fruit were reduced but not eliminated by washing, waxing, and fungicide treatment in the packinghouse. Since C. acutatum does not produce postharvest anthracnose, the risk of introduction of this pathogen to disease-free areas is minimal. However, if fruit were harvested during a PFD outbreak, C. acutatum might survive standard packinghouse treatment and shipment as quiescent infections.
Verticillium Wilt of Paprika Caused by a Highly Virulent Isolate of Verticillium dahliae
Authors: Tsror (Lahkim) Leah , Erlich Orly , Amitai Sarit , Hazanovsky Marina
Published: May 2007

Verticillium dahliae caused wilting, stunting and early dying of paprika plants in Israel, resulting in a 22% reduction in yield. A V. dahliae isolate from diseased paprika plants was slower growing on agar medium than V. dahliae isolates from potato, tomato, watermelon, and Dodonaea, but formed microsclerotia earlier. The paprika isolate of V. dahliae was highly virulent to paprika in pathogenicity tests. Disease severity indices obtained from three paprika cultivars ranged from 3.7 to 4.9 (on a scale of 0 to 5). The disease caused height reductions of 43 to 62% in the three inoculated paprika cultivars, and pathogen colonization levels were 10- to 35-fold higher in stems than in leaves. The potato isolate of V. dahliae did not produce symptoms or cause stunting of paprika, and could not be detected in stems or leaves. The tomato, watermelon, and Dodonaea isolates did not cause disease symptoms in paprika, although they colonized the plant tissue. In potato and eggplant, the paprika isolate caused a higher incidence of disease with more severe symptoms and a higher level of tissue colonization than did the potato isolate.
First Report of Choanephora Flower Spot and Blight of Periwinkle
Authors: Holcomb G. E.
Published: May 2007

Periwinkle or vinca (Catharanthus roseus (L.) G. Don) is widely planted as a flowering annual in home and business landscapes in hardiness zones 9 and 10 and the southernmost portions of zone 8. Many improved selections, such as those in the Pacifica, Tropicana, and Cooler cultivar series, are currently available. Dark gray flower spots that often coalesced and led to blighting of flowers under conditions of high humidity, were observed on all of 18 periwinkle cultivars in a variety trial at Burden Research Plantation in September 1997. The disease affected only the flowers and was also observed on periwinkle in commercial landscape plantings around Baton Rouge. Fungi were isolated from flower spots by plating necrotic tissue on acidified potato dextrose agar (PDA). Fungal isolates were maintained on PDA and 20% V8 juice agar under continuous fluorescent light. A fungus that produced cottony, white mycelium and black spore masses was consistently isolated from diseased tissue. Pathogenicity tests were conducted by misting a spore suspension (70,000 per ml produced on V8 juice agar) onto detached flowers held in a moist chamber and to flowers on intact plants. Inoculated plants were held for 24 h in a dew chamber at 25°C. Typical irregular dark spots appeared on attached and detached flowers within 18 h after inoculation and flowers held for longer periods under high humidity developed a soft rot. Koch's postulates were fulfilled by reisolating the fungal pathogen, which was identified as Choanephora cucurbitarum (Berk. & Ravenel) Thaxt. (1). This is the first report of the occurrence of C. cucurbitarum on periwinkle.

Reference: (1) P. M. Kirk. Mycol. Pap. 152:1, 1984.
Squash Yellow Leaf Curl Virus: A New Whitefly-Transmitted Poty-Like Virus
Authors: Zouba A. A. , Lopez M. V. , Anger H.
Published: May 2007

A severe yellow and leaf curl disease affecting field squash was found in the Batinah region of the Sultanate of Oman. The symptoms appear as small yellow spots, diffuse veinal yellowing, and leaf curling of young leaves. The inciting virus was easily transmitted by mechanical inoculation and by the whitefly Bemisia tabaci in a semi-persistent manner. The host range of the virus was restricted to two cucurbit species. Leaf dip preparations contained few flexuous particles about 700 to 750 nm long. Pinwheel-like inclusion bodies were observed in thin sections of diseased squash tissues. Serological tests by enzyme-linked immunosorbent assay showed that the virus is serologically related to watermelon mosaic virus-2, but not to zucchini yellow mosaic virus or papaya ring spot virus (watermelon strain). In view of these properties, this virus is considered to be a newly described virus and is tentatively named squash yellow leaf curl virus.
Association of a Phloem-Limited Bacterium with Yellow Vine Disease in Cucurbits
Authors: Bruton B. D. , Fletcher J. , Pair S. D. , Shaw M. , Sittertz-Bhatkar H.
Published: May 2007

Since 1991, a new disease of cucurbits in central Texas and Oklahoma, designated yellow vine, has resulted in the decline and plant death of watermelon, cantaloupe, squash, and pumpkin. Affected plants are characterized by leaf yellowing, phloem discoloration, and plant collapse. Year-to-year variation in disease incidence has ranged from spotty outbreaks to complete crop loss in early-planted watermelon fields. A systematic investigation to determine the causal agent of the disease included pathogen isolation attempts, transmission tests, serological assays with various antisera (enzyme-linked immunosorbent assay and Western blotting), and DNA hybridizations with selected probes (dot and Southern blots). None of these tests revealed a consistent relationship between the expression of yellow vine symptoms and the presence of a particular microorganism or virus in the plant. However, transmission electron microscopic examination showed the consistent presence of a bacterium in the phloem sieve elements of symptomatic plants. The rod-shaped bacteria, observed only in symptomatic cucurbits, measured 0.25 to 0.5 μm in width and 1.0 to 3.0 μm in length and were surrounded by a triple-layered cell envelope.
Response of Soybean Accessions from Provinces in Southern China to Phytophthora sojae
Authors: Kyle D. E. , Nickell C. D. , Nelson R. L. , Pedersen W. L.
Published: May 2007

Phytophthora rot, caused by Phytophthora sojae, is a damaging disease of soybean (Glycine max (L.) Merr.) throughout the soybean-producing regions of the world. The discovery of new sources of resistance in soybean is vital in maintaining control of Phytophthora rot, because races of the pathogen have been discovered that can attack cultivars with commonly used resistance genes. The objectives of this study were to investigate the distribution and diversity of Phytophthora-resistant soybean in southern China and identify sources that confer resistance to multiple races for implementation into breeding programs. Soybean accessions obtained from southern China were evaluated for their response to races 1, 3, 4, 5, 7, 10, 12, 17, 20, and 25 of P. sojae using the hypocotyl inoculation technique in the greenhouse at Urbana, Illinois in 1996 and 1997. Accessions were identified that confer resistant responses to multiple races of the pathogen. These accessions may provide sources of resistance for control of Phytophthora rot of soybean in the future. The majority of the accessions with resistance to eight or more of the ten races tested were from the provinces of Hubei, Jiangsu, and Sichuan in southern China. Based on the evaluated accessions, these provinces appear to be valuable sources of Phytophthora-resistant soybean.
First Report of Three Phaeoacremonium spp. Causing Young Grapevine Decline in California
Authors: Scheck H. J. , Vasquez S. J. , Gubler W. D. , Fogle D.
Published: May 2007

A grapevine decline of unknown etiology is currently under investigation in California. Two- to 5-year-old vines show low vigor with undersized trunks, short internodes, uneven wood maturity, sparse foliage, and stunted, chlorotic leaves with interveinal chlorosis and necrosis. Trunks viewed in cross section show dark streaking in few to most of the vascular elements. Pith is compacted and discolored; the surrounding wood is dry with a silvery sheen. Primary roots also show dark streaking in the vascular elements and total root biomass is reduced. Phaeoacremonium spp. were consistently isolated from the roots, crowns, and lower portions of the rootstocks of declining vines but not from adjacent healthy vines. Phaeoacremonium spp. grew slowly out of infected tissues, but sporulated abundantly in culture. Identification was verified from a published key (1). Phaeoacremonium chlamydosporum and P. inflatipes were isolated throughout the northern and central California production areas, but P. aleophilum was isolated only in Riverside County. Koch's postulates were completed for Phaeoacremonium spp. by dipping roots of 2-month-old Carignane grape seedlings (n = 80) in a 108 spores per ml suspension for 30 min. Plants were potted in an artificial soil mix and held in a growth chamber at 25°C. Over 50% of plants inoculated with Phaeo-acremonium spp. developed root, stem, and vascular symptoms within 8 weeks. Each of the individual pathogen species was reisolated from over 75% of the inoculated plants but never from the controls. Similarly, all three Phaeoacremonium spp. are associated with wilt and decline diseases in grapevines in Africa (1) and Europe (2) but this is the first report in North America. While several names for this disease have been used previously with older grapevines, including Esca, apoplexy, and black measles (3), we propose using Phaeoacremonium grapevine decline to describe the diseases caused by P. aleophilum, P. chlamydosporum, and P. inflatipes on young vines.

References: (1) P. W. Crous et al. Mycologia 88:786, 1996. (2) P. Larignon and B. Dubos. Euro. J. Plant Pathol. 103:147, 1997. (3) R. Pearson and A. Goheen. 1988. Compendium of Grape Diseases. American Phytopathological Society, St. Paul, MN.
First Report of Hibiscus Chlorotic Ringspot Carmovirus in Tuvalu
Authors: Jones P. , Devonshire J. , Dabek A. , Howells C.
Published: May 2007

In September 1997, plants of Hibiscus manihot (locally called nambele) were observed on Vaitupu Island, Tuvalu, exhibiting an angular leaf mosaic and chlorosis that was not always clearly discernible. Electron microscopy of negatively stained sap from affected leaves revealed the presence of numerous isometric virus particles 28 nm in diameter. Poly-acrylamide gel electrophoresis of purified virus gave a single protein band of Mr 38,000 similar to that of the carmoviruses. Immunosorbent electron microscopy tests with antisera kindly provided by N. Spence showed the virus to be hibiscus chlorotic ringspot carmovirus (HCRSV) (1). This virus is also reported from El Salvador, the U.S., Australia, Thailand, Malaysia, Fiji, the Solomon Islands, and Vanuatu. It is not known how the virus reached Tuvalu but we suspect it was via infected cuttings, which were imported for the production of food supplements to combat acute deficiencies of vitamins A and C in the population. The virus is most likely to have been disseminated throughout the islands and atolls of Tuvalu through infected cuttings. Local spread within fields could occur through contaminated hands and cutting implements because of the ease with which the virus is mechanically transmitted.

Reference: (1) H. E.Waterworth et al. Phytopathology 66:570, 1976.
Pathogenesis of Tomato Spotted Wilt Virus in Peanut Plants Dually Infected with Peanut Mottle Virus
Authors: Hoffmann K. , Geske S. M. , Moyer J. W.
Published: May 2007

Peanut (Arachis hypogaea) plants dually infected with tomato spotted wilt tospovirus (TSWV) and peanut mottle potyvirus (PMV) exhibited a wide variety of symptoms, ranging from PMV-like symptoms of transient mild leaf mottle to TSWV-like symptoms of severe leaf distortion and stunting of the plant. Dual infection did not cause greater symptom severity than infection with either virus alone. In the early stages of disease development, PMV symptoms were similar to the first leaf symptoms of TSWV infection, suggesting that identification of TSWV in field-grown peanuts should not depend on visual observation. The virus titer, determined by enzyme-linked immunosorbent assay, indicated a delay in TSWV disease progress in doubleinfected plants, compared to plants infected with TSWV alone. In the later phase of disease progress, the virus titer in dually infected plants was not significantly different from that of singly infected plants. Infection with TSWV and PMV alone and with both viruses in combination was consistent among commercially grown peanut cultivars. In plants inoculated with TSWV or PMV alone or with both viruses in combination, the length of the latent period and final disease incidence, as measured by the number of plants showing symptoms, did not depend on the cultivar.
Effects of Barley Yellow Dwarf Virus on Yield and Yield Components of Drilled Winter Wheat
Authors: Hoffman T. K. , Kolb F. L.
Published: May 2007

Yield reduction in eight soft red winter wheat cultivars (Triticum aestivum) in response to barley yellow dwarf (BYDV) infection was evaluated in drilled plots. The experiment was conducted in 1993 and 1994 at the Crop Sciences Research and Education Center of the University of Illinois at Urbana-Champaign. Cultivars Caldwell, Cardinal, Clark, Howell, IL 87-2834, Tyler, and Pioneer brands 2548 and 2555 were selected for the study based on root system size, yield potential, and adaptation to local growing conditions. Plots were planted with a six-row drill to approximate conditions in growers' fields. A split-plot treatment design was used, with treatments as whole plots, and cultivars as subplots. The three treatments were BYDV-inoculated, natural BYDV infection, and a control (sprayed with Cygon to control naturally occurring aphids). Significant yield reductions in inoculated plots indicated the potential for severe yield loss due to BYDV infection under drilled conditions. The component of yield most severely affected by virus infection was number of kernels per spike. Kernel weight was affected but to a lesser extent than kernels per spike. Tiller number was generally not altered by infection but was positively correlated with yield in infected plots. Since kernels per spike and kernel weight were reduced by BYDV infection, it may be possible to select for tolerant genotypes by identifying lines in which these parameters are least affected by BYD disease pressure.
A Quantitative Method for Determining Soil Populations of Streptomyces and Differentiating Potential Potato Scab-Inducing Strains
Authors: Conn Kenneth L. , Leci Edlira , Kritzman Giora , Lazarovits George
Published: May 2007

A procedure is described for estimating Streptomyces populations in soil. Soils are air-dried, 10g quantities are shaken in plastic bags containing 0.1% water agar and homogenized with a Stomacher homogenizer, serial dilutions are plated on a semi-selective culture (STR) medium and incubated for 2 weeks at 22°C, and the Streptomyces colonies are enumerated. Use of STR medium reduced the bacterial and fungal colonies recovered from soil to levels below that of the Streptomyces spp. while not affecting the number of Streptomyces colonies compared with those enumerated on yeast malt extract medium. A procedure for screening large numbers of Streptomyces strains for thaxtomin production, a phytotoxin recognized as a virulence marker in S. scabies, is also described. Strains are grown on oatmeal medium, and the thaxtomin is extracted from the medium by facilitated diffusion and detected by miniature thin layer chromatography. S. scabies and S. acidiscabies strains (approximately 130 from Ontario and 70 from other locations in North America) that produced thaxtomin did not form aerial mycelia or sporulate on STR medium within 2 weeks at 22°C. Ontario S. scabies strains that produced thaxtomin A also produced melanin on STR medium. All S. scabies strains from scab lesions that produced thaxtomin A had this colony morphology, whereas only 4 to 9% of strains from soil with this colony morphology produced thaxtomin A. Using these procedures, we determined that the population of thaxtomin-producing S. scabies in soil from a potato field in Ontario with a history of potato scab was about 20,000 CFU/g soil.
Production of Bright Greenish Yellow Fluorescence in Figs Infected by Aspergillus Species in California Orchards
Authors: Doster Mark A. , Michailides Themis J.
Published: May 2007

The relationship of bright greenish yellow fluorescence (BGYF) of dried figs under longwave UV light to colonization by Aspergillus fungi was determined. BGYF in naturally infected figs was associated with decay by only four fungal species: the aflatoxin-producing species Aspergillus flavus (both L and S strains) and A. parasiticus, and the aflatoxin nonproducers A. tamarii and A. alliaceus. BGYF was more likely to be visible internally (after cutting open the fig) than externally. For all four species associated with BGYF, some infected figs did not show BGYF. The absence of fluorescence is probably not associated with the fungal strain or isolate involved, since isolating Aspergillus spp. from nonfluorescent figs followed by inoculating other figs with these isolates resulted in BGYF. Many of the nonfluorescent figs had small fungal colonies (<7 mm in diameter), even though some figs with large colonies were also nonfluorescent. The additional colonization of figs by other fungi did not affect the occurrence of BGYF in figs colonized by fungi in Aspergillus section Flavi. Figs infected with A. flavus or A. parasiticus and showing no BGYF were occasionally contaminated with aflatoxin, while other figs showing BGYF and infected with A. flavus or A. tamarii had no aflatoxins. Although not as promising as originally hoped, BGYF might be of use to remove aflatoxin-contaminated figs for certain specific situations in California.
First Report of Premature Boll Rot Associated with Cotton in Louisiana
Authors: McLean K. S. , Lawrence G. W.
Published: May 2007

A premature boll rot has been observed with increasing frequency in association with cotton (Gossypium hirsutum) in the Delta region of Louisiana-Mississippi. The initial developing cotton boll, sepals, and peduncle rapidly become necrotic and mummified. A dark brown to black lesion approximately 1 cm in length develops at the base of the peduncle, extending down the petiole below the diseased cotton boll. The diseased boll and peduncle remain attached to the petiole, hanging by a small portion of peduncle tissue. In an initial survey, the symptomatic boll rot was observed in 95% of the cotton fields in the Delta in 1996. A Phomopsis sp. was isolated from 58% of the diseased bolls, 42% of the cotton boll peduncles, and 52% of the leaf petioles collected from three cotton varieties. Fusarium spp. and Alternaria alternata were isolated from the diseased bolls with a frequency of 18 and 11%, respectively. Phomopsis sp. mycelium is dense, immersed, septate, and hyaline to pale brown in color. Stromata are pulvinate, less than 5 mm in diameter and form in a ring pattern. Pycinidia are erumpet, dark brown to black, separate or aggregated, and globose with ostiolate necks. Conidia are unicellular and hyaline, with alpha conidia oblong-elliptical and biguttulate while beta conidia are filiform and hamate in shape. The ratio of alpha to beta spores varies depending on the age of the culture. Pathogenicity tests with the sterile toothpick inoculation technique were conducted in a field planted with cotton cv. DPL 50. Developing cotton bolls approximately 5 to 8 mm in diameter were inoculated with either sterile toothpicks or toothpicks infested with a Phomopsis sp. Characteristic symptoms identical to the original boll rot were observed on 80% of the inoculated bolls 7 days after inoculation. A Phomopsis sp. was reisolated from the diseased bolls, completing Koch's postulates. No symptoms developed nor was the pathogen reisolated from the controls.
Anemone - an Additional Perennial Ornamental Host of Tobacco Rattle Virus in the U.S.
Authors: Lockhart B. E. , Westendorp J. A.
Published: May 2007

A previous report (1) drew attention to the occurrence in the U.S. of tobacco rattle tobravirus (TRV) in several perennial ornamentals that move freely in international trade. Here we report the occurrence of TRV in an additional host plant of this type. The virus was identified in anemone (Anemone × hybrida cv. Honorine Jobert) with leaf symptoms consisting of chlorotic blotches, chlorotic line patterns, and distortion. Characteristic tobravirus-like particles with modal lengths of 50, 80, 130, and 180 nm were observed by electron microscopy in partially purified extracts of symptomatic but not of asymptomatic plants. These particles reacted specifically with antibodies to TRV and pea early-browning (PEBV) tobraviruses in immunoelectron microscopic (IEM) assays, produced typical TRV-induced symptoms in Nicotiana benthamiana and N. clevelandii, in which similar particles were detected by IEM, but, like other TRV isolates, did not infect pea (2). No other viruslike particles were observed in partially purified extracts of symptomatic anemone plants. This is the first report of TRV infection in anemone. While TRV occurs widely in Europe, it had been identified previously in the U.S. only in Oregon, Washington, and California (1,2,3). This virus is an important pathogen of several crops, including potato. Several areas of the Midwest, including Minnesota and Wisconsin, have significant seed-potato industries, and further introduction and possible dissemination of TRV pose potential regulatory and quarantine issues. This example of the movement of an exotic pathogen of potential economic importance into new areas underlines the need for closer monitoring of plant material entering international trade in an era of increasing globalization.

References: (1) B. E. Lockhart et al. Plant Dis. 79:1249, 1995. (2) B. E. L. Lockhart and H. U. Fischer. Phytopathology 66:1391, 1976. (3) J. M. Crosslin and P. E. Thomas. Am. Potato J. 72:605, 1995.
Seed Transmission of Pantoea stewartii in Field and Sweet Corn
Authors: Block C. C. , Hill J. H. , McGee D. C.
Published: May 2007

Seed transmission of Pantoea stewartii was evaluated by assays of more than 76,000 plants in greenhouse and field grow-out trials. Fourteen P. stewartii-infected seed lots were obtained from two dent corn inbreds and two sweet corn cultivars that were inoculated with either a rifampicin and nalidixic acid-resistant strain (rif-9A) or a wild-type strain (SS104) of P. stewartii. Four additional seed lots were collected from naturally infected inbreds. Percentages of infected kernels ranged from 0.8 to 72%, as determined by agar plating or by individual-kernel enzyme-linked immunosorbent assay (ELISA). Plants grown from this seed were assayed by a stem-printing technique that consisted of cutting and pressing a cross-section of each stem onto agar media. Prints were examined for development of P. stewartii colonies after 24 and 48 h. The transmission rate from seed produced on the inoculated plants was 0.066% (28 of 42,206 plants), based on all seedlings assayed. Transmission was estimated to be 0.14% from infected kernels. The transmission rate from seed produced on naturally infected plants was 0.0029% (1 of 34,924 plants), based on all seedlings, and 0.022% from infected kernels. Seed transmission occurred significantly less often (P = 0.034) from seed produced on naturally infected plants than from seed produced on inoculated plants, probably due to greater kernel damage caused by ear shank inoculation. The rarity of seed transmission of P. stewartii from heavily infected seed lots that would ordinarily be rejected due to poor germination suggests that the likelihood of seed transmission from good quality commercial seed corn is virtually nonexistent.
First Report of Leaf and Stem Rust Caused by Puccinia sherardiana on Sphaeralcea grossulariaefolia in North America and S. munroana in Wyoming
Authors: Briere S. C. , Franc G. D.
Published: May 2007

Diseased samples of globe mallow, Sphaeralcea grossulariaefolia and S. munroana, were submitted by an ornamental seed producer in Wyoming to our Extension Plant Pathology Laboratory in July 1997. Dark brown, amphigenous telia surrounded by chlorotic halos were present on both foliage and stems. Mean teliospore dimensions observed were 30.8 × 44.8 μm. The teliospores germinated readily on water agar at 20°C and formed basidiospores within 24 h. Aecia and uredinia were not found. Based on characteristics mentioned above, this fungus was identified as Puccinia sherardiana Körn (1). This microcyclic rust was previously described on 12 other Sphaeralcea spp. plus other plant species in the Malvaceae family (1,2). Stem and foliar symptoms were reproduced in a greenhouse on 8-week-old plants of S. grossulariaefolia and S. munroana. These plants were inoculated with teliospores removed from the original diseased plant material. Immediately after inoculation, plants were misted and placed in plastic bags and incubated for 36 h at 100% relative humidity and 20°C. Plants continued growth with natural lighting and with day and night temperatures of 20 and 15°C, respectively. Symptoms developed within 12 days with initial telia rupturing the host epidermis 13 days after inoculation. Telia were examined microscopically to complete Koch's postulates.

References: (1) J. C. Arthur. Manual of Plant Rusts in United States and Canada. Hafner Pub., 1962. (2) D. F. Farr et al. Fungi on Plants and Plant Products in the United States. American Phytopatholical Society, St. Paul, MN, 1989.
First Report of Root Rot of Hydroponically Grown Lettuce Caused by Pythium myriotylum in a Commercial Production Facility
Authors: Stanghellini M. E. , Kim D. H. , Rakocy J. , Gloger K. , Klinton H.
Published: May 2007

Commercial cultivation of lettuce (Lactuca sativa L.) under hydroponic conditions was initiated in August 1997 in the U.S. Virgin Islands. One week following transplant into an outdoor growout system, several plants wilted and died. Over the next 2 weeks, approximately 50% of the 30,000 plants died and the remaining plants were severely stunted. Temperature of the nutrient solution ranged from 28 to 30°C. Root specimens received for diagnosis consistently yielded pure cultures of Pythium myriotylum Drechsler. To confirm Koch's postulates, lettuce seedlings were reared hydroponically in a greenhouse. Temperature of the nutrient solution ranged from 27 to 29°C. After 14 days, one plant in each hydroponic chamber (which contained six lettuce plants) was removed and the root system of the plant was placed in a beaker containing approximately 1,000 zoospores of P. myriotylum. After a 30-min incubation period, the artificially inoculated plant was replanted in the hydroponic chamber. Within 5 to 7 days all plants were severely wilted and exhibited extensive root rot. P. myriotylum was consistently reisolated from symptomatic plants. No wilt occurred on respective noninoculated plants. The above study was conducted three times with similar results. Although P. myriotylum has previously been isolated from hydroponically grown lettuce in experimental systems (1), this report demonstrates the destructiveness of this zoosporic pathogen in a commercial hydroponic lettuce production facility. Factors that contributed to the epidemic were an abundance of a susceptible host, a temperature regime optimum for pathogen growth and reproduction, and a mechanism for the rapid dispersal of the pathogen via the recirculating nutrient solution. Although the source of pathogen introduction into the facility is not known, the hydroponic system was located in an open field. Thus, the pathogen could have been introduced aerially via wind-blown dust, rain, or insects. We do know, however, that the transplants were pathogen-free.

Reference: (1) A. C. Schuerger and K. G. Pategas. Phytopathology 74:796, 1984.
Detection of Soilborne Alternaria radicina and Its Occurrence in California Carrot Fields
Authors: Pryor B. M. , Davis R. M. , Gilbertson R. L.
Published: May 2007

Alternaria radicina, causal agent of black rot disease of carrot, was recovered from soil by plating dilutions on a semi-selective medium, A. radicina semi-selective agar. The efficiency of this soil assay was 93% based on recovery of the fungus from non-infested field soil amended with A. radicina conidia. Soilborne A. radicina was recovered from five of six carrot-growing areas in California, but was only commonly found in the Cuyama Valley, where the fungus was detected in 83% of sampled fields. Over a 3-year period of sampling, A. radicina soil populations in Cuyama Valley fields prior to carrot planting ranged from 0 to 317 CFU/g. There was a positive correlation between A. radicina soil populations in these fields and the incidence of black rot disease at harvest. A. radicina was recovered from dry soil after 4 years of storage, and the fungus survived in this soil as solitary conidia or as conidia associated with organic debris.
Variability in Sensitivity to Metalaxyl in vitro, Pathogenicity, and Control of Pythium spp. on Sugar Beet
Authors: Brantner J. R. , Windels Carol E.
Published: May 2007

Pythium ultimum var. sporangiiferum (76 isolates) and P. aphanidermatum (21 isolates) cultured from diseased sugar beet seedlings in Minnesota and North Dakota were tested for sensitivity to metalaxyl, pathogenicity on sugar beet, and disease control by metalaxyl seed treatment. Sensitivity to metalaxyl (effective concentration causing 50% growth inhibition [EC50]) was determined by linear growth on corn meal agar amended with 0, 0.01, 0.1, 1, 10, and 100 μg a.i. metalaxyl ml-1 after 48 h in the dark at 21 ± 1°C. Variation among isolates was significant (P = 0.05) within and between species, and EC50 values averaged 0.16 (range: 0.05 to 1.30 μg ml-1) for P. ultimum var. sporangiiferum and 2.06 (range: 1.19 to 3.12 μg ml-1) for P. aphanidermatum. In pathogenicity tests on sugar beet, most isolates of P. ultimum var. sporangiiferum (72 of 76) and all of P. aphanidermatum significantly (P = 0.05) decreased final stands compared to the noninoculated control. There was no correlation between aggressiveness in the absence of metalaxyl and in vitro sensitivity to metalaxyl. When Pythium-infested soil was planted with seed treated with metalaxyl at the standard (0.625 g a.i. kg-1) or half rate, some isolates that were least sensitive to metalaxyl in vitro resulted in a significant (P = 0.05) reduction in disease control. These results may explain, at least in part, why producers do not attain expected stands when they plant metalaxyl-treated sugar beet seed.
Molecular Diagnosis of Tomato Spotted Wilt Tospovirus Infection of Peanut and Other Field and Greenhouse Crops
Authors: Jain R. K. , Pappu S. S. , Pappu H. R. , Culbreath A. K. , Todd J. W.
Published: May 2007

Tomato spotted wilt tospovirus (TSWV) is a major disease constraint to peanut, tomato, pepper, and tobacco production in Georgia. Rapid molecular diagnosis of TSWV infection in peanut and its molecular studies were severely hampered by the lack of practical and rapid procedures for the extraction and amplification of the genomic nucleic acid. To circumvent this technical constraint, we adapted an immunocapture-procedure (ICP) for enriching the peanut tissue extracts for TSWV, and combined the ICP with a single-buffer, one-tube reverse transcription polymerase chain reaction (RT-PCR) to achieve rapid and reliable amplification of TSWV sequences from peanut. Both leaf and root tissue of peanut provided PCR-quality templates. Immunocapture, RT, and PCR were done in the same tube, allowing higher throughput. The technique was applicable to a wide range of TSWV-susceptible crops such as tomato, pepper, tobacco, gloxinia, and impatiens. Primers derived from the nucleocapsid protein gene as well as from the large RNA of the viral genome were able to amplify the target sequences in a highly specific and reproducible manner. This approach facilitated rapid molecular typing of natural populations of TSWV in Georgia.
Evaluation of Application Methods of Metam Sodium for Management of Fusarium Crown and Root Rot in Tomato in Southwest Florida
Authors: McGovern R. J. , Vavrina C. S. , Noling J. W. , Datnoff L. A. , Yonce H. D.
Published: May 2007

Experiments were conducted during 1992 to 1995 to evaluate the effectiveness of application methods of metam sodium (MS; sodium N-methyldithio-carbamate) for the management of Fusarium crown and root rot (FCRR) caused by Fusarium oxysporum f. sp. radicis-lycopersici in mulched and staked tomatoes (Lycopersicon esculentum Mill.) grown on raised beds in commercial fields in southwest Florida. Efficacy of MS was compared with soil-injection of methyl bromide-chloropicrin (MBC), the current industry practice for production of tomatoes in Flor-ida. The incidence of FCRR was consistently high in nontreated plots (80 to 100%), but disease severity varied by site, and yields were reduced by 10 to 57% at sites with high disease severity when compared to sites treated with MBC at 336 to 448 kg/ha. Application of MBC reduced FCRR incidence in all experiments. Chemigation with MS at 701 or 935 liters/ha into mulched beds using either one or two drip irrigation tubes placed on the soil surface, and soil injection of MS at 935 liters/ha, failed to reduce the disease. The application of MS at 935 liters/ha to the soil surface prior to bed formation produced variable results. Rotovation of MS at the same rate into preformed beds consistently produced reductions in the incidence of FCRR equivalent to those achieved by MBC.
Botrytis Blossom Blight of Southern Blueberries: Cultivar Susceptibility and Effect of Chemical Treatments
Authors: Smith Barbara J.
Published: May 2007

The susceptibility of blueberry flowers at each developmental stage was evaluated by inoculating potted blueberry bushes of the rabbiteye cultivars Climax, Premier, and Tifblue, and the southern highbush cultivars Gulfcoast and Cooper, during bloom with a conidial suspension of Botrytis cinerea and incubating in a dew chamber for 2 days at 20°C and 100% relative humidity. Flower stage was rated at the beginning of each study and at 2 and 4 weeks after inoculation. The efficacy of five fungicides (benomyl, captan, cyprodinil, cyprodinil + CGA173506, and propiconazole) and a surfactant for control of Botrytis blossom blight was evaluated by inoculating Climax and Gulfcoast plants 2 days before or 2 days after treatment with each fungicide. The effect of chemicals used during bloom on the severity of Botrytis blossom blight was evaluated by treating Tifblue and Cooper plants with gibberellic acid, surfactant, and fungicide combinations 1 day prior to inoculation. Botrytis disease symptoms were scored 2 and 4 weeks after inoculation on a visual scale of 0 to 7. Flower susceptibility increased as flower stage at inoculation increased. Tifblue flowers at or near full bloom (stages 5 and 6) at the time of inoculation were very susceptible to Botrytis blossom blight. Flowers treated with benomyl, cyprodinil, and cyprodinil + CGA173506 2 days after inoculation had lower Botrytis severity scores than inoculated flowers not treated with fungicides. Flowers treated with gibberellic acid 1 day prior to inoculation had lower Botrytis scores 2 and 4 weeks later than untreated flowers, while flowers treated with a nonionic surfactant received the same Botrytis severity scores as untreated flowers.
Bacterial Streak and Bulb Rot of Sweet Onion: II. Epiphytic Survival of Pseudomonas viridiflava in Association with Multiple Weed Hosts
Authors: Gitaitis R. , MacDonald G. , Torrance R. , Hartley R. , Sumner D. R. , Gay J. D. , Johnson W. C.
Published: May 2007

A semiselective agar medium (T-5) was used to sample environment and plant material as a habitat for Pseudomonas viridiflava. Soil, irrigation water, soybean foliage, and foliage from various weeds in an onion-growing area were assayed over a 5-year period. P. viridiflava was recovered only as an epiphytic resident from weed species that included cutleaf evening primrose, dandelion, common fumitory, purple cudweed, spiny sowthistle, Virginia pepperweed, and wild radish. The bacterium apparently overseasons in association with these weeds, because its presence was detected prior to, as well as during, the onion-growing season. Preliminary tests indicated that weed control may suppress bacterial streak and bulb rot levels.
First Report of Naemacyclus fimbriatus Infecting Pitch Pine (Pinus rigida)
Authors: Vujanovic Vladimir , St.-Arnaud Marc , Neumann Peterjürgen
Published: May 2007

This is the first report of Naemacyclus fimbriatus (Schwein.) DiCosmo, Peredo & Minter (Rhytismatales) on Pinus rigida, and the first observation of this fungus infecting living needles. N. fimbriatus is known to occur on cone scales of P. brucia, P. halepensis, P. nigra, P. resinosa, and P. sylvestris, as well as fallen needles of P. maritima and P. pinaster, in Europe and North America (1). In September 1997, chlorotic and necrotic second- and third-year needles of pitch pine were observed to have ascomata fruiting bodies that were amphigenous, dark brown to black, immersed to erumpent, circular to subcircular, and 200 to 500 × 150 to 250 μm in size. Asci were club-shaped, eight-spored, and 83 to 98× 8.9 to 9.7 μm. Mature ascospores were phragmo-scolecosporous, 7-septate, and 78 to 91 × 2 to 2.5 μm. From these symptomatic needles, N. fimbriatus was frequently (>70%) isolated on 2% malt agar. In October 1997, fruiting bodies were also observed on dead fallen cones. During the autumn, the fungus produced 1 to 3 brown mycelial cords, 50 to 100 μm in diameter, which grew throughout the litter from the ascomata. The nature of the cords is still unknown. Pitch pine is rare in Québec, and this northernmost population is located about 10 km north of New York State, in the St. Lawrence Valley of Québec. We found that pitch pine was colonized by the fungus in a wide range of edaphic conditions, but more frequently on dry rock outcrops. We believe that unfavorable conditions such as the more than 200 days with frost and thin organic or mineral soil layer may predispose pitch pine to infection by this fungus.

Reference: (1) F. Di Cosmo et al. Mycotaxon 21:1, 1984.