bluuebunny/crossref_metadata_2025 huggingface dataset:
First Report of Brown Rot Caused by Monilinia fructicola on Imported Peach in Hungary
Authors: Petróczy M. , Palkovics L.
Published: May 2007

Brown rot caused by Monilinia fructicola is one of the most important diseases of peach. The pathogen is included in the EPPO A2 list of quarantine organisms for Europe (2). M. laxa and M. fructigena are common in Hungary, but M. fructicola has never been reported in orchards, in trade, or in markets. In early October 2005, brown rot was observed on imported peaches from Italy and Spain at a vegetable market and some supermarkets in Budapest. The variety of peach was identified as ‘Michellini’ by colleagues in the Department of Pomology of Corvinus University. The pathogen was identified as M. fructicola on the basis of morphological and molecular characteristics. Symptoms began with a small, circular brown spot, and the rot spread rapidly. At the same time, numerous small, grayish stromata developed. Finally, the whole surface of the fruit was covered with conidial tufts. The conidia were one-celled, lemon-shaped, hyaline, 15.7 × 10.3 μm, and produced in branched monilioid chains. Conidia from infected fruit were transferred to potato dextrose agar. Fungal mycelium grew at a linear rate of 10.7 mm per 24 h at 22°C in the dark. The color of the colony was grayish, and the sporulation showing concentric rings was abundant (sporulation is sparse in M. laxa or M. fructigena). The colony was not rosetted and the margin was not lobed, in contrast with M. laxa. Pathogenicity was tested by inoculating surface-sterilized, mature peach fruits with conidia. Inoculated and control fruits were placed in a sterilized glass container at room temperature. After 5 days of incubation, typical brown rot symptoms developed on inoculated fruits while control fruits remained healthy. M. fructicola was reisolated from the inoculated fruits. PCR was used to identify the fungus (1). Species-specific internal transcribed spacer (ITS) primers for M. fructicola, M. laxa, and M. fructigena were used to amplify the DNA of isolates. Three type-cultures were used as the positive control. Following the removal of the mycelia from the agar, total DNA was extracted using a cetyltrimethylammoniumbromide extraction. The nucleic acid-containing pellet was resuspended in RNase containing Tris-EDTA buffer. DNA quality was assessed by gel electrophoresis on 1% agarose gel stained with ethidium bromide. The molecular genetic identification method confirmed the results of morphological identification. To our knowledge, this is the first report of M. fructicola on peaches in Hungary or in eastern Europe.

References: (1) R. Ioos and P. Frey. Eur. J. Plant Pathol. 106:373, 2000. (2) OEPP/EPPO. List of A2pests regulated as quarantine pests in the EPPO region. Version 2005-09. Online publication, 2005.
Distribution and Fungicide Sensitivity of Fungal Pathogens Causing Anthracnose-like Lesions on Tomatoes Grown in Ohio
Authors: Chapin Laura J. Gutierrez , Wang Ying , Lutton Elizabeth , Gardener Brian B. McSpadden
Published: May 2007

The primary causal agents of anthracnose-like fruit rots in Ohio and their potential resistance to fungicides commonly used to control these fungal pathogens were determined. Nineteen tomato production fields throughout the state were sampled in 2002 and 2003 for fruit with anthracnose-like lesions. Fungi were isolated from these samples, classified using restriction fragment length polymorphism analysis, and identified by internal transcribed spacer sequence analysis. Some of the fungi isolated may represent secondary invaders of preexisting wounds or lesions. Colletotrichum spp. were most abundant in our collection, representing 136 of the 187 isolates. In addition, there were 23 Alternaria, 12 Fusarium, 12 Phomopsis, and 4 Mucor isolates. Colletotrichum, Alternaria, and Fusarium spp. were found throughout the major tomato production areas in the state. In a laboratory investigation, a subset of the Colletotrichum, Alternaria, and Fusarium isolates caused symptoms similar to early development of anthracnose on wounded tomato fruit. In vitro inhibition assays indicated that most Colletotrichum isolates were sensitive to labeled rates of azoxystrobin, chlorothalonil, and mancozeb. However, some Alternaria isolates were less sensitive to azoxystrobin and chlorothalonil than the Colletotrichum isolates. In addition, most Fusarium isolates were also more insensitive to azoxystrobin and mancozeb, and most Phomopsis isolates were not inhibited by azoxystrobin at the levels tested. The patterns of insensitivity to azoxystrobin and chlorothalonil were also observed in situ with excised fruit. Because the fungicides tested are not currently labeled for control of tomato diseases caused by Fusarium or Phomopsis, these results indicate that some pathogen species that can cause anthracnose-like symptoms may not be entirely sensitive to fungicides commonly used in tomato production.
Investigating the Presence of Biotic Agents Associated with Mundulla Yellows
Authors: Luck Joanne E. , Crnov Rosa , Czerniakowski Barbara , Smith Ian W. , Moran Jane R.
Published: May 2007

The role of biotic agents in the dieback syndrome Mundulla Yellows (MY) was investigated by analysis of 40 Eucalyptus camaldulensis, E. leucoxylon, or E. cladocalyx trees and soil samples from South Australia and Victoria, Australia. No pathogenic fungi, bacteria, phytoplasmas, or insect pests or vectors were found to be associated with MY. However, nematode analysis identified Merlinius spp. to be associated with soil, but not roots, from symptomatic trees. Interveinal chlorosis symptoms were not transmissible by seed, mechanical inoculation, or grafting using plant material derived from symptomatic trees. Virus-like particles were detected at a single symptomatic study site using transmission electron microscopy. MY symptoms were induced in E. camaldulensis seedlings by sowing seed from asymptomatic trees into sterilized and unsterilized soil collected from underneath symptomatic trees. Significantly, sterilized soil induced more severe symptoms in seedlings than unsterilized soil. Soil collected from under asymptomatic trees did not induce MY symptoms. This preliminary investigation indicates that, with the exception of Merlinius spp., pathogenic organisms and pests were not consistently associated with MY symptoms.
Induction of Cankers on Pear Tree Branches by Neofabraea alba and N. perennans, and Fungicide Effects on Conidial Production on Cankers
Authors: Henriquez Jose L. , Sugar David , Spotts Robert A.
Published: May 2007

Cankers formed on pear branches after inoculations with mycelia of Neofabraea alba or N. perennans, causal agents of bull's eye rot of pear fruit. The highest proportions of successful infections followed inoculations made in fall and winter. Cankers induced by N. perennans were larger than those induced by N. alba. Small, superficial cankers were obtained after inoculations with conidia of N. perennans on wounded branches of pear trees. Sporulation of both pathogens on mycelial-induced cankers occurred throughout the year, with the largest amount of conidia produced at the end of summer and during fall. Sporulation on cankers induced by N. perennans spanned at least 2 years. Copper sulfate reduced sporulation on cankers induced by N. alba, while copper sulfate, trifloxystrobin, and ziram applied to sporulating cankers reduced germination of conidia of N. perennans.
First Report of Tomato spotted wilt virus in Leek (Allium porrum) in the United States
Authors: Nischwitz C. , Mullis S. W. , Gitaitis R. D. , Csinos A. S. , Olson S. M.
Published: May 2007

Tomato spotted wilt virus (TSWV) is a member of the family Bunyaviridae. It has many important crop hosts including tomato, pepper, tobacco, peanut, and onion. In Georgia, Vidalia onions (Allium cepa), a close relative of leek, can be infected by TSWV and Iris yellow spot virus (IYSV), which is another thrips-vectored tospovirus (2). For this reason, samples of leek transplants with virus-like symptoms in one field at the border of Georgia and Florida were tested for the presence of TSWV and IYSV. The transplants had been grown from seed in a greenhouse at the same location. The sampled plants exhibited extended bleaching of leaf tips and necrotic lesions. These symptoms were also seen on onion plants infected with TSWV and IYSV. The only natural infections of leek with IYSV have been reported thus far only from Reunion Island (4) and Slovenia (1), but to our knowledge, TSWV has not been reported as a pathogen of leek. Green tissue near the necrotic lesions and bleached tips of one symptomatic leaf per plant was sampled and analyzed using a double-antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) (Agdia, Inc., Elkhart, IN). Of 90 plants tested, eight were positive for TSWV and none were positive for IYSV. Leek samples testing positive using ELISA were blotted onto FTA cards (Whatman Inc., Brentford, UK) to bind viral RNA for preservation and then processed according to the manufacturer's protocol. Punch-outs from the FTA cards were used for reverse transcription polymerase chain reaction (RT-PCR) with the TSWV-specific forward primer (5′-TTAAGCAAGTTCTGTGAG-3′) and reverse primer (5′-ATGTCTAAGGTTAAGCTC-3′) (3) to confirm the identity of TSWV. The primers are specific to the viral nucleocapsid gene. An amplicon of the expected size (774 bp) was produced from TSWV ELISA-positive leek plants, but not from healthy controls. TSWV has been found in many plants worldwide, but to our knowledge this is the first report of TSWV infecting leek. The effect that TSWV has on leek production is currently unknown.

References: (1) D. A. Benson et al. Nucleic Acids Res. 1:32 (Database issue):D23-6, 2004. (2) S. W. Mullis et al. Plant Dis. 88:1285, 2004. (3) H. R. Pappu et al. Tob. Sci. 40:74, 1996. (4) I. Robène-Soustrade et al. Online publication. New Dis. Rep. 11, 2005.
First Report of Tomato apical stunt viroid in Tomato in Tunisia
Authors: Verhoeven J. Th. J. , Jansen C. C. C. , Roenhorst J. W.
Published: May 2007

In May 2005, the Plant Protection Service in the Netherlands received two tomato (Lycopersicon esculentum) plant specimens for diagnosis from a protected crop production facility of 2.5 ha near Kebili in Tunisia. Growth of the plants was reduced and leaves were chlorotic and brittle. Ripening of the fruits was delayed and their storage life was reduced from 3 weeks to 1 week. The grower reported that initially only 5% of plants showed symptoms; however, the number of symptomatic plants increased quickly to 100% as a result of increasing temperatures in the production facility. Test plant species Chenopodium quinoa, Datura stramonium, Nicotiana glutinosa, N. hesperis-67A, N. occidentalis-P1, and L. esculentum ‘Money-maker’ were mechanically inoculated with sap from the affected plants. Symptoms including chlorosis and stunting were observed only on L. esculentum. Reverse transcriptase-polymerase chain reaction (RT-PCR) with universal pospiviroid primers Pospi1-RE/FW (2) yielded amplicons of the expected size (196 bp) for each of the two samples. One of these amplicons was sequenced and showed the highest identity to the four isolates of Tomato apical stunt viroid (TASVd) in the NCBI Gen-Bank. Subsequently, the complete sequence of the Tunisian isolate (Gen-Bank Accession No. DQ144506) was determined by sequencing the am-plicon obtained after RT-PCR using primers developed for the detection of Citrus exocortis viroid (CEVd) (1). The isolate consisted of 363 nucleotides and showed the highest sequence identity (96.7%) to tomato isolates of TASVd from Indonesia and Israel (GenBank Accession Nos. X06390 and AY062121, respectively), 92.6% to a tomato isolate from the Ivory Coast (GenBank Accession No. K00818), and 87.7% to an isolate from Solanum pseudocapsicum (GenBank Accession No. X95293). The next highest sequence identity was 81.5% to an isolate of CEVd (GenBank Accession No. X53716). On the basis of these results, the viroid was identified as TASVd. To our knowledge, this is the first report of TASVd in Tunisia.

Reference: (1) N. Önelge. Turkish J. Agric. For. 21:419, 1997. (2) J. Th. J. Verhoeven et al. Eur. J. Plant Pathol. 110:823, 2004.
Production and Dispersal of Conidia ofLeucostoma cinctumin Peach and Cherry Orchards Under Irrigation in Eastern Washington
Authors: Grove Gary G. , Biggs Alan R.
Published: May 2007

The objectives of this study were to determine the seasonal production patterns of Leucostoma cinctum conidia in peach and cherry orchards and the effects of irrigation on dispersal of conidia. Conidia were trapped throughout the year and were present in highest numbers during spring and summer on both cherry and peach. The pathogen was dispersed 1.0 m by water drops that simulated irrigation drops that would impact cankers during over-the-canopy irrigation. Spore production and dispersal also resulted from the use of over-the-canopy and under-tree impact sprinklers. Although the two irrigation methods were not directly compared, the latter mode dispersed propagules of L. cinctum over horizontal distances of about 6 m, a distance sufficient to account for the movement of the pathogen between trees within and across orchard rows. It is concluded that disease management could be improved by alteration of horticultural and irrigation practices.
Soybean Response to Flooded Soil Conditions and the Association with Soilborne Plant Pathogenic Genera
Authors: Kirkpatrick M. T. , Rupe J. C. , Rothrock C. S.
Published: May 2007

The role of soilborne pathogens in flood damage on soybeans, Glycine max, was examined using six genotypes representing a reputed range of flood tolerances. Genotypes were planted in single-row plots from 1996 to 1998 with flood treatments of no flood, flood at emergence (3-day duration), or flood at the fourth leaf node growth stage (7-day duration). Three or four days after removing each flood treatment, plant stands were estimated and 15 plants were collected from each plot, weighed, and rated for root discoloration. Roots were assayed for the presence of fungi and other filamentous eukaryotic organisms. Plant stands were reduced by flooding at emergence compared with the nonflooded control. Flooding at both growth stages caused significant increases in root discoloration compared with nonflooded soybeans. Plant weights were reduced in 2 of 3 years for flooding at emergence. Pythium was the only genus of filamentous organisms whose isolation frequency increased with flooding. Of the 60 Pythium isolates evaluated representing the different cultural groups based on appearance and growth rate on potato dextrose agar, cornmeal agar, and V8 agar, 47% were moderately to highly virulent on soybean. Pythium spp. isolated from soybean included the pathogenic species P. ultimum, P. aphanidermatum, P. irregulare, and P. vexans and Group HS. Nonpathogenic P. oligandrum also was isolated from soybean.
New Method for Screening Cowpea Germ Plasm for Resistance to Cucumber mosaic virus
Authors: Gillaspie A. G.
Published: May 2007

Utilizing the Cucumber mosaic virus(CMV)-resistant cowpea germ plasm line, GC-86L-98, a new method of screening for resistance in the greenhouse followed by field screening was developed. A uniform source of CMV inoculum (freeze-dried infected cowpea tissue) was diluted to provide an infection rate in GC-86L-98 similar to that observed under field conditions. Plants of test lines were mechanically inoculated with this standard inoculum rate and assessed under greenhouse conditions. Lines considered equivalent in infection percentage with GC-86L-98 were then evaluated in field tests. Test line plants were exposed to virus from susceptible cultivar Coronet when plants were at the first or second trifoliolate leaf stage, and then leaf samples were assayed by direct antigen coating-enzyme-linked immunosorbent assay. Lines with infection percentages similar to or lower than the resistant control were considered resistant. A new line (PI 441917) with CMV resistance and several lines with Blackeye cowpea mosaic virus resistance were found. Newly discovered CMV-resistant lines will help to control the serious cowpea stunt disease caused by synergism of the two viruses.
Survival and Subsequent Dispersal of Rice Sclerotial Disease Fungi, Rhizoctonia oryzae and Rhizoctonia oryzae-sativae, in Paddy Fields
Authors: Guo Qingyuan , Kamio Akiko , Sharma Bhim Sen , Sagara Yukiko , Arakawa Masao , Inagaki Kimiharu
Published: May 2007

In 1998 to 2001, a commercial rice (Oryza sativa) paddy field (area: ca. 0.14 ha) was surveyed for Rhizoctonia oryzae and R. oryzae-sativae, causal agents of bordered sheath spot and brown sclerotium disease of rice plants, respectively, to determine their survival in soil and stubble during the pretransplanting season, and the effect on disease development during the maturation season of rice. Then, infection by these fungi of weeds belonging to 17 families, which grew in the four neighboring fields, was examined during rice growing seasons. All field isolates of the fungi from soil, stubble, rice sclerotial disease lesions (diseased tissues), and weeds were assorted into mycelial compatibility groups (MCGs) based on the barrage zone reaction of paired isolates. In R. oryzae, 3 to 8 MCGs were annually found from soil/stubble, 2 to 4 MCGs from rice bordered sheath spot lesions, and 4 to 9 MCGs from 4 to 14 weeds. MCGs common to both soil/stubble and diseased tissues, soil/stubble and weeds, and diseased tissues and weeds numbered 1 to 2 in all cases. In R. oryzae-sativae, MCGs common to both soil/stubble and brown sclerotium disease lesions, and soil/stubble and weeds, numbered 1 to 4 and 0 to 5, respectively. In R. oryzae and R. oryzae-sativae, a few MCGs were common to soil/stubble, diseased tissues and weeds, and some were also common to diseased tissues in 1998 and soil/stubble in 1999, or weed in 1998 and diseased tissues in 1999. Members belonging to a single MCG from rice diseased tissues were detected from maximally five weeds growing in the neighboring fields. These results indicate that fungi that had caused sclerotial diseases at the maturation stage of rice plants survived on and in soil and stubble until the pretransplanting season of the next year, followed by wide dispersal in and out of fields and by infection and disease development on rice plants and various weeds.
First Report of Rice yellow mottle virus in Rice in Uganda
Authors: Pinel-Galzi A. , Fargette D. , Hull R.
Published: May 2007

Rice yellow mottle virus (RYMV) of the genus Sobemovirus is a major biotic constraint to rice production in Africa. First reported in Kenya in 1966, RYMV was later found in most countries in Africa where rice (Oryza sativa) is grown (2). During July 2000, plants with leaf yellowing and mottling symptoms were observed in Uganda in a subsistence rice field northeast of Lake Victoria, close to the Nile River. RYMV was detected by using enzyme-linked immunosorbent assay with polyclonal RYMV antisera (1) in the four samples collected. Discriminant monoclonal antibodies revealed that the samples contained RYMV serotype 4, a serotype found in eastern Africa (Madagascar, Kenya, and Tanzania) (2). The 720-nt long coat protein gene of two isolates was amplified by reverse transcriptase-polymerase chain reaction and sequenced (1). The two Ugandan isolates had 99% nt sequence identity (EMBL Accession Nos. AM114523 and AM114524). They belonged to a monophyletic group (97% nt identity) containing isolates from eastern Kenya and northern Tanzania (close to the Lake Victoria). These form a sister group (93% identity) of isolates from Lake Malawi Region in western Tanzania and are more distantly related (88% identity) to the basal strains from eastern Tanzania (2). Isolation of the Lake Victoria Region from the rest of the Tanzania by distance, physical barriers, and patchy rice cultivation explains the specificity of the strain. Year-round growth of wild and cultivated rice around the lake ensures host continuity in time and space that facilitates spread that accounts for the homogeneity of the isolates of this area. Knowledge of the presence of RYMV in Uganda is important since rice cultivation is intensified in this country and is planned in neighboring southern Sudan.

References: (1) A. Pinel et al. Arch. Virol. 145:1621, 2000. (2) O. Traoré et al. Mol. Ecol. 14:2097, 2005.
Widespread Occurrence of Wheat spindle streak mosaic virus in Belgium
Authors: Vaïanopoulos C. , Legrève A. , Lorca C. , Moreau V. , Steyer S. , Maraite H. , Bragard C.
Published: May 2007

In order to assess the occurrence of Wheat spindle streak mosaic virus (WSSMV) in Belgium, a reverse-transcription polymerase chain reaction (RT-PCR) was developed, targeting WSSMV isolates from Canada, France, Germany, Italy, and the United States. The primers also were designed for virus quantification by real-time RT-PCR with SYBR-Green. No cross-reaction with soilborne cereal viruses such as Barley mild mosaic virus, Barley yellow mosaic virus, Soilborne cereal mosaic virus, and Soil-borne wheat mosaic virus was observed. The RT-PCR and real-time quantitative RT-PCR allowed a more sensitive detection of WSSMV than enzymelinked immunosorbent assay. The incidence of WSSMV in Belgium was evaluated using a bioassay with wheat cvs. Cezanne and Savannah and rye cv. Halo, grown in 104 Belgian soils. The presence of WSSMV was detected from plants grown in 32% of the soils. The RT-PCR methods developed here, combined with large sampling, allowed WSSMV to be detected for the first time in Belgium. The real-time quantitative RT-PCR was developed as a tool for evaluating the resistance to WSSMV by quantifying the virus concentration in wheat cultivars.
Localized Distribution of Iris yellow spot virus Within Leeks and Its Reliable Large-Scale Detection
Authors: Smith Tracey N. , Wylie Stephen J. , Coutts Brenda A. , Jones Roger A. C.
Published: May 2007

In a survey to determine the incidence of Iris yellow spot virus (IYSV) in crops of several host species, samples of one leaf tip/plant were collected at random. When tested by enzyme-linked immunosorbent assay (ELISA) using IYSV-specific antibodies and a blocking step that improved test reliability, the virus was detected only in leek and onion. It was found in 11 of 21 leek and 2 of 26 onion plantings with apparent incidences of 1 to 7 and 1%, respectively. However, the figures for leek crops greatly underestimate IYSV incidence due to localization of infection within plants. Thus, in tests on multiple subsections from individual plants, IYSV was detected in one or more leaves but never in all leaves. Within infected leaves, it was localized in patches of infection found mainly in the middle and top subsections of the unfurled leaves, but infrequently in their bases. It never was found in the furled leaves that make up the stems, or in the basal plates or roots. Therefore, to obtain reliable estimates of IYSV incidences in largescale surveys of leek crops, the randomly collected samples tested by ELISA should consist of combined tissue subsections from the tops and middles of several leaves from each plant sampled.
Distribution of Chrysoporthe Canker Pathogens on Eucalyptus and Syzygium spp. in Eastern and Southern Africa
Authors: Nakabonge G. , Roux J. , Gryzenhout M. , Wingfield M. J.
Published: May 2007

Chrysoporthe cubensis and C. austroafricana, collectively known as Cryphonectria cubensis in the past, are important canker pathogens of Eucalyptus spp. worldwide. Previous studies have suggested that Chrysoporthe austroafricana occurs only in South Africa, whereas C. cubensis occurs in Australia, Cameroon, Tanzania, Democratic Republic of Congo, Republic of Congo, Southeast Asia, and South, Central, and North America. In South Africa, C. austroafricana is a pathogen on nonnative Eucalyptus (Myrtaceae) and Tibouchina (Melastomataceae) spp., both residing in the order Myrtales. Recently, the fungus also has been found on native Syzygium cordatum trees in the country, leading to the hypothesis that it is native to Africa. In contrast, C. cubensis is thought to have been introduced into Africa and is known only on non-native Eucalyptus spp. and S. aromaticum (clove) in four countries. The aim of this study was to consider the distribution of Chrysoporthe spp. on non-native Eucalyptus spp. as well as on native Myrtales in southern and eastern Africa. Isolates were collected from as many trees as possible and characterized based on their morphology and DNA sequence data for two gene regions. Results show, for the first time, that C. cubensis occurs in Kenya, Malawi, and Mozambique on nonnative Eucalyptus spp. C. austroafricana was found for the first time in Mozambique, Malawi, and Zambia on non-native Eucalyptus spp. and native S. cordatum. The known distribution range of C. austroafricana within South Africa also was extended during these surveys.
An Improved Method for Infecting Tomato Leaves or Seedlings with Oospores of Phytophthora infestans Used to Investigate F1 Progeny
Authors: Rubin Evgenia , Cohen Yigal
Published: May 2007

An improved, soil-free laboratory method was developed to induce late blight infection in detached tomato leaves or tomato seedlings with in vivo-produced oospores of Phytophthora infestans. Oospores were produced in detached tomato leaves infected with an inoculum mixture of A1 and A2 isolates. The infected leaves were homogenized in distilled water. The homogenates were exposed to two cycles of drying and wetting to kill sporangia, zoospores, and mycelia and, thereafter, mixed with perlite and water. Tomato leaves or seed were floated on the perlite mixture in petri dishes and incubated for up to 30 days. Results from 13 experiments showed that, in dishes containing oospores, 96 of 820 leaflets (11.7%) developed late blight lesions within 6 to 30 days; whereas, in 3 experiments with seedlings, 12 of 1,400 plants (0.9%) were blighted within 17 to 26 days. No late blight developed in leaflets or seedlings maintained in dishes containing homogenates of the control leaves infected with either A1 or A2 inoculum. In all, 234 single-sporangium F1 isolates recovered from 24 leaf lesions produced by four crosses and 27 isolates recovered from 12 seedlings infected with two crosses were examined for sensitivity to metalaxyl and mating type. Results showed that, although the parent isolates were either S (sensitive) or R (resistant) to metalaxyl, most F1 progeny isolates exhibited various levels of intermediate resistance to metalaxyl. Most isolates belonged to either the A1 or the A2 mating type, depending on the cross and lesion. However, some isolates belonged to the unusual mating type A1A2 or were sterile. Current experiments are intended to elucidate the virulence and aggressiveness of these F1 progenies to tomato. This improved method may facilitate our understanding of the role of in vivo-produced oospores in the epidemiology of late blight in tomato.
Fungicide Sensitivity of Sclerotinia homoeocarpa from Golf Courses in Ohio
Authors: Jo Young-Ki , Niver Amy L. , Rimelspach Joseph W. , Boehm Michael J.
Published: May 2007

Managing dollar spot, the most common and chronic disease on intensively cultivated turfgrass, relies on the judicious use of fungicides. The heavy use of fungicides has led to the development of isolates of Sclerotinia homoeocarpa insensitive to several classes of fungicides, including benzimidazoles, demethylation-inhibitors, and dicarboximides. In vitro fungicide sensitivity assays using single discriminatory concentrations of thiophanate-methyl, propiconazole, and iprodione were developed in this study for evaluating field efficacy of these fungicides and the prevalence of fungicide insensitivity within S. homoeocarpa isolated from golf courses throughout Ohio. Discriminatory concentrations for these fungicides were determined to be: thiophanate-methyl = 1,000 μg a.i. ml-1, propiconazole = 0.1 μg a.i. ml-1, and iprodione = 1.0 μg a.i. ml-1. Effective concentration that produces 50% inhibition (EC50) was estimated based on relative mycelial growth of S. homoeocarpa on potato dextrose agar (PDA) versus PDA amended with the discriminatory concentration of each fungicide. Field trials conducted at 3 locations in 2002 and 10 locations in 2003 revealed that the in vitro assays accurately predicted field efficacy for thiophanate-methyl. When used to screen 192 S. homoeocarpa isolates collected previously from 55 golf courses throughout Ohio, the in vitro assays revealed that 34 of the golf courses sampled had S. homoeocarpa resistant to thiophanate-methyl. S. homoeocarpa with reduced in vitro sensitivities was isolated from 18 and 1 golf courses for propiconazole and iprodione, respectively.
First Report of Puccinia sorghi on Maize in Oman
Authors: Deadman M. L. , Al Sa'di A. , Al Maqbali Y. , Livingston S. , Aime M. C.
Published: May 2007

Maize (Zea mays L.) is an important annual forage crop cultivated in the Sultanate of Oman, especially during the summer months. It is used for green fodder and grains and often intercropped in fruit orchards, especially under date palms. In April of 2005, leaf samples showing rust symptoms were collected from Samail, 100 km south of Muscat. Oval-shaped, red-brown pustules covered both sides of the leaves and yielded urediniospores typical of Puccinia sorghi Schwein. Urediniospores were roughly subglobose, measured 23 to 28 × 20 to 25 μm, echinulate, with three or four equitorial germ pores (2). Teliospores (38 to 42 × 16 to 19 μm) were observed, but few in numbers, most probably because of the time of year of collection. Pathogen identity was confirmed by nuclear ribosomal large subunit (28S) and internal transcribed spacer region 2 (ITS-2) DNA analysis (voucher sequence deposited in GenBank, Accession No. DQ345724, voucher specimen deposited in the U.S. National Fungus Collections, BPI 871134). P. sorghi has previously been reported from Yemen and Saudi Arabia (1) but not from Oman. Maize is grown throughout the year in Oman, and pathogen survival probably does not require the presence of the alternate host, nonetheless, Oxalis species are present and current research is attempting to locate and confirm the presence of the aecial stage in Oman.

References: (1) CMI Distribution Maps of Plant Diseases. Map No. 279. Ed. 4. CABI, Wallingford, UK, 1978. (2) D. G. White, ed. Compendium of Corn Diseases. The American Phytopathological Society, St Paul, MN, 1999.
First Report of Powdery Mildew Caused by Leveillula clavata on Poinsettia (Euphorbia pulcherrima) in Italy
Authors: Garibaldi A. , Minuto A. , Gullino M. L.
Published: May 2007

Euphorbia pulcherrima (poinsettia) is a winter-flowering plant grown primarily for Christmas sales. During the fall of 2005, severe outbreaks of a previously unknown powdery mildew were observed on cv. Gala in a commercial greenhouse located in Albenga (northern Italy). The abaxial surfaces of green leaves were irregularly covered with white mycelia and conidia, while the adaxial surfaces only showed slight chlorotic round lesions. As the disease progressed, mycelium turned from rose to reddish. Symptoms and signs were never observed on red bracts. Conidia were clavate (55 to 95 × 20 to 40 μm, average 70 × 23 μm) and borne singly on conidiophores that emerged through stomata. On the basis of host, morphological characteristics, and microscopic observations of the intercellular colonization of mesophyll cells, the pathogen was identified as a species of Oidiopsis. Although chasmothecia were not observed, the causal agent based on the literature is believed to be Leveillula clavata Nour (2). Pathogenicity was confirmed by inoculating young leaves of three 4-month-old E. pulcherrima plants, cv. Gala, with a conidial suspension (3 × 105 conidia/ml). Three noninoculated plants sprayed with deionized water served as control. After inoculation, plants were maintained in a growth chamber at 18°C with relative humidity ranging from 56 to 100%. After 20 days, powdery mildew symptoms were observed on leaves of inoculated plants. Noninoculated plants remained healthy. The pathogenicity test was carried out twice. To our knowledge, this is the first report of L. clavata on poinsettia in Italy and probably in Europe. It presently is restricted to a few commercial farms. L. clavata previously has been observed on poinsettia in Kenya (1,2). Voucher specimens are available at the AGROINNOVA Collection, University of Torino.

References: (1) M. L. Daughtrey et al. Powdery Mildew Diseases. Pages 39–42 in: Compendium of Flowering Potted Plant Diseases. The American Phytopathological Society, St. Paul, MN, 1995. (2) M. A. Nour. Trans. Brit. Mycol. Soc. 40:477, 1957.
Pseudomonas viridiflava Causing Necrotic Leaf Spots and Defoliation on Hebe spp. in Northern Spain
Authors: González A. J. , Rodicio M. R.
Published: May 2007

Hebe spp. is gaining interest as an ornamental crop in Spain. In October of 2003, plants of Hebe spp. (cv. Pink Paradise, Recurva, and Topiaria) grown in a nursery located in a northern region of Spain (Principality of Asturias) developed dark reddish spots in leaves. The spots (favored by high-humidity conditions) appeared initially in internal and lower leaves, but eventually progressed to the rest of the plant causing extensive defoliation. Samples from symptomatic leaves were processed for microbiological analysis. From the samples, Stemphylium sp. and fluorescent Pseudomonas sp., identified by conventional microbiological methods (1,3), were consistently recovered. Two isolates of the fungi and two of the bacterium (LPPA 365 and LPPA 366) were used in artificial inoculations of healthy plants (cv. New Zeeland) and all were performed in duplicate. A Stemphylium sp. was inoculated by irrigation of four seedlings with a suspension obtained by homogenization of the mycelium collected from two plates of potato dextrose agar in 100 ml of sterile distilled water. An equal number of seedlings were sprayed with a bacterial suspension (108 CFU/ml) in yeast extract peptone glucose broth. The same methods were used to inoculate all four combinations of fungi and bacteria. The seedlings were maintained at 22°C during 1 month with a 16/8-h photo-period, but in inoculations with bacteria they were initially kept under transparent plastic bags for 48 h to facilitate entry. Seedlings treated with sterile distilled water were included as controls. Although a powdery film of sooty mold was observed in some of the leaves irrigated with one of the two Stemphylium sp. strains, rusty lesions and defoliation did not occur on plants inoculated with the fungal isolates alone. In contrast, symptoms comparable with those observed in the field developed in plants inoculated with the bacteria, either alone or together with the fungus. Reisolation of fluorescent Pseudomonas sp. from symptomatic leaves taken from inoculated plants confirmed pathogenicity on Hebe spp. The pathogenic isolates were tentatively identified as atypical Pseudomonas viridiflava on the basis of biochemical tests (2,3), and their identity was then confirmed by sequencing of the gene encoding the 16S rRNA (3; GenBank Accession Nos. AM182933 and AM182934 for LPPA 365 and 366, respectively). To our knowledge, this is the first report of P. viridiflava as the cause of necrotic leaf spots and defoliation in Hebe spp.

References: (1) H. L. Barnett and B. B. Hunter. Illustrated Genera of Imperfect Fungi. 3rd ed. Burgess Publishing Co, Minneapolis, MN, 1972. (2) A. J. González et al. Appl. Environ. Microbiol. 69:2936, 2003. (3) R. A. Lelliott et al. J. Appl. Bacteriol. 29:470. 1966.
Strains of Leptosphaeria maculans with the Capacity to Cause Crown Canker on Brassica carinata are Present in Western Australia
Authors: Khangura R. , Aberra M.
Published: May 2007

Blackleg, caused by Leptosphaeria maculans (Desm.) Ces. et de Not., is the most important disease of canola (Brassica napus L.) in Australia, Europe, Canada, and North America (2). During the early 1990s, new cultivars of canola with resistance to blackleg were released in Australia. Despite good adult-plant resistance, these cultivars still suffered significant yield losses from blackleg under high disease pressure. Potential new sources of blackleg resistance such as B. nigra L., B. carinata L., and Sinapis alba L. are being evaluated. B. carinata is believed to be highly resistant to blackleg by virtue of its B-genome. However, some L. maculans isolates that can attack B. carinata have been reported from Germany (1). During the 2003 growing season, 22 isolates of L. maculans were collected from different canola-growing areas of Western Australia and tested for their reaction on 24 seedlings of each of various Brassica genotypes, including B. carinata, in a controlled environment chamber. Twenty-four seeds per genotype were sown in 100-ml plastic pots (12 seeds per pot) and both cotyledons of 10-day-old seedlings were wound inoculated with a conidial suspension (1 × 107 conidia/ml) of each isolate of L. maculans. Disease assessments were made 2 weeks after inoculation. The majority of isolates induced a noninvasive hypersensitive reaction on B. carinata without pycnidial development. However, four of the isolates caused lesions with abundant pycnidia on B. carinata cotyledons. The lesion size ranged between 3 and 7 mm and appeared similar to that on susceptible B. napus cultivars. B. carinata seedlings were grown for another 8 weeks in a glasshouse, and crown cankers were observed from plants inoculated with three of the four seedling virulent isolates. The severity of crown cankers as percent of stem circumference (percent disease index) ranged between 20 and 54%. Twenty-five stem pieces from mature B. carinata plants infected with one of the three isolates were plated on V8 juice agar and L. maculans was recovered from 70% of pieces. Abundant pycnidia were also observed on these stem pieces. These results have important implications for using B. carinata as a source of blackleg resistance in canola breeding. To our knowledge, this is the first report of L. maculans isolates with the capacity to induce crown cankers on B. carinata in Australia.

References: (1) C. Sjöidin and K. Glimelius. J. Phytopathol. 123:322, 1988. (2) J. West et al. Plant Pathol. 51:454, 2002.
Pre- and Post-Infection Activity of Pyraclostrobin for Control of Anthracnose Fruit Rot of Strawberry Caused by Colletotrichum acutatum
Authors: Turechek William W. , Peres Natália A. , Werner Nicole A.
Published: May 2007

The effect of pre- and post-infection-period applications of pyraclostrobin (Cabrio EG) on the development of anthracnose fruit rot was characterized in a controlled-climate study and validated in field studies in New York and Florida. Plants of the day-neutral cv. Tristar were inoculated with C. acutatum and placed into mist chambers at 14, 22, or 30°C. The plants were removed from the chambers after 3, 6, 12, or 24 h of misting and placed on greenhouse benches to allow disease development. The fungicide pyraclostrobin was applied to the berries at a concentration equivalent to 168 g a.i./ha at 3, 8, 24, and 48 h prior to inoculation and exposure to their wetting period, or 3, 8, 24, and 48 h following inoculation and exposure to their wetting period. All pyraclostrobin treatments suppressed disease compared with the corresponding untreated control treatments. The highest incidence of disease occurred on plants exposed to the longest wetness durations (12 and 24 h) or highest temperature treatments (22 and 30°C). Post-infection applications of pyraclostrobin provided significant control when applications were made within 3 and often up to 8 h after wetting, but generally were less effective than protective sprays. We further tested the ability of pyraclostrobin to control anthracnose when applied as a protectant or as an after-infection application in inoculated field plots exposed to a short (8 h) or long (24 h) wetting period in Florida and in New York. In three of the four experimental plots, disease control equivalent to or better than the protective spray was achieved when pyraclostrobin was applied up to 24 h after infection for long and short wetting periods. In the remaining plot, conditions for disease development were exceptionally favorable. The protective treatment provided approximately 75% control, whereas the best post-infection treatment provided only 50% control. Our study indicates that for short wetting events, such as those associated with seasonal thunderstorms, growers can wait until after such an infection event before applying pyraclos-trobin and achieve control equivalent to a protective application.
Seedborne Infection of Pyrethrum by Phoma ligulicola
Authors: Pethybridge Sarah J. , Hay Frank , Jones Suzanne , Wilson Calum , Groom Tim
Published: May 2007

The incidence of Phoma ligulicola in Tasmanian pyrethrum seed and methods of managing seedborne mycoflora were determined. Fourteen different fungi were regularly isolated from seed, including Alternaria tenuissima, Stemphylium botryosum, and P. ligulicola, which have been documented as pathogens of pyrethrum. Comparisons between the incidence of these fungi from seed surface-sterilized with sodium hypochlorite and nontreated seed indicated they occurred both within and on the outside of the seed. A polymerase chain reaction (PCR) test for the detection of P. ligulicola was also developed, with a detection limit of 800 fg of fungal DNA. The assay detected infested seed lots down to an incidence of 0.5%. Reliable amplification of the target DNA was achieved with the addition of bovine serum albumin to reduce the influence of inhibitors from pyrethrum seed. Agar plate tests and PCR demonstrated variability with pyrethrum cultivars in the presence and viability of P. ligulicola in seed. Effective management strategies for the reduction of seedborne P. ligulicola included the regular use of fungicides for reducing foliar disease intensity in the seed fields prior to harvest. Seed treatments with fludioxonil and thiabendazole/thiram also significantly reduced the incidence of seedborne P. ligulicola and increased seed germination and seedling survival.
Aphis glycines as a Vector of Persistently and Nonpersistently Transmitted Viruses and Potential Risks for Soybean and Other Crops
Authors: Wang R. Y. , Kritzman A. , Hershman D. E. , Ghabrial S. A.
Published: May 2007

The recently introduced soybean aphid (Aphis glycines), which is widespread in the soybean-growing regions in the United States, is the only aphid able to develop large colonies on soybean. Although its potential as a vector of plant viruses is recognized, reports on virus transmission efficiency by this aphid species are limited. In the present study, we examined the ability of A. glycines to transmit several economically important viruses. The results showed that A. glycines transmitted the potyviruses Bean yellow mosaic virus (BYMV) and Soybean mosaic virus from soybean to soybean more efficiently than Myzus persicae. However, M. persicae transmitted the alfamovirus Alfalfa mosaic virus and the potyviruses Tobacco etch virus (TEV) and Tobacco vein mottling virus (TVMV) from tobacco to tobacco more efficiently than A. glycines. This is the first report to demonstrate that the soybean aphid can vector TEV and TVMV, two economically important tobacco viruses. This also is the first report to document successful transmission of BYMV by A. glycines. All attempts to transmit the nepovirus Tobacco ringspot virus by A. glycines were unsuccessful, regardless of the length of the acquisition and inoculation feeding periods. Although the luteovirus Soybean dwarf virus (SbDV) was widely distributed in red and white clover in Kentucky, it was not detected in soybean. All transmission experiments of SbDV by A. glycines were unsuccessful. A reverse-transcription polymerase chain reaction (RT-PCR) assay was developed to detect SbDV in single aphids using a pair of primers designed to amplify a 372-bp PCR fragment in the coding region of SbDV coat protein. Although A. glycines was not a vector of SbDV, the virus was detected in 100% of tested aphids by RT-PCR after a 24- to 48-h virus acquisition access feeding. The practical applications of RT-PCR in detecting persistently transmitted viruses are discussed.
The Effect of Solar Irradiance on the Mortality of Phakopsora pachyrhizi Urediniospores
Authors: Isard S. A. , Dufault N. S. , Miles M. R. , Hartman G. L. , Russo J. M. , De Wolf E. D. , Morel W.
Published: May 2007

Soybean rust, caused by Phakopsora pachyrhizi, may be the most important foliar disease of soybean. Within the last 10 years, the fungus has moved to many new geographical locations via spread of airborne urediniospores. The objective of this study was to determine the relationship between urediniospore viability and exposure to solar radiation. Urediniospores of P. pachyrhizi were exposed in Capitán Miranda, Paraguay, to determine the deleterious effects of sunlight. Concomitant total solar (0.285 to 2.8 μm) and ultraviolet (0.295 to 0.385 μm) irradiance measurements were used to predict urediniospore germination. Urediniospores exposed to doses of solar and ultraviolet (UV) radiation ≥27.3 MJ/m2 and ≥1.2 MJ/m2, respectively, did not germinate. The proportions of urediniospores that germinated, normalized with respect to the germination proportion for unexposed urediniospores from the same collections, were a linear function of solar irradiance (R2 = 0.83). UV measurements predicted normalized germination proportions equally well. Results of inoculation experiments with exposed P. pachyrhizi urediniospores supported the results of the germination trials, although the effects of moderate levels of irradiance varied. The relationship between urediniospore viability and exposure to solar radiation has been incorporated into the U.S. Department of Agriculture's soybean rust aerobiological model that provides North American soybean growers with decision support for managing soybean rust.
First Detection of Wheat dwarf virus in Barley in Spain Associated with an Outbreak of Barley Yellow Dwarf
Authors: Achon M. A. , Serrano L. , Ratti C. , Rubies-Autonell C.
Published: May 2007

Severe dwarfing, yellowing, and crop failure were observed on barley in northeastern Spain during March and April of 2003. Leaves from 106 plants collected from 15 barley fields were analyzed using enzyme-linked immunosorbent assay (ELISA) with commercial antisera (Loewe Biochemica, Munich) specific for Barley mild mosaic virus (BaMMV), Barley yellow mosaic virus (BaYMV), the PAV and MAV serotypes of Barley yellow dwarf virus (BYDV), Barley yellow striate mosaic virus (BYSMV), Barley stripe mosaic virus (BSMV), Brome mosaic virus (BMV), Brome streak mosaic virus, (BStMV), Cereal yellow dwarf virus (CYDV), Wheat streak mosaic virus (WSMV), Wheat spindle streak mosaic virus (WSSMV), Soilborne cereal mosaic virus (SBCMV), and Wheat dwarf virus (WDV). In 70 samples, BYDV-PAV was the sole virus detected; in 20 other samples, this virus was detected in association with WDV, WSMV, BaMMV, and/or BaYMV. Mixed infections were further analyzed using reverse transcriptase-polymerase chain reaction (RT-PCR) or PCR with specific primers that amplify 445 bp of BaMMV (3), 433 bp of BaYMV (1), 600 bp of WSMV (primer 1: 5′CGAAACGCAGCG TTATTTC3′, primer 2: 5′CATCTGAAG GGCTTGACG3′), and 1,200 bp of WDV (4). Eight samples gave the expected amplicons for WDV, two samples gave the expected amplicon for BaMMV, and one sample gave the BaMMV and BaYMV amplicons. No samples gave the amplicon for WSMV. In addition, 10 samples that were positive with ELISA for BYDV, either as a single or as multiple infections with other viruses, were analyzed with specific primers that amplify 600 bp of the BYDV genome (2) and all gave the expected RT-PCR product. ELISA and RT-PCR results agreed completely for WDV and BYDV samples, but agreed poorly for BaMMV and BaYMV (three of seven ELISA-positive samples). PCR products of WDV were subsequently cloned and sequenced. Sequence analysis confirmed the presence of WDV in these barley samples. This report shows the high occurrence of BYDV in barley fields and its association with BaMMV, BaYMV, and WDV infections that induces barley crop failure. To our knowledge, this is the first detection of WDV in Spain.

References: (1) M. A. Achon et al. Plant Dis.87:1004, 2003. (2). E. S. G. Canning et al. J. Virol. Methods 56:191, 1996. (3) D. Hariri et al. Eur. J. Plant Pathol. 106:365, 2000. (4) A. Kvarnheden et al. Arch Virol. 147:206, 2002.