bluuebunny/crossref_metadata_2025 huggingface dataset:
First Report of Plum pox virus (Sharka Disease) in Prunus persica in the United States
Authors: Levy L. , Damsteegt V. , Welliver R.
Published: May 2007

Plum pox (Sharka) is the most important virus disease of Prunus in Europe and the Mediterranean region and is caused by Plum pox potyvirus (PPV). In September 1999, PPV-like symptoms were observed in peach fruit culls in a packinghouse in Pennsylvania. All symptomatic fruit originated from a single block of peach (P. persica cv. Encore) in Adams County. Trees in the block exhibited ring pattern symptoms on their leaves. A potyvirus was detected in symptomatic fruit using the Poty-Group enzyme-linked immunosorbent assay (ELISA) test from Agdia (Elkhart, IN). Reactions for symptomatic peach fruit and leaves also were positive using triple-antibody sandwich ELISA with the PPV polyclonal antibody from Bioreba (Carrboro, NC) for coating, the Poty-Group monoclonal antibody (MAb; Agdia) as the intermediate antibody, and double-antibody sandwich ELISA with PPV detection kits from Sanofi (Sanofi Diagnostics Pasteur, Marnes-La-Coquette, France) and Agdia and the REAL PPV kit (Durviz, Valencia, Spain) containing universal (5B) and strain typing (4DG5 and AL) PPV MAbs (1). PPV also was identified by immunocapture-reverse transcription-polymerase chain reaction (IC-RT-PCR) amplification and subsequent sequencing of the 220-bp 3′ noncoding region (2) (>99% sequence homology to PPV) and by IC-RT-PCR amplification of a 243-bp product in the coat protein (CP) gene (1). The virus was identified as PPV strain D based on serological typing with strainspecific MAbs and on PCR-restriction fragment length polymorphism of the CP IC-RT-PCR product with Rsa1 and Alu1 (1). This is the first report of PPV in North America.

References: (1) T. Candresse et al. Phytopathology 88:198, 1998. (2) L. Levy and A. Hadidi. EPPO Bull. 24:595, 1994.
Natural Infection of Alstroemeria caryophyllea with Ornithogalum mosaic virus
Authors: Bouwen I. , van der Vlugt R. A. A.
Published: May 2007

During a survey for a European Union-funded project on the viruses of Alstroemeria, an A. caryophyllea plant was found expressing virus-like symptoms, including dark green vein banding, necrotic spots, and flower color breaking. In enzyme-linked immunosorbent assays (ELISA), no positive reaction was obtained with antisera to Alstroemeria mosaic, Alstroemeria carla, Cucumber mosaic, Freesia mosaic, or Tobacco rattle virus. A positive ELISA reaction was obtained with potyvirus-specific monoclonal antibodies (Agdia, Elkhart, IN) and antiserum to Ornithogalum mosaic virus (OrMV) (1). In electron microscopy leaf dip preparations of A. caryophyllea, potyvirus-like particles were observed. Using sapinoculation, the virus was transferred to Chenopodium amaranticolor and C. quinoa, resulting in local lesions 6 days postinoculation. The presence of OrMV in both Chenopodium spp. was confirmed by electron microscopy and ELISA with antiserum to OrMV. Sequence alignment of DNA fragments (740 bp) obtained in immunocapture-reverse transcription-polymerase chain reaction on RNA isolated from the suspect virus, using a potyvirus-specific primer set (2), showed 91% homology with the corresponding region of OrMV RNA (GenBank accession no. D00615). The results confirm the infection of A. caryophyllea by OrMV. This is the first report of natural infection of Alstroemeria by OrMV.

References: (1) J. T. Burger and M. B. von Wechmar. Phytopathology 79:385, 1989. (2) R. A. A. van der Vlugt et al. Phytopathology 89:148, 1999.
Evaluation of Mint Mutants, Hybrids, and Fertile Clones for Resistance to Verticillium dahliae
Authors: Johnson Dennis A. , Cummings Tom F.
Published: May 2007

Peppermint and spearmint clones derived from cobalt 60 gamma irradiation and peppermint seed fertile clones and hybrids were evaluated for resistance to Verticillium dahliae in inoculation tests in the greenhouse. Mutant and fertile clones and hybrids varied significantly for wilt resistance. One peppermint mutant clone, three peppermint hybrids, and four peppermint fertile clones had low but varying wilt-severity values. Native spearmint and mutant lines derived from native spearmint had high levels of resistance. The wilt-severity scale used to assess disease levels was correlated with the number of CFU of V. dahliae from inoculated stems.
Improved Control of Apple and Citrus Fruit Decay with a Combination of Candida saitoana and 2-Deoxy-D-Glucose
Authors: El-Ghaouth Ahmed , Smilanick Joseph L. , Wisniewski Michael , Wilson Charles L.
Published: May 2007

A combination of Candida saitoana with 0.2% 2-deoxy-D-glucose to control decay of apple, lemon, and orange fruit was evaluated. Growth of C. saitoana in vitro was reduced by 2-deoxy-D-glucose; however, in apple wounds, the yeast grew as well in the presence of 2-deoxy-D-glucose as in its absence. When applied to fruit wounds before inoculation, the combination of C. saitoana with 0.2% 2-deoxy-D-glucose was more effective in controlling decay of apple, orange, and lemon caused by Botrytis cinerea, Penicillium expansum, and P. digitatum than either C. saitoana or the application of a 0.2% solution of 2-deoxy-D-glucose alone. Increasing the concentration of 2-deoxy-D-glucose from 0.2 to 0.5% did not improve control significantly. The combination of C. saitoana with 0.2% 2-deoxy-D-glucose was also effective against infections established up to 24 h before treatment. When applied within 24 h after inoculation, the combination of C. saitoana with 0.2% 2-deoxy-D-glucose was very effective in controlling blue mold of apple and green mold of orange and lemon. The level of control of green mold was equivalent to imazalil treatment. When either C. saitoana or 0.2% 2-deoxy-D-glucose was applied within 24 h after inoculation, neither had an effect on disease development on apple, orange, or lemon, and the incidence of decay was similar to the water-treated control.
Effect of Protectant Fungicide Application Schedules on Gummy Stem Blight Epidemics and Marketable Yield of Watermelon
Authors: Keinath Anthony P.
Published: May 2007

The watermelon cultivar Royal Star was grown in fall 1996, spring and fall 1997, and spring 1998 and treated with 2.52 kg a.i./ha of the protectant fungicides mancozeb or chlorothalonil. Spray application schedules used in the experiments included two initiation times, sprays every 7, 10, or 14 days, and two termination times. Severity of gummy stem blight, caused by Didymella bryoniae, was high in fall 1996 and 1997, moderate in spring 1997, and low in spring 1998. In each experiment, fungicide applications reduced the area under the disease progress curve (AUDPC), percent leaf area diseased at the end of the season, time to reach 25% disease severity, or all three disease measurements relative to the nonsprayed control. In the 1996 and both 1997 experiments, 7-day spray intervals provided more effective disease control than 14-day intervals. In general, initiating sprays early reduced gummy stem blight compared with delayed sprays, but spray termination times did not affect AUDPC. In both fall experiments, fungicide applications increased yield of marketable fruit over the no-fungicide control. A 7-day spray interval increased marketable weight compared with a 14-day interval only in fall 1996. Weight of marketable fruit did not differ among treatments in either spring experiment. Differences in disease control among treatments often did not correspond to differences in marketable yields.
Evaluation of the Effect of Seed Treatments, Bactericides, and Cultivars on Bacterial Leaf Spot of Lettuce Caused by Xanthomonas campestris pv. vitians
Authors: Carisse O. , Ouimet A. , Toussaint V. , Philion V.
Published: May 2007

As a part of a broader program for management of bacterial leaf spot, the effects of lettuce-seed treatments, greenhouse application of bactericides, and cultivars were evaluated. Seed artificially inoculated with Xanthomonas campestris pv. vitians was treated with bactericides or heat treated and evaluated for the incidence of contaminated seed and seed germination. Seed soaked in 1% sodium hypochlorite for 5 and 20 min had an incidence of contaminated seed of less than 10%. Dry-heat (1 h), hot-water (50°C, 2 h), and organic-acid treatments significantly reduced seed germination. Considering both the effects on incidence of contaminated seed and seed germination, the best treatments were soaking the seeds in 1% sodium hypochlorite for 5 or 20 min. Copper sulfate, alone or mixed with Zineb or Dithane, failed to control the disease and caused phytotoxicity. All of the other bactericides significantly reduced the severity of bacterial leaf spot. However, the differences among bactericide efficacy were too small to allow comparison between the different forms of copper used, as well as the effect of adding manganese and zinc (Dithane) or zinc alone (Zineb) to the copper product. Nevertheless, copper hydroxide alone, mixed with Zineb or mixed with Dithane, and basic copper sulfate reduced disease severity by 86.89, 78.67, 80.42, and 81.82%, respectively, without causing phytotoxicity. For the two years of cultivar evaluation, no significant difference in mean disease severity was observed among the cultivars. Based on disease incidence, the most susceptible cultivar was Bellagreen. Cvs. Ideal cos, Grand Teton, Great Lakes, Paris Island, Ithaca, and Optima showed intermediate susceptibility, and the least-susceptible cultivars were Waldmann's and Grand Rapids, both green-leaf type. There was no significant difference between the three romaine (cos) cultivars and between the two crisphead cultivars, but a significant difference was observed between the two butterhead types, Bellagreen and Optima, which had 80.04 and 48.01%, respectively, of their leaves diseased at the time of harvest.
Rice Pest Constraints in Tropical Asia: Quantification of Yield Losses Due to Rice Pests in a Range of Production Situations
Authors: Savary Serge , Willocquet Laetitia , Elazegui Francisco A. , Castilla Nancy P. , Teng Paul S.
Published: May 2007

A series of experiments was conducted where a range of injuries due to rice pests (pathogens, insects, and weeds) was manipulated simultaneously with a range of production factors (fertilizer input, water supply, crop establishment method, variety) in different seasons and years. These factors were chosen to represent lowland rice production situations characterized in surveys conducted in tropical Asia and their corresponding range of attainable yield. Experiments complemented one another in exploring the response surface of rice yields to yield-limiting and yield-reducing factors. The resulting experimental data base consisted of 445 individual plots and involved 11 manipulated injuries in a range of attainable yields of 2 to 11 t ha-1. A first, nonparametric, multivariate analysis led to a hierarchy of potential injuries, from marginally (e.g., bacterial leaf blight) to extremely harmful (e.g., rice tungro disease). A second, parametric, multivariate approach resulted in a multiple regression model involving factors generated by principal component analysis on injuries that adequately described the variation in actual yield. One major finding was that some (attainable yield × injury factors) interactions significantly contributed to the description of variation in actual yield, indicating that some injuries (or their combinations) had a stronger or weaker yield-reducing effect, depending on the level of attainable yield. For instance, yield losses due to sheath blight, weed infestation, and rice tungro disease tend to increase, remain stable, and decrease, respectively, with increasing attainable yields. Back-computations using the principal component regression model estimated yield losses caused by individual injuries, using the mean injury levels in a population of farmers' fields surveyed across tropical Asia. The results indicate that sheath blight, brown spot, and leaf blast are diseases that cause important losses (between 1 and 10%) regionally. Among the insect injuries, only white heads caused by stem borers appear of relevance (2.3% yield losses). These injuries, however, do not match in importance those caused by weeds, whether outgrowing the rice crop canopy (WA) or not (WB), both types of injuries causing about 20% yield losses when considered individually. When all mean injuries were combined into one mean injury profile occurring at a regional attainable yield of 5.5 t ha-1, a mean yield loss of 37.2% was estimated, indicating that injuries were less than additive in their yield-reducing effects. Scenario analyses were conducted in a set of (production situations × injury profiles) combinations characterized from surveys in farmers' fields in tropical Asia. Depending on the scenario chosen, losses ranging from 24 to 41% were found.
Bacterial Blight, a New Disease of Broccoli Caused by Pseudomonas syringae in California
Authors: Koike S. T. , Cintas N. A. , Bull C. T.
Published: May 2007

In 1998 and 1999, a new disease was detected in commercial broccoli (Brassica oleracea var. botrytis) grown in the Salinas Valley, Monterey County, CA. Initial symptoms consisted of large, water-soaked, dark green, angular leaf sections that were bordered by major leaf veins. Diseased areas were as large as 10 × 3 cm. As the disease developed, affected areas turned tan and papery, and leaf margins sometimes became tattered. The numerous small (<1 cm diameter), round to angular spots that also were present retained their size and did not develop into larger lesions. A blue-green fluorescing pseudomonad was consistently isolated from both types of lesions on King's medium B. Strains were levan positive, oxidase negative, and arginine dihydrolase negative. Strains did not rot potato slices but induced a hypersensitive reaction in tobacco (Nicotiana tabacum L. ‘Turk’). Fatty acid methyl ester analysis (MIS-TSBA version 4.10, MIDI, Inc., Newark, DE) indicated that the strains were highly similar (similarity ≥0.843) to Pseudomonas syringae. Biolog GN (version 3.50, Biolog, Inc., Hayward, CA) profiles also identified the strains as P. syringae. Therefore, the bacterium associated with the disease was identified as P. syringae. Pathogenicity of 13 strains was demonstrated by greenhouse tests. The strains were grown as nutrient broth shake cultures for 48 h at 24°C, diluted to 106 CFU/ml, and misted onto broccoli (cvs. Patriot and Titleist) and broccoli raab (B. rapa subsp. rapa cv. Spring). Control plants were misted with sterile nutrient broth. After 4 to 5 days in a greenhouse (24 to 26°C), large angular leaf lesions developed on all inoculated broccoli and broccoli raab plants. Strains were reisolated from symptomatic tissue and identified as P. syringae. Control plants remained symptomless. The results of two sets of pathogenicity tests were the same. Unlike most P. syringae strains, those isolated from broccoli were sensitive to a bacteriophage recovered from a P. syringae pathovar that infects broccoli raab. These results suggest that the broccoli pathogen may be related to the bacterial blight pathogen of broccoli raab (1). This is the first report of this pathogen causing a disease on commercially grown broccoli.

Reference: (1) S. T. Koike et al. Plant Dis. 82:727, 1998.
Rust on Ground-Ivy Found for the First Time in North America
Authors: Herbaria M.Scholler , Herbaria Arthur , Herbaria Kriebel
Published: May 2007

Ground-ivy or gill-over-the-ground (Glechoma hederacea) is a perennial and a member of the mint family (Lamiaceae). It is characterized by creeping stems that root at the nodes, blue to violet blossoms, and rotund leaves. The plant is native to Eurasia but was introduced to and has become widespread in North America. It is found predominantly in nutrient-rich, shady meadows but also occurs in forests and disturbed habitats. There are several rusts known on G. hederacea in Eurasia. One of them, Puccinia glechomatis, has been introduced to North America. The only two collections of this fungus were made in the United States in August 1998 (near Syracuse University, NY) and in October 1999 (west of West Lafayette, IN) in shady, continuously mowed lawns in private gardens. The specimens were identified by reference to Gaeumann (2) and deposited in the Arthur Herbarium, Purdue University, West Lafayette. P. glechomatis is a microcyclic rust fungus that forms only telia (spore stage III). The sori are up to 1 mm in diameter, forming round cushion-like galls on abaxial leaf surfaces and depressions on adaxial leaf surfaces, opposite galls. The colorless to pale brown teliospore is characterized by its acute apex. Most teliospores germinate immediately and do not function as overwintering spores. It seems likely that the rust species has been in North America for a long time given that the two collections are from widely separated areas. The fungus may have been overlooked. So far, P. glechomatis has been found only on species of the genus Glechoma (including G. urticifolia, which is often placed in the genus Meehania) and seems to be restricted to this genus. The only inoculation experiments made with P. glechomatis proved that the rust does not infect Salvia spp. (sage) (1). There is no evidence that this rust can infect plants indigenous to North America.

References: (1) L. Corazza and L. Luongo. Plant Dis. 83:487, 1999. (2) E. G. Simmons. Mycotaxon 37:79, 1990.
Phytophthora cinnamomi as a Cause of Oak Mortality in the State of Colima, Mexico
Authors: Tainter F. H. , O'Brien J. G. , Hernández A. , Orozco F. , Rebolledo O.
Published: May 2007

This research identifies the root pathogen Phytophthora cinnamomi as the primary cause of mortality in a 300-ha disease center of mixed oak trees in a native forest in southern Mexico. In increasing order of apparent field resistance to the disease, the major oak species are Quercus glaucoides, Q. peduncularis, and Q. salicifolia. P. cinnamomi was isolated from soil in the affected area from symptomatic trees and was successfully used to perform Koch's postulates on these three oak species. Artificial and natural infections produced vertically elongated discolorations in the outer xylem and distinctive phloem canker lesions with a sharp demarcation line between healthy and affected tissues. In Q. glaucoides there is little evidence that this oak species is able to resist the girdling effects of the phloem lesions, but in Q. peduncularis, and especially in Q. salicifolia, increased production of callus tissue around the phloem canker lesions suggests an active resistance mechanism that may allow these infected trees to survive somewhat longer. This particular incident is unlike other recent reports in other parts of the world of oak mortality caused by P. cinnamomi because the initial appearance of disease in this area is known (just prior to 1987), and it has subsequently expanded to the present area of 300 ha (in 1999) as a distinctive infection locus with periodically advancing infection fronts. This incident is also another dramatic illustration of the potential environmental damage that can result when P. cinnamomi is introduced into a simple forest ecosystem where the major overstory trees are susceptible to infection and are killed.
Effect of Nitrogen Fertilization on Disease Progress of Rice Blast on Susceptible and Resistant Cultivars
Authors: Long D. H. , Lee F. N. , TeBeest D. O.
Published: May 2007

The effects of three nitrogen fertilization treatments on the development of rice blast were studied on eight cultivars under field conditions in Arkansas in 1995 and 1996. The eight cultivars (Kaybonnet, Cypress, Lacassine, Mars, Adair, Alan, Newbonnet, and RT7015) ranged from resistant to susceptible to blast according to previous field observations. The recommended nitrogen levels for the eight cultivars varied from 123 to 168 kg/ha/year. Three treatments, consisting of different rates and timing of nitrogen applications, were tested over 2 years at one location. The first treatment consisted of a single nitrogen (N) application applied to plots at the recommended rate at preflood during the midtillering stage. The second treatment consisted of applying nitrogen as a single preflood application but at 1.5 times the recommended N rate used in treatment one. The third treatment (control) consisted of applying the recommended amount of nitrogen fertilizer used in treatment one, but in a three-way-split application with 56 to 100 kg/ha (depending on the cultivar) of urea applied at preflood followed by the application of 34 kg/ha of N applied approximately 10 and 20 days after the panicle differentiation (PD) growth stage. Inoculated spreader plots were used to initiate rice blast epidemics in the test plots. The results indicate that the disease progress for rice blast, regardless of N treatments, followed a unimodal curve, whereby disease incidence and total lesion area per plant reached a maximum near midseason (PD growth stage) and then gradually declined. This decline in disease was attributed to adult resistance, leaf senescence, and the formation of new (noninfected) leaves. Application of nitrogen above the recommended rate for any given cultivar significantly increased disease incidence and total lesion area per plant on all cultivars except Kaybonnet, a highly resistant cultivar. Furthermore, a differential cultivar response to nitrogen was observed when measuring both disease incidence and total lesion area per plant. Leaf blast was significantly more severe on the susceptible and very susceptible cultivars when N fertilizer was applied as a single application at preflood than in the split application treatment. Nitrogen treatments did not significantly affect the incidence of collar rot or neck blast.
Relations Among Sorghum Ergot Isolates from the Americas, Africa, India, and Australia
Authors: Pažoutová Sylvie , Bandyopadhyay Ranajit , Frederickson Debra E. , Mantle Peter G. , Frederiksen Richard A.
Published: May 2007

Sorghum ergot, initially restricted to Asia and Africa, was recently found in the Americas and Australia. Three species causing the disease have been reported: Claviceps sorghi in India, C. sorghicola in Japan, and C. africana in all ergot-positive countries. The objective of our study was to study the intraspecific variation in C. africana isolates in the Americas, Africa, India, and Australia. We confirmed C. africana, C. sorghi, and C. sorghicola as different species using differences in nucleotide sequences of internal transcribed spacer 1 and 5.8S rDNA regions. Sequences of this region obtained from the representative American, Indian, and Australian isolates of C. africana were identical. In addition, random amplified polymorphic DNA (RAPD) banding patterns of sorghum ergot pathogen isolates from the United States, Mexico, Puerto Rico, Bolivia, Australia, and India were evaluated with nearly 100 primers. A total of 65 primers gave identical patterns for all isolates, which confirmed that all were C. africana. The identity of RAPD pattern and rDNA sequence of Indian isolates with those of C. africana confirmed that the species is now present in India. Only 20 primers gave small pattern differences and 7 of them were used for routine testing. All of the American isolates were identical and three isolates of the same type were also found in South Africa, suggesting Africa as the origin of the invasion clone in the Americas. Australian and Indian isolates were distinguishable by a single band difference; therefore, migration from the Asian region to Australia is suspected. Another distinct group was found in Africa. Cluster analysis of the informative bands revealed that the American and African group are on the same moderately (69%) supported clade. Isolates from Australia and India belonged to another clade.
Detection of Acidovorax avenae subsp. citrulli in Watermelon Seed Using Immunomagnetic Separation and the Polymerase Chain Reaction
Authors: Walcott R. R. , Gitaitis R. D.
Published: May 2007

An immunomagnetic separation and polymerase chain reaction (IMS-PCR)-based assay was developed for detecting Acidovorax avenae subsp. citrulli in watermelon seed. IMS yielded a 10-fold increase in recovery of A. avenae subsp. citrulli over direct spread-plating on King's Medium B; however, the presence of seed debris reduced IMS efficiency. Synthetic oligonucleotide primers were designed based on the 16S rRNA gene of a known A. avenae subsp. citrulli strain and tested for specific DNA amplification by PCR. The primers amplified DNA from all A. avenae subsp. citrulli strains tested but also yielded amplicons with several closely related bacteria. IMS-PCR resulted in a 100-fold increase in A. avenae subsp. citrulli detection sensitivity over direct PCR and was unaffected by PCR inhibitors in watermelon seed. The threshold of A. avenae subsp. citrulli detection for IMS-PCR was 10 CFU/ml in watermelon seed wash, and seedlots with 0.1% infestation were consistently detected. IMS-PCR represents an efficient and sensitive approach to detecting A. avenae subsp. citrulli in watermelon seedlots.
First Report of the Telial Stage of Gymnosporangium exiguum on Ashe Juniper Adjacent to Hawthorn with Rust in Southwest Texas
Authors: Black M. C. , Grand L. F. , Vernia C. S.
Published: May 2007

The telial stage of Gymnosporangium exiguum (2) on Ashe juniper (Juniperus ashei) was observed in Bandera County, TX, in April and May 1999 after rain events. Symptomatic plants with multiple lesions were found at low frequencies in dense J. ashei populations. Orange telia formed on scales and bark and on 2- to 3-mm-diameter twigs and became nearly inconspicuous when dry. No hypertrophy was observed. Previously reported telial hosts include J. californica and J. excelsa cv. Stricta in California; J. mexicana and J. scopulorum in Oklahoma; J. virginiana in Texas; and J. deppeana var. pachyphloea in Oklahoma and Texas (1). An aecial stage identified as G. exiguum has been observed for many years on native hawthorns (Crataegus crus-galli, C. greggiana, C. mollis, C. stevensiana, C. tracyi, C. turnerorum, C. viridis var. desertorum, and several natural hybrids) in Bandera, Bexar, Edwards, Gillespie, Kendall, Kimble, Real, and Uvalde counties, Texas. Prominent roestelioid aecia were observed on hawthorn leaves, petioles, fruits, peduncles, thorns, and, less often, on twigs. In two experimental plantings of hawthorns in Bandera County, rust severity was rated as low to moderate in six populations of C. greggiana and hybrids; moderate in two populations each of C. stevensiana and C. tracyi; moderate to severe in three populations of C. crus-galli and hybrids; and severe in one population each of C. mollis and C. viridis var. desertorum. G. exiguum was previously reported on a Crataegus sp. in Texas and on Heteromeles arbutifolia in California (1). Flowers, fruits, plant forms, and drought tolerances are characteristics of some endemic hawthorns that provide landscape and wildlife advantages. G. exiguum causing rust disease may limit the ornamental potential of highly susceptible hawthorn species in southwest Texas. Inconspicuous infections on susceptible ornamental Juniperus spp. also could have phytosanitary implications. Voucher specimens (aecia and telia) are on deposit in the Mycological Herbarium, Department of Plant Pathology, North Carolina State University, Raleigh.

References: (1) D. F. Farr et al. 1989. Fungi on Plants and Plant Products in the United States. The American Phytopathological Society, St. Paul, MN. (2) F. D. Kern. 1973. A Revised Taxonomic Account of Gymnosporangium. The Pennsylvania State University Press, University Park.
First Report of Web Blight on Verbena Caused by Rhizoctonia solani
Authors: Holcomb G. E. , Carling D. E.
Published: May 2007

Web blight was observed on verbena (Verbena × hybrida) during July 1999 in a cultivar trial planting at Burden Research Plantation in Baton Rouge, LA. Foliage blight, stem lesions, and branch death were common symptoms on 12 of 24 cultivars in the trial. Plant death occurred in cvs. Babylon Florena (one of four plants), Purple Princess (two of four plants), and Taylortown Red (two of four plants). Isolations from infected leaves and stems on acidified water agar consistently yielded a fungus with the mycelial and cultural characteristics of Rhizoctonia solani. Pathogenicity tests were carried out by placing 5-day-old fungal mycelial plugs, grown on acidified potato dextrose agar, at the base of healthy verbena stems and holding plants in a dew chamber at 26°C. After 3 days, foliage blight and stem lesions appeared on inoculated plants, and plants were moved to a greenhouse where temperatures ranged from 23 to 32°C. Seven of nine inoculated plants died after 7 days; noninoculated plants remained healthy. The fungal pathogen was reisolated from all inoculated plants. The fungus was identified as R. solani anastomosis group (AG)-1 IB based on multinucleate condition, type of sclerotia produced, and ability to anastomose with R. solani tester isolates of AG-1 IB. This is the first report of web blight on verbena.
A Foliar Disease of European Hackberry Endemic in Sicily
Authors: Cacciola S. O.
Published: May 2007

European hackberry (Celtis australis L.; Ulmaceae), a semideciduous tree or shrub that produces small edible berries was originally grown in Italy to produce charcoal and timber and was particularly suitable for making whipstocks, carriage wheel spokes, and hoe handles. European hackberry is currently used for reforestation and as shade trees in parks and roadside plantings. Recently, a foliar disease caused by the dematiaceous hyphomycetous fungus Sirosporium celtidis (Biv.-Bern. ex Sprengel) M.B. Ellis on hackberry saplings in a nursery was observed in the Piedmont Region (northern Italy) by Giannetti et al. (2), who referred to it as a rare disease. However, during a survey in the nature reserve of the Anapo River Valley, in the Sicily Region (southern Italy), where European hackberry and a closely related species (C. tournefortii Lam.) grow naturally, most hackberry plants were found to be infected by S. celtidis, with variable intensity. During autumn, symptoms appeared on lower leaf surfaces as reddish brown to dark black-brown subcircular velvety spots (up to 10 to 15 mm wide) surrounded by narrow paler margins that were evenly distributed over the leaf surface and later confluent. Nonspecific symptoms on upper leaf surfaces were visible only in advanced stages and consisted of necrotic areas, usually apical or marginal, that were at first red-brown and later turned gray. A few trees were prematurely defoliated. Usually, however, severely affected leaves were necrotic, withered, and curled but remained attached. Spots on lower leaf surfaces were covered by mycelium, conidiophores, and conidia that corresponded to the description of S. celtidis published by Ellis (1). Conidia were straight, flexuous, occasionally markedly curved or coiled, cylindrical or obclavate, smooth, wrinkled or verrucose, subhyaline to golden or reddish brown, typically multicellular with 1 to 32 transverse septa, and occasionally had longitudinal or oblique septa that were often constricted, more than 100 μm long and up to 5 to 8 μm thick, with an inconspicuous scar at the base. From 1997 to 1999, infection by S. celtidis in the Anapo River Valley occurred each year, probably favored by the moist environment. S. celtidis, first described in Sicily as early as 1815 (1), has been recorded on various hackberry species in many countries, including the United States (3). Apparently this pathogen is of little economic and ecological significance in natural ecosystems; however, the fungus could become a serious problem in nurseries (2).

References: (1) M. B. Ellis. 1963. Mycological Papers, No. 87. Commonw. Mycol. Inst. Kew, England. (2) G. Giannetti et al. Inform. Fitopatol. 49:39, 1999. (3) D. H. Linder. Ann. Mo. Bot. Garden 18:31, 1931.
Reactions in the Annual Medicago Core Germ Plasm Collection to Two Isolates of Peronospora trifoliorum from Alfalfa
Authors: Yaege J. R. , Stuteville D. L.
Published: May 2007

Peronospora trifoliorum causes downy mildew of alfalfa throughout the temperate regions of the world, but little is known about its host range within the annual Medicago species (medics). Several medics have characteristics potentially beneficial to sustainable agriculture programs and to the genetic improvement of alfalfa. Therefore, we evaluated resistance in 199 accessions representing 33 species of the annual Medicago core germ plasm collection to P. trifoliorum isolates I7 and I8 from alfalfa from Kansas and southern California, respectively. Seedlings at the cotyledonary growth stage were inoculated with conidia suspended in water. One week later, the plants were rated resistant (no conidium production) or susceptible (conidium production). High levels of resistance existed in all species. All plants in 142 (71%) of the accessions were resistant to both isolates, but plants in only 24 of those resistant accessions were free of chlorotic to necrotic hypersensitive reactions on the inoculated cotyledons. All but one of the medic accessions had a higher percentage of plants resistant to both isolates than did cv. Saranac alfalfa, the resistant control. Conidium production generally was much less intense on the susceptible medic plants than on the alfalfa controls. A greater percentage of plants in four medic accessions was more resistant to I8 than to I7, and 22 were more resistant to I7 than to I8.
Biocontrol of Botrytis cinerea by Ulocladium atrum in Different Production Systems of Cyclamen
Authors: Köhl J. , Gerlagh M. , Grit G.
Published: May 2007

Ten experiments in six different commercial greenhouses were conducted to study the effect of spraying conidial suspensions of the saprophytic fungus Ulocladium atrum (1 × 106 conidia per ml) on infection of leaves and flower petioles of cyclamen by Botrytis cinerea (gray mold). The greenhouses represented the range of Dutch growing systems of cyclamen, differing considerably in the arrangement of plants, irrigation system, heating system, and material of pots. Applications of U. atrum suspensions were carried out at 4-week intervals only twice on young plants or were continued during the whole growing season until 4 weeks before plants were marketable. The antagonistic treatments were compared with untreated or water-treated controls and with fungicide applications as applied by growers. After applications of U. atrum at 4-weeks intervals, disease development was significantly reduced in experiments carried out in five different greenhouses. In no case did treatments with fungicides give better control than U. atrum treatments. Two applications of U. atrum resulted in sufficient control when plants were marketed within 60 days after the last application. In one greenhouse with an extremely high disease pressure, neither U. atrum nor fungicide applications controlled leaf rot. In additional experiments, the fate of U. atrum conidia on leaves of cyclamen grown in a system with top-irrigation three times per week was studied during a period of 70 days. The number of conidia per square centimeter of green leaves declined by 50% during the first 10 days of the experiment but remained stable during the following 60 days. The percentage of germinated conidia on green leaves increased during the experiment to approximately 50%. After additional incubation of leaf samples in moist chambers, more than 75% of the conidia had germinated, indicating that viable inoculum was present on leaves during the whole experiment. Artificial necrosis of leaves was induced by removing leaves from the plants. U. atrum colonized these leaves and competed successfully with B. cinerea on such leaves, even when they had been removed 70 days after the U. atrum application. Our results show that U. atrum has the potential to control leaf rot of cyclamen under a broad range of commercial growing conditions.
Winter Survival and Source of Primary Inoculum of Powdery Mildew of Dogwood in Tennessee
Authors: Mmbaga Margaret T.
Published: May 2007

A 3-year study (1996-1998) on the epidemiology of dogwood powdery mildew showed that Microsphaera pulchra is the primary powdery mildew pathogen of dogwoods (Cornus spp.) in mid-Tennessee, and the occurrence of Phyllactinia guttata is insignificant. Cleistothecia harvested from leaf debris in spring contained viable asci and ascospores and produced powdery mildew infection on disease-free plants. Ascospores that were morphologically similar to those of M. pulchra were trapped on sticky slides in the vicinity of dogwoods throughout spring. Previously infected plants that did not harbor cleistothecia failed to develop signs of infection under growth-chamber and greenhouse conditions conducive to powdery mildew infections. Results from these studies indicate that cleistothecia on leaf debris rather than mycelia on dormant buds constitute the main winter survival structure and primary sources of spring inoculum in mid-Tennessee.
A North American System of Nomenclature for Puccinia coronata f. sp. avenae
Authors: Chong J. , Leonard K. J. , Salmeron J. J.
Published: May 2007

A nomenclature system for designating virulence phenotypes of Puccinia coronata f. sp. avenae, the causal agent of oat crown rust, is proposed. Sixteen single gene oat (Avena sativa) lines, with seedling resistance genes Pc38, 39, 40, 45, 46, 48, 50, 51, 52, 54, 56, 58, 59, 62, 64, and 68, are the primary differentials. The host lines are arranged into groups of four (subset 1 = Pc40, 45, 46, 50; subset 2 = Pc38, 39, 48, 68; subset 3 = Pc51, 52, 58, 59; subset 4 = Pc54, 56, 62, 64). Avirulence and virulence of Puccinia coronata f. sp. avenae isolates on each line are indicated by low and high infection types, respectively. A letter from the 16 consonants B through T is assigned to each of the 16 possible combinations of low and high infection types on the four differentials of each subset. Designations for P. coronata f. sp. avenae virulence phenotypes are indicated by a four-letter code for the virulence combinations on all four subsets, one letter for each subset. Local differential series are separated from the four-letter code by a dash, followed by an additional letter code describing the virulence combinations of the isolates on the local supplemental differentials. When fewer than four differentials are used in the supplemental series, virulence combination on these differentials for each isolate is described by a listing of the Pc gene(s) to which the isolate was virulent, following the four-letter code and a dash. This nomenclature system for P. coronata f. sp. avenae is similar to the nomenclature system in use for P. graminis f. sp. tritici and P. triticina.
First Report of Phytophthora Root Rot of Sugar Beet, Caused by Phytophthora cryptogea, in Greece
Authors: Karaoglanidis G. S. , Karadimos D. A. , Klonari K.
Published: May 2007

A severe rot of sugar beet roots was observed in the Amyndeon area of Greece during summer 1998. Infected plants initially showed a temporary wilt, which became permanent, and finally died. Slightly diseased roots showed necrotic spots toward the base, whereas more heavily diseased roots showed a more extensive wet rot that extended upward. Feeder roots also were infected and reduced in number because of decay. Rotted tissue was brown with a distinguishing black margin. In most of the isolations, carried out on potato dextrose agar (PDA), the pathogen obtained was identified as Phytophthora cryptogea Pethybr. & Lafferty Mycelium consisted of fairly uniform, fine hyphae that showed a slightly floral growth pattern. In autoclaved soil-extract medium, chains or clusters of hyphal swellings (average 12 µm diameter) formed. Sporangia were not produced on solid media but were abundant in soil-extract medium. Sporangia were oval to obpyriform in shape, nonpapillate with rounded bases, and varied in size (39 to 80 × 24 to 40 µm). Oospores were plerotic, thick-walled, and averaged 25 µm in diameter. The isolated pathogen, cultured on PDA, could not grow at all at 36°C. The closely related species P. drechsleri Tucker has been reported to cause similar root rot symptoms on sugar beet (3). However, P. drechsleri grows well at 36°C, while P. cryptogea cannot grow at this temperature; this is the major distinguishing feature that separates the two species (1). To test the pathogenicity of the organism, surface-sterilized sugar beet roots (cv. Rizor) were inoculated with 5-mm-diameter PDA plugs containing actively growing mycelium. Sterile PDA plugs were used to inoculate control sugar beet roots. Inoculated roots were kept at 27°C in the dark for 10 days. Extensive decay of inoculated roots developed, similar to decay observed in the field, whereas control roots showed no decay. P. cryptogea was reisolated from rotted tissues. This pathogen has been recognized previously as a cause of root rot of sugar beet in Japan (1) and Wyoming (2). This is the first report of Phytophthora root rot of sugar beet in Greece.

References: (1) D. C. Erwin and O. K. Ribeiro. 1996. Phytophthora Diseases Worldwide. The American Phytopathological Society, St. Paul, MN. (2) P. C. Vincelli et. al. Plant Dis. 74:614, 1990. (3) E. D. Whitnew and J. E. Duffus, eds. 1986. Compendium of Beet Diseases and Insects. The American Phytopathological Society, St. Paul, MN.
First Report of Phomopsis vexans on Apricot in the Americas
Authors: Bello G. Dal , Sisterna M.
Published: May 2007

Prunus armeniaca L. plants with blight symptoms on leaves and twigs were observed near La Plata (Argentina) in 1999. On leaves, symptoms ranged from small (up to 4 mm diameter) and dispersed brown circular spots to irregular blighted areas with numerous pycnidia. Twig blight developed initially on buds as necrosis that expanded and caused shoots to wilt. A Phomopsis sp. was isolated from necrotic tissues. Pathogenicity was assessed by inoculating healthy mature leaves with a spore suspension (1 × 106 conidia per ml). Detached sterile twigs were placed in Roux tubes with water (1) and were infected by needle-stab inoculation. Controls were treated with sterile water. Inoculated leaves and controls were left in bags for 48 h. After 5 to 14 days, symptoms were similar to those described for field samples. The Phomopsis sp. was reisolated from necrotic lesions and characterized as identical to the original isolates. On potato dextrose agar, the fungus had white floccose mycelium and produced numerous black, globose to irregular pycnidia (up to 300 µm). Alpha-conidia were one-celled, hyaline, and ellipsoidal (4.5 to 10.3 µm long × 1.8 to 2.1 µm wide); beta-conidia were one-celled, hyaline, filiform, and straight or curved (16.8 to 27.5 µm long × 1.0 µm wide). A pure culture was identified as Phomopsis vexans (Sacc. & Syd.) Harter based on morphology and host specificity. This is the second report of P. vexans on apricot since the disease was cited in Algeria (2).

References: (1) T. A. Gally. Fitopatologia 10:87, 1975. (2) D. V. Narendra et al. FAO Plant Prot. Bull. 27:132, 1979.
Wheat yellow mosaic virus Widely Occurring in Wheat (Triticum aestivum) in China
Authors: Han Chenggui , Li Dawei , Xing Yiming , Zhu Kun , Tian Zhaofeng , Cai Zhunan , Yu Jialin , Liu Yi
Published: May 2007

Wheat yellow mosaic virus (WYMV) was identified in 25 of 27 wheat (Triticum aestivum) samples from six provinces in China using reverse-transcription polymerase chain reaction. Wheat spindle streak mosaic virus was not detected. Thus, contrary to previous reports, WYMV was the only bymovirus detected in wheat in China. The cDNA fragments corresponding to coat protein coding regions of five WYMV isolates from China were cloned and sequenced. Deduced amino acid comparison of coat proteins among these five isolates, another Chinese WYMV isolate HC, and one isolate from Japan showed very high sequence conservation, particularly in both the N- and C- termini. However, a highly virulent isolate HC from Henan Province showed four amino acid substitutions in highly conserved amino acid positions which might play a role in its pathogenic variation.
Effect of Chloride and Soybean Cultivar on Yield and the Development of Sudden Death Syndrome, Soybean Cyst Nematode, and Southern Blight
Authors: Rupe J. C. , Widick J. D. , Sabbe W. E. , Robbins R. T. , Becton C. B.
Published: May 2007

Yields of irrigated soybean in Arkansas are threatened by two problems: chloride toxicity and sudden death syndrome (SDS). Soybeans are sensitive to chloride, which accumulates in the upper soil profile when water with high salt content is used for irrigation. Sudden death syndrome is a soilborne disease often associated with well-irrigated fields. Even though these problems both affect irrigated soybeans, there are no reports on the effect of chloride toxicity on SDS. To determine if there is an effect of chloride toxicity on SDS, a test was established at the Cotton Branch Station, Marianna, AR, in 1995 and 1996. Four cultivars were selected that were either susceptible to SDS (S) or resistant to SDS (R) and either translocated chloride to the leaves (includer, I) or confined chloride in the roots (excluder, E). The cultivars were Hartz 6686 (SE), Terra Vig 6653 (SI), Hartz 6200 (RE), and Asgrow 6297 (RI). Soil chloride concentrations were adjusted by the addition of KCl. Before planting, KCl was applied to achieve the recommended concentration of K over the entire field. At V4, chloride treatments were applied by either adding no additional KCl (low Cl) or adding 1,120 kg of KCl per ha (moderate Cl) or 2,240 kg of KCl per ha (high Cl). Soil samples were taken within the center two rows of each plot at planting, flowering (R2), and harvest and assayed for populations of Fusarium solani and Heterodera glycines. Soil chloride concentrations were determined at R2, and leaf chloride levels were determined at R3. Weekly disease ratings were made on SDS and converted to area under the disease progress curve (AUDPC). Plant lodging and the incidence of southern blight (Sclerotium rolfsii) were determined during mid-reproductive growth. Leaf chloride concentrations were influenced by both chloride treatment and cultivar: elevated concentrations occurred with the includer cultivars in the moderate and the high Cl treatments. Soil concentrations of chloride reflected the chloride treatments in 1995, but not 1996. Soil populations of F. solani did not respond consistently to either chloride treatment or cultivar; however, H. glycines egg densities increased with increased soil chloride treatments in Hartz 6686 (SE) and Terra Vig 6653 (SI) at R2, but not at harvest. Increased soil chloride treatments increased SDS in both years with Hartz 6686 (SE), but did not affect this disease in the other cultivars. Higher soil chloride treatments decreased yield in all cultivars except Hartz 6200 (RE) in 1996. Although Terra Vig 6653 (SI) did not develop severe levels of SDS foliar symptoms, it did have increased lodging and significant increases in southern blight with moderate and high soil chloride treatments. These results indicate that growers with fields that have both elevated concentrations of soil chloride and SDS should select SDS-resistant excluder cultivars to minimize yield losses due to both problems.