bluuebunny/crossref_metadata_2025 huggingface dataset:
Tobacco Transgenic for the Flax Rust Resistance Gene L Expresses Allele-Specific Activation of Defense Responses
Authors: Frost Donna , Way Heather , Howles Paul , Luck Joanne , Manners John , Hardham Adrienne , Finnegan Jean , Ellis Jeff
Published: May 2007

Tobacco was transformed with three different alleles (L2, L6, and L10) of the flax rust resistance gene L, a member of the toll interleukin-1 receptor, nucleotide-binding site, leucine-rich repeat (TIR-NBS-LRR) class of plant disease resistance genes. L6 transgenics had a stunted phenotype, expressed several defense response genes constitutively, and had increased resistance to the fungus Cercospora nicotianae and the oomycete Phytophthora parasitica pv. nicotianae. L2 and L10 transgenics, with one exception for L10, did not express these phenotypes, indicating that the activation of tobacco defense responses is L6 allele-specific. The phenotype of the exceptional L10 transgenic plant was associated with the presence of a truncated L10 gene resulting from an aberrant T-DNA integration. The truncated gene consisted of the promoter, the complete TIR region, and 39 codons of the NBS domain fused in-frame to a tobacco retrotransposon-like sequence. A similar truncated L10 gene, constructed in vitro, was transiently expressed in tobacco leaves and gave rise to a strong localized necrotic reaction. Together, these results suggest that defense signaling properties of resistance genes can be expressed in an allele-specific and pathogen-independent manner when transferred between plant genera.
Global Changes in Gene Expression in Sinorhizobium meliloti 1021 under Microoxic and Symbiotic Conditions
Authors: Becker Anke , Bergès Hélène , Krol Elizaveta , Bruand Claude , Rüberg Silvia , Capela Delphine , Lauber Emmanuelle , Meilhoc Eliane , Ampe Frédéric , de Bruijn Frans J. , Fourment Joëlle , Francez-Charlot Anne , Kahn Daniel , Küster Helge , Liebe Carine , Pühler Alfred , Weidner Stefan , Batut Jacques
Published: May 2007

Sinorhizobium meliloti is an α-proteobacterium that alternates between a free-living phase in bulk soil or in the rhizosphere of plants and a symbiotic phase within the host plant cells, where the bacteria ultimately differentiate into nitrogen-fixing organelle-like cells, called bacteroids. As a step toward understanding the physiology of S. meliloti in its free-living and symbiotic forms and the transition between the two, gene expression profiles were determined under two sets of biological conditions: growth under oxic versus microoxic conditions, and in free-living versus symbiotic state. Data acquisition was based on both macro- and microarrays. Transcriptome profiles highlighted a profound modification of gene expression during bacteroid differentiation, with 16% of genes being altered. The data are consistent with an overall slow down of bacteroid metabolism during adaptation to symbiotic life and acquisition of nitrogen fixation capability. A large number of genes of unknown function, including potential regulators, that may play a role in symbiosis were identified. Transcriptome profiling in response to oxygen limitation indicated that up to 5% of the genes were oxygen regulated. However, the microoxic and bacteroid transcriptomes only partially overlap, implying that oxygen contributes to a limited extent to the control of symbiotic gene expression.
Mutations in Potato virus Y Genome-Linked Protein Determine Virulence Toward Recessive Resistances in Capsicum annuum and Lycopersicon hirsutum
Authors: Moury Benoît , Morel Caroline , Johansen Elisabeth , Guilbaud Laurent , Souche Sylvie , Ayme Valérie , Caranta Carole , Palloix Alain , Jacquemond Mireille
Published: May 2007

The recessive resistance genes pot-1 and pvr2 in Lycopersicon hirsutum and Capsicum annuum, respectively, control Potato virus Y (PVY) accumulation in the inoculated leaves. Infectious cDNA molecules from two PVY isolates differing in their virulence toward these resistances were obtained using two different strategies. Chimeras constructed with these cDNA clones showed that a single nucleotide change corresponding to an amino acid substitution (Arg119His) in the central part of the viral protein genome-linked (VPg) was involved in virulence toward the pot-1 resistance. On the other hand, 15 nucleotide changes corresponding to five putative amino acid differences in the same region of the VPg affected virulence toward the pvr21 and pvr22 resistances. Substitution models identified six and five codons within the central and C terminal parts of the VPg for PVY and for the related potyvirus Potato virus A, respectively, which undergo positive selection. This suggests that the role of the VPg-encoding region is determined by the protein and not by the viral RNA apart from its protein-encoding capacity.
MAPK Regulation of Sclerotial Development in Sclerotinia sclerotiorum Is Linked with pH and cAMP Sensing
Authors: Chen Changbin , Harel Arye , Gorovoits Rena , Yarden Oded , Dickman Martin B.
Published: May 2007

Sclerotial development is fundamental to the disease cycle of the omnivorous broad host range fungal phytopathogen Sclerotinia sclerotiorum. We have isolated a highly conserved homolog of ERK-type mitogen-activated protein kinases (MAPKs) from S. sclerotiorum (Smk1) and have demonstrated that Smk1 is required for sclerotial development. The smk1 transcription and MAPK enzyme activity are induced dramatically during sclerotiogenesis, especially during the production of sclerotial initials. When PD98059 (a specific inhibitor of the activation of MAPK by MAPK kinase) was applied to differentiating cultures or when antisense expression of smk1 was induced, sclerotial maturation was impaired. The smk1 transcript levels were highest under acidic pH conditions, suggesting that Smk1 regulates sclerotial development via a pH-dependent signaling pathway, involving the accumulation of oxalic acid, a previously identified pathogenicity factor that functions at least in part by reducing pH. Addition of cyclic AMP (cAMP) inhibited smk1 transcription, MAPK activation, and sclerotial development. Thus, S. sclerotiorum can coordinate environmental signals (such as pH) to trigger a signaling pathway mediated by Smk1 to induce sclerotia formation, and this pathway is negatively regulated by cAMP.
Characterization of the Multiple-Copy Host-Selective Toxin Gene, ToxB, in Pathogenic and Nonpathogenic Isolates of Pyrenophora tritici-repentis
Authors: Martinez J. Patrick , Oesch Nicholas W. , Ciuffetti Lynda M.
Published: May 2007

ToxB, a gene that encodes a 6.6-kDa host-selective toxin (HST), is present in several races of the wheat pathogen Pyrenophora tritici-repentis. To learn more about the multiple ToxB open reading frames (ORFs), six of the estimated nine copies from a race 5 isolate were cloned and analyzed. All six copies of ToxB have identical 261-bp ORFs and thus encode the same form of Ptr ToxB. Sequence analysis of regions flanking the cloned ToxB loci revealed that the majority of loci are associated with portions of retrotransposons and a transposon-like sequence. Data indicate that ToxB loci reside on two chromosomes, 3.5 and 2.7 Mb, with the majority of copies located on the 2.7 Mb chromosome. A related gene, referred to as toxb, from a nonpathogenic race 4 isolate was also cloned and characterized. This is interesting because, until now, HST genes have only been found in toxin-producing, pathogenic isolates of plant pathogenic fungi. The toxb gene from nonpathogenic isolates is 86% similar to ToxB, and data suggest that toxb is a single-copy gene. No toxb transcript was detected under culture conditions that favor the expression of ToxB; therefore, these genes differ in their transcriptional regulation.
The Avirulence Domain of Cauliflower mosaic virus Transactivator/Viroplasmin Is a Determinant of Viral Virulence in Susceptible Hosts
Authors: Kobayashi Kappei , Hohn Thomas
Published: May 2007

Cauliflower mosaic virus (CaMV) transactivator/viroplasmin (Tav) is a multifunctional protein essential for basic replication of CaMV. It also plays a role in viral pathogenesis in crucifer and solanaceous host plants. Deletion mutagenesis revealed that N- and C-terminal parts of Tav are not essential for CaMV replication in transfected protoplasts. Two deletion mutants having only minimal defects in basic replication were infectious in turnips but only with highly attenuated virulence. This was shown to be due to delayed virus spread within the inoculated leaves and to the upper leaves. Unlike the wild-type virus, the mutant viruses successfully spread locally without inducing a host defense response in inoculated Datura stramonium leaves, but did not spread systemically. These results provide the first evidence that a Tav domain required for avirulence function in solanaceous plants is not essential for CaMV infectivity but has a role in viral virulence in susceptible hosts.
Two PAK Kinase Genes, CHM1 and MST20, Have Distinct Functions in Magnaporthe grisea
Authors: Li Lei , Xue Chaoyang , Bruno Kenneth , Nishimura Marie , Xu Jin-Rong
Published: May 2007

In the rice blast fungus Magnaporthe grisea, the Pmk1 mitogen-activated protein (MAP) kinase is essential for appressorium formation and infectious growth. PMK1 is homologous to yeast Fus3 and Kss1 MAP kinases that are known to be regulated by the Ste20 PAK kinase for activating the pheromone response and filamentation pathways. In this study, we isolated and characterized two PAK genes, CHM1 and MST20, in M. grisea. Mutants disrupted in MST20 were reduced in aerial hyphae growth and conidiation, but normal in growth rate, appressorium formation, penetration, and plant infection. In chm1 deletion mutants, growth, conidiation, and appressorium formation were reduced significantly. Even though appressoria formed by chm1 mutants were defective in penetration, chm1 mutants were able to grow invasively on rice leaves and colonize through wounds. The chm1 mutants were altered in conidiogenesis and produced conidia with abnormal morphology. Hyphae of chm1 mutants had normal septation, but the length of hyphal compartments was reduced. On nutritionally poor oatmeal agar, chm1 mutants were unstable and produced sectors that differed from original chm1 mutants in growth rate, conidiation, or colony morphology. However, none of the monoconidial cultures derived from these spontaneous sectors were normal in appressorial penetration and fungal pathogenesis. These data suggest that MST20 is dispensable for plant infection in M. grisea, but CHM1 plays a critical role in appressorium formation and penetration. Both mst20 and chm1 deletion mutants were phenotypically different from the pmk1 mutant that is defective in appressorium formation and infectious hyphae growth. It is likely that MST20 and CHM1 individually play no critical role in activating the PMK1 MAP kinase pathway during appressorium formation and infectious hyphae growth. However, CHM1 appears to be essential for appressorial penetration and CHM1 and MST20 may have redundant functions in M. grisea.
Influence of Environmental Conditions on the Production of Phenazine-1-Carboxamide by Pseudomonas chlororaphis PCL1391
Authors: van Rij E. Tjeerd , Wesselink Monique , Chin-A-Woeng Thomas F. C. , Bloemberg Guido V. , Lugtenberg Ben J. J.
Published: May 2007

Pseudomonas chlororaphis PCL1391 produces the secondary metabolite phenazine-1-carboxamide (PCN), which is an antifungal metabolite required for biocontrol activity of the strain. Identification of conditions involved in PCN production showed that some carbon sources and all amino acids tested promote PCN levels. Decreasing the pH from 7 to 6 or decreasing the growth temperature from 21 to 16°C decreased PCN production dramatically. In contrast, growth at 1% oxygen as well as low magnesium concentrations increased PCN levels. Salt stress, low concentrations of ferric iron, phosphate, sulfate, and ammonium ions reduced PCN levels. Fusaric acid, a secondary metabolite produced by the soilborne Fusarium spp. fungi, also reduced PCN levels. Different nitrogen sources greatly influenced PCN levels. Analysis of autoinducer levels at conditions of high and low PCN production demonstrated that, under all tested conditions, PCN levels correlate with autoinducer levels, indicating that the regulation of PCN production by environmental factors takes place at or before autoinducer production. Moreover, the results show that autoinducer production not only is induced by a high optical density but also can be induced by certain environmental conditions. We discuss our findings in relation to the success of biocontrol in the field.
Glutamine Utilization by Rhizobium etli
Authors: Tatè Rosarita , Ferraioli Simona , Filosa Stefania , Cermola Michele , Riccio Anna , Iaccarino Maurizio , Patriarca Eduardo J.
Published: May 2007

We undertook the study of the use of glutamine (Gln) as the source of carbon and energy by Rhizobium etli. Tn5-induced mutagenesis allowed us to identify several genes required for Gln utilization, including those coding for two broad-range amino acid transporters and a glutamate dehydrogenase. The isolated mutants were characterized by the analysis of their capacity i) to grow on different media, ii) to transport Gln (uptake assays), and iii) to utilize Gln as the C energy source (CO2 production from Gln). We show that Gln is degraded through the citric acid cycle and that its utilization as the sole C source is related to a change in the bacterial cell shape (from bacillary to coccoid form) and a high susceptibility to a thiol oxidative insult. Both these data and the analysis of ntr-dependent promoters suggested that Gln-grown bacteria are under a condition of C starvation and N sufficiency, and as expected, the addition of glucose counteracted the morphological change and increased both the bacterial growth rate and their resistance to oxidative stress. Finally, a nodulation analysis indicates that the genes involved in Gln transport and degradation are dispensable for the bacterial ability to induce and invade developing nodules, whereas those involved in gluconeogenesis and nucleotide biosynthesis are strictly required.
The avrRxo1 Gene from the Rice Pathogen Xanthomonas oryzae pv. oryzicola Confers a Nonhost Defense Reaction on Maize with Resistance Gene Rxo1
Authors: Zhao Bingyu , Ardales Edna Y. , Raymundo Asuncion , Bai Jianfa , Trick Harold N. , Leach Jan E. , Hulbert Scot H.
Published: May 2007

Maize lines that contain the single dominant gene Rxo1 exhibit a rapid hypersensitive response (HR) after infiltration with the rice bacterial streak pathogen Xanthomonas oryzae pv. oryzicola, but not with the rice bacterial blight pathogen X. oryzae pv. oryzae. The avirulence effector gene that corresponds to Rxo1, designated avrRxo1, was identified in an X. oryzae pv. oryzicola genomic library. When introduced into X. oryzae pv. oryzae, clones containing avrRxo1 induced an HR on maize with Rxo1, but not on maize without Rxo1. The avrRxo1 gene is 1,266 bp long and shows no significant homology to any database sequences. When expressed in an X. oryzae pv. oryzae hrpC mutant that is deficient in the type III secretion system, avrRxo1 did not elicit the HR, indicating that the avrRxo1-Rxo1 interaction is dependent on type III secretion. Transient expression of avrRxo1 in onion cells after biolistic delivery revealed that the protein product was associated with the plasma membrane. Transient expression in maize lines carrying Rxo1 resulted in cell death, suggesting that AvrRxo1 functions from inside maize cells to elicit Rxo1-dependent pathogen recognition.
Potato Plants Genetically Modified to Produce N-Acylhomoserine Lactones Increase Susceptibility to Soft Rot Erwiniae
Authors: Toth I. K. , Newton J. A. , Hyman L. J. , Lees A. K. , Daykin M. , Ortori C. , Williams P. , Fray R. G.
Published: May 2007

Many gram-negative bacteria employ N-acylhomoserine lactones (AHL) to regulate diverse physiological processes in concert with cell population density (quorum sensing [QS]). In the plant pathogen Erwinia carotovora, the AHL synthesized via the carI/expI genes are responsible for regulating the production of secreted plant cell wall-degrading exoenzymes and the antibiotic carbapen-3-em carboxylic acid. We have previously shown that targeting the product of an AHL synthase gene (yenI) from Yersinia enterocolitica to the chloroplasts of transgenic tobacco plants caused the synthesis in planta of the cognate AHL signaling molecules N-(3-oxohexanoyl)-L-homoserine lactone (3-oxo-C6-HSL) and N-hexanoylhomoserine lactone (C6-HSL), which in turn, were able to complement a carI¯ QS mutant. In the present study, we demonstrate that transgenic potato plants containing the yenI gene are also able to express AHL and that the presence and level of these AHL in the plant increases susceptibility to infection by E. carotovora. Susceptibility is further affected by both the bacterial level and the plant tissue under investigation.
Pathogenic Fungi Causing Symptoms Similar to Phaeosphaeria Leaf Spot of Maize in Brazil
Authors: Do Amaral A. L. , Dal Soglio F. K. , De Carli M. L. , Neto J. F. Barbosa
Published: May 2007

This study aimed to identify and characterize the pathogens associated with symptoms similar to Phaeosphaeria leaf spot (PLS) of maize in different environmental conditions in Brazil. During the last decade, PLS became an important disease of maize in Brazil. However, doubt persists about the causal agent. Maize leaves with PLS-like lesions were collected from two locations (Cristalina, Goiás State [GO] and Vila Maria, Rio Grande do Sul State [RS]) in two growing seasons. Fungi associated with leaf lesions were isolated and cultured for taxonomic identification. Pathogenicity tests were carried out and the results indicated that three fungi (a Phyllosticta sp., Phoma sorghina, and a Sporormiella sp.) caused leaf spot similar to PLS on maize. The composition of pathogenic fungi in PLS-like lesions varied depending on locations and growing seasons. The fungi P. sorghina and a Phoma sp. (Plenodomus section) occurred in all environments, but the Sporormiella and Phyllosticta spp. were restricted to GO and RS, respectively. The results support the hypothesis that various pathogens are involved in PLS-like symptoms of maize and environmental conditions may influence the predominance of a specific agent.
Influence of Soil Temperature and Moisture on Eruptive Germination and Viability of Sclerotia of Sclerotinia minor and S. sclerotiorum
Authors: Matheron M. E. , Porchas M.
Published: May 2007

The effect of soil temperature and moisture on eruptive germination and viability of sclerotia of Sclerotinia minor and S. sclerotiorum in field soil was examined. In two trials at constant temperatures, the proportion of sclerotia of both pathogens that germinated in wet soil ( ≥-0.02 MPa) tended to decrease as soil temperature increased from 15 to 40°C, with no germination of sclerotia of S. minor and S. sclerotiorum detected after 1 and 2 weeks, respectively, at 40°C. In contrast, after 1 to 4 weeks in dry soil ( ≤-100 MPa) at 40°C, germination of sclerotia of S. minor and S. sclerotiorum ranged from 28 to 55% and 42 to 77%, respectively. In field trials, the germination rate of sclerotia of S. minor and S. sclerotiorum after 2 to 8 weeks in irrigated soil on the surface or buried at a depth of 5 cm was significantly lower than that for sclerotia maintained in dry soil at the same depths. On the other hand, after burial at a depth of 10 cm, germination of sclerotia in irrigated and dry soil did not differ significantly after 2 to 8 weeks for S. minor and after 2, 4, and 8 weeks for S. sclerotiorum. For both pathogens, germination of sclerotia from 2 to 8 weeks in irrigated soil with a mean temperature of 32°C was significantly lower than that for sclerotia in irrigated soil with a mean temperature of 26°C. In microplot trials conducted in July and August, no sclerotia of S. minor and S. sclerotiorum germinated after 2 and 3 weeks, respectively, after recovery from flooded soil with mean soil temperatures ranging from 30 to 33°C. A flood irrigation is often applied to fields for salt management during July or August in the Yuma lettuce production region. Results from these studies suggest that maintaining this flooding event for 2 to 3 weeks in fields with a history of lettuce drop caused by S. minor and S. sclerotiorum could significantly reduce the population of viable sclerotia.
Leaf Rust and Stem Rust Resistance in Triticum dicoccoides Populations in Israel
Authors: Anikster Y. , Manisterski J. , Long D. L. , Leonard K. J.
Published: May 2007

A total of 742 single plant accessions of Triticum dicoccoides were collected from 26 locations in Israel. All accessions were evaluated for leaf rust (Puccinia triticina) resistance in field plots at Tel Aviv, and subsets of 284 and 468 accessions were tested in the greenhouse in Tel Aviv and St. Paul, MN, respectively, for seedling resistance to leaf rust; 460 accessions were also tested for seedling resistance to stem rust (Puccinia graminis f. sp. tritici) in St. Paul. One accession was highly resistant to leaf rust in seedling tests in Tel Aviv, and 21 others had moderately susceptible to moderately resistant seedling resistance. Four accessions were highly resistant to leaf rust in seedling tests in St. Paul, and 11 were resistant to at least one stem rust race. Adult resistance to leaf rust was more common than seedling resistance among the accessions; 21 accessions had less than 25% leaf rust severity in field plots compared with 80 to 90% severity for highly susceptible accessions. Most of the accessions with effective adult plant resistance came from two nearby locations in Upper Galilee, a region where populations of T. dicoccoides are most extensive and genetically diverse. These accessions may provide valuable new partial resistance genes for durable protection against leaf rust in cultivated wheat.
Effect of Simulated Wind-Driven Rain on Duration and Distance of Dispersal of Xanthomonas axonopodis pv. citri from Canker-Infected Citrus Trees
Authors: Bock C. H. , Parker P. E. , Gottwald T. R.
Published: May 2007

Dynamics of dispersal of the bacteria that causes citrus canker (Xanthomonas axonopodis pv. citri) were assessed in simulated wind-driven rain splash. The wind/rain-splash events were simulated using electric blowers to generate turbulent wind (15 to 20 m s-1) and sprayer nozzles to produce water droplets entrained in the wind flow. The splash was blown at an inoculum source of canker-infected trees 1 m downwind. The splash downwind of the source of the infected trees was collected by vertical panel samplers and funnel samplers. The duration over which bacteria were dispersed in spray was assessed in continuous wind at intervals from 0 to 52 h after commencing the simulated rain splash event. In one experiment on 11 February 2003, a total of 1.48 × 106 bacteria were collected by panels 1 m downwind from the inoculum source during the first 10 min of dispersal, but the numbers declined to 3.60 × 105 bacteria after 1 h and ranged between 1.42 × 105 and 1.93 × 104 up to 52 h. In a more detailed study (15 July 2003) of dispersal duration over 4 h, the greatest quantity of bacteria collected by panel samplers were dispersed in the first 5-min period (1.01 × 108 bacteria collected). By 10 min after initiation of dispersal, approximately one-third (3.09 × 107 bacteria collected) of the initial number was being dispersed, and by the end of the first hour, only one-tenth (1.31 × 107 bacteria collected) of the initial quantity was dispersed. Funnel samplers placed at ground level under the trees showed a similar trend. The distance to which bacteria were dispersed in wind-blown splash was also tested under simulated conditions: on 18 September 2003, bacteria were collected by panel samplers at all distances sampled (1, 2, 4, 6, 8, 10, and 12 m) with the greatest number of bacteria deposited at 1 m (4.93 × 106 bacteria collected), while 2.22 × 103 bacteria were deposited over a 10-min period 12 m from the inoculum source. Wind speed declined from 19.5 m s-1 upwind of the trees to 2.8 m s-1 1 m downwind, and by 4 m downwind from the inoculum source, movement was similar to the surrounding air. The data on duration and distance of dispersal were best described by power law regression models compared to exponential models. Citrus canker is readily dispersed in wind-driven rain and is dispersed in large quantities immediately after the stimulus occurs, upon which wind-driven splash can disperse inoculum over a prolonged period and over a substantial distance.
First Report of Erwinia persicina from Phaseolus vulgaris in Spain
Authors: González A. J. , Tello J. C. , Cara M. de
Published: May 2007

A previously unreported leaf spot disease of common bean, which caused losses as much as 50% of the crops, was observed in southeastern Spain (Almería, Granada, and Málaga provinces) in November 2003. In 2004, samples of cv. Donna with chlorotic and necrotic leaf spots were collected from Granada and processed for microbiological analysis. Bacteria isolated from the symptomatic leaves were determined to be fermentative on the basis of the ability to metabolize glucose in aerobic and anaerobic conditions. Three isolates were selected for pathogenicity tests. Bacterial suspensions (108 CFU/ml) were spray inoculated on bean seedlings (3 true leaves) of cv. Andecha. Beans were covered with transparent plastic bags for 2 days and held in an incubation chamber at 22°C and 80% relative humidity with a 12-h photoperiod. Assays were repeated at least twice. Symptoms that developed on plants inoculated with the three isolates were similar to those originally observed, while symptoms did not occur on control plants (inoculated with distilled water). The pathogenic isolates were identified by sequencing of the 16S rDNA after amplification (2). The amplified sequences were compared to available DNA sequences in databases by using BLAST (1); 99% homology with 16S rDNA of Erwinia persicina was shown. Microbiological characteristics (gram staining, motility, morphology, and results of biochemical tests) were in agreement with the molecular identification of the isolates. E. persicina has been isolated from bean in the United States (4) and described on tomato, banana, and cucumber in Japan (3). To our knowledge, this is the first report of E. persicina from common bean in Spain and in Europe.

References: (1) S. F. Altschul et al. J. Mol. Biol. 215:403, 1990. (2) U. Edwards et al. Nucleic Acids Res. 17:7843, 1989. (3) M. V. Hao et al. Int. J. Syst. Bacteriol. 40:379, 1990. (4) M. L. Schuster et al. Fitopatol. Bras. 6:345, 1981.
Identifying Soft Red Winter Wheat Cultivars Tolerant to Barley yellow dwarf virus
Authors: Weisz Randall , Tarleton Barry , Murphy J. Paul , Kolb Frederic L.
Published: May 2007

Barley yellow dwarf virus (BYDV) is a serious disease of soft red winter wheat. Although there has been interest in tolerant cultivars, identification and development has been slow due to a lack of precision in rating plants for response to BYDV. Visual ratings of symptoms are commonly used to evaluate cultivars, but these ratings have proven to be inconsistent. The objectives of this research were to assess BYDV visual symptom ratings of wheat cultivars under field conditions, to measure disease-related yield reductions in these cultivars, to determine if a relationship exists between BYDV visual symptoms and yield reductions, and to determine BYDV cultivar tolerance. A split-plot design with insecticide treatment (main plot) and 11 cultivars (subplots) was employed over 4 years. The overall relationship between symptom ratings and BYDV yield reductions was weak (R2 = 0.40) and not consistent across years or cultivars. A consistency of performance analysis showed cultivars clustered into five distinct tolerance classes. Under conditions of high BYDV infestation, visual symptom ratings could be cautiously used to identify highly tolerant cultivars. The most reliable method for rating cultivar tolerance was a direct measure of disease-induced yield reduction across multiple environments.
Toxicity of Fungicides to Urediniospores of Six Rust Fungi That Occur on Ornamental Crops
Authors: Mueller D. S. , Jeffers S. N. , Buck J. W.
Published: May 2007

The recent introduction and rapid spread of rust on daylilies, caused by Puccinia hemerocallidis, suggested a need for fungicide treatments that reduce urediniospore viability on plant surfaces. Twelve fungicides in seven chemical classes were evaluated in vitro for toxicity to urediniospores of rust fungi that occur on daylily (P. hemerocallidis), geranium P. pelargonii-zonalis), iris (P. iridis), oxalis (P. oxalis), mint (P. menthae), and Florida azalea (Pucciniastrum vaccinii). Germination of urediniospores of all six rust fungi on potato dextrose agar in the absence of fungicides ranged from 54 to 88%. Germination of urediniospores of all rust species during and after exposure to azoxystrobin, chlorothalonil, copper sulfate pentahydrate, mancozeb, and trifloxystrobin was less than or near 1%. Germination during exposure to fenhexamid, iprodione, myclobutanil, propiconazole, thiophanate-methyl, triadimefon, and triflumizole ranged from 0 to 60% and usually was greater (0 to 75%) after fungicide residues had been removed. Germination of urediniospores of P. pelargonii-zonalis decreased when exposed to azoxystrobin, copper sulfate pentahydrate, and mancozeb for 1 min and was nearly eliminated after a 30-min exposure, while exposure to trifloxystrobin and chlorothalonil eliminated germination after 4 and 8 h, respectively. Urediniospores that had been allowed to imbibe water for 4 h had no further germination or germ tube growth after a 24-h exposure to azoxystrobin, chlorothalonil, copper sulfate pentahydrate, mancozeb, and trifloxystrobin. Less than one lesion per plant developed on seedlings inoculated with urediniospores of P. pelargonii-zonalis that had been sprayed with azoxystrobin, chlorothalonil, copper sulfate pentahydrate, and mancozeb, whereas seedlings inoculated with spores not exposed to fungicides developed 148 lesions per plant. The strobilurin (azoxystrobin and trifloxystrobin), broad-spectrum protectant (chlorothalonil and mancozeb), and inorganic copper (copper sulfate pentahydrate) fungicides were fungicidal to urediniospores of the six rust fungi. However, the benzimidazole (thiophanate-methyl), dicarboximide (iprodione), hydroxyanilide (fenhexamid), and demethylation-inhibiting (myclobutanil, propiconazole, triadimefon, and triflumizole) fungicides were only fungistatic to rust urediniospores.
Viral Etiology of Diseases Detected in Melon in Guatemala
Authors: Jordá C. , Font M. I. , Martínez-Culebra P. , Tello J.
Published: May 2007

At the beginning of 1999, 30 melon (Cucumis melo L.) plots on several farms (1,500 ha) in the Zacapa Valley of Guatemala were visited, and melon plants with two different symptomologies were observed. One group of plants exhibited stem necrosis at the crown level, and less frequently, small necrotic spots on leaves. Some plants exhibited necrosis of veins and yellow areas that evolved into interveinal necrosis and often expanded into large necrotic interveinal lesions. Roots were poor and lacked secondary rootlets. In some cases, wilt and plant death were detected. Affected plants appeared as localized patches in various areas of the plots on farms that were visited. Double-antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) serological analyses were carried out with 34 symptomatic plants. In these plants, a mixture of the crown and root were analyzed with two repetitions and two lots of different Melon necrotic spot virus (MNSV) polyclonal antisera (Loewe No. 07097 and Sanofi No. 70217). All 34 plants were positive for this virus. These results were confirmed using reverse transcription-polymerase chain reaction (RT-PCR) with specific MNSV primers (1). Spores of Olpidium bornovanus, the vector of MNSV, were seen on all ELISA-positive plants after staining rootlets with potassium hydroxide and neutralization with hydrochloric acid. In the same fields, another group of melon plants showed yellowing, curling, and mottling of leaves. Leaves collected from five symptomatic plants gave positive results in triple-antibody sandwich-ELISA using a Tomato yellow leaf curl begomovirus antiserum (DSMZ AS-0421 and DSMZ AS-0546/2). In 2001, these results were confirmed using PCR with degenerate primers that amplify the core region of most begomovirus coat protein genes (P. Martínez-Culebras, M. I. Font, and C. Jordá, unpublished). A 560-bp DNA fragment was amplified in these symptomatic melon samples. Three of the PCR products were sequenced and each showed 99% identity with the Melon chlorotic leaf curl virus isolate from Guatemala (GenBank Accession No. AF325497). Only one mixed infection of MNSV and MCLCV was found. During the four years subsequent to 1999, the number of melon plants showing both types of symptoms has increased. This study provides information on the current status of virus diseases in melon crops in Guatemala, and to our knowledge, this is the first report of MNSV in Guatemala.

Reference: (1) B. Gosalvez et al. J. Virol. Methods 113:87.
First Report of Barley as Host of a Phytoplasma Belonging to Group 16SrI, Subgroup B, and Ribosomal Protein Subgroup rpI-B in Lithuania
Authors: Urbanaviciene L. , Jomantiene R. , Davis R. E.
Published: May 2007

Numerous diseased plants of barley (Hordeum vulgaris L.) exhibiting twisted, abnormally thin and yellowed awns, reduced spikelets, and general stunting and yellowing were observed in fields in the Vilnius and Kaisiadorys regions of Lithuania. The possible association of a phyto-plasma with the disease, termed barley deformation (BaDef), was assessed using polymerase chain reaction (PCR). Three phytoplasma universal primer pairs (P1/P7, R16F2n/R16R2, and rpF1/rpR1) (1,2,4) were employed to amplify ribosomal (r) RNA gene (rDNA) and ribosomal protein (rp) gene sequences. Template DNA extractions and PCR (direct and nested) were conducted as previously described (4). Although DNA was amplified in PCRs containing template extracted from diseased plants, no amplification was observed in PCRs containing DNA from symptomless plants sampled from the same fields. The BaDef phytoplasma was identified and classified according to Lee et al. (4) through restriction fragment length polymorphism (RFLP) analysis of 1.2-kbp 16S rDNA amplified in the PCR primed by primer pair R16F2n/R16R2 and analysis of the 1.2-kbp rp gene sequences amplified in PCR primed by primer pair rpF1/rpR1. On the basis of collective RFLP patterns of amplified 16S rDNA and rp gene sequences, the BaDef phytoplasma was classified as a member of group 16SrI (group I, aster yellows phytoplasma group), subgroup B (16SrI-B), and rp subgroup rpI-B. Ribosomal protein subgroup B was distinguished from other rp subgroups on the basis of the presence of a recognition site for HpaII. The 1.8-kbp rDNA product of PCR primed by P1/P7 and the 1.2-kbp rpF1/rpR1 PCR product were cloned and sequenced, and the sequences were deposited in GenBank under Accession No. AY734453 for the BaDef 16S rDNA and Accession No. AY735448 for the BaDef rp gene sequence. Previously, only oat proliferation (OatP) phytoplasma, a member of subgroup 16SrI-A, had been characterized in a cereal crop (Avena sativa L.) in Europe (3); BaDef is another phytoplasmal disease threatening cereal crops in the region.

References: (1) S. Deng and D. Hiruki. J. Microbiol. Methods 14:53, 1991. (2) D. E. Gundersen and I. M. Lee. Phytopathol. Mediterr. 35:144, 1996. (3) R. Jomantiene et al. Plant Dis. 86:443, 2002. (4) I. M. Lee et al. Int. J. Syst. Bacteriol. 48:1153, 1998.
First Report of an Alternaria Leaf Spot Caused by Alternaria brassicae on Crambe abyssinicia in Australia
Authors: You M. P. , Simoneau P. , Dongo A. , Barbetti M. J. , Li Hua , Sivasithamparam K.
Published: May 2007

Crambe abyssinicia Hochst. is grown sporadically worldwide for its value as a source of high erucic acid industrial oils and secondary commercial products. While there is increasing interest in cropping C. abyssinicia in Australia, for these potentials and also as a source of oil for biodiesel production, currently, there have been no commercial crops of this species. In September 2004, inspection of a small experimental field crop in Beverley, Western Australia indicated the presence of significant leaf spotting just prior to commencement of flowering. The symptoms of this disease included as many as 10 to 15 spot lesions per leaf that were generally rounded and varied between 0.5 to 11 mm in diameter. Clusters of these lesions were often associated with chlorosis of the region of leaves where they occurred. More than 95% of plants inspected showed these symptoms. When affected leaves were incubated in moist chambers, typical conidia of Alternaria brassicae (Berk.) Sacc. were observed. The description of these conidia matched that of the Commonwealth Mycological Institute for this pathogen (1) showing obclavate conidia 105 to 210 μm long and 20 to 30 μm thick, with 11 to 15 transverse septa and 0 to 3 longitudinal or oblique septa, predominantly with a pronounced beak 5 to 8 μm thick extending 0.3 to 0.5 μm of the length of the conidium. Single-spore isolations were made onto potato dextrose agar. Subcultures of these isolates were identified using a polymerase chain reaction (PCR)- based assay (2). This assay involved the use of two sets of A. brassicae-specific primers selected for conventional and real-time PCR. The colonies were confirmed to belong to A. brassicae. In a pathogenicity test to confirm Koch's postulates, single-spore isolates were inoculated onto cotyledons and leaves of 10-day-old C. abyssinicia seedlings. Symptoms on inoculated plants appeared within a period of 14 days of inoculation, matching those found on the affected plants in the field, and A brassicae was reisolated. A. brassicae causes an important worldwide disease of crucifers, for example, it can be a devastating disease of rapeseed and the other cruciferous crops in the United States and Canada. Since A. brassicae has already been reported on other species of crucifers Australia-wide, it may pose a threat to any potential Crambe spp. industry in this country.

References: (1) M. B. Ellis No. 162 in: Descriptions of Pathogenic Fungi and Bacteria. CMI, Kew, England, 1966. (2) T. Guillemette et al. Plant Dis. 88:490, 2004.
First Report of the Rust Fungus Olivea scitula on Vitex doniana in Zambia
Authors: Kapooria R. G. , Aime M. C.
Published: May 2007

Vitex doniana Sweet (Verbenaceae) is a semideciduous tree that occurs throughtout Africa from Senegal to the Sudan and in Somalia, Angola, Botswana, South Africa, and most provinces of Zambia. Wood from V. doniana is used in construction, making boxes and furniture; jam and wine are made from the vitamin-rich fruits; the leaves provide cattle feed; and other plant parts are used in traditional medicines. The tree itself is a favorite for hanging bark beehives. In September 2004, leaves of V. doniana trees (20 km southeast of Lusaka) were found bearing brown uredinia, which were subsequently identified as the rust fungus, Olivea scitula Syd. The following description is based on the Zambian material that has slightly smaller spores than those of the original published description (2). Uredinia were hypophyllous, brown, round, at first scattered irregularly in the interveinal areas, then coalescing to form a continuous erumpent covering on the base, margin, or middle of the leaflet. Urediniospores were yellow brown, verrucose, globose, triangular or oval, 20 to 25 × 20 μm, with densely filled oil globules, and the wall 2 to 2.5 μm thick. Paraphyses were peripheral, incurved, basally united, and 50 to 75 × 5 to 6.25 μm. The pathogen has been reported previously from Sierra Leone, Uganda, and Nigeria (1). To our knowledge, this is the first report of Olivea spp. in Zambia and the first report of O. scitula from Central Africa.

References: (1) D. F. Farr et al. Fungal Databases. Systematic Botany and Mycology Laboratory, On-line publication. ARS, USDA, 2004. (2) A. H. Sydow. Ann. Mycol. 35:251, 1937.
A Survey of Citrus Viroids in Campania (Southern Italy)
Authors: Malfitano M. , Barone M. , Alioto D. , Duran-Vila N.
Published: May 2007

Within a certification program of citrus, a survey covering 14 citrus fields not previously screened were randomly selected in seven areas of the Campania Region of southern Italy to evaluate the presence and distribution of citrus viroids in the region. During the last 3 years, 112 trees were visually inspected and sampled including 14 ‘Navelina’, 8 ‘Washington navel’, 13 ‘Biondo Commune’, 10 ‘Tarocco’, 6 ‘Valencia late’, 1 ‘Sanguinello’, and 1 ‘Vanilla’ sweet oranges (Citrus sinensis), four sour oranges (C. aurantium), 21 ‘Commune’ and 7 ‘Monreale’ clementines (C. clementina), 8 ‘Common’ and 2 ‘Avana’ mandarins (C. reticulata), 8 ‘Ovale di Sorrento’ and 6 ‘Zagara’ lemons (C. lemon), 2 Tangelos (C. reticulata × C. paradisi), and 1 grapefruit (C. paradisi). Nearly all (37 of 38) mandarin and clementine trees showed cachexia-like symptoms. Severe bark scaling that is characteristic of exocortis disease was observed on a single ‘Ovale di Sorrento’ lemon, the only tree incidentally found to be grafted onto the exocortis-sensitive trifoliate orange (Poncirus trifoliata) rootstock, since sour orange (C. aurantium) is the main rootstock used in Campania. Samples (104 of 112) that had been graft-inoculated into Arizona 861-S1 ‘Etrog citron’ (C. medica L.) on rough lemon (C. jambhiri Lush.) rootstock showed typical viroid symptoms. Viroid infection was confirmed by sequential polyacrylamide gel electrophoresis analysis (2) and molecular hybridization of imprinted membranes (1). Citrus exocortis viroid (CEVd), Hop stunt viroid (HSVd), and Citrus viroid III (CVd-III) were the most frequently detected, accounting respectively, for 67.9, 86.6, and 84.8% of the infected samples. Citrus viroid IV (CVd-IV) and Citrus bent leaf viroid (CBLVd) were found in 24.1 and 13.4% of the sources. CBLVd was detected in sweet orange (‘Tarocco’ and ‘Biondo Commune’) and lemon (‘Ovale di Sorrento’ and ‘Zagara’), while CVd-IV was detected in sweet orange (‘Tarocco’, ‘Biondo Commune’, and ‘Washington navel’), lemon (‘Ovale di Sorrento’ and ‘Zagara’), clementine (‘Commune’), and sour orange. Most trees (82.1%) were infected with more than one viroid species. The most frequent viroid combinations were CEVd + HSVd + CVd-III (40.2%), HSVd + CVd-III (16.1%), and CEVd + CBLVd + HSVd + CVd-III + CVd-IV (12.5%). To our knowledge, this is the first report of CEVd, CBLVd, HSVd, CVd-III, and CVd-IV in the Campania Region and the first report of CBLVd and CVd-IV in Italy.

References: (1) A. Palacio et al. Eur. J. Plant Pathol.105:897, 2000. (2) R. F. Rivera-Bustamante et al. Anal. Biochem. 156:91, 1986.
Partial Resistance of Pepper to Bacterial Wilt Is Oligogenic and Stable Under Tropical Conditions
Authors: Lafortune Denis , Béramis Michel , Daubèze Anne-Marie , Boissot Nathalie , Palloix Alain
Published: May 2007

Genetic analysis of resistance of pepper to bacterial wilt was performed in the doubled haploid progeny from a cross between a resistant parental line PM 687 and a susceptible cultivar Yolo Wonder. After artificial inoculation with a local isolate of Ralstonia solanacearum, the progeny consisting of 90 lines was transplanted into a naturally infested field in Guadeloupe, Lesser Antilles. The 2 years of experimentation resulted in repeatable results, with a high heritability of the resistance, attesting the reliability of the evaluation procedure and the stability of the resistance over years. Two to five genes with additive effects were estimated to control the resistance, indicating an oligogenic control as observed in tomato sources of resistance. Relationships with resistance to other soilborne or tropical diseases were examined. Susceptibility to Tobacco mosaic virus (TMV) and to nematodes (Meloidogyne spp.) were significantly linked with resistance to bacterial wilt, whereas neither resistance to Phytophthora capsici nor to Leveillula taurica were linked. The similarity of the genetics of resistance to bacterial wilt in pepper and tomato and linkage with TMV resistance locus warrant the comparative mapping of the resistance quantitative trait loci in the genomes of the two species.
Tomato spotted wilt virus Identified in Desert Rose in Florida
Authors: Adkins S. , Baker C. A.
Published: May 2007

Desert rose (Adenium obesum (Forssk.) Roem. & Schult), a member of the family Apocynaceae, is characterized by fleshy stems and leaves and colorful flowers. This exotic ornamental, originally from southeast Africa, is propagated vegetatively and is a perennial in warm climates. Virus-like foliar symptoms, including chlorotic ring and line patterns, were observed in the fall of 2004 on one of five stock plants being maintained in a greenhouse in Fort Pierce, FL. Inclusion body morphology suggested the presence of a Tospovirus in the symptomatic plant, and Tomato spotted wilt virus (TSWV) was specifically identified in this plant using a commercially available double antibody sandwich-enzyme linked immunosorbent assay (DAS-ELISA; Agdia, Elkhart, IN). TSWV was not detected in symptomless desert rose plants nor was Impatiens necrotic spot virus detected in any of the plants using DAS-ELISA. Graft transmission of TSWV to other desert rose plants was successful. Sequence analysis of a nucleocapsid (N) protein gene fragment amplified by reverse transcription-polymerase chain reaction (RT-PCR) with primers TSWV723 and TSWV722 (1) from total RNA of the symptomatic plant confirmed the diagnosis. Nucleotide and deduced amino acid sequences of a 579-bp region of the RT-PCR product were 95 to 99% and 95 to 100% identical, respectively, to TSWV N-gene sequences in GenBank. No product was amplified from symptomless plants. Since these 3-year-old plants were grown on-site from seed and only expressed symptoms 2 months following damage to the greenhouse by hurricanes Frances and Jeanne, it is likely that viruliferous thrips were introduced from local vegetable or ornamental production areas during or following the storms. To our knowledge, this is the first report of TSWV infection of desert rose in Florida, although TSWV was observed in this plant in Europe approximately 10 years ago (3,4). Because of the wide distribution of TSWV in the United States, the increasing popularity of desert rose, and the recent identification of Cucumber mosaic virus in this host (2), attention to sanitation and insect vector management is merited during desert rose propagation and production.

References: (1) S. Adkins and E. N. Rosskopf. Plant Dis. 86:1310, 2002. (2) C. A. Baker et al. Plant Dis. 87:1007, 2003. (3) J. Mertelik et al. Acta Hortic. 432:368, 1996. (4) J. Th. J. Verhoeven and J. W. Roenhorst. Acta Hortic. 377:175, 1994.
Epiphytic Survival of Xanthomonas axonopodis pv. allii and X. axonopodis pv. phaseoli on Leguminous Hosts and Onion
Authors: Gent David H. , Lang Jillian M. , Schwartz Howard F.
Published: May 2007

Xanthomonas leaf blight of onion (Allium cepa), caused by Xanthomonas axonopodis pv. allii, and common bacterial blight of dry bean (Phaseolus vulgaris), caused by Xanthomonas axonopodis pv. phaseoli, are perennial problems in the Central High Plains of the United States. Onion and dry bean are commonly grown in rotation in Colorado, but it is unknown if X. axonopodis pv. allii and X. axonopodis pv. phaseoli survive epiphytically or pathogenically on dry bean and onion, respectively. Under high humidity growth chamber conditions, epiphytic X. axonopodis pv. allii populations increased on alfalfa, chickpea, dry bean, lentil, and soybean, but the epiphytic populations were at least 10-fold greater on onion. When artificially inoculated under field conditions, epiphytic populations of X. axonopodis pv. allii were recovered from dry bean, lentil, and onion, but the bacterium did not persist on chickpea or soybean. Epiphytic X. axonopodis pv. phaseoli was recovered from symptomless onion plants in fields cropped to dry bean the prior year, but not from fields cropped to a host other than dry bean. Close rotation of onion and dry bean may allow X. axonopodis pv. allii and X. axonopodis pv. phaseoli to persist epiphytically, and crop rotation schemes may need to be altered to reduce survival of these pathogens in onion and dry bean cropping systems.