bluuebunny/crossref_metadata_2025 huggingface dataset:
Distribution of Typhula spp. and Typhula ishikariensis Varieties in Wisconsin, Utah, Michigan, and Minnesota
Authors: Chang S. W. , Scheef E. , Abler R. A. B. , Thomson S. , Johnson P. , Jung G.
Published: May 2007

Snow molds are psychrophilic fungi that grow under snow cover by taking advantage of carbohydrate-depleted, dormant plants. Typhula snow molds caused by Typhula incarnata, T. phacorrhiza, and T. ishikariensis are the most important winter diseases of perennial grasses and winter cereals in the United States. Colonized turfgrass samples with sclerotia were collected from 135 golf courses in Wisconsin, Utah, Michigan, and Minnesota in spring 2001 and 2002. Species and varieties from a total of 2,864 samples were identified using Typhula spp.-specific polymerase chain reaction markers. All three species were found throughout the states sampled, except T. phacorrhiza, which was not found in Minnesota. T. incarnata was distributed in areas of shorter snow cover duration and higher mean temperature than T. ishikariensis. Canonical correspondence analysis indicated that snow cover days and mean temperature were significantly correlated with frequency of Typhula spp. and T. ishikariensis varieties infecting turfgrasses on golf courses in Wisconsin, and that T. incarnata, T. phacorrhiza, and T. ishikariensis were ecologically distinct based on the 2001 data. However, because these two variables accounted for a relatively small proportion of total variation, other environmental variables also may be important in characterizing the distribution of these pathogens and require further study.
A Virulence-Reducing Mutation in the Postharvest Citrus Pathogen Alternaria citri
Authors: Katoh H. , Isshiki A. , Masunaka A. , Yamamoto H. , Akimitsu K.
Published: May 2007

Alternaria citri causes Alternaria black rot, a postharvest fruit disease, on a broad range of citrus cultivars. We previously described that an endopolygalacturonase minus mutant of A. citri caused significantly less black rot in citrus fruit. To search for other essential factors causing symptoms in addition to endopolygalacturonase, a random mutation analysis of pathogenicity was performed using restriction enzyme-mediated integration. Three isolates among 1,694 transformants of A. citri had a loss in pathogenicity in a citrus peel assay, and one of these three mutants was a histidine auxotroph. Gene AcIGPD that encodes imidazole glycerol phosphate dehydratase, the sixth enzyme in the histidine biosynthetic pathway, was cloned, and the mutant containing the disrupted target gene, AcIGPD, caused less black rot.
Molecular Mapping and Marker-Assisted Selection of Genes for Septoria Speckled Leaf Blotch Resistance in Barley
Authors: Zhong Shaobin , Toubia-Rahme Hala , Steffenson Brian J. , Smith Kevin P.
Published: May 2007

Septoria speckled leaf blotch (SSLB), caused by Septoria passerinii, has emerged as one of the most important foliar diseases of barley in the Upper Midwest region of the United States. To map and tag genes for SSLB resistance, we developed two populations derived from the resistant accessions CIho 4780 and CIho 10644 and the susceptible malting cv. Foster. Segregation analysis of F2 plants or F2:3 families from the Foster/CIho 4780 and Foster/CIho 10644 populations revealed that a single dominant gene conferred resistance at the seedling stage. Bulked segregant analysis identified an amplified fragment length polymorphism marker, E-ACT/M-CAA-170, that co-segregated with the SSLB resistance gene Rsp2 in the Foster/CIho 4780 F2 population. Southern hybridization analysis with DNA from the wheat/barley addition lines localized E-ACT/M-CAA-170 on the short arm of the barley chromosome 5(1H). Restriction fragment length polymorphism analysis with DNA clones previously mapped to the short arm of chromosome 5(1H) placed Rsp2 at a position flanked by the markers Act8 and ksuD14. A sequence-characterized amplified region (SCAR) marker (E-ACT/M-CAA-170a) was developed that co-segregated with not only Rsp2 in the Foster/CIho 4780 population but also resistance gene Rsp3 in the Foster/CIho 10644 population. This result indicates that Rsp3 is closely linked to Rsp2 on the short arm of chromosome 5(1H). The utility of SCAR marker E-ACT/M-CAA-170a for selecting Rsp2 in two different breeding populations was validated.
Genetic Relationships BetweenCercospora kikuchiiPopulations from South America and Japan
Authors: Imazaki I. , Homma Y. , Kato M. , Vallone S. , Yorinori J. T. , Henning A. A. , Iizumi H. , Koizumi S.
Published: May 2007

A collection 160 isolates of Cercospora kikuchii was made from South America and 245 from Japan. DNA fingerprint patterns were analyzed based on amplified fragment length polymorphism among the sample isolates, dividing the isolates into seven lineages (I to VII). Partial nucleotide sequence analyses of the β-tubulin gene supported this division into seven lineages. Lineages I and III commonly existed in South America and Japan. In all, 136 of the 160 isolates from South America and 223 of the 245 isolates from Japan belonged to lineage I, indicating that lineage I was the major lineage in each area; 5 isolates from South America and 8 isolates from Japan belonged to lineage III. Lineages II (12 isolates) and IV (2 isolates) were specific to Japan and lineages V (3 isolates), VI (1 isolate), and VII (15 isolates) specifically existed in South America. These results suggest that the population genetic structure of C. kikuchii was different between South America and Japan, but the dominance of lineage I was common between the two areas.
Comparison of Genetic and Virulence Diversity ofMelampsora larici-populinaPopulations on Wild and Cultivated Poplar and Influence of the Alternate Host
Authors: Gérard Pierre R. , Husson Claude , Pinon Jean , Frey Pascal
Published: May 2007

The aims of this study were, first, to compare the genetic and virulence diversity between populations of the rust fungus Melampsora larici-populina on wild and cultivated poplar stands and, second, to investigate the influence of the presence of the alternate host of the pathogen, larch, on which its sexual reproduction occurs, on these diversities. Nine French M. larici-populina populations collected from poplar trees in autumn and four populations collected from larch trees during the following spring were analyzed using both virulence factors and neutral markers. In all, 30 pathotypes were identified within the 13 populations studied. The pathotypic structure clearly distinguished the cultivated stands with high richness and complexity from the wild stands with low richness and complexity. High linkage disequilibria between virulences indicated preferential virulence associations, probably due to selection by the host. In all, 19 random amplified polymorphic DNA (RAPD) markers were used, which revealed a very high genetic diversity in the 743 isolates analyzed. The nine populations from poplar appeared moderately differentiated, indicating long-distance gene flow, and no isolation by distance was found. Linkage disequilibria between RAPD markers generally were low, indicating frequent recombination, but they were not lower in populations located near larch, probably due to long-distance dispersal.
Host Specificity of Ascochyta spp. Infecting Legumes of the Viciae and Cicerae Tribes and Pathogenicity of an Interspecific Hybrid
Authors: Hernandez-Bello M. A. , Chilvers M. I. , Akamatsu H. , Peever T. L.
Published: May 2007

Ascochyta spp. (teleomorphs: Didymella spp.) infect a number of legumes, including many economically important species, and the diseases they cause represent serious limitations of legume production worldwide. Ascochyta rabiei, A. fabae, A. pisi, A. lentis, and A. viciae-villosae are pathogens of chickpea (Cicer arietinum), faba bean (Vicia faba), pea (Pisum sativum), lentil (Lens culinaris), and hairy vetch (V. villosa), respectively. Inoculations in the greenhouse and in growth chambers demonstrated that A. fabae, A. lentis, A. pisi, A. rabiei, and A. viciae-villosae were host specific. Isolates caused no visible disease symptoms on “nonhost” plants (plants other than the hosts they were originally isolated from) but were recovered consistently from inoculated, surface-disinfested, nonhost tissues. Interspecific crosses of A. pisi × A. fabae and A. viciae-villosae × A. lentis produced pseudothecia with viable ascospores, and the hybrid status of the ascospore progeny was verified by the segregation of mating type and amplified fragment length polymorphism (AFLP) markers. Interspecific progeny were morphologically normal in culture but exhibited more phenotypic variation compared with progeny from intraspecific crosses. Mating type and the majority of AFLP markers segregated in Mendelian 1:1 ratios in both intraspecific and interspecific crosses. A total of 11 and 7% of AFLP markers showed segregation distortion among progeny from interspecific crosses and intraspecific crosses, respectively; however, this difference was not significant (P = 0.90). Only 30 of 114 progeny isolates from the A. fabae × A. pisi cross inoculated in the greenhouse caused lesions on pea and only 4 caused disease on faba bean. In all, 15 of 110 progeny isolates were pathogenic to pea and none were pathogenic to faba bean under growth chamber conditions. Although no obvious postzygotic, intrinsic isolating barriers were identified in any of the interspecific crosses, it appears that host specialization may act as both a prezygotic, ecological isolating barrier and a postzygotic, extrinsic, ecological isolating barrier in these fungi. Host specificity, coupled with low pathogenic fitness of hybrids, may be an important speciation mechanism contributing to the maintenance of hostspecific, phylogenetic lineages of these fungi.
Posttranscriptional Gene Silencing Does Not Play a Significant Role in Potato virus X Coat Protein-Mediated Resistance
Authors: Bazzini A. A. , Hopp H. E. , Beachy R. N. , Asurmendi S.
Published: May 2007

The expression of a gene that encodes coat protein (CP) of Potato virus X (PVX) in transgenic tobacco plants confers a high level of CP-mediated rresistance (CP-MR) against PVX infection. To determine if posttranscriptional gene silencing (PTGS) plays a role in resistance, transgenic plants expressing PVX CP were challenged against PVX under conditions in which PTGS was suppressed by low temperatures or using viruses carrying PTGS suppressors. The data demonstrate that PTGS does not play a significant role in PVX CP-MR.
Simultaneous Detection of Nine Grapevine Viruses by Multiplex Reverse Transcription-Polymerase Chain Reaction with Coamplification of a Plant RNA as Internal Control
Authors: Gambino Giorgio , Gribaudo Ivana
Published: May 2007

A multiplex reverse transcription-polymerase chain reaction (mRT-PCR) was developed for simultaneous detection of nine grapevine viruses: Arabis mosaic virus, Grapevine fanleaf virus, Grapevine virus A, Grapevine virus B, Rupestris stem pitting-associated virus, Grapevine fleck virus, Grapevine leafroll-associated virus-1, -2, and -3, in combination with a plant RNA internal control used as an indicator of the effectiveness of RNA extraction and RT-PCR. Primers were designed from conserved regions of each virus and their specificity was confirmed by sequencing PCR products. Two plant total RNA extraction methods (silica capture and modified RNeasy method) and two RT-PCR systems (onestep and two-step) were evaluated to develop a reliable protocol for mRT-PCR. One to nine fragments specific for the viruses were simultaneously amplified from infected samples and identified by their specific molecular sizes in agarose gel electrophoresis. In the two-step mRT-PCR, the detection limits were 10-3or 10-4extract dilutions, depending on the virus. Leaves, phloem from dormant cuttings, and in vitro plantlets from 103 naturally infected and healthy grapevines were analyzed. The mRT-PCR provided a reliable and rapid method for detecting grapevine viruses from a large number of samples.
Rusted Root of Ginseng (Panax quinquefolius) Is Caused by a Species of Rhexocercosporidium
Authors: Reeleder R. D. , Hoke S. M. T. , Zhang Yun
Published: May 2007

Rusted root (also known as rusty root) of ginseng (Panax quinquefolius) was first described over 70 years ago, but the causal agent has not been clearly established. The disease is characterized by slightly raised reddish-brown to black root lesions of varying size. The lesions, regardless of size, remain superficial; however, peridermal tissue is ruptured and sloughed off, giving the root a scabbed appearance. Culture-independent techniques were used to demonstrate that a fungal internal transcribed spacer (ITS) region DNA fragment was strongly associated with diseased but not healthy root tissue. The fragment (≈ 650 bp in length) was cloned. Restriction enzyme digests of cloned DNA indicated that the 650-bp fragment represented a single taxon. BLAST analysis following sequencing of the fragment found that the nearest matches in GenBank were anamorphic genera associated with discomycetes, in particular Rhexocercosporidium spp. This putative identification was supported further by isolating fungi from diseased tissue using a semiselective agar medium. With this procedure, a Rhexocercosporidium-like fungus was isolated; DNA extracted from fungal cultures and amplified using ITS oligonucleotide primers was found to be identical to similarly amplified DNA from the 650-bp bands. However, the isolates were distinct, with respect to growth rate on agar media and ITS sequence, from Rhexocercosporidium carotae, the only described species in this genus. The ability to reproduce symptoms on ginseng roots was confirmed in pathogenicity tests. Oligonucleotide primers based on ITS sequences were designed to amplify DNA of Rhexocercosporidium spp. Polymerase chain reaction assays on DNA extracted from naturally infected root tissue showed that the fungus was present in nearly all symptomatic roots but was infrequent in healthy-appearing roots. The most probable cause of rusted root of ginseng is a previously undescribed species of Rhexocercosporidium.
Inhibition of Blumeria graminis f. sp. tritici Germination and Partial Enhancement of Wheat Defenses by Milsana
Authors: Randoux Béatrice , Renard Delphine , Nowak Emmanuel , Sanssené Jean , Courtois Josiane , Durand Roger , Reignault Philippe
Published: May 2007

The prophylactic efficiency of Milsana against powdery mildew was evaluated on wheat (Triticum aestivum). A single short spraying on 10-day-old plantlets reduced the infection level by 85% and two long sprayings led to the total restriction of the disease. Although microscopic studies showed that Milsana treatments enhance hydrogen peroxide accumulation at the fungal penetration site, biochemical analysis did not allow us to correlate this accumulation with the activation of several enzyme activities involved in active oxygen species (AOS) metabolism. Only lipoxygenase activity, which is involved in both AOS metabolism and lipid peroxidation, showed a 26 to 32% increase 48-h posttreatment in leaves infiltrated with Milsana. This weak effect of Milsana on wheat lipid metabolism was confirmed at the lipid peroxidation level, which surprisingly, was shown to decrease in treated plants. In order to explain the high efficacy of Milsana, the fungistatic effect on conidia germination was also examined. In planta, we showed that a Milsana treatment resulted in a higher proportion of abnormally long appressorial germ tubes, whereas in vitro, it dramatically inhibited fungal conidia germination. The partial activity of Milsana in terms of defense response induction in the wheat/powdery mildew pathosystem and its newly described direct fungistatic activity are discussed.
Saprophytic Activity and Sporulation ofCryphonectria parasiticaon Dead Chestnut Wood in Forests with Naturally Established Hypovirulence
Authors: Prospero S. , Conedera M. , Heiniger U. , Rigling D.
Published: May 2007

Sustainable biological control of the chestnut blight fungus Crypho-nectria parasitica with hypovirulence depends on the production and dissemination of hypovirus-infected propagules of the pathogen. We investigated the ability of C. parasitica to sporulate and produce hypo-virus-infected spores on recently dead chestnut wood in coppice stands in southern Switzerland where hypovirulence has been naturally established. The number and type (active, inactive, or none) of cankers was assessed on experimentally cut and stacked stems, firewood stacks, and natural dead wood. Hypovirus-free and hypovirus-infected strains readily survived for more than 1 year in the chestnut blight cankers of the stacked stems. Sporulation of C. parasitica was observed on the surface of preexisting inactive and active cankers, as well as on newly colonized bark areas and was significantly more abundant than on comparable cankers on living stems. On all types of dead wood, we observed more stromata with perithecia than with pycnidia; however, a large proportion of the stromata was not differentiated. All perithecia examined yielded only hypovirus-free ascospores. The incidence of pycnidia that produced hypovirus-infected conidia ranged from 5% on natural dead wood to 41% on the experimental stacks. The mean virus transmission rate into conidia was 69%. Our study demonstrates a considerable saprophytic activity of C. parasitica on recently dead chestnut wood and supports the hypothesis of a role of this saprophytic phase in the epidemiology of hypovirulence.
Quantitative and Molecular Epidemiology of Bacterial Blight of Onion in Seed Production Fields
Authors: Humeau L. , Roumagnac P. , Picard Y. , Robène-Soustrade I. , Chiroleu F. , Gagnevin L. , Pruvost O.
Published: May 2007

Onion, a biennial plant species, is threatened by the emerging, seed-borne, and seed-transmitted Xanthomonas axonopodis pv. allii. Bacterial blight epidemics were monitored in seed production fields over two seasons. Temporal disease progress was different between the two seasons, with final incidence ranging from 0.04 to 0.06 in 2003 and from 0.44 to 0.61 in 2004. The number of hours with temperatures above 24°C was the best descriptor for predicting the number of days after inoculation for bacterial blight development on inoculated plants. Fitting the β-binomial distribution and binary power law analysis indicated aggregated patterns of disease incidence data. The β-binomial distribution was superior to the binomial distribution for 97% of the examined data sets. Spatial dependency ranged from 5.9 to 15.2 m, as determined by semivariance analysis. Based on amplified fragment length polymorphism (AFLP) analysis, it was concluded that plots predominantly were infected by the inoculated haplotype. A single other haplotype was identified by AFLP in all plots over the 2 years, and its detection in the field always followed wind-driven rains. X. axonopodis pv. allii-contaminated seed were detected by semiselective isolation and a nested polymerase chain reaction assay at levels up to 0.05% when final disease incidence was 0.61. Contaminated seed originated from both diseased and asymptomatic plants.
Interactions Among a Soil Organic Amendment, Nematodes, and the Nematode-Trapping Fungus Dactylellina candidum
Authors: Jaffee B. A.
Published: May 2007

When alfalfa leaves (Medicago sativa) are added to soil, both the nematode-trapping fungus Dactylellina candidum and microbivorous nematodes increase. To determine whether the response of the fungus to alfalfa depends on consumption of bacterivorous and fungivorous nematodes, soil microcosm experiments were performed. D. candidum did not increase if alfalfa leaves were added to soil lacking nematodes, but did increase if nematodes were added to soil lacking alfalfa leaves. Although these results indicate that the response of D. candidum to alfalfa depends on nematodes, D. candidum and microbivorous nematodes did not exhibit classical predator-prey dynamics (i.e., D. candidum seldom reduced numbers of resident nematodes and, after initially increasing in alfalfa amended soil, numbers of D. candidum then decreased, whereas numbers of nematodes continued to increase). Fungivorous nematodes were abun dant in alfalfa-amended soil, and their potential to suppress trapping fungi requires more research.
Interactions Between the Soybean Cyst Nematode and Fusarium solani f. sp. glycines Based on Greenhouse Factorial Experiments
Authors: Gao X. , Jackson T. A. , Hartman G. L. , Niblack T. L.
Published: May 2007

The soybean cyst nematode, Heterodera glycines, and the fungus that causes sudden death syndrome (SDS) of soybean, Fusarium solani f. sp. glycines, frequently co-infest soybean (Glycine max) fields. The interactions between H. glycines and F. solani f. sp. glycines were investigated in factorial greenhouse experiments with different inoculum levels of both organisms on a soybean cultivar susceptible to both pathogens. Measured responses included root and shoot dry weights, H. glycines reproduction, area under the SDS disease progress curve, and fungal colonization of roots. Both H. glycines and F. solani f. sp. glycines reduced the growth of soybeans. Reproduction of H. glycines was suppressed by high inoculum levels but not by low levels of F. solani f. sp. glycines. The infection of soybean roots by H. glycines did not affect root colonization by the fungus, as determined by real-time polymerase chain reaction. Although both pathogens reduced the growth of soybeans, H. glycines did not increase SDS foliar symptoms, and statistical interactions between the two pathogens were seldom significant.
Identification, Characterization, and Detection of Black raspberry necrosis virus
Authors: Halgren Anne , Tzanetakis Ioannis E. , Martin Robert R.
Published: May 2007

A serious disease was observed in black raspberry (Rubus occidentalis) in Oregon in the last decade. Plants showing mosaic symptoms declined rapidly and, in many cases, died after several years. Double-stranded RNA extraction from symptomatic black raspberry revealed the presence of two high molecular weight bands which were cloned and sequenced. Sequence analysis disclosed the presence of a novel virus that was tentatively named Black raspberry decline-associated virus (BRDaV). The complete sequences of the two genomic RNAs, excluding the 3′ poly-adenosine tails, were 7,581 and 6,364 nucleotides, respectively. The genome organization was identical to that of Strawberry mottle virus, a member of the genus Sadwavirus. The C terminus of the RNA 1 poly-protein is unique within the genus Sadwavirus, with homology to AlkB-like domains, suggesting a role in repair of alkylation damage. A reverse-transcriptase polymerase chain reaction test was designed for the detection of BRDaV from Rubus tissue, and tests revealed that BRDaV was associated consistently with the observed decline symptoms. While this publication was under review, it came to our attention that scientists at the Scottish Crop Research Institute had molecular data on Black raspberry necrosis virus (BRNV), a virus that shared many biological properties with BRDaV. After exchange of data, we concluded that BRDaV is a strain of BRNV, a previously described yet unsequenced virus. The North American strain was vectored nonpersistently by the large raspberry aphid and the green peach aphid. Phylogenetic analysis indicates that BRNV belongs to the genus Sadwavirus.
Identification and Characterization of a Novel Whitefly-Transmitted Member of the Family Potyviridae Isolated from Cucurbits in Florida
Authors: Adkins Scott , Webb Susan E. , Achor Diann , Roberts Pamela D. , Baker Carlye A.
Published: May 2007

A novel whitefly-transmitted member of the family Potyviridae was isolated from a squash plant (Cucurbita pepo) with vein yellowing symptoms in Florida. The virus, for which the name Squash vein yellowing virus (SqVYV) is proposed, has flexuous rod-shaped particles of ≈840 nm in length. The experimental host range was limited to species in the family Cucurbitaceae, with the most dramatic symptoms observed in squash and watermelon, but excluded all tested species in the families Amaranthaceae, Apocynaceae, Asteraceae, Chenopodiaceae, Fabaceae, Malvaceae, and Solanaceae. The virus was transmitted by whiteflies (Bemisia tabaci) but was not transmitted by aphids (Myzus persicae). Infection by SqVYV induced inclusion bodies visible by electron and light microscopy that were characteristic of members of the family Potyviridae. Comparison of the SqVYV coat protein gene and protein sequences with those of recognized members of the family Potyviridae indicate that it is a novel member of the genus Ipomovirus. A limited survey revealed that SqVYV also was present in watermelon plants suffering from a vine decline and fruit rot recently observed in Florida and was sufficient to induce these symptoms in greenhouse-grown watermelon, suggesting that SqVYV is the likely cause of this disease.
A Quantitative Review of Tebuconazole Effect on Fusarium Head Blight and Deoxynivalenol Content in Wheat
Authors: Paul P. A. , Lipps P. E. , Hershman D. E. , McMullen M. P. , Draper M. A. , Madden L. V.
Published: May 2007

A meta-analysis of the effect of tebuconazole (e.g., Folicur 3.6F) on Fusarium head blight and deoxynivalenol (DON) content of wheat grain was performed using data collected from uniform fungicide trials (UFTs) conducted at multiple locations across U.S. wheat-growing regions. Response ratios (mean disease and DON levels from tebuconazole-treated plots, divided by mean disease and DON levels from untreated check plots) were calculated for each of 139 studies for tebuconazole effect on Fusarium head blight index (IND; field or plot-level disease severity, i.e., mean proportion of diseased spikelets per spike) and 101 studies for tebuconazole effect on DON contamination of harvested grain. A random-effects meta-analysis was performed on the log-transformed ratios, and the estimated mean log ratios were transformed to estimate the mean (expected) percent control for IND ( CIND ) and DON ( CDON). A mixed effects meta-analysis was then done to determine the effects of wheat type (spring versus winter wheat) and disease and DON levels in the controls on the log ratios. Tebuconazole was more effective at limiting IND than DON, with CIND and CDON values of 40.3 and 21.6%, respectively. The efficacy of tebuconazole as determined by the impact on both IND and DON was greater in spring wheat than in winter wheat (P < 0.01), with a 13.2% higher CIND and a 12.4% higher CDON in spring wheat than in winter wheat. In general, CIND and CDON were both at their lowest values (and not significantly different from 0) when mean IND and DON in the controls, respectively, were low (≤2% for IND and <1 ppm for DON). CIND was 25% higher in studies with mean IND between 2 and 15% than in studies with mean IND ≤ 2%, whereas CDON was 28.8% higher in studies with mean DON between 1 and 10 ppm than in studies with mean DON < 1 ppm. The between-study variance was significantly greater than 0 (P < 0.01), indicating considerable (unexplained) variability in percent control.
Induced Systemic Resistance by Fluorescent Pseudomonas spp.
Authors: Bakker Peter A. H. M. , Pieterse Corné M. J. , van Loon L. C.
Published: May 2007

Fluorescent Pseudomonas spp. have been studied for decades for their plant growth-promoting effects through effective suppression of soilborne plant diseases. The modes of action that play a role in disease suppression by these bacteria include siderophore-mediated competition for iron, antibiosis, production of lytic enzymes, and induced systemic resistance (ISR). The involvement of ISR is typically studied in systems in which the Pseudomonas bacteria and the pathogen are inoculated and remain spatially separated on the plant, e.g., the bacteria on the root and the pathogen on the leaf, or by use of split root systems. Since no direct interactions are possible between the two populations, suppression of disease development has to be plant-mediated. In this review, bacterial traits involved in Pseudomonas-mediated ISR will be discussed.
UsingPseudomonasspp. for Integrated Biological Control
Authors: Stockwell Virginia O. , Stack James P.
Published: May 2007

Pseudomonas spp. have been studied for decades as model organisms for biological control of plant disease. Currently, there are three commercial formulations of pseudomonads registered with the U.S. Environmental Protection Agency for plant disease suppression, Bio-Save 10 LP, Bio-Save 11 LP, and BlightBan A506. Bio-Save 10 LP and Bio-Save 11 LP, products of Jet Harvest Solutions, Longwood, FL, contain Pseudomonas syringae strains ESC-10 and ESC-11, respectively. These products are applied in packinghouses to prevent postharvest fungal diseases during storage of citrus, pome, stone fruits, and potatoes. BlightBan A506, produced by NuFarm Americas, Burr Ridge, IL, contains P. fluorescens strain A506. BlightBan A506 is applied primarily to pear and apple trees during bloom to suppress the bacterial disease fire blight. Combining BlightBan A506 with the antibiotic streptomycin improves control of fire blight, even in areas with streptomycin-resistant populations of the pathogen. BlightBan A506 also may reduce fruit russet and mild frost injury. These biocontrol products consisting of Pseudomonas spp. provide moderate to excellent efficacy against multiple production constraints, are relatively easy to apply, and they can be integrated with conventional products for disease control. These characteristics will contribute to the adoption of these products by growers and packinghouses.
Modifications of the Helper Component-Protease of Zucchini yellow mosaic virus for Generation of Attenuated Mutants for Cross Protection Against Severe Infection
Authors: Lin Shih-Shun , Wu Hui-Wen , Jan Fuh-Jyh , Hou Roger F. , Yeh Shyi-Dong
Published: May 2007

A nonpathogenic mild strain is essential for control of plant viruses by cross protection. Three amino acid changes, Arg180→Ile180 (GA mutation), Phe205→Leu205 (GB mutation), and Glu396→Asn396 (GC mutation), of the conserved motifs of the helper component-protease (HC-Pro) of a severe strain TW-TN3 of Zucchini yellow mosaic virus (ZYMV), a member of the genus Potyvirus, were generated from an infectious cDNA clone that carried a green fluorescent protein reporter. The infectivity of individual mutants containing single, double, or triple mutations was assayed on local and systemic hosts. On Chenopodium quinoa plants, the GB mutant induced necrotic lesions; the GA, GC, and GBC mutants induced chlorotic spots; and the GAB and GAC mutants induced local infection only visualized by fluorescence microscopy. On squash plants, the GA, GB, GC, and GBC mutants caused milder mosaic; the GAC mutant induced slight leaf mottling followed by recovering; and the GAB mutant did not induce conspicuous symptoms. Also, the GAC mutant, but not the GAB mutant, conferred complete cross protection against the parental virus carrying a mite allergen as a reporter. When tested on transgene-silenced transgenic squash, the ability of posttranscriptional gene silencing suppression of the mutated HC-Pro of GAC was not significantly affected. We concluded that the mutations of the HC-Pro of ZYMV reduce the degrees of pathogenicity on squash and also abolish the ability for eliciting the hypersensitive reaction on C. quinoa, and that the mutant GAC is a useful mild strain for cross protection.
Application of Real-Time and Multiplex Polymerase Chain Reaction Assays to Study Leaf Blotch Epidemics in Barley
Authors: Fountaine J. M. , Shaw M. W. , Napier B. , Ward E. , Fraaije B. A.
Published: May 2007

Leaf blotch, caused by Rhynchosporium secalis, was studied in a range of winter barley cultivars using a combination of traditional plant pathological techniques and newly developed multiplex and real-time polymerase chain reaction (PCR) assays. Using PCR, symptomless leaf blotch colonization was shown to occur throughout the growing season in the resistant winter barley cv. Leonie. The dynamics of colonization throughout the growing season were similar in both Leonie and Vertige, a susceptible cultivar. However, pathogen DNA levels were approximately 10-fold higher in the susceptible cultivar, which expressed symptoms throughout the growing season. Visual assessments and PCR also were used to determine levels of R. secalis colonization and infection in samples from a field experiment used to test a range of winter barley cultivars with different levels of leaf blotch resistance. The correlation between the PCR and visual assessment data was better at higher infection levels (R2 = 0.81 for leaf samples with >0.3% disease). Although resistance ratings did not correlate well with levels of disease for all cultivars tested, low levels of infection were observed in the cultivar with the highest resistance rating and high levels of infection in the cultivar with the lowest resistance rating.
Relationships Among Resistances to Fusarium and Aspergillus Ear Rots and Contamination by Fumonisin and Aflatoxin in Maize
Authors: Robertson-Hoyt Leilani A. , Betrán Javier , Payne Gary A. , White Don G. , Isakeit Thomas , Maragos Chris M. , Molnár Terence L. , Holland James B.
Published: May 2007

Fusarium verticillioides, F. proliferatum, and Aspergillus flavus cause ear rots of maize and contaminate the grain with mycotoxins (fumonisin or aflatoxin). The objective of this study was to investigate the relationships between resistance to Fusarium and Aspergillus ear rots and fumonisin and aflatoxin contamination. Based on a previous study of 143 recombinant inbred lines from the cross NC300 × B104, 24 lines with the highest and 24 lines with the lowest mean fumonisin concentration were selected for further evaluation. Paired plots of each line were inoculated with F. verticillioides and F. proliferatum or with A. flavus in replicated trials in 2004 and 2005 in Clayton, NC, and College Station, TX. The low-fumonisin group had significantly lower levels of fumonisin, aflatoxin, and Fusarium and Aspergillus ear rots. Across year-location environments, all four traits were significantly correlated; the genotypic correlation (rG) ranged from rG = 0.88 (aflatoxin and Aspergillus ear rot) to rG = 0.99 (Fusarium and Aspergillus ear rots). Quantitative trait loci (QTLs) were identified and their effects estimated. Two QTLs affected both toxin concentrations, one QTL affected both ear rots, and one QTL affected Aspergillus and Fusarium rots and fumonisin. These results suggest that at least some of the genes involved in resistance to ear rots and mycotoxin contamination are identical or genetically linked.
Virulence Phenotypes of a Worldwide Collection of Puccinia triticina from Durum Wheat
Authors: Ordoñez M. E. , Kolmer J. A.
Published: May 2007

A total of 78 isolates of Puccinia triticina from durum wheat from Argentina, Chile, Ethiopia, France, Mexico, Spain and the United States and 10 representative isolates of P. triticina from common wheat from the United States were tested for virulence phenotypes on seedling plants of 35 near-isogenic lines of Thatcher wheat. Isolates with virulence on lines with leaf rust resistance genes Lr10, Lr14b, Lr20, Lr22a, Lr23, Lr33, Lr34, Lr41, and Lr44 represented the most frequent phenotype. Cluster analysis showed that P. triticina from durum wheat from South America, North America, and Europe had an average similarity in virulence of 90%, whereas isolates from Ethiopia were <70% similar to the other leaf rust isolates collected from durum wheat. Of the 11 isolates from Ethiopia, 7 were avirulent to Thatcher and all near-isogenic lines of Thatcher. The isolates from common wheat had an average similarity in virulence of 60% to all leaf rust isolates from durum wheat. P. triticina from durum wheat was avirulent to many Lr genes frequently found in common wheat. It is possible that P. triticina currently found on durum wheat worldwide had a single origin, and then spread to cultivated durum wheat in North America, South America, and Europe, whereas P. triticina from Ethiopia evolved on landraces of durum wheat genetically distinct from the cultivated durum lines grown in Europe and the Americas.
Soybean mosaic virus Helper Component-Protease Alters Leaf Morphology and Reduces Seed Production in Transgenic Soybean Plants
Authors: Lim Hyoun Sub , Ko Tae Seok , Hobbs Houston A. , Lambert Kris N. , Yu Jun Myoung , McCoppin Nancy K. , Korban Schuyler S. , Hartman Glen L. , Domier Leslie L.
Published: May 2007

Transgenic soybean (Glycine max) plants expressing Soybean mosaic virus (SMV) helper component-protease (HC-Pro) showed altered vegetative and reproductive phenotypes and responses to SMV infection. When inoculated with SMV, transgenic plants expressing the lowest level of HC-Pro mRNA and those transformed with the vector alone initially showed mild SMV symptoms. Plants that accumulated the highest level of SMV HC-Pro mRNA showed very severe SMV symptoms initially, but after 2 weeks symptoms disappeared, and SMV titers were greatly reduced. Analysis of SMV RNA abundance over time with region-specific probes showed that the HC-Pro region of the SMV genome was degraded before the coat protein region. Transgenic soybean plants that expressed SMV HC-Pro showed dose-dependent alterations in unifoliate leaf morphologies and seed production where plants expressing the highest levels of HC-Pro had the most deformed leaves and the lowest seed production. Accumulation of microRNAs (miRNAs) and mRNAs putatively targeted by miRNAs was analyzed in leaves and flowers of healthy, HC-Pro-transgenic, and SMV-infected plants. Neither expression of SMV HC-Pro nor SMV infection produced greater than twofold changes in accumulation of six miRNAs. In contrast, SMV infection was associated with twofold or greater increases in the accumulation of four of seven miRNA-targeted mRNAs tested.
Involvement of Gluconic Acid and Glucose Oxidase in the Pathogenicity of Penicillium expansum in Apples
Authors: Hadas Yoav , Goldberg Israel , Pines Ophry , Prusky Dov
Published: May 2007

The contribution of gluconic acid secretion to the colonization of apple tissue by Penicillium expansum was analyzed by modulation (increase or decrease) of gluconic acid accumulation at the infection court. P. expansum isolates that express the most gox2 transcripts and concomitant glucose oxidase (GOX) activity and that secrete the most gluconic acid cause disease of apple at the fastest rate. Cultures grown under reduced oxygen concentration generated fewer gox2 transcripts, produced less gluconic acid, and led to a 15% reduction in disease. Furthermore, the detection of significantly high levels of transcripts of gox2 and GOX activity at the edge of the decaying tissue emphasize the involvement of GOX in tissue acidification of the decaying tissue. Taken together, these results emphasize the importance of GOX in the production of the gluconic acid that leads, in turn, to host tissue acidification. This acidification enhanced the expression of pectolytic enzymes and the establishment of conditions for necrotrophic development of P. expansum.
Characterization of Phytophthora capsici from Michigan Surface Irrigation Water
Authors: Gevens A. J. , Donahoo R. S. , Lamour K. H. , Hausbeck M. K.
Published: May 2007

Phytophthora capsici infects cucurbitaceous and solanaceous crops worldwide. In free water, P. capsici sporangia release zoospores that may be disseminated by moving surface water. Surface irrigation sources (river system, ponds, and ditches) in three Michigan counties with a history of P. capsici-susceptible crop production were monitored for the pathogen during four growing seasons (2002 to 2005). Pear and cucumber baits were suspended in water at monitoring sites for 3- to 7-day intervals and water temperature was recorded. Baits were washed and lesions were excised and cultured on water agar amended with rifampicin and ampicillin. P. capsici was detected at monitoring sites in multiple years, even when non-host crops were planted nearby. Recovered isolates (N = 270) were screened for sensitivity to the fungicide mefenoxam and characterized for mating type (MT). P. capsici isolates resistant to mefenoxam were common in water sources from southwest and southeast Michigan. Most monitoring sites yielded isolates of a 1:1 ratio of A1:A2 MTs. Amplified fragment length polymorphism analysis of select isolates from 2002 to 2004 indicated a lack of similarity groups persisting over time and in specific geographical locations. Data suggest that P. capsici did not overwinter in any of the surface water sources monitored. Water temperatures were correlated to positive P. capsici detection from all monitoring sites. The frequent detection of P. capsici in surface water used for irrigation in the primary vegetable growing regions in Michigan suggests that this is an important means of pathogen dissemination.
Survival Dynamics ofAphanomyces cochlioidesOospores Exposed to Heat Stress
Authors: Dyer A. T. , Windels C. E. , Cook R. D. , Leonard K. J.
Published: May 2007

To determine how exposure to heat effects their survival, oospores of Aphanomyces cochlioides isolate C22 were exposed in water to 35, 40, 45, or 50°C for prescribed times and then examined for viability. The Weibull model was modified to represent the effects of temperature on survival of oospores. The final fitted model gave lethal doses for 50% of the oospores of 251, 49.8, 9.8, and 1.9 h at 35, 40, 45, and 50°C, respectively. To determine if alternating high and low temperatures resulted in (i) recovery from heat damage during low temperature periods, (ii) increased susceptibility to heat damage, or (iii) if effects of heat damage were cumulative, oospores were examined after each of four 24-h cycles at 45°C for 4 h and 21°C for 20 h. Survival of oospores exposed to alternating high and low temperatures fit the cumulative effects model. Significant variability in heat tolerance among five isolates was observed (P< 0.001) but model parameters successfully accommodated this variability (R2= 0.96, P < 0.001). This research shows that under wet conditions, there are predictable patterns to mortality for A. cochlioides oospores exposed to continuous or fluctuating high temperatures.
Green Mold Diseases of Agaricus and Pleurotus spp. Are Caused by Related but Phylogenetically Different Trichoderma Species
Authors: Hatvani L. , Antal Z. , Manczinger L. , Szekeres A. , Druzhinina I. S. , Kubicek C. P. , Nagy A. , Nagy E. , Vágvölgyi C. , Kredics L.
Published: May 2007

Producers of champignon (Agaricus bisporus) and oyster mushroom (Pleurotus ostreatus) are facing recent incidents of green mold epidemics in Hungary. We examined 66 Trichoderma strains isolated from Agaricus compost and Pleurotus substrate samples from three Hungarian mushroom producing companies by a polymerase chain reaction-based diagnostic test for T. aggressivum, sequence analysis of the internal transcribed spacer region 1 (ITS1) and ITS2 and (selectively) of the fourth and fifth intron of translation elongation factor 1α (tef1α), and restriction fragment length polymorphism of mitochondrial DNA. Seven Trichoderma species were identified: T. aggressivum f. europaeum (17 isolates), T. harzianum (three isolates), T. longibrachiatum (four isolates), T. ghanense (one isolate), T. asperellum (four isolates), T. atroviride (nine isolates), and a still undescribed phylogenetic species, Trichoderma sp. DAOM 175924 (28 isolates). T. aggressivum f. europaeum was exclusively derived from A. bisporus compost, whereas Trichoderma sp. DAOM 175924 exclusively occurred in the substrate for Pleurotus cultivation. Sequences of the latter strains were co-specific with those for Trichoderma pathogens of P. ostreatus in Korea. The widespread occurrence of this new species raises questions as to why infections by it have just only recently been observed. Our data document that (i) green mold disease by T. aggressivum f. europaeum has geographically expanded to Central Europe; (ii) the green mold disease of P. ostreatus in Hungary is due to the same Trichoderma species as in Korea and the worldwide distribution of the new species indicates the possibility of spreading epidemics; and (iii) on mushroom farms, the two species are specialized on their different substrates.
Two Resistance Modes to Clover yellow vein virus in Pea Characterized by a Green Fluorescent Protein-Tagged Virus
Authors: Andrade Marcelo , Sato Masanao , Uyeda Ichiro
Published: May 2007

This study characterized resistance in pea lines PI 347295 and PI 378159 to Clover yellow vein virus (ClYVV). Genetic cross experiments showed that a single recessive gene controls resistance in both lines. Conventional mechanical inoculation did not result in infection; however, particle bombardment with infectious plasmid or mechanical inoculation with concentrated viral inocula did cause infection. When ClYVV No. 30 isolate was tagged with a green fluorescent protein (GFP) and used to monitor infection, viral cell-to-cell movement differed in the two pea lines. In PI 347595, ClYVV replicated at a single-cell level, but did not move to neighboring cells, indicating that resistance operated at a cell-to-cell step. In PI 378159, the virus moved to cells around the infection site and reached the leaf veins, but viral movement was slower than that in the susceptible line. The viruses observed around the infection sites and in the veins were then recovered and inoculated again by a conventional mechanical inoculation method onto PI 378159 demonstrating that ClYVV probably had mutated and newly emerged mutant viruses can move to neighboring cells and systemically infect the plants. Tagging the virus with GFP was an efficient tool for characterizing resistance modes. Implications of the two resistance modes are discussed.
Spread of Heterobasidion annosum in Christmas Tree Plantations of the United States Pacific Northwest
Authors: Dart N. L. , Chastagner G. A. , Peever T. L.
Published: May 2007

The population structure of Heterobasidion annosum in the Pacific Northwest (PNW) Christmas tree plantations was estimated at two spatial scales to assess the relative importance of primary and secondary infection, colonization, and spread of the pathogen. Ninety-three isolates from single trees in 27 discrete mortality pockets and 104 isolates from 12 individual root systems of noble and Fraser fir trees were sampled near Mossyrock, Washington. Isolates were genotyped using somatic compatibility assays and microsatellite markers to determine the spatial scale at which dispersal of single genotypes (genets) was occurring. All isolates sampled from different trees in discrete mortality pockets had distinct genotypes, whereas the root systems of single trees were dominated by one or two genotypes. These results suggest that infection of PNW Christmas trees results from frequent primary infection events of adjacent stumps and localized secondary spread within root systems rather than clonal spread of the pathogen between adjacent trees. We hypothesize that mortality pockets may be due to availability of infection courts and/or variation in inoculum levels during selective harvesting of patches of mature trees.