bluuebunny/crossref_metadata_2025 huggingface dataset:
Frankliniella cephalica, a New Vector for Tomato spotted wilt virus
Authors: Ohnishi J. , Katsuzaki H. , Tsuda S. , Sakurai T. , Akutsu Katsumi , Murai T.
Published: May 2007

Frankliniella cephalica (Crawford) is an invasive species of thrips found in the islands of Yaeyama in the Okinawa Prefecture, Japan. During the late 1990s to early 2000s, a species of thrips was isolated from wild flowers of Bidens pilosa L. and Ipomoea batatas L. growing close to cultivated fields. They were subsequently identified as F. cephalica using fine morphological characteristics with the help of Steve Nakahara (U.S. Department of Agriculture, Beltsville, MD) and Laurence Mound (CSIRO, Australia). Voucher specimens were deposited in the Laboratory of Insect Resources, Faculty of Agriculture, Tokyo University of Agriculture by Shuji Okajima (2). We investigated the ability of F. cephalica to vector Tomato spotted wilt virus (TSWV) by experimentally determining virus transmission efficiency. Newly hatched larvae as much as 12 h old underwent a viral acquisition-access period (AAP) of 24 h, during which they fed on the leaves of Datura stramonium infected with TSWV-O, a Japanese type isolate. Transmission efficiency of adults 4 days after emergence from molt (14 days after the AAP) was determined by a petunia leaf disk assay (3) in which the adults were individually allowed to feed for successive 24-h inoculation access periods (IAP) on two different leaf disks of Petunia × hybrida cv. Polo Blue. Transmission of the virus by the adults was considered positive if at least one of the leaf disks showed viral necrotic spot. We tested 20 randomly selected leaf disks with clear necrotic spots using a simplified rapid immunofilter paper assay. All selected disks were positive for TWSV. The transmission efficiencies were 24.6% for female (n = 57) and 54.4% for male (n = 125) adults. The efficiency was significantly different between sexes (Fisher's exact probability test, P < 0.001). We also examined changes in the virus infection site at different developmental stages in thrips using immunofluorescence microscopy with a polyclonal antibody to N protein of the virus (4). After a 6-h AAP feeding by first instar larvae, the virus was found initially to infect the epithelial cells and then spread throughout the midgut tissue in the second instar larvae 5 days after acquisition of the virus. In viruliferous adults, the virus was present in the salivary glands and on the basement membrane of the midgut tissue. These data indicate that F. cephalica is a new insect vector for TSWV. F. cephalica is a major insect pest of tropical crops in tropical and subtropical coastal belts (1). The presence of a thrips vector in weed hosts surrounding cultivated fields might increase the chance of crops in this habitat becoming infected with viruses.

References: (1) M. Lamberts and J. H. Crane. Page 337 in: Advances in New Crops. J. Janick and J. E. Simon, eds. Timber Press, Portland, OR, 1990. (2) M. Masumoto and S. Okajima. Jpn. J. Appl. Entomol. Zool. 48:225, 2004. (3) T. Sakurai et al. Appl. Entomol. Zool. 39:71, 2004. (4) S. Tsuda et al. Ann. Phytopathol. Soc. Jpn. 60:216, 1994.
First Report of Seedling Blight Caused by Sclerotium rolfsii on Wheat in Oklahoma
Authors: Choppakatla V. , Hunger R. M. , Melouk H. A.
Published: May 2007

Wheat (Triticum aestivum L.) is an important crop in Oklahoma and throughout the Central Plains of the United States. The soilborne fungus, Sclerotium rolfsii, is a major pathogen on peanut (Arachis hypogaea L.) but is not known to cause major damage on wheat. During September of 1998, damping-off and rotting of young wheat seedlings were observed in breeder plots in Payne County, OK. The occurrence of symptoms was sporadic with an estimated stand reduction of 10 to 15%. Symptomatic plants were collected from the field and brought to the laboratory. Sclerotia-like bodies from the symptomatic plants were surface disinfested in aqueous 1% NaOCl for 2 min and allowed to germinate at 25 ± 2°C on sterile filter paper moistened with a 1% aqueous solution of methanol. Aerial mycelia from germinating sclerotia were transferred to potato dextrose agar amended with 100 ppm of streptomycin (SPDA) to obtain pure cultures. Pure cultures had coarse, white mycelium distinctive of S. rolfsii and produced very small (0.05 to 0.1 mm), abundant, round, brown sclerotia on the surface of the medium after 15 days of incubation. Pathogenicity was tested on three hard red winter wheat cultivars commonly grown in Oklahoma (Jagger, 2137, and 2174). Four plants of each cultivar were inoculated at the two-leaf stage (Feekes' scale stage 1) by placing a 0.5-cm agar disk removed from a 3-day-old culture onto a 1-cm diameter filter paper that was then pressed to the base of the shoot. Noninoculated plants were used as a control. After inoculation, pots were covered with polyethylene sheets to maintain 95 to 100% relative humidity and incubated at 25 ± 2°C in the greenhouse. Lesions were initially superficial, yellowish, and water soaked. Lesions expanded and resulted in damping-off of seedlings. Noninoculated plants were free of disease and remained healthy. No significant difference (P ≤ 0.05) in disease severity was observed among the cultivars. To fulfill Koch's postulates, the fungus was reisolated onto SPDA where it had the same characteristics as the initial culture. To our knowledge, this is the first report of S. rolfsii on wheat in Oklahoma. Even though S. rolfsii is not expected to pose a significant risk to wheat production, infection of wheat may enhance survival of S. rolfsii and facilitate infection and losses in a following peanut crop. This is especially important in certain areas of Oklahoma where a wheat-peanut rotation is occasionally practiced.
Assessment of Regional Site-Specific Sorghum Ergot Severity Potential Using Radar-Rainfall Measurement
Authors: Workneh F. , Narasimhan B. , Srinivasan R. , Rush C. M.
Published: May 2007

Sorghum ergot, caused by Claviceps africana, generally requires cool weather and humid conditions for optimum infection. Rainfall reportedly is not required for infection as long as relative humidity is high. However, occurrence of high humidity in the Texas Panhandle during the summer is usually associated with rain showers, and ergot incidence in the region has been observed to be associated with rain events. These events are often irregular and can vary within a small area both in incidence and intensity. Existing ground weather stations are too far apart to provide accurate representation of localized rainfall events. Radar-based precipitation measurements have a resolution of 4 × 4 km out to 230 km from the radar location. In the present study, radar rainfall measurements were used to assess regional site-specific sorghum ergot potential in the Texas Panhandle. The results have a potential for development of a web-based ergot risk assessment system in which growers can enter the GPS locations of their fields and determine whether management actions are necessary.
Inoculum Sources of Botrytis cinerea Important to Pear Orchards in Oregon
Authors: Spotts Robert A. , Serdani Maryna
Published: May 2007

Botrytis cinerea was capable of colonizing and persisting in tissue pieces of six common weed species found in pear orchards in Oregon from midsummer until pear harvest in early September. Sporulation occurred on blackberry mummies in orchard perimeters and ranged from 5,700 to 55,000 conidia per mummy at pear harvest. Conidia of B. cinerea also were observed on fresh blackberry fruit in 2 of 3 years. Sclerotia were present on only a few of the naturally infected pear fruit on the orchard floor through November; however, sclerotia production increased greatly between mid-November and mid-December. Over 90% of sclerotia from naturally infected, overwintered fruit germinated in the laboratory when collected 6 to 8 months after infection. Sclerotia formed on pear fruit inoculated with 28 different paired combinations of 22 isolates in the laboratory. Viability of sclerotia in inoculated pear fruit that overwintered on the orchard floor was 44 to 59% in March and April, and then declined steadily to about 25% at pear harvest. Germination of sclerotia was both sporogenic and myceliogenic. No apothecia were observed in the field or laboratory. An integrated approach to control is needed to deal with these multiple sources of potential inoculum.
First Report of Root-Knot Nematode Meloidogyne javanica on Chrysanthemum in Colombia
Authors: Agudelo P. A. , Lewis S. A. , Abril M. A.
Published: May 2007

Severe plant stunting, chlorosis, and extensive root galling were observed on chrysanthemum (Dendrathema grandiflora cv. Yellow Vero) in a commercial cut-flower production facility in Rionegro, Antioquia, northwestern Colombia. Examination of the root samples from selected infected plants revealed the presence of abundant root-knot nematodes. Juveniles, males, and females were extracted for species identification using morphological characteristics. Identification was confirmed by perineal patterns and esterase phenotype analysis of females. All methods of identification were consistent with typical Meloidogyne javanica. No other root-knot nematode species were found on this farm, but the presence of other Meloidogyne species in the region is possible. Root-knot nematodes have been reported to cause economic losses in cut-flower plantations in Colombia (1), but there are no reports of the species involved. M. javanica has an extensive host range and wide distribution. The identification and distribution of M. javanica in chrysanthemum production is relevant because nematode-fungus interactions may depend on the nematode species involved. Only M. javanica, and not M. hapla or M. incognita, has been found to increase the severity of Fusarium wilt on chrysanthemum (2). To our knowledge, this is the first report of M. javanica on chrysanthemum in Colombia.

References: (1) G. Arbeláez. Acta Hortic. 482:91, 1999. (2) A. W. Johnson and R. H. Littrell. J. Nematol. 1:122. 1969.
Sawadaea tulasnei Powdery Mildew of Norway Maple (Acer platanoides) in North America
Authors: Weiland J. , Stanosz G.
Published: May 2007

Norway maple leaves bearing powdery mildew were collected from one location in the fall of 2003 and four locations (as much as 1.5 km apart) in the fall of 2005 in Buffalo, NY. No powdery mildew was observed on leaves collected from sugar maples (Acer saccharum) that were present in the vicinity of affected Norway maples at two locations. Trees were located along streets and in yards. Diseased leaves were present throughout tree crowns but lower leaves were more commonly affected. White mycelium was present in irregular, discrete, scattered spots only on the upper surface of leaves and on both sides of wings of samaras. Typically, <10% of the upper leaf area bore visible mycelium. Cleistothecia were present singly or in groups on the mycelium. Morphology of cleistothecia on leaves collected each year, including simple and bifid appendages with uncinate to circinate apices, was sufficient to identify the pathogen to the genus Sawadaea (1). Other characteristics were not sufficiently distinct to make an identification of S. bicornis or S. tulasnei (1), each a European species found on Acer spp. However, a sample from 2003 was supplied by the authors for use in a study of phylogeny of the genus (2) that served as a first report of the species in the United States. Analysis of nuclear rDNA ITS sequence of this specimen (GenBank Accession No. AB193390) placed the sample in a clade with S. tulasnei specimens from Europe. In the same study, powdery mildew samples from Acer spp. in Ohio and Montreal, Canada also were placed in this clade. Thus, occurrence of S. tulasnei in North America is confirmed. S. bicornis was recently identified (based on morphology) on Norway maple in the western United States (3). Specimens from Buffalo, NY have been deposited in the U.S. National Fungus Collections (BPI 871210).

References: (1) U. Braun. The Powdery Mildews (Erysiphales) of Europe. Gustav Fischer Verlag, Jena-Stuttgart-New York, 1995. (2) S. Hirose et al. Mycol. Res. 109:912, 2005. (3) C. Nischwitz and G. Newcombe. Plant Dis. 87:451, 2003.
Molecular Characterization of a Distinct Tomato-Infecting Begomovirus Associated with Yellow Leaf Curl Diseased Tomato in Lembang, Java Island of Indonesia
Authors: Tsai W. S. , Shih S. L. , Green S. K. , Akkermans D. , Jan F.-J.
Published: May 2007

Three distinct tomato-infecting begomoviruses have been identified from Indonesia (GenBank Accessions Nos. AB100304, AB100305, and DQ083765). Severe yellow leaf curl epidemics have been observed on tomato on Java Island since the late 1990s. Viral DNA was extracted (2) from one such sample collected in Lembang, West Java in 1998. Polymerase chain reaction with previously described primers was used to detect the presence of geminiviral DNA-A (4), DNA-B (3), and associated satellite DNA (1). The predicted 1.4-kb DNA-A fragment was amplified with the general primer pair PAL1v1978/PAR1c715 and then cloned and sequenced. DNA-B and satellite DNA were not detected in the sample. On the basis of the partial DNA-A sequences, specific primers were designed to amplify and sequence the complete DNA-A component (2,762 nucleotides, GenBank Accession No. AF189018). The DNA-A sequence contained the geminivirus-conserved nanosequence TAATATTAC in the loop of the hairpin structure of the intergenic region and six open reading frames including two in the virus sense and four in the complementary sense. Pairwise comparison of the full-length DNA-A sequence with those of other begomoviruses available in the GenBank database was done by the MegAlign software (DNASTAR, Inc, Madison, WI). Highest nucleotide sequence identity (74.1%) was with Tomato leaf curl Mayotte virus-[Kahani] (GenBank Accession No. AJ865340). Comparison of the full-length DNA-A sequence with the three above mentioned tomato-infecting begomoviruses from Indonesia also showed less than 71% nucleotide sequence identities. Because the DNA-A sequence had less than 89% identity with other begomoviruses, it should be classified as a distinct virus according to the International Committee on Taxonomy of Viruses. The name Tomato yellow leaf curl Indonesia virus-[Lembang] (TYLCIDV-[Lem]) is proposed. The presence of at least four distinct tomato-infecting begeminiviruses on Java Island needs to be considered when developing tomato cultivars with stable resistance to tomato (yellow) leaf curl disease.

References: (1) R. W. Briddon et al. Virology 312:106, 2003. (2) R. L. Gilbertson et al. J. Gen. Virol. 72:2843, 1991. (3) S. K. Green et al. Plant Dis. 85:1286, 2001. (4) M. R. Rojas et al. Plant Dis. 77:340, 1993.
Long-Term Prediction of Soybean Rust Entry into the Continental United States
Authors: Pan Z. , Yang X. B. , Pivonia S. , Xue L. , Pasken R. , Roads J.
Published: May 2007

This special report demonstrates the feasibility of long-term prediction of intercontinental dispersal of Phakopsora pachyrhizi spores, the causal agent of the devastating Asian soybean rust (SBR) that invaded the continental United States in 2004. The climate-dispersion integrated model system used for the prediction is the combination of the particle transport and dispersion model (HYSPLIT_4) with the regional climate prediction model (MM5). The integrated model system predicts the trajectory and concentration of P. pachyrhizi spores based on three-dimensional wind advection and turbulent transport while incorporating simple viability criteria for aerial spores. The weather input of the model system is from a seasonal global climate prediction. The spore source strength and distribution were estimated from detected SBR disease severity and spread. The model system was applied to the known P. pachyrhizi spore dispersal between and within continents while focusing on the disease entry into the United States. Prediction validation using confirmed disease activity demonstrated that the model predicted the 2004 U.S. entry months in advance and reasonably forecast disease spread from the south coast states in the 2005 growing season. The model also simulated the dispersal from Africa to South America and from southern South America to Columbia across the equator. These validations indicate that the integrated model system, when furnished with detailed source distribution, can be a useful tool for P. pachyrhizi and possibly other airborne pathogen prediction.
Aggressiveness of Puccinia striiformis f. sp. tritici Isolates in the South-Central United States
Authors: Milus E. A. , Seyran E. , McNew R.
Published: May 2007

Although stripe rust, caused by Puccinia striiformis f. sp. tritici, has been an occasional problem on wheat in the south-central United States from 1941 until 1999, the disease has been consistently severe in the region since 2000. Furthermore, since 2000, the geographic range of stripe rust in the eastern United States has expanded, and the old population of races has been replaced by a new population. The objective of this study was to determine whether new isolates of the pathogen were more aggressive and better adapted to warmer temperatures than old isolates. In all, 6 old isolates (collected before 2000) and 14 new isolates (collected since 2000) were evaluated at 12 and 18°C for latent period on wheat seedlings and urediniospore germination on Noble agar. At 12°C, old and new isolates had similar latent periods and spore germination percentages. However, at 18°C, new isolates averaged 2 days less for latent period and double the spore germination compared with old isolates. Therefore, the new isolates are better adapted and, thus, more aggressive at warmer temperatures than the old isolates. These differences may have contributed to the severity of recent epidemics in the region and to the expanded geographic range for stripe rust.
Almond Replant Disease and Its Management with Alternative Pre-Plant Soil Fumigation Treatments and Rootstocks
Authors: Browne G. T. , Connell J. H. , Schneider S. M.
Published: May 2007

Trials were conducted in orchards near Chico, CA and microplots near Parlier, CA to examine symptoms and control measures for a replant disease (RD) on almond (Prunus dulcis). In the orchard trials, areas with a recent history of severe RD were cleared, given soil fumigation treatments in the fall, and replanted with almond trees on various rootstocks the following winter. The replants in nonfumigated soil developed severe RD (stunting, wilting, chlorosis, defoliation) by the following summer, while those in most fumigated treatments remained healthy. Trees in nonfumigated soil developed smaller trunk diameters and fewer healthy roots ≤1 mm diameter, compared with the healthy trees. Almond developed RD on all rootstocks evaluated (Marianna 2624, Lovell, and Nemaguard), but the trees on Marianna 2624 were the most severely affected. Pre-plant tree-site (spot) fumigation treatments with methyl bromide (MB), chloropicrin (CP), 1,3-dichloropropene (1,3-D), 1,3-D + CP, iodomethane, and iodomethane + CP all prevented severe RD. Broadcast soil fumigation with CP also was effective, but broadcast MB and 1,3-D were ineffective. In microplots filled with RD-conducive soil, CP was more potent than MB for prevention of RD on Nemaguard peach. There was no association between nematodes and RD in orchard or microplot trials. The RD apparently was mediated by a biological agent(s) other than nematodes and can be prevented by appropriate fumigation with CP or other MB alternatives.
Influence of Temperature, Relative Humidity, Ascospore Concentration, and Length of Drying of Colonized Dry Bean Flowers on White Mold Development
Authors: Harikrishnan R. , del Río L. E.
Published: May 2007

Growth chamber studies were conducted using rehydrated dry bean (Phaseolus vulgaris) flowers (RDBF) to assess the influence of temperature (18 and 22°C), relative humidity (RH; 25 and 90%), and ascospore concentrations (102, 103, and 104 ascospores/ml) on white mold incidence in dry bean. Additional studies were carried out to determine the influence of inoculum type (ascospore and mycelium) and to estimate the effect of duration of drying of colonized RDBF on viability of Sclerotinia sclerotiorum and white mold incidence. There was a linear increase in white mold incidence with increase in ascospore concentration but neither temperature nor RH levels significantly affected disease development. In the inoculum type study, both temperature and RH levels significantly affected white mold incidence; however, neither ascospore nor mycelial inocula had a significant effect on white mold incidence. Drying colonized RDBF for up to 96 h did not affect S. sclerotiorum viability; but the amount of white mold incidence depended more on post-inoculation RH and drying duration than on the temperatures tested. Colonized RDBF dried for 96 h took approximately three times longer to achieve 100% white mold incidence compared with colonized RDBF dried for 24 h. These results suggest the potential for greater white mold development with higher ascospore availability and the potential of dry S. sclerotiorum-colonized dry bean flowers as a viable inoculum source.
Management of Sclerotinia Blight of Peanut with the Biological Control Agent Coniothyrium minitans
Authors: Partridge D. E. , Sutton T. B. , Jordan D. L. , Curtis V. L. , Bailey J. E.
Published: May 2007

Sclerotinia blight, caused by Sclerotinia minor, is an important disease of peanut in North Carolina. The effectiveness of Coniothyrium minitans, a mycoparasite of sclerotia of Sclerotinia spp., was studied in a 5-year field experiment and in eight short-term experiments in northeastern North Carolina. The 5-year experiment was initiated in November 1999 to evaluate the effectiveness of repeated soil applications of C. minitans (commercial formulation, Contans WG) at 2 and 4 kg ha-1 in reducing Sclerotinia blight. In addition, individual commercial peanut fields were selected in 2001 and 2002 to evaluate a single application of C. minitans at 4 kg ha-1. No differences were found between the 2 and 4 kg ha-1 rates of C. minitans in reducing Sclerotinia blight. In 2002, there was less disease in plots receiving applications of C. minitans for either 1 or 3 years compared with the nontreated control; whereas, in 2003, C. minitans applications for 1, 2, or 3 years reduced disease and the number of sclerotia isolated from soil. A single application of C. minitans reduced sclerotia in only two of the eight short-term experiments. The integration of consecutive years of soil applications of C. minitans at 2 kg ha-1 with moderately resistant cultivars and fungicide applications may aid in the management of Sclerotinia blight in peanut.
Effects of Soil-Applied Late Blight Foliar Fungicides on Infection of Potato Tubers by Phytophthora infestans
Authors: Porter L. D. , Cummings T. F. , Johnson D. A.
Published: May 2007

Potato tuber infection was assessed under greenhouse and outdoor conditions when late blight foliar fungicides were applied to soil 24 h prior to soil infestation with a suspension of zoospores and sporangia of Phytophthora infestans. Spore viability of P. infestans in soil treated with various fungicides was determined using buried healthy whole tubers and by assaying infested soil applied to freshly cut tuber disks. Protection of tubers and tuber disks from infection was more effective when soil was treated with mancozeb, metiram, and cyazofamid than with other fungicides. Whole tuber infections were significantly less in soils treated with mancozeb, metiram, fluazinam, and fenamidone than when treated with distilled water. Infection of buried tubers and tuber disks was prevented for 3 to 5 days following a single soil application of mancozeb or metiram under outdoor conditions. The tuber disk method was more sensitive in determining the efficacy of a fungicide in inhibiting infection and spore viability than using whole buried tubers. However, both methods of determining viability may determine different modes of action of some fungicides that inhibit infection since whole tubers were not infected when protected by some fungicides but tuber disks were infected.
First Report of Rust Caused by Phakopsora pachyrhizi on Soybean and Kudzu in Texas
Authors: Isakeit T. , Miller M. E. , Saldaña R. , Barnes L. W. , McKemy J. M. , Palm M. E. , Zeller K. A. , DeVries-Paterson R. , Levy L.
Published: May 2007

The Asian soybean rust fungus, Phakopsora pachyrhizi H. Sydow & Sydow, was found on a 0.4-ha patch of kudzu (Pueraria lobata) near Dayton (Liberty County) in East Texas on November 2, 2005. Nearly 100% of the 300 leaflets examined were diseased with severity ranging from 5 to >100 lesions per leaflet. Eleven soybean fields as much as 20 km away were scouted and no infected plants were found. Asian soybean rust was also found on a 0.4-ha field of soybean (Glycine max cv. Vernal) on February 14, 2006 at the Texas A&M Agricultural Experiment Station in Weslaco (Hidalgo County) in the Lower Rio Grande Valley (LRGV) of Texas. Disease incidence was 100% (severity ranging from 5 to >100 lesions per leaflet) on 50 younger plants with green leaves along the edges of the field, whereas most of the plants in this field had senesced. These plants were not symptomatic and were at the R6 stage (full seed) when this field was previously scouted on December 19, 2005. Lesions on leaflets of kudzu and soybean were small and angular with erumpent uredinia typical of P. pachyrhizi. Urediniospores were ovoid or globose, hyaline, and measured 25 to 30 × 14 to 21 μm. Leaf samples with pustules were positive for P. pachyrhizi using enzyme-linked immunosorbent assay (ELISA) (Envirologix, Portland, ME). Morphological and polymerase chain reaction (PCR) identification of P. pachyrhizi from kudzu and soybean samples were confirmed by the USDA-APHIS-PPQ NIS and CPHST laboratories in Beltsville, MD as previously described (2). The kudzu in East Texas is not likely to support overwintering of the pathogen because it usually dies back during the winter. Leaves at this site were dead by January 17, 2006. This is the southernmost infestation of kudzu in Texas known to us. In contrast, the LRGV has a subtropical climate that would favor year-round survival of the fungus (3). This area, where 120 to 160 ha of soybeans are grown, may be a source of inoculum for soybean rust epidemics in the Midwest. Spore movement would follow the same pattern as seen with cereal rusts (1). However, soybeans are typically absent from the LRGV between late December and early March, so survival of the fungus during this interval would require other hosts. Regardless of whether the fungus overwinters here, or moves in from elsewhere, the LRGV spring crop could serve as an early indicator of a potential rust epidemic.

References: (1) M. G. Eversmeyer and C. L. Kramer. Annu. Rev. Phytopathol. 38:491, 2000. (2) J. M. Mullen et al. Plant Dis. 90:112, 2006. (3) S. Pivonia et al. Plant Dis. 89:678, 2005.
First Report of Phakopsora pachyrhizi, the Causal Agent of Asian Soybean Rust, on Florida Beggarweed in the United States
Authors: Sconyers L. E. , Kemerait R. C. , Brock J. H. , Gitaitis R. D. , Sanders F. H. , Phillips D. V. , Jost P. H.
Published: May 2007

Phakopsora pachyrhizi Syd. & P. Syd., which causes Asian soybean rust (SBR), was observed on Florida beggarweed, Desmodium tortuosum (Sw) DC., in Attapulgus, GA during late October and early November 2005. Tan to brown lesions (<1.0 mm in diameter) consistent with symptoms of SBR (2) were observed on older leaves of several plants collected near an SBR-infected soybean trial. Dissection (40 to 60×) and compound microscopy (×200 to 400) revealed conical pustules and ellipsoid, echinulate urediniospores (average size 15 × 20 μm) on the abaxial leaf surface. Polymerase chain reaction (PCR) (primers Ppm1 and Ppa2) (1) was conducted on four samples to confirm identification of P. pachyrhizi or P. meibomiae. Three were positive for P. pachyrhizi, and one was negative for both species. Using morphology and real-time PCR, SBR was confirmed as P. pachyrhizi by the USDA/APHIS in Beltsville, MD. Six noninfected Florida beggarweed plants were transplanted to pots during December 2005 and grown at 22 to 24°C in a greenhouse. On 11 January 2006, a water suspension of urediniospores collected from SBR-infected soybeans (1 × 105 spores per ml) was spray inoculated on all leaves to almost runoff and incubated for 48 h in a plastic humidity chamber. Lesions, pustules, and urediniospores consistent with SBR (2) were observed on 3 February 2006. A PCR assay was conducted on six samples from the infected greenhouse plants and all were positive for P. pachyrhizi. Florida beggarweed is widespread in the southern United States and may serve as an additional overwintering source for P. pachyrhizi and a potential inoculum source for the soybean crop.

References: (1) R. D. Fredrick et al. Phytopathology 92:217, 2002. (2) J. B. Sinclair and G. L. Hartman. Soybean rust. Pages 25–26 in: Compendium of Soybean Diseases. 4th ed. G. L. Hartman et al., eds. The American Phytopathological Society, St. Paul, MN, 1999.
A Yellow Mosaic Disease of Soybean in Northern India is Caused by Cotton leaf curl Kokhran virus
Authors: Raj S. K. , Khan M. S. , Snehi S. K. , Srivastava S. , Singh H. B.
Published: May 2007

Soybean, Glycine max (L.) Merr., is a protein- and oil-rich crop cultivated in India and abroad. A yellow mosaic disease was observed on soybean with 80 to 90% disease incidence during August 2005 at fields of the National Botanical Research Institute, Lucknow, in northern India. Soybean plants were found to be infested with whiteflies (Bemisia tabaci) suggesting begomovirus etiology. The disease agent was transmitted experimentally by whiteflies, and symptoms developed after 23 days. Total DNA was isolated from 51 leaf samples collected from 42 symptomatic and 9 asymptomatic plants. Polymerase chain reaction was performed using begomovirus coat protein-specific primers 5′-ATGGCGAA GCGACCAG-3′ and 5′-TTAATTTGTGACCGAATCAT-3′ (AM180920/ AM180921). An amplicon of the expected size (~800 bp) was obtained in all 42 symptomatic leaves but not from any of the nine asymptomatic leaf samples. The amplicon was cloned, and the identical sequence of three clones was submitted to GenBank (Accession No. DQ343283). BLAST search of nucleotide sequences revealed 95% identity with Cotton leaf curl Kokhran virus (CLCKV) (GenBank Accession Nos. AJ002449, AJ002448, AJ496286, and AY456683) and 57% identity with Mungbean yellow mosaic India virus (MYMIV-Sb, GenBank Accession No. AY049772). Results indicated that the virus associated with yellow mosaic disease of soybean is an isolate of CLCKV rather than MYMIV-Sb (1) reported earlier on soybean from northern India. To our knowledge, this is the first report of soybean as a new host of Cotton leaf curl Kokhran virus.

Reference: (1) K. S. Usharani et al. Curr. Sci. 86:845, 2004.
Field Trials of Plum Clones Transformed with the Plum pox virus Coat Protein (PPV-CP) Gene
Authors: Malinowski T. , Cambra M. , Capote N. , Zawadzka B. , Gorris M. T. , Scorza R. , Ravelonandro M.
Published: May 2007

Transgenic clones C2, C3, C4, C5, C6, and PT-6, of plum (Prunus domestica L.) transformed with the coat protein (CP) gene of Plum pox virus (PPV), PT-23 transformed with marker genes only, and nontransgenic B70146 were evaluated for sharka resistance under high infection pressure in field trials in Poland and Spain. These sites differed in climatic conditions and virus isolates. Transgenic clone C5 showed high resistance to PPV at both sites. None of the C5 trees became naturally infected by aphids during seven (Spain) or eight (Poland) years of the test, although up to 100% of other plum trees (transgenic clones and nontransgenic control plants) grown in the same conditions showed disease symptoms and tested positively for PPV. Although highly resistant, C5 trees could be infected artificially by chip budding or via susceptible rootstock. Infected C5 trees showed only a few mild symptoms on single, isolated shoots, even up to 8 years post inoculation. These results clearly indicate the long-term nature and high level of resistance to PPV obtained through genetically engineered resistance.
Influence of Temperature, Inoculation Interval, and Dosage on Biofumigation withMuscodor albusto Control Postharvest Gray Mold on Grapes
Authors: Gabler F. Mlikota , Fassel R. , Mercier J. , Smilanick J. L.
Published: May 2007

Control of postharvest gray mold, caused by Botrytis cinerea, on Thompson Seedless grape by biofumigation with a rye grain formulation of Muscodor albus, a fungus that produces volatiles lethal to many microorganisms, was evaluated. The influences of temperature, biofumigant dosage, and interval between inoculation and treatment on disease incidence and severity on detached single berries were assessed. When biofumigation began within 24 h after inoculation, higher M. albus dosages (≥50 g of the M. albus grain formulation per kilogram of grapes at 20°C or 100 g/kg at 5°C) stopped infections and control persisted after M. albus removal. Biofumigation was more effective at 20 than 5°C. Among inoculated clusters inside clamshell boxes incubated for 7 days at 15°C, gray mold incidence was reduced from 20.2% among untreated grape fruit to less than 1%, when ≥5 g of the formulation per kilogram of grapes was added. Among grape berries commercially packaged in ventilated polyethylene cluster bags incubated for 7 days at 15°C, gray mold incidence was 40.5% among untreated fruit and 11.1 or 6.7% when the formulation at 5 or 20 g/kg, respectively, had been added. In the same packaging, among grape berries incubated for 28 days at 0.5°C, gray mold incidence was 42.8% among untreated fruit and 4.8 or 4.0% when the formulation at 5 or 10 g/kg, respectively, had been added. Lower dosages (≤20 g/kg) suppressed disease development while M. albus was present; however, after their removal, B. cinerea resumed growth and gray mold incidence increased. Placement of M. albus inside grape packages significantly controlled gray mold and may be a feasible approach to manage postharvest decay of table grape.
Virulence and Diversity of Blumeria graminis f. sp. hordei in Israel and in the Czech Republic
Authors: Dreiseitl Antonín , Dinoor Amos , Kosman Evsey
Published: May 2007

Three hundred and nine isolates were obtained from three natural populations of Blumeria graminis f. sp. hordei occurring on wild barley (Hordeum vulgare subsp. spontaneum) at two locations in Israel during 1997 and 1999. Their virulence frequency was determined on 32 differential lines. No isolate was virulent on the differential lines possessing the genes Mla13, mlo, Mlf1, and Mli, and conversely no isolate was avirulent on the differential lines possessing the genes MlRu2, MlLa, Mlh, Mla8, Mla25, and Mlj. The frequencies of isolates overcoming the genes Mlg, Mla7, and Mla27 were 0 to 16% at individual locations; frequencies of isolates overcoming the genes Mla9, Mla17, and Mla18 ranged from 37 to 78%, and frequencies of virulences to genes Mla1, Mla3, Mla6, Mlp1, Mlat, Mla12, Mlra, Mlk1, Mla19, Mla20, Mla26, Mla28, Mla29, Mla30, Mla32, and mlt1 were 79 to 99%. Based on examination of 376 isolates collected in the same years from the Czech Republic, these populations differed greatly from the Israeli ones. The Czech populations showed greater diversity of virulence and lower mean virulence complexity than the Israeli populations. Diversity in the Israeli populations differed also among clusters of niches at the same location.
Initiation of Rice Sheath Blight Epidemics and Effect of Application Timing of Azoxystrobin on Disease Incidence, Severity, Yield, and Milling Quality
Authors: Groth D. E. , Bond J. A.
Published: May 2007

The lack of sheath blight-resistant cultivars requires rice (Oryza sativa) farmers to use fungicides to control the disease and avoid significant reductions in grain and milling yield. Sheath blight (Rhizoctonia solani) epidemics can begin over a period of weeks during the growing season, and initiation date can have significant effects on crop damage and fungicide application timing. Studies were conducted to determine how different epidemic initiation and azoxystrobin application timings affect disease development, rice yield, and milling quality. Sheath blight epidemics in field plots were initiated by inoculation at the green ring (GR), panicle differentiation (PD), early boot (EB), and late boot (LB) growth stages in 2002 to 2004. Azoxystrobin was applied to the foliage at 0.17 kg a.i. ha-1 at 7 days after PD (PD+7), midboot (B), and 50% heading (H). Inoculation significantly increased sheath blight severity and incidence and reduced yield and milling quality. There were no significant effects of inoculation timing at the GR, PD, EB, and LB growth stages. Fungicide applications made between PD+7 and H reduced sheath blight severity and incidence, resulting in higher yield and head rice milling yield compared with inoculated but nonsprayed plots.
Frequency and Pathogenicity of Dematiaceous Hyphomycetes on Annual Ryegrass Overseeded on Bermudagrass in Mississippi
Authors: Pratt R. G.
Published: May 2007

Fungal diseases of annual ryegrass (Lolium multiflorum Lam.), a cool-season species grown for forage and turf in the southeastern United States, and bermudagrass (Cynodon dactylon (L.) Pers.), a warm-season perennial, usually are considered distinct. In May 2002 and 2004, symptoms of leaf and stem necrosis were observed simultaneously in forage bermudagrass and overseeded annual ryegrass on a swine waste application site in Mississippi. Sporulation by nine species of Bipolaris, Curvularia, Drechslera, and Exserohilum was observed on symptomatic leaves of ryegrass that were surface disinfested and plated on agar each year, and axenic cultures were established by spore transfers. These isolations represent four new worldwide and two new North American records of occurrence of fungal pathogens on ryegrass, and three new records for the southeastern United States and Mississippi. Bipolaris cynodontis, a common bermudagrass pathogen, and Drechslera dictyoides were observed most frequently on ryegrass during both years. In excised leaves of ryegrass inoculated with infested agar discs, most isolates of B. cynodontis from ryegrass and bermudagrass were equally virulent and caused necrosis equal to or greater than that caused by D. dictyoides, an established ryegrass pathogen. Isolates of B. cynodontis from both hosts also caused similar symptoms in foliage of ryegrass and bermudagrass following spore inoculations. Pathogenicity to ryegrass of five other species of dematiaceous hyphomycetes that represented new worldwide or North American records of occurrence also was demonstrated by foliar inoculations. All pathogens were reisolated from symptomatic tissues and grown in axenic culture for fulfillment of Koch's postulates. Results demonstrate that most of the same species of dematiaceous hyphomycetes infect both forage ryegrass and bermudagrass in Mississippi and indicate that B. cynodontis, in particular, may be a common and virulent pathogen of ryegrass in the southeastern United States.
The Occurrence of PVYO, PVYN, and PVYN:O Strains of Potato virus Y in Certified Potato Seed Lot Trials in Washington and Oregon
Authors: Crosslin J. M. , Hamm P. B. , Hane D. C. , Jaeger J. , Brown C. R. , Shiel P. J. , Berger P. H. , Thornton R. E.
Published: May 2007

Totals of 960 and 286 certified potato seed lots from locations across North America were planted in trials in Washington and Oregon, respectively, in 2001 to 2003 and tested for strains of Potato virus Y (PVY). The incidence of PVYO-infected lots averaged 16.4 and 25.9% in the Washington and Oregon trials, respectively. There was a general trend of increasing incidence of the PVYO, PVYN:O, and PVYN strains during this period, as evidenced by more infected cultivars, sites of seed origin, and number of seed growers providing infected seed lots. In particular, there was a dramatic increase in seed lots with the PVYN:O strain from 2002 to 2003. PVYN:O, in contrast to PVYO, which only causes yield reduction, also causes internal and external damage to tubers, making them unmarketable. In 2003, PVYN:O occurred in seed lots originating in eight states and three Canadian provinces. The increased incidence of PVYN:O was likely due to the difficulty in differentiating this strain from PVYO. The prevalence of PVY in potato seed lots documented herein poses a threat to potato production in the United States and suggests that current measures to reduce the incidence of this virus are inadequate.
First Report of Botryosphaeria dothidea on Sycamore, Red Oak, and English Oak in Northwestern Italy
Authors: Turco E. , Marianelli L. , Vizzuso C. , Ragazzi A. , Gini R. , Selleri B. , Tucci R.
Published: May 2007

The Parco Nord Milano, Italy is a 600-ha green area (45°53′71″N, 9°20′97″E). Since the spring of 2002, extensive and unknown decline was observed on 20-year-old sycamore (Acer pseudoplatanus), red oak (Quercus rubra), and English oak (Q. robur) plantations. The trees showed branch and twig dieback associated with bark cankering along the whole stem and an irregular to wilted crown. A closer inspection of the inner part of the symptomatic trunk and roots revealed a dark bluish tissue discoloration. From the symptomatic trunk and root tissue, a dark gray abundant mycelium was consistently isolated on potato dextrose agar (PDA). The sequenced internal transcribed spacer (ITS) regions of rDNA (GenBank Accession Nos. DQ198265, DQ198266, and DQ198267) showed 99% identity to Botryosphaeria dothidea strain CBS110302 (GenBank Accession No. AY259092). A Fusicoccum sp. with black pycnidia was consistently collected from the cankers. The conidia were hyaline, aseptate, fusiform to narrowly ellipsoidal, with a truncate base (22 × 4.5 μm), referred to as Fusicoccum aesculi (CBS identification), the anamorph of B. dothidea (2). Pathogenicity tests were conducted for all three hosts by stem inoculation on 18-month-old seedlings growing in plastic pots containing a 2:1 turf/sand mixture. Two experiments were conducted using two inoculation techniques. In the first trial, 6-mm-diameter mycelial plugs of B. dothidea were applied to 6-mm-long bark wounds. The same inoculation method was used for application to bark without wounding. Control seedlings were inoculated with sterile agar plugs in a similar fashion as above. Inoculated and control seedlings were kept in a growth chamber and watered once per week. In the second trial, segments of branches 15-cm long were inoculated with 6-mm-diameter B. dothidea plugs (1), with and without any wounding. Control segments of branches were treated with sterile agar plugs in place of fungal mycelium. The branches were incubated at 23°C in moist chambers. For both experiments, the inoculated stem portions were wrapped with Parafilm to prevent desiccation. There were three replicate seedlings per inoculation technique, experiment, and plant species. After 2 months, all seedlings showed bark cankers and pycnidial formation, while the controls were symptomless. An inner dark bluish stem tissue discoloration was observed. The symptoms were more abundant on the segment of branches where the inoculum was applied to the wounded bark. B. dothidea was successfully reisolated, confirming Koch's postulates. To our knowledge, although it is accepted as synonymous of B. berengeriana (2), this is the first report of B. dothidea on sycamore, red oak, and English oak in Italy. The fungus was previously reported in Italy to cause canker on Platanus spp.

References: (1) M. E. Sanchez et al. Plant Dis. 87:1515, 2003. (2) B. Slippers et al. Mycologia 96:83, 2004.
First Report of the Barley Root-Knot Nematode Meloidogyne naasi Infecting Annual Bluegrass on a Golf Course in Quebec, Canada
Authors: Bélair G. , Simard L. , Eisenback J. D.
Published: May 2007

Annual bluegrass, Poa annua L., is an important component of the vegetation on golf course greens and fairways throughout Canada and is widely distributed across the world (2). The barley root-knot nematode, Meloidogyne naasi Franklin, infects and damages cereals such as barley (Hordeum vulgare), sorghum (Sorghum vulgare), and wheat (Triticum durum and T. vulgare), mainly in Europe. Of the root-knot species, M. naasi in particular, prefers grasses over other hosts, and infestations of this nematode can reduce the growth and vigor of turfgrasses (1). In July 2005, annual bluegrass at Beaconsfield Golf Club in Pointe Claire (45°26′N, 73°50′W), Quebec showed signs of an unidentified disease. Irregular yellowish/chlorotic patches were observed on the collar of one golf green. Lower turfgrass density in the turf areas with symptoms was noted. When roots were examined under a dissecting microscope, galling was observed. Upon dissection of washed galls, root-knot nematode egg masses and mature females inside the roots were observed. Nematode extractions of the soil from two samples of 50 g from the green and around the collar and perimeter were also done by the modified Baermann pan method. No juveniles were recovered from soil samples from the healthy area and an average of 400 and 1,500 juveniles/kg dry soil were counted in collar and perimeter samples of the patches. Morphological identification of mature females and juveniles were performed and confirmed to be M. naasi. Currently, there are no regulations to control the introduction of this nematode into Canada. To our knowledge, this is the first report of the occurrence of M. naasi in Canada where it is causing noticeable damage to turfgrass in Quebec. A soil survey is currently underway to examine the distribution of this nematode on golf course turfgrasses in Ontario and Quebec.

References: (1) R. Cook and G. W. Yeates. Nematode pests of grassland and forage crops. Pages 305–350 in: Plant Parasitic Nematodes in Temperate Agriculture. K. Evans et al., eds. CAB International, Wallingford, UK, 1993. (2) S. I. Warwick. Can. J. Plant Sci. 59:1053, 1979.