bluuebunny/crossref_metadata_2025 huggingface dataset:
Adult Citrus Leafminers (Phyllocnistis citrella) Are Not Efficient Vectors for Xanthomonas axonopodis pv. citri
Authors: Belasque J. , Parra-Pedrazzoli A. L. , Rodrigues Neto J. , Yamamoto P. T. , Chagas M. C. M. , Parra J. R. P. , Vinyard B. T. , Hartung J. S.
Published: May 2007

Interest in the interaction between the citrus leafminer (Phyllocnistis citrella) and citrus bacterial canker, caused by Xanthomonas axonopodis pv. citri, has increased as a greater incidence and severity of canker-diseased plants was observed in groves infested with the citrus leafminer. To determine whether adults of the citrus leafminer could act as vectors of citrus canker, we investigated two potential mechanisms for direct spread by leafminer adults using experimental microcosms. First, adult leafminers were raised on canker-infected foliage and were allowed to mate and lay eggs on healthy plants. These plants then were observed for development of citrus canker symptoms. In a second set of experiments, adults raised on healthy plants were given free access to canker-diseased plants during the period in which they mated and laid eggs on healthy plants. In all, 3,119 mines were produced by developing larvae on a total of 2,384 leaves examined for citrus canker symptoms. No symptoms of citrus bacterial canker disease were observed on any of the healthy test plants in 37 independent experimental trials conducted to test these two potential mechanisms of spread of citrus canker, and the pathogen was not recovered from insects exposed to symptomatic Rangpur lime plants. The upper limit on the rate of transmission was estimated to be less than 0.2% per oviposition event based on the binomial probability distribution. However, when adult P. citrella insects were artificially contaminated with high levels of X. axonopodis pv. citri, transmission to Rangpur lime plants with the induction of citrus canker was observed. This suggests that the ability of P. citrella to transmit X. axonopodis pv. citri is limited by the rate at which it can acquire inoculum from infected plants. The results support the conclusion that adult citrus leafminers are not efficient vectors for citrus canker bacteria, and the disease is unlikely to be spread this way.
Breeding for Resistance to Soybean Rust
Authors: Hartman Glen L. , Miles Monte R. , Frederick Reid D.
Published: May 2007

Soybean rust occurs in all major soybean-growing regions of the world including the North American mainland. Soybean rust, caused by Phakopsora pachyrhizi, is the most destructive foliar disease of soybean, and yield losses of over 50% are common when environmental conditions are conducive for disease development. Heavily infected plants defoliate and mature more rapidly than plants not infected with rust. P. pachyrhizi has a broad host range and can infect many other legumes including some native to Australia. A number of physiological races of the fungus have been reported on these native legumes from Australia and on soybean. In addition, four single genes for rust resistance were previously identified in four different soybean plant introductions. These sources of resistance also have been reported to be susceptible in some field locations and when challenged with certain isolates of P. pachyrhizi. Partial resistance, expressed as reduced pustule number and increased length of latent period, has also been reported but has not been widely used in breeding programs. Yield stability has been used in the past and compares percentage of yields in fungicide and nonfungicide plots. Cultivars or lines with a higher percentage of yield have greater yield stability in the presence of rust. Although soybean rust only recently was found in the continental United States, a proactive project to evaluate the USDA soybean germ plasm collection for rust resistance was initiated in 2002 at the Fort Detrick plant biocontainment facility and at six international locations. Part of this project is to discover soybean lines with greater yield stability, and additional single and partial resistance. To help minimize the impact of soybean rust, the first line of defense will be fungicides, with host resistance and yield stability augmenting the long-term management of soybean rust.
Epidemics of Soybean Rust (Phakopsora pachyrhizi) in Brazil and Paraguay from 2001 to 2003
Authors: Yorinori J. T. , Paiva W. M. , Frederick R. D. , Costamilan L. M. , Bertagnolli P. F. , Hartman G. E. , Godoy C. V. , Nunes J.
Published: May 2007

In 5 March 2001, a severe rust outbreak was recorded at Pitapó, Paraguay, and the causal organism was determined to be Phakopsora pachyrhizi using polymerase chain reaction (PCR) and DNA sequence analysis. In May, rust surveys showed spread throughout most of Paraguay and into western and northern Parana, Brazil. In the 2001-02 season, rust was widespread in Paraguay, but losses were reduced due to severe drought; however, in Brazil it spread to more than 60% of the soybean acreage, causing field losses estimated at 0.1 million metric tons (MMT). In 2003, the disease was observed in more than 90% of the fields in Brazil, and the projected losses in Mato Grosso and Bahia alone are 2.2 MMT (US$487.3 million). Approximately 80% of the soybean acreage in Brazil was sprayed twice with fungicides at the cost of US$544 million. Differences in efficacy have been observed among the commercial strobilurin and triazol fungicides.
First Report of Downy Mildew Caused by Peronospora sp. on Basil (Ocimum basilicum) in France
Authors: Garibaldi A. , Minuto A. , Gullino M. L.
Published: May 2007

Sweet basil (Ocimum basilicum) is an economically important herb in several Mediterranean countries. Approximately 30 ha are grown annually in France for fresh and processed consumption. During the spring and fall of 2004, a damaging foliar disease was observed in some crops near Saint Tropez in the French Riviera Region. More than 50% of plants were affected in an organically produced field-grown crop at an altitude of 250 m. Leaves of infected plants were initially slightly chlorotic, especially near the central vein. Within 2 to 3 days, a characteristic gray, furry growth was evident on the lower leaf surface and sometimes on the upper leaf surface. The appearance and severity of the disease was affected by overhead sprinkler irrigation. Basal leaves were severely affected. Microscopic observations revealed sporangiophores branching two to seven times. Sporangiophores, with a length of 250 to 500 μm (average 350 μm), ended with sterigmata bearing single sporangia. Sporangia measured 15 to 25 × 20 to 35 μm (average 22 × 28 μm), were elliptical and grayish in mass. The pathogen was identified as Peronospora sp. on the basis of its morphological characteristics (4). Pathogenicity was confirmed by inoculating leaves of 40-day-old healthy plants with a sporangial suspension (1 × 105 conidia/ml). Three containers with 150 plants each of O. basilicum cv Genovese gigante were used as replicates. Noninoculated plants served as controls. Plants were maintained in a growth chamber at 20°C (12 h of light per day) and 90 to 95% relative humidity. The pathogenicity test was carried out twice. After 6 days, typical symptoms of downy mildew developed on the inoculated plants, and Peronospora sp. was observed on the leaves. Noninoculated plants did not show symptoms. To our knowledge, this is the first report of Peronospora sp. on basil in France. Peronospora sp. was previously reported on sweet basil in Italy (1) and P. lamii on sweet basil in Uganda (3). Seed transmission (2) is suspected as the reason for recent outbreaks in Europe.

References: (1) A. Garibaldi et al. Plant Dis. 88:312, 2004. (2) A. Garibaldi et al. Z. Pflanzenkr. Pflanzenschutz 111:465, 2004 (3) C. G. Hansford. Rev. Appl. Mycol. 12:421, 1933. (4) D. M. Spencer. The Downy Mildews. Academic Press, NY, 1981.
First Report of White Mold Caused by Sclerotinia sclerotiorum on Echium (Echium vulgare)
Authors: del Río L. E. , Bradley C. A. , Johnson B. L.
Published: May 2007

Echium, also known as common viper's bugloss, is a member of the botanical family Boraginaceae. Echium is being evaluated for its potential use as an oilseed crop in North Dakota. In 2003, 40% of echium plants in a field in Cass County were observed showing classical symptoms of infection by Sclerotinia sclerotiorum. Plants in advanced stages of infection were dead. Stems of dead plants peeled off easily when touched and numerous cylindrical, black sclerotia that were 2 to 3 mm in diameter and 4 to 7 mm long were found in the pith. Younger stem lesions were watery soft, many of them with a white cottony growth on them. Sclerotia and infected stem tissues collected from the field were surface disinfested in a 0.5% NaOCl solution for 30 s, rinsed with sterile distilled water, and air dried before plating on potato dextrose agar (PDA). Samples were incubated at room temperature for 1 week. White mycelium and black sclerotia, characteristic of S. sclerotiorum (Lib.) de Bary, were produced in all dishes. Koch's postulates were fulfilled using the petiole inoculation technique (2). Briefly, 4-mm agar plugs containing hyphal tips of a 2-day-old S. sclerotiorum colony growing on PDA were excised and loaded in the wide opening of 100-μl pipette tips. The second true leaf of 15 3-week-old echium seedlings, growing in plastic pots containing Ready-Mix soil, was cut off with a razor blade leaving an approximately 25-mm long petiole attached to the stem. The leafless petioles of 10 seedlings were capped with a loaded pipette, agar plug first, until the petiole tip broke the inner surface of the plug and the petiole came in contact with the mycelium. The other five seedlings were inoculated with agar plugs without mycelium and used as control plants. Three days after inoculation, all seedlings inoculated with S. sclerotiorum wilted and expressed symptoms similar to those observed in the field. None of the control plants showed symptoms of infection. Black sclerotia were retrieved from infected stems 2 weeks after inoculation, and the pathogen was successfully reisolated onto PDA. Several important North Dakota crops are susceptible to S. sclerotiorum. The identification of echium as a new host for S. sclerotiorum should be considered in the event that this crop is promoted as an alternative for North Dakota agriculture. To our knowledge, this is the first report on the susceptibility of echium to S. sclerotiorum. Other members of the Boraginaceae have been identified as hosts for this pathogen (1).

References: (1) G. J. Boland and R. Hall. Can. J. Plant Pathol. 16:93, 1994. (2) L. E. del Río et al. (Abstr.) Phytopathology 91 (suppl.):S176, 2001.
First Report of the Stubby-Root Nematode Paratrichodorus teres Associated with Artichoke (Cynara scolymus) in Greece
Authors: Karanastasi E. , Decraemer W. , Kyriakopoulou P. E. , Neilson R.
Published: May 2007

The polyphagous stubby-root nematode species, Paratrichodorus teres (Hooper) Siddiqi, was first described from soil under lettuce near Norwich, UK and subsequently reported from South Africa and the United States, but predominantly from temperate regions within Europe (4). P. teres is one of 13 economically important trichodorid species known to be vectors of Tobacco rattle virus (TRV) (4). Artichokes planted during 2000 in a field located in the Kandia area of the Argolis Region, Greece (37°32′N, 22°56′E) exhibited symptoms of a virus infection. Sampling was done to ascertain the presence of Longidorus fasciatus, a vector of artichoke Italian latent nepovirus known to occur in the area (1,4). In addition to L. fasciatus, an unknown trichodorid species and Tylenchorhyncus sp. were recovered from the root zone of artichoke at a number of sites within the field. Measurements and morphological examination of the female (n = 13, body length = 741.7 ± 25.5 μm, onchiostyle = 43.7 ± 0.8 μm, and position of vulva from anterior region relative to total body length V% = 53.8 ± 0.4 μm) and male (n =1, body length = 720.5 μm, onchiostyle = 43.5 μm, spicule length = 51.7 μm, and number of ventromedian precloacal supplements = 3) trichodorids isolated from soil samples conformed to the original description of P. teres and the generic polytomous key (2). Furthermore, morphological identification was supported by molecular data. DNA was extracted from seven individual trichodorids, each of which were placed into separate 0.5-ml micro-centrifuge tubes containing 20 μl of 0.25 M NaOH and incubated at 25°C overnight. Thereafter, samples were incubated at 99°C for 3 min and 10 μl of 0.25 M HCl, 5 μl of 0.5 M Tris-HCl, (pH 8.0) and 5 μl of 2% Triton X-100 were added to each tube. Samples were incubated at 99°C for a further 3 min and stored at -20°C. Template DNA was amplified using polymerase chain reaction with primers specific for 18S rDNA and sequenced (3). The resultant consensus sequence had 99.8% homology to P. teres populations isolated from Portugal and good homology (95 to 98%) with five other Paratrichodorus spp. listed on public sequence databases, e.g., NCBI GenBank. This constitutes a new geographic record and a possible association of P. teres on artichoke.

References: (1) D. J. F. Brown et al. Eur. J. Plant Pathol. 103:501, 1997. (2) W. Decraemer. Fundam. Appl. Nematol. 21:37, 1998. (3) C. M. G. Oliveira et al. J. Nematol. 36:153, 2004. (4) C. E. Taylor and D. J. F. Brown. Nematode Vectors of Plant Viruses, CAB International Mycological Institute, Wallingford, UK, 1997.
First Report of Powdery Mildew Caused by Golovinomyces orontii on Corn-Salad in the United States
Authors: Koike S. T. , Saenz G. S.
Published: May 2007

Corn-salad or lamb's lettuce (Valerianella locusta) is a specialty leafy green, annual vegetable that is grown commercially in California for use in salads. During the summer (June through August) of 2004, field plantings in coastal California (Monterey County) showed symptoms and signs of a powdery mildew. White, ectophytic mycelia and conidia were present on leaves and petioles. Extensively colonized leaves were slightly twisted and later developed a tan necrosis. Mycelial growth was spread out, flat, sometimes dense, and colonized both sides of the leaf. Growth was more extensive on the upper leaf surfaces. Hyphae were 5 to 7.5 μm wide with nipple-shaped appressoria. Conidiophores were straight and had foot cells that were simple, mostly curved, measured 50 to 65 × 10 to 12.5 μm, and followed by two to three cells of equal size. Conidia developed in short chains. Conidia were cylindric to doliform, measured 27.5 to 32.5 × 15 to 17.5 μm, and lacked fibrosin bodies. Conidial length-to-width ratios were usually less than or equal to 2.0. Conidia germinated at the ends (cichoracearum-type) and had germ tube lengths that ranged from short to 1.0 to 1.5 times the length of the conidium; germ tubes had swollen tips. Cleistothecia were not observed. On the basis of these characteristics, the fungus is identified as Golovinomyces (Erysiphe) orontii(Cast.) Heluta (1). To demonstrate pathogenicity, heavily colonized corn-salad leaves from commercial plantings were collected and gently pressed onto leaves of potted corn-salad plants. Plants were then maintained in a greenhouse (22 to 24°C). After 8 to 10 days, symptoms and signs of powdery mildew developed on the foliage of inoculated plants, and the pathogen morphology matched that of the originally observed pathogen. Noninoculated control plants did not develop powdery mildew. To our knowledge, this is the first report of powdery mildew of corn-salad caused by G. orontii in the United States. This corn-salad disease has been reported from a number of countries in Europe (2). Because the presence of powdery mildew on the harvested foliage made the leaves unmarketable, part of the crop could not be sold.

References: (1) U. Braun. Nova Hedwigia 89:1, 1987. (2) U. Braun. The Powdery Mildews (Erysiphales) of Europe. Gustav Fischer Verlag, Jena, Germany, 1995.
First Demonstration of Koch's Postulates for Lasiodiplodia theobromae Fruit Spot on Eggplant (Solanum melongena)
Authors: Woodward J. E. , Langston D. B. , Brock J. H. , Kemerait R. C. , Brenneman T. B. , Beard G. H.
Published: May 2007

During October 2004, diseased eggplant fruit from a commercial farm in Colquitt County, Georgia, developed circular, tan, water-soaked lesions. Gray, septate mycelia quickly covered the fruit. Diseased fruit became shriveled, spongy, and mummified. Disease incidence in the field was approximately 1%. Lasiodiplodia theobromae (Pat.) Griffon & Maubl. (synonym Botryodiplodia theobromae Pat.) (2) was isolated from the margins of lesions and cultured on acidified potato dextrose agar. The fungus produced grayish colonies with aerial hyphae and black ostiolate pycnidia massed into stroma. Mature elliptical conidia (25.8 × 15.6 μm) were brown, had a single septation, and longitudinal striations. Isolates obtained from peanut and pecan were included in the pathogenicity tests. Mature fruit cv. Nightshade were surface disinfested for 30 s in 70% ethanol, followed by 60 s in 0.5% sodium hypochlorite, rinsed twice in sterile distilled water, and allowed to dry. Inoculations were made by placing an agar plug containing L. theobromae mycelial side down on the surface of the fruit or wounding with a sterile toothpick containing mycelium of the fungus. Fruit similarly inoculated with agar plugs or sterile toothpicks served as controls. There were a total of three replicates. Fruit were placed in plastic containers lined with moistened paper towels. Containers were placed in a dew chamber and incubated (28°C, relative humidity >95%) for 3 days, and then evaluated. Symptoms identical to those observed on naturally infected fruit developed on inoculated fruit. Controls remained disease free. L. theobromae was reisolated from all symptomatic tissue, satisfying Koch's postulates. Disease damage on wounded fruit was twice that of nonwounded fruit. However, seven of nine inoculations with agar plugs containing L. theobromae resulted in infection. Lesion lengths from wound inoculations were 9.8, 7.3, and 5.2 cm for isolates from peanut, pecan, and eggplant, respectively. Generally, L. theobromae is considered a facultative wound pathogen or a secondary invader (3). However, this study suggests that direct infection can occur. Although fruit spot has been reported previously on eggplant (1), to our knowledge, this is the first report verifying L. theobromae as the causal agent.

References: (1) S. A. Alfieri et al. Index of Plant Diseases in Florida. Fla. Dep. Agric. Consum. Serv. Bull. 11, 1984. (2) H. L. Barnett and B. B. Hunter. Illustrated Guide of Imperfect Fungi. 4th ed. The American Phytopathological Society St. Paul, MN, 1998. (3) P. M. Phipps and D. M. Porter. Plant Dis. 82:1205, 1998.
First Report of Anthracnose Caused by Colletotrichum orbiculare f. sp. from A. officinalis of Marsh Mallow (Althaea officinalis) in Switzerland
Authors: Michel V. V.
Published: May 2007

Marsh mallow is cultivated in Switzerland for the production of candies of an internationally known brand. Since 2000, important losses have been caused by a new disease with typical anthracnose symptoms, i.e., dark lesions on leaves and stems including stem girdling and wilting, especially after abundant rainfall in the spring and summer. In older lesions with a clear center, black dots appeared and setae were observed with a dissecting microscope. When incubated with high relative humidity, abundant, pink spore masses were produced. During 2002, spores were isolated on potato dextrose agar (PDA) containing an antibiotic, and the size of the conidiospores and setae produced in acervuli were measured. Artificial inoculation of a range of potential host plants including Althaea officinalis, A. rosea (hollyhock), Lavatera trimestris, Malva alcea, M. crispa, M. moschata, M. silvestris, Fragariae × ananassa (strawberry), and Hypericum perforatum (St. John's-wort) was carried out in a glasshouse. A spore suspension of 106 spores per ml was sprayed on plants at the 4- to 6-leaf stage until runoff. High temperature (30/20°C, day/night) and relative humidity (>95%) was maintained for 2 weeks after which the plants were inspected visually for the occurrence of disease symptoms. Althaea officinalis, A. rosea, and M. alcea showed typical anthracnose symptoms and were considered as host plants after reisolation of the pathogen from lesions. On the basis of the restricted host range and form and size of the conidiospores (length of 10 to 13 μm and width of 3 to 4 μm), and setae (length of 62 to 75 μm), the pathogen was identified as Colletotrichum orbiculare f. sp. from A. officinalis (1). During 2003, a laboratory investigation was conducted to determine whether C. orbiculare f. sp. from A. officinalis is seed transmitted in marsh mallow. The appearance of the disease in marsh mallow fields simultaneously in several regions of Switzerland, where all growers plant the same variety from the same seed source, instigated this work. Seeds from this variety were tested on CGPIM, a semiselective medium for the isolation of Colletotrichum spp. (2). Per seed lot, 400 grains were placed on CGPIM, and C. orbiculare f. sp. from A. officinalis was found in 15% of seeds harvested from a highly diseased plant. Detection in commercial seed was hindered by extensive contamination with Alternaria spp. and Fusarium spp., but nevertheless, C. orbiculare f. sp. from A. officinalis could be found at low frequency (1%). The occurrence of Colletotrichum malvarum on marsh mallow was recently described in Europe (3), but to our knowledge, this is the first observation of seed transmission of C. orbiculare f. sp. from A. officinalis on marsh mallow seeds.

References: (1) J. A. Bailey et al. Phytopathology 86:1076, 1996. (2) J. B. Manandhar et al. Plant Dis. 79:376, 1995. (3) L. Tosi et al. Plant Dis. 88:425, 2004.
Verticillium Wilt of African Daisy (Osteospermum sp.) in Italy Caused by Verticillium dahliae
Authors: Garibaldi A. , Minuto A. , Gullino M. L.
Published: May 2007

During the winter of 2004, container-grown African daisy (Osteospermum sp.) plants, cv Seaside, showing symptoms of a wilt disease were observed in an open field in Albenga located in northern Italy. Symptoms were first observed on 120-day-old plants grown in a peat/composted bark/clay/pumice (50:20:10:20) substrate. The vascular tissues of affected plants appeared brown. These plants were stunted and developed yellow leaves with brown or black streaks in the vascular tissue. Verticillium dahliae was consistently and readily isolated from symptomatic vascular tissue when cultured on potato dextrose agar. Healthy rooted plants (40-day-old cv Seaside) were inoculated by root dip with a conidial suspension (5 × 107 CFU/ml) from one of three isolates of V. dahliae isolated from infected plants and transplanted into pots filled with steam-sterilized soil. Noninoculated plants served as control treatments. Plants (10 per treatment) were grown in a glasshouse at an average temperature of 25°C. First wilt symptoms and vascular discoloration in the roots, crown, and veins developed within 15 days on each inoculated plant and become very evident after 50 days. Noninoculated plants remained healthy. V. dahliae was consistently reisolated from inoculated plants. The pathogenicity test was conducted twice. To our knowledge, this is the first report of V. dahliae on Osteospermum sp. in Italy and in Europe. Verticillium wilt has been previously reported on O. fruticosum in California (1).

Reference: (1) A. M. French. California Plant Disease Host Index. Calif. Dep. Food Agric. 1989.
Integration of Biological Control Agents and Systemic Acquired Resistance Inducers Against Bacterial Spot on Tomato
Authors: Obradovic A. , Jones J. B. , Momol M. T. , Olson S. M. , Jackson L. E. , Balogh B. , Guven K. , Iriarte F. B.
Published: May 2007

Two strains of plant growth-promoting rhizobacteria, two systemic acquired resistance inducers (harpin and acibenzolar-S-methyl), host-specific unformulated bacteriophages, and two antagonistic bacteria were evaluated for control of tomato bacterial spot incited by Xanthomonas campestris pv. vesicatoria in greenhouse experiments. Untreated plants and plants treated with copper hydroxide were used as controls. The plant growth-promoting rhizobacteria or a tap water control were applied as a drench to the potting mix containing the seedlings, while the other treatments were applied to the foliage using a handheld sprayer. The plant growth-promoting rhizobacteria strains, when applied alone or in combination with other treatments, had no significant effect on bacterial spot intensity. Messenger and the antagonistic bacterial strains, when applied alone, had negligible effects on disease intensity. Unformulated phage or copper bactericide applications were inconsistent in performance under greenhouse conditions against bacterial spot. Although acibenzolar-S-methyl completely prevented occurrence of typical symptoms of the disease, necrotic spots typical of a hypersensitive reaction (HR) were observed on plants treated with acibenzolar-S-methyl alone. Electrolyte leakage and population dynamics experiments confirmed that acibenzolar-S-methyl-treated plants responded to inoculation by eliciting an HR. Application of bacteriophages in combination with acibenzolar-S-methyl suppressed a visible HR and provided excellent disease control. Although we were unable to quantify populations of the bacterium on the leaf surface, indirectly we determined that bacteriophages specific to the target bacterium reduced populations of a tomato race 3 strain of the pathogen on the leaf surface of acibenzolar-S-methyl-treated plants to levels that did not induce a visible HR. Integrated use of acibenzolar-S-methyl and phages may complement each other as an alternative management strategy against bacterial spot on tomato.
Impact of Stale Seedbed Production on Seedling Diseases in Cotton
Authors: Colyer P. D. , Vernon P. R.
Published: May 2007

Cotton production using conservation tillage practices has increased in the past decade. Most studies involving reduced tillage have shown a reduction in plant populations, which has been attributed to seedling diseases. Although most of these studies have focused on no-till production, cotton planted in the mid-south is often planted using stale seedbeds. The objective of this research was to compare the effect of stale seedbed production and conventional tillage with and without in-furrow fungicides on the incidence and severity of seedling diseases. Tillage systems were established in the fall to focus on the effect of tillage on inoculum density and distribution and to minimize differences in the soil environment between tillage treatments. From 1998 to 2001, cotton was planted and seedling disease was evaluated by counting surviving plant populations, estimating stand uniformity, and conducting root and hypocotyl disease indices. Soil populations of Pythium spp. and Rhizoctonia spp. were also estimated. Plant populations were significantly different between tillage treatments in 1998 and between in-furrow treatments in 2000. Skip variables were not different in any year. Soil populations of Rhizoctonia spp. were highly variable and not significantly different among treatments in any year. Populations of Pythium spp. were higher in stale seedbed plots in 2000 and 2001. There were no differences in seed cotton yield in any year. In this study, stale seedbed production increased the incidence and severity of seedling diseases of cotton in only one of four years, but the disease was effectively managed with the application of in-furrow fungicides. These results indicate that the potential for an increase in seedling diseases associated with stale seedbed production is minimal and is not sufficient to overlook the potential benefits of this tillage system.
Phlyctema vagabunda Causes Coin Canker of Ash (Fraxinus spp.) in North America
Authors: Putnam M. L. , Adams G. C.
Published: May 2007

During the spring of 2001, nursery-grown ash trees in Michigan and Ontario, Canada displayed coin cankers that were previously described (1). Cankered cultivars included Cimmaron®, ChampTree®, and Urbanite® (Fraxinus pennsylvanica), and Autumn Purple® (F. americana). Tissue from surface-sterilized cankers (0.06% sodium hypochlorite or 70% ethanol, 3 min) was placed onto one-half strength potato dextrose agar amended with 200 ppm of streptomycin sulfate (½ SPDA). Plates were incubated at 20 and 4°C in the dark. Phlyctema vagabunda (anamorph of Neofabraea alba (E.J. Guthrie) Verkley, (1999)) was isolated on the 4°C plates from most tissue pieces from all cultivars. P. vagabunda causes stem cankers of apple (Malus spp.) (1) but its pathogenicity to ash has never been demonstrated (2). Inoculations with P. vagabunda were made to green and white ash to fulfill Koch's postulates. Apple trees were also inoculated with the ash isolate. In Corvallis, OR, 2-year-old, bare-root ash trees and 15 1-year-old apple seedlings were inoculated in January, 2003. In Michigan, 10 trees each of cvs. Cimmaron® and Autumn Purple® were inoculated in December, 2002. The trees were inoculated with a wound-freezing method (3). Wounded sites received a 5-mm-diameter plug of ½ SPDA on which a 30-day-old culture derived from a single conidium of P. vagabunda AR3664 was actively growing, with sterile ½ SPDA used as a negative control. The plugs were held in place with Parafilm. Each ash in Oregon received three inoculations per stem. Six trees each of cvs. Autumn Purple®, ChampTree®, and Urbanite® and four trees of cv. Cimmeron® were inoculated with the fungus. Four additional trees of each cultivar were treated with sterile ½ SPDA (three sites per tree). Ten seedling apple trees were also inoculated with the fungus (three sites per tree) and five additional trees (five sites per tree) were inoculated with negative control plugs. In Michigan, each tree received two plugs of inoculum and two negative control plugs. All trees were evaluated 4 to 6 months after inoculation. Cankers similar to the originals formed on all ash cultivars in Oregon and Michigan; 97 of 106 inoculated wounds developed cankers on ash, and 29 of 30 inoculated wounds on Malus spp. developed cankers. P. vagabunda was recovered from cankers on each of the inoculated ash and apple trees. Five of 88 controls developed necrotic areas, but Phlyctema spp. were not recovered from any of these wounds. To our knowledge, this is the first report that P. vagabunda causes cankers on Fraxinus spp. and the first to show that Malus spp. can be infected with an ash isolate.

References: (1) T. D. Gariépy et al. Mycol. Res. 107:528, 2003. (2) A. Y. Rossman et al. Plant Dis. 86:442, 2002. (3) R. Scorza and P. L. Pusey. Phytopathology 74:569, 1984.
Safflower: A New Host of Cercospora beticola
Authors: Lartey R. T. , Caesar-TonThat T. C. , Caesar A. J , Shelver W. L. , Sol N. I. , Bergman J. W.
Published: May 2007

Safflower is an oilseed crop adapted to the small-grain production areas of the western Great Plains, including the Northern Plains Area (NPA). In the NPA, safflower production is being evaluated for potential rotation with sugar beet. Safflower is susceptible to Cercospora carthami, whereas sugar beet is susceptible to C. beticola C. carthami has not been observed on safflower in the NPA but C. beticola is ubiquitous on sugar beet. Observation of unusual leaf spots on irrigated safflower cv. Centennial at Sidney, MT prompted this investigation of safflower as a potential alternate host of C. beticola. Safflower plants were inoculated with four isolates of C. beticola (C1, C2, Sid1, and Sid2) and incubated in growth chambers; leaf spot symptoms appeared between 3 and 4 weeks later. Polymerase chain reaction (PCR) amplification of extracts from lesion leaf tissue with C. beticola-specific primers produced fragments comparable with amplified fragments from purified cultures of control C. beticola. PCR assay of cultures of single spores from diseased safflower leaf lesions also produced fragments comparable with fragments from C. beticola cultures. Antibody that was raised from isolate C2 also bound to antigens from the single-spore cultures of the four C. beticola isolates. Inoculum from single-spore cultures from infected safflower also infected sugar beet and produced typical Cercospora leaf spot symptoms. Assay of these leaf lesions by PCR resulted in amplification of target fragments with the C. beticola-specific primers. Our results demonstrate that safflower is a new host of C. beticola.
Analysis of 16S rDNA Sequences from Citrus Huanglongbing Bacteria Reveal a Different “Ca. Liberibacter” Strain Associated with Citrus Disease in São Paulo
Authors: Coletta-Filho H. D. , Takita M. A. , Targon M. L. P. N. , Machado M. A.
Published: May 2007

Citrus huanglongbing (HLB, ex greening) is one of the most serious and destructive citrus diseases in the world. It is caused by a phloem-limited and nonculturable bacterium, “Candidatus Liberibacter”. The disease occurs in some Asian and African countries and recently has been reported in the state of São Paulo, Brazil. Analysis of the 16S ribosomal (r)DNA of the HLB bacteria from orchards in São Paulo revealed the presence of two distinct strains of “Ca. Liberibacter”. One of them, named LSg1 (Liberibacter sequence group 1), was 100% identical to strains from Japan (GenBank accessions AB038369 and AB008366), the Asian forms of the bacteria. The other, LSg2, is genetically distant from the Asian (96.1 to 96.3% identity) and African (95.8 to 96.1% identity) strains. Comparison of the 16S rDNA sequences from the LSg2 and the Asian strain revealed the presence of INDELs and point mutations. Specific primers designed for this Brazilian Liberibacter strain revealed that it is more widely distributed throughout the São Paulo orchards compared with the LSg1 strain. The HLB symptoms caused by both strains are almost identical and, interestingly, both strains were found in the same sample, revealing mixed infection in a citrus plant.
Bacterial Blight in Carrot Seed Crops in the Pacific Northwest
Authors: du Toit Lindsey J. , Crowe Fred J. , Derie Mike L. , Simmons Rhonda B. , Pelter Gary Q.
Published: May 2007

Carrot (Daucus carota subsp. sativus) seed crops in Oregon and Washington were surveyed in 2001-02 and 2002-03 for development of Xanthomonas campestris pv. carotae, causal agent of bacterial blight. For each state and season, 20 plants were sampled from each of 7 to 12 direct-seeded crops twice in the fall or winter and three times from spring to summer; and from each of 2 to 4 steckling (root-to-seed) crops three times from spring to summer. X. campestris pv. carotae was detected in 1 of 15 and 6 of 32 stock seed lots planted in the fall in Oregon and Washington, respectively, and in 2 of 6 steckling shipments planted in each state in the spring. The pathogen was detected at 102to 108CFU/g foliage in 1 of 22 and 10 of 14 direct-seeded crops within 2 months of planting in 2001 and 2002, respectively. The prevalence of X. campestris pv. carotae then increased through the season in most seed crops, although bacterial blight symptoms were not observed until April in Oregon and July in Washington in both seasons. In August 2002 and 2003, X. campestris pv. carotae was detected in all 10 and 13 crops surveyed in Oregon, respectively; and in 11 of 12 and 7 of 10 crops in Washington, respectively. The pathogen was typically less prevalent in steckling versus direct-seeded crops. X. campestris pv. carotae was detected in 20 of 22 and 19 of 23 harvested seed lots in Oregon and Washington, respectively, at populations ranging from 1.3 × 101to 1.4 × 108CFU/g seed. Airborne X. campestris pv. carotae, detected ≤1,600 m downwind of crops being threshed in Oregon in September of 2003 and 2004, may provide a source of inoculum for newly planted seed crops between overlapping biennial seasons for carrot seed production. Despite the prevalence of this pathogen in the Pacific Northwest, carrot seed lots free of X. campestris pv. carotae were detected, demonstrating the ability to produce clean seed in this region by adhering to recommended practices for management of bacterial blight.
First Report of Soybean Rust Caused by Phakopsora pachyrhizi in Uruguay
Authors: Stewart S. , Guillin E. A. , Díaz L.
Published: May 2007

Phakopsora pachyrhizi is a fairly new pathogen in South America and has become a serious threat for soybean production in the region (3). During May 2004, soybean (Glycine max) leaves with rust symptoms were observed on an experimental trial at La Estanzuela, National Institute for Agricultural Research in Colonia, southwestern Uruguay, on late-maturing genotypes (R7 stage). Small, necrotic, reddish brown lesions, suggestive of soybean rust, were detected on the upper surface of leaves. Uredinia and urediniospores were found on the underside of the leaves. The National Service of Plant Health (DGSA) was informed immediately. There the genus Phakopsora was confirmed on the basis of urediniospore morphology. These spores were minutely equinulated and measured 21 × 26.3 μm (range 18 to 24 and 22 to 30 μm, respectively), which was within the range described by Ono et al. (2). Leaf samples showing rust symptoms were submitted to the Instituto Ewald A. Favret (Instituto Nacional de Tecnología Agropecuaria, Argentina) for polymerase chain reaction assay using primer pairs Ppa1/Ppa2 (P. pachyrhizi) and Pme1/Pme2 (P. meibomiae) (1). Results showed P. pachyrhizi as the causal agent of soybean rust, while P. meibomiae tests yielded negative results. Pathogenicity tests were carried out on 10 V4 soybean plants, cv. Don Mario 5800, grown in the greenhouse at 20 to 22°C and a 14-h photoperiod. Urediniospores were collected with a cyclone spore collector into glass tubes, which were then filled with nonphytotoxic light industrial oil. Spore suspension was atomized onto eight plants, while two plants were sprayed only with oil as controls. Plants were placed in a dew chamber at 20°C and 100% relative humidity for 20 h and then returned to prior conditions. Symptoms of the disease were reproduced 10 days after inoculation. Two or three sporulating uredinia were observed only on the inoculated plants. Soybean rust caused by P. pachyrhizi was officially recognized as present in Uruguay in August 2004.

References: (1) R. D. Frederick et al. Phytopathology 92:217, 2002. (2) Y. Ono et al. Mycol. Res. 96:825, 1992. (3) J. T. Yorinori. Page 447 in: Proc. World Soybean Res. Conf. 7th, 2004.
First Report of Sclerotinia Stem Rot and Death of Osteospermum spp. Hybrid Cultivars Caused by Sclerotinia sclerotiorum in Louisiana
Authors: Holcomb G. E.
Published: May 2007

Osteospermum spp. Hybrids, belong to Asteraceae, commonly called African daisy or cape daisy with over 214 named cultivars, are popular flowering plants grown as winter landscape plants in southern Louisiana. During January of 2005, plants growing in a wholesale nursery using polyethylene-film-covered greenhouses were observed with symptoms of wilt that began with tan stem lesions and progressed to stem rot, wilt, and plant death. Plants had been purchased out-of-state as rooted cuttings and transplanted to a commercial bark potting mix in 11.4-cm (4.5-in.) plastic pots. Signs of fungal infection included the presence of white cottony mycelium and black sclerotia. Disease incidence was 50% on cv. Soprano White but less than 1% among the four other cultivars being grown (Ostica Blue Eye, Ostica Pink, Lemon Symphony, and Soprano Purple). Differences in disease incidence among cultivars may have been due to differences in susceptibility since all were grown on the same greenhouse bench. Sclerotinia sclerotiorum was consistently isolated from sections of diseased stems that had been surfaced disinfested (30 to 60 s in 70% ethyl alcohol) and placed on acidified potato dextrose agar. Inoculum for pathogenicity tests consisted of mixed mycelia and sclerotia that had been grown on twice-sterilized wheat grain for 14 days. Ten flowering-age Osteospermum sp. plants of cv. Soprano White were inoculated with 1 g of inoculum placed at the base of each plant. One group of five plants was kept in a dew chamber at 22°C for 40 h after which they were removed to a greenhouse. The second group of five plants was placed in a single, plastic bag with the top left open and kept in the greenhouse. Ten noninoculated plants of the same cultivar served as controls with five kept in the dew chamber for 40 h and the other five held in a plastic bag in the greenhouse. Inoculated plants that had been held in the dew chamber developed stem lesions and rot after 2 days, wilted permanently after 5 days, and were desiccated and dead by day 7. Inoculated plants held in the bag in the greenhouse followed a similar disease development pattern but did not show wilt symptoms until 8 days after inoculation and were dead after 12 days. White cottony mycelium and black sclerotia developed on stems and at the base of all inoculated plants. S. sclerotiorum was reisolated from inoculated diseased plants. All noninoculated control plants remained disease free. An outbreak of this disease was previously reported on Osteospermum spp. planted along highways in southern California (1). To our knowledge, this is the first report of the disease in Louisiana and the first report of its occurrence in greenhouse production of Osteospermum spp.

Reference: (1) H. S. Gill. Plant Dis. Rep. 59:82, 1975
The Fate of Xylella fastidiosa in Vineyard Weeds and Other Alternate Hosts in California
Authors: Wistrom C. , Purcell A. H.
Published: May 2007

The fate of Xylella fastidiosa, the bacterium that causes Pierce's disease of grape, was assessed in 29 species of plants associated with vineyards in California's San Joaquin Valley. Bacterial populations and movement in greenhouse-grown plants were measured 1, 3, and 9 weeks after mechanical and insect inoculation. X. fastidiosa was recovered in 27 of 29 species in greenhouse tests, with common sunflower (Helianthus annuus), cocklebur (Xanthium strumarium), annual bur-sage (Ambrosia acanthicarpa), morning glory (Ipomoea purpurea), horseweed (Conyza canadensis), sacred datura (Datura wrightii), poison hemlock (Conium maculatum), and fava bean (Vicia faba cv. Aquadulce) being infected in more than 50% of inoculation attempts. Twenty-three species supported bacterial populations in excess of 104 CFU/g of plant tissue. X. fastidiosa populations increased for 9 weeks after inoculation in six species, and were static or declined in 16 species. Although the blue-green sharpshooter (Graphocephala atropunctata) was more efficient than mechanical inoculation for infecting plants, median populations and systemic movement for the two methods did not differ significantly. X. fastidiosa colonization of greenhouse and field-grown plants was compared in five alternate hosts. X. fastidiosa was recovered from 23 and 34% of field-grown plants, compared with 49 and 67% of greenhouse-grown plants, in the winter and summer, respectively, with at least 10 times fewer bacteria in field plants in the winter. Although X. fastidiosa has a wide host plant range, its fate in most species is variable and heavily influenced by field conditions.
First Report of Tomato leaf curl New Delhi virus Infecting Tomato in Bangladesh
Authors: Maruthi M. N. , Rekha A. R. , Cork A. , Colvin J. , Alam S. N. , Kader K. A.
Published: May 2007

Tomato is an important cash crop for resource-poor farmers and accounts for 20% of the 2 million t of vegetables grown annually in Bangladesh. Tomato cultivation is affected by Tomato leaf curl virus (ToLCV), which can cause as much as 100% yield loss. Plants exhibiting typical ToLCV disease symptoms of yellowing, severe leaf curling, and stunting were collected at Jessore, Bangladesh during September 2003. The putative virus was transmitted from tomato to tomato by the whitefly Bemisia tabaci. In two separate experiments, 100% transmission was achieved by using 10 viruliferous B. tabaci adults for each of the 20 test plants that was confirmed by comparing the symptoms on test and virus source plants. Total DNAs were extracted from the symptomatic leaves, and the putative viral genomes were amplified by polymerase chain reaction by using the Deng A and B primers (1). Sequences generated from these primers were used to design virus-specific primers that were used to obtain complete viral sequences. Full-length DNA-A (2,740 nt; GenBank Accession No. AJ875157) and DNA-B (2,688 nt; GenBank Accession No. AJ875158) sequences of a bipartite Tomato leaf curl New Delhi virus from Jessore (ToLCNDV-[Jes]) were obtained, which were most similar to the corresponding sequences of ToLCNDV-(Lucknow) (GenBank Accession No. Y16421) at 95.7% and Tomato leaf curl Gujarat virus-(Varanasi) (Gen-Bank Accession No. AY190291) at 90.6% nt identities, respectively. DNA-A sequences had only 73.2% nt identity with the previously reported monopartite Tomato leaf curl Bangladesh virus (GenBank Accession No. AF188481) (2), confirming the occurrence of mono- and bipartite bego-moviruses in Bangladesh. The virus diversity poses a challenge for ToLCVD management in Bangladesh.

References: (1) D. Deng et al. Ann. Appl. Biol. 125:327, 1994. (2) S. K. Green et al. Plant Dis. 85:1286, 2001.
Phytophthora Leaf Spot and Foliar Blight of Pieris japonica Caused by Phytophthora citricola in California
Authors: Koike S. T. , Browne G. T. , Bhat R. G. , Lee R. C. M. , Tjosvold S. A. , Buermeyer K.
Published: May 2007

During 2004, containerized nursery stock of lily-of-the-valley-bush (Pieris japonica ‘Flamingo’, family Ericaceae) in Santa Cruz County was affected by a foliar disease. Symptoms consisted of large leaf spots, many developing at the leaf tips that ranged in size from 1 to greater than 4 cm in diameter. Spots were dark brown to almost black, generally oval to round, visible from both sides of the leaf, and did not exhibit signs of any pathogen. Lesions typically expanded and affected the entire leaf, leaf petiole, and stems, resulting in blight-like symptoms. Severely affected leaves abscised from the plant. In advanced stages of the disease, the foliage of the plant was killed. These symptoms resembled those caused by the sudden oak death (SOD) pathogen, Phytophthora ramorum (3). A Phytophthora sp. was isolated consistently from symptomatic leaf tissue. However, the species was identified as P. citricola based on morphological traits that included the following: production of semipapillate, noncaducous sporangia that were irregular in shape and occasionally had more than one apex; presence of oospores with paragynous antheridia in single culture; and radiate to slightly petaloid colony morphology (1). P. ramorum and other fungi were not recovered. Pathogenicity of four representative isolates was confirmed by gently abrading the adaxial surfaces of attached leaves with a sterile wire brush, placing a colonized agar plug (5 mm in diameter) on the surface, misting the leaf with sterile water, and then covering the plug with a plastic cap that was secured with a wire clip. Control leaves were treated in the same manner but received sterile agar plugs. Plants were maintained in a greenhouse at 23 to 25°C. After 2 days, all leaves inoculated with the isolates exhibited dark brown lesions and by day 6, lesions measured 3 cm in diameter. P. citricola was reisolated from symptomatic lesions. Sterile plug control leaves developed no symptoms. The test was repeated and the results were similar. To our knowledge, this is the first report of P. citricola causing a foliar disease of Pieris japonica in California. P. citricola has been reported as a pathogen on Pieris spp. in Ohio (2). Our finding is important because P. ramorum causes very similar symptoms on this same host (3). The occurrence of these two foliar Phytophthora spp. on this ornamental plant may complicate P. ramorum field detection during inspections and laboratory confirmations as established by quarantine regulations.

References: (1) D. C. Erwin and O. K. Ribeiro. Morphology and Identification of Phytophthora Species. Pages 96–144 in: Phytophthora Diseases Worldwide. The American Phytopathological Society, St. Paul, MN, 1996. (2) W. W. P. Gerlach et al. Phytopathology 64:1368, 1974. (3) P. W. Tooley et al. Plant Dis. 88:993, 2004.