bluuebunny/crossref_metadata_2025 huggingface dataset:
Inhibition of Fungal Spore Adhesion by Zosteric Acid as the Basis for a Novel, Nontoxic Crop Protection Technology
Authors: Stanley Michele S. , Callow Maureen E. , Perry Ruth , Alberte Randall S. , Smith Robert , Callow James A.
Published: May 2007

To explore the potential for nontoxic crop protection technologies based on the inhibition of fungal spore adhesion, we have tested the effect of synthetic zosteric acid (p-(sulfo-oxy) cinnamic acid), a naturally occurring phenolic acid in eelgrass (Zostera marina L.) plants, on spore adhesion and infection in two pathosystems: rice blast caused by Magnaporthe grisea and bean anthracnose caused by Colletotrichum lindemuthianum. We have shown that zosteric acid inhibits spore adhesion to model and host leaf surfaces and that any attached spores fail to develop appressoria, and consequently do not infect leaf cells. Low concentrations of zosteric acid that are effective in inhibiting adhesion are not toxic to either fungus or to the host. The inhibition of spore adhesion in the rice blast pathogen is fully reversible. On plants, zosteric acid reduced (rice) or delayed (bean) lesion development. These results suggest that there is potential for novel and environmentally benign crop protection technologies based on manipulating adhesion.
Association with the Syndrome “Basses Richesses” of Sugar Beet of a Phytoplasma and a Bacterium-Like Organism Transmitted by a Pentastiridius sp.
Authors: Gatineau F. , Jacob N. , Vautrin S. , Larrue J. , Lherminier J. , Richard-Molard M. , Boudon-Padieu E.
Published: May 2007

The syndrome “basses richesses” of sugar beet (SBR) was first observed in 1991 in Burgundy, France. A cixiid planthopper, Pentastiridius beieri, has been proved to be involved in the transmission to sugar beet of a stolbur phytoplasma, which could be detected in some affected plants. In 2000, periwinkle and sugar beet exposed to field-collected cixiids developed symptoms similar to SBR on sugar beet. Use of 4′-6-diamidino-2-phenylindole (DAPI) staining and transmission electron microscopy confirmed the presence of phytoplasma in some of the plants, which were also positive for this pathogen in a polymerase chain reaction (PCR) analysis. A phloem-restricted gram-negative bacteria was seen in all other plants with symptoms but PCR-negative for phytoplasma. Three primer pairs reported as diagnostic for phloem-limited bacteria were tested but only primers specific for ‘Candidatus Phlomobacter fragariae’ gave a positive signal, which related to the presence of DAPI-stained bacteria-like objects in diseased plants. Although phytoplasma and bacterium-like organisms were associated with the same macroscopic symptoms on sugar beet, histochemical analysis of phloem cells showed that phytoplasma were associated with cell necrosis and cell wall lignification, while bacteria were associated with these same abnormalities as well as deposit of phenolic compounds in the lumen of phloem cells.
Morphological, Pathogenic, and Molecular Characterization of Alternaria Isolates Associated with Alternaria Late Blight of Pistachio
Authors: Pryor Barry M. , Michailides Themis J.
Published: May 2007

Alternaria isolates were obtained from various pistachio tissues collected in five orchards in California. For all isolates, morphological characteristics of the colony and sporulation apparatus were determined and compared with those of representative isolates of A. alternata, A. tenuissima, A. arborescens, and A. infectoria. A selection of the pistachio isolates and the representative Alternaria isolates were evaluated for pathogenicity to pistachio. Molecular characteristics of these isolates were determined using random amplified polymorphism DNA (RAPD) analysis, polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP) analysis of nuclear intergenic spacer rDNA, and sequence analysis of nuclear internal transcribed spacer (ITS) rDNA. Based on morphological characteristics, the pistachio isolates were grouped as identical or very similar to either A. alternata, A. tenuissima, A. arborescens, or A. infectoria. Isolates from the alternata, tenuissima, and arborescens species-groups were pathogenic to pistachio and no significant differences in pathogenicity were observed. Isolates from the infectoria species-group were only weakly pathogenic to pistachio. Based on cluster analysis of RAPD and PCR-RFLP data, three distinct clusters were evident; the infectoria cluster, the arborescens cluster, and a combined alternata/tenuissima cluster. Based on analysis of ITS sequence data, the infectoria species-group was phylogenetically distinct from the other species-groups. Isolates of the alternata, tenuissima, and arborescens species-groups comprised a monophyletic clade in which the three species-groups could not be further resolved.
Biometric Analyses of the Inheritance of Resistance toDidymella rabieiin Chickpea
Authors: Lichtenzveig J. , Shtienberg D. , Zhang H. B. , Bonfil D. J. , Abbo S.
Published: May 2007

Historically, the response of chickpea (Cicer arietinum L.) to Didymella rabiei (causal agent of Ascochyta blight) has been mainly related to as complete resistance and it was commonly assayed with qualitative (nonparametric) scales. Two reciprocal populations, derived from intra-specific crosses between a moderately resistant late flowering Israeli cultivar and a highly susceptible early flowering Indian accession, were tested at F3and F4generations in 1998 and 1999, respectively. A quantitative (parametric) assessment (percent disease severity) was used to evaluate the chickpea field response to Ascochyta blight. The transformed relative area under the disease progress curve (tRAUDPC) was calculated for each experimental unit for further analyses. Heritability estimates of the tRAUDPC were relatively high (0.67 to 0.85) in both generations for both reciprocal populations. The frequency distributions of tRAUDPC of the populations were continuous and significantly departed from normality (Shapiro-Wilk W test; P of W < 0.0001), being all platykurtic and skewed toward either the resistant or the susceptible parental lines. The presence of major genes was examined by testing the relationship between the F3and F4family means and the within-family variances (Fain's test). Analyses of these relationships suggested that segregation of a single (or few) quantitative trait locus with major effect and possibly other minor loci was the predominant mode of inheritance. The correlation estimates between the resistance and days to flower (r = -0.19 to -0.44) were negative and significantly (P = 0.054 to 0.001) different from zero, which represents a breeding constraint in the development of early flowering cultivars with Ascochyta blight resistance.
Nonpathogenic Isolates of the Citrus Black Spot Fungus, Guignardia citricarpa, Identified as a Cosmopolitan Endophyte of Woody Plants, G. mangiferae (Phyllosticta capitalensis)
Authors: Baayen R. P. , Bonants P. J. M. , Verkley G. , Carroll G. C. , van der Aa H. A. , de Weerdt M. , van Brouwershaven I. R. , Schutte G. C. , Maccheroni W. , de Blanco C. Glienke , Azevedo J. L.
Published: May 2007

The population structure of Guignardia citricarpa sensu lato (anamorph: Phyllosticta citricarpa), a fungus of which strains pathogenic to citrus are subject to phytosanitary legislation in the European Union and the United States, was investigated. Internal transcribed spacer sequences revealed two phylogenetically distinct groups in G. citricarpa. This distinction was supported by amplified fragment length polymorphism analysis that also supported the exclusion of two isolates that had apparently been misclassified as G. citricarpa. On cherry decoction agar, but not on other media, growth rates of group I isolates were lower than those of group II isolates. Conidial dimensions were similar, but group I isolates formed conidia with barely visible mucoid sheaths, whereas those of group II formed conidia with thick sheaths. Cultures of isolates belonging to group I produced rare infertile perithecia, whereas fertile perithecia were formed by most isolates of group II. Colonies of isolates belonging to group I were less dark than those of group II, with a wider translucent outer zone and a lobate rather than entire margin. On oatmeal agar, exclusively group I isolates formed a yellow pigment. Group I harbored strains from citrus fruits with classical black spot lesions (1 to 10 mm in diameter) usually containing pycnidia. Group II harbored endophytic strains from a wide range of host species, as well as strains from symptomless citrus fruits or fruits with minute spots (<2-mm diameter) without pycnidia. These observations support the historic distinction between slowly growing pathogenic isolates and morphologically similar fast-growing, nonpathogenic isolates of G. citricarpa. The latter proved to belong to G. mangiferae (P. capitalensis), a ubiquitous endophyte of woody plants with numerous probable synonyms including G. endophyllicola, G. psidii, P. anacardiacearum, and P. theacearum. G. mangiferae occurs in the European Union and the United States on many host species including citrus, and does not cause symptoms of citrus black spot, justifying its exclusion from quarantine measures.
Quantification of Raindrop Kinetic Energy for Improved Prediction of Splash-Dispersed Pathogens
Authors: Lovell D. J. , Parker S. R. , Van Peteghem P. , Webb D. A. , Welham S. J.
Published: May 2007

An electronic sensor, based on a piezoelectric transducer, was tested in the laboratory using simulated raindrops, and in natural rainfall. Data were also collected for splash dispersal using tracer dyes in laboratory experiments and the Long Ashton splashmeter in field experiments. Droplets impacting on sensor produce sound waves that are detected by an omnidirectional microphone sealed within an acoustic chamber. An electrical charge, proportional to the sound wave, is produced by the microphone and is converted to a categorical scale and then stored to provide an accumulation of impacts over a specified period of time. Calibration of the sensor was done using single-droplet impacts of known mass and impacting velocity. A linear relationship was shown between the categorical scale and the kinetic energy of impacting droplets (adjusted r2 = 0.99). The best relationship fitted between splash dispersal from dye cup, and kinetic energy was a second-order polynomial (adjusted r2 > 0.99). Splash height, recorded by the Long Ashton splashmeter during 41 natural rainfall events, was correlated closely with sensor output (adjusted r2 = 0.87). Our studies indicate that the sensor provides quantitative data which could be incorporated into disease management systems to provide estimates of inoculum dispersal gradients within crop canopies.
Characterization of Botryosphaeria dothidea Isolates Collected from Pistachio and Other Plant Hosts in California
Authors: Ma Zhonghua , Michailides Themis J.
Published: May 2007

Eighty-six isolates of Botryosphaeria dothidea, the causal agent of Botryosphaeria panicle and shoot blight of pistachio, were collected from pistachio and other plant hosts in California. The isolates were characterized by microsatellite-primed polymerase chain reaction (MP-PCR), sequences of the nuclear ribosomal DNA internal transcribed spacer region (ITS1, 5.8S gene, and ITS2), morphological and cultural characters, osmotic and fungicide sensitivity, and pathogenicity on pistachio. Three groups of these isolates were identified based upon analysis of MP-PCR data and ITS sequences. Group I contained 43 pycnidiospore-derived isolates collected from pistachio and other hosts. Group II consisted of 20 ascosporic isolates obtained from a single sequoia plant. Group III consisted of 20 ascosporic isolates from three shoots on a single blackberry plant, two pycnidiospore-derived isolates from incense cedar, and one from pistachio. Group I predominated over the other two groups in California pistachio orchards. B. dothidea isolates of group III grew faster on acidified potato dextrose agar (APDA) than the isolates of groups I and II. Isolates of group III produced pycnidia on both APDA and autoclaved pistachio shoots, but the isolates of the other two groups produced pycnidia on only autoclaved pistachio shoots. Additionally, significant differences in osmotic and fungicide sensitivities were observed among these three groups. Results from lathhouse inoculations demonstrated that the representative isolates for each of the three groups were all capable of infecting pistachio and producing characteristic disease symptoms of Botryosphaeria blight. The virulence of group II isolates on pistachio was, however, significantly lower than that of group I isolates.
Helper Component-Transcomplementation in the Vector Transmission of Plant Viruse
Authors: Froissart Rémy , Michalakis Yannis , Blanc Stéphane
Published: May 2007

Plant viruses are most frequently transmitted from one host plant to another by vectors. In noncirculative vector transmission, the virus does not process through a cycle within the vector body. Instead, upon acquisition by the vector, viruses are retained in the mouth parts or the anterior gut; from there, they will be subsequently released in a new host plant. Two molecular strategies have been described for the virus—vector interaction. In the capsid strategy, the virus coat interacts directly with binding sites in the vector mouth parts, whereas an additional nonstructural protein, designated helper component (HC), is required in the helper strategy. The HC and virus particles can be acquired sequentially, and this property introduces the possibility that an HC acquired first by the vector assists the transmission of virus particles located in the same cell, in other cells, or even in other host plants probed by the vector. Such a phenomenon is here called HC-transcomplementation. Surprisingly, the existing definition of HC does not explicitly include the concept of HC-transcomplementation, and it is generally omitted in the literature in any consideration of the virus biology other than the molecular interaction with the vector. Here we propose an extended definition of HC and emphasize the concept of HC-transcomplementation that distinguishes the helper strategy from any other type of vector transmission and may have consequences at the level of the virus population genetics and evolution.
Comparison of Membrane Filters as a Tool for Isolating Pythiaceous Species from Irrigation Water
Authors: Hong Chuanxue , Richardson Patricia A. , Kong Ping
Published: May 2007

Filter-based isolation is the primary approach for quantifying plant pathogens in irrigation water; however, the performance of various membranes is largely unknown. This study evaluated nine hydrophilic membranes for recovery of pythiaceous species, a group of very common and destructive pathogens on numerous ornamental plants and many agronomic crops. Three sources of water samples and three plating methods were used for the membrane comparison. Durapore5, Millipore5, and Osmonics5 filtered 100 ml of irrigation water or 50 ml of irrigation runoff in 10 s or less, whereas the other membranes required 34 s to 13.5 min or even a second membrane to filter the same water sample volume. Millipore5 and Durapore5 showed greater recovery rates than other membranes for all water sources when the membranes were directly inverted onto agar plates. Durapore5 was also one of the top two membranes for spore suspension and irrigation water samples when membrane washings were spread over the agar surface. Durapore5 was the only membrane that consistently performed well for both spore suspension and irrigation water samples. These data suggest that use of Durapore5 not only increases the sensitivity of filter-based isolation for quantifying pythiaceous species in irrigation water but also saves filtering time.
Detection of Two Orchid Viruses Using Quartz Crystal Microbalance-Based DNA Biosensors
Authors: Eun Alvin Jin-Cherng , Huang Liqun , Chew Fook-Tim , Fong-Yau Li Sam , Wong Sek-Man
Published: May 2007

We have developed a piezoelectric DNA-sensor based on DNA-RNA hybridization for the detection of two orchid viruses, Cymbidium mosaic virus (CymMV) and Odontoglossum ringspot virus (ORSV). Specific oligonucleotide probes modified with a mercaptohexyl group at the 5′-phosphate end were directly immobilized onto 10-MHz AT-cut quartz crystal microbalance (QCM). QCMs coated with such oligonucleotide probes were exposed to test solutions containing viral RNA for hybridization. Various experimental conditions evaluated were (i) DNA probe coating concentration, (ii) sensitivity and specificity of the probes at different hybridization temperatures, and (iii) effects of incubation temperature on the hybridization time. The specific nucleotide probe-coated QCM-based DNA sensors were able to detect both CymMV and ORSV in quantities as low as approximately 1 ng in purified RNA preparations and 10 ng in the crude sap of infected orchids. This is the first application of a DNA biosensor for the detection of plant viruses.
Potato Cultivars from the Mexican National Program: Sources and Durability of Resistance Against Late Blight
Authors: Grünwald Niklaus J. , Cadena Hinojosa Mateo A. , Covarrubias Oswaldo Rubio , Peña Antonio Rivera , Niederhauser John S. , Fry William E.
Published: May 2007

The Mexican National Potato Program has produced several cultivars with high levels of field resistance. We evaluated the durability of resistance to potato late blight of a selection of 12 such cultivars using data from 1960 to the present. Data were extracted from the field notebooks located in the archives of the Mexican National Potato Program in the John S. Niederhauser Library in Toluca, Mexico. There was a trend indicating that field resistances to potato late blight of Mexican cultivars released between 1965 to 1999 were durable. At least two of the cultivars, namely ‘Sangema’ and ‘Tollocan’, have been grown on at least 4 to 5% of the potato acreage and over long periods of time without decay in levels of field resistance. Pedigrees of the 12 cultivars indicate that most of the field resistance was introgressed from Solanum demissum. Field resistance might also be derived from commonly grown land-race cultivars such as ‘Amarilla de Puebla’ and ‘Leona’. These have been grown in Mexico since about the 1780s. They have the appearance of S. andigena-derived material but their genetic background is unknown.
Host Range and Characterization ofSunflower mosaic virus
Authors: Gulya T. J. , Shiel P. J. , Freeman T. , Jordan R. L. , Isakeit T. , Berger P. H.
Published: May 2007

Sunflower mosaic is caused by a putative member of the family Potyviridae. Sunflower mosaic virus (SuMV) was characterized in terms of host range, physical and biological characteristics, and partial nucleotide and amino acid sequence. Cells infected with SuMV had cytoplasmic inclusion bodies typical of potyviruses. Of 74 genera tested, only species in Helianthus, Sanvitalia, and Zinnia, all Asteraceae, were systemic hosts. Commercial sunflower hybrids from the United States, Europe, and South Africa were all equally susceptible. The mean length of purified particles is approximately 723 nm. The virus was transmitted by Myzus persicae and Capitphorus elaegni, and also was seedborne in at least one sunflower cultivar. Indirect enzyme-linked immunosorbent assay tests with a broad-spectrum potyvirus monoclonal antibody were strongly positive. SuMV-specific polyclonal antisera recognized SuMV and, to a lesser extent, Tobacco etch virus (TEV). When tested against a panel of 31 potyvirus-differentiating monoclonal antibodies, SuMV was distinct from any potyvirus previously tested. SuMV shared four epitopes with TEV, but had a reaction profile more similar to Tulip breaking virus (TBV). SuMV did not possess epitopes unique only to TBV. The predicted coat protein had a molecular weight of 30.5 kDa. The 3′ end of the virus genome was cloned and sequenced. Phylogenetic analysis of the coat protein amino acid sequence revealed that SuMV is a distinct species within the family Potyviridae, most closely related to TEV.
Nonrandom Distribution of Virulences Within Two Field Collections of Uromyces appendiculatus
Authors: Groth J. V. , Ozmon E. A.
Published: May 2007

Two collections of urediniospores of Uromyces appendiculatus, each from a different commercial bean field, were characterized for associations of virulence among individuals within each collection. Four bean (Phaseolus vulgaris) lines with distinct, race-specific resistance to which virulence in each population was polymorphic were used to obtain measures of all six possible pairwise virulence associations for each collection. We inoculated one of the lines and collected urediniospores only from the segment of the population that was virulent on that line. This segment, when compared with nonselected collections from susceptible Pinto 111, gave a direct measure of degree of association as the change in frequency of virulence observed. Plants of the second bean line were inoculated in separate sets with both selected and unselected collections. Frequencies of virulence were estimated from the numbers of susceptible-type and resistant-type infections. Reciprocals of each pairing also were made. For collection P21, all virulences were significantly associated, either positively or negatively, except one pair (in one direction of selection only); whereas, for collection M5, all virulences were significantly associated. Virulence association in P21 was shown to be the result of predominance of phenotypes with certain combinations of virulence by inoculation of the four bean lines with 10 randomly chosen single-uredinial individuals. In support of this, a large random-mated F1 population derived from each collection showed much less virulence association, with the majority of pairs of virulences showing nonsignificant changes in virulence frequency after passage through the first line. Random mating also significantly changed virulence frequency from that of the original population in all instances. Changes were in both directions, suggesting either that virulences were not all recessive, or that heterozygote frequency was sometimes above and sometimes below the Hardy-Weinberg expectation in the field populations.
Interspecific Transmission of Double-Stranded RNA and Hypovirulence fromSclerotinia sclerotiorumtoS. minor
Authors: Melzer M. S. , Ikeda S. S. , Boland G. J.
Published: May 2007

Interspecific transmission of a hypovirulence-associated double-stranded RNA (dsRNA) and hypovirulent phenotype was attempted from hypovirulent isolate Ss275 of Sclerotinia sclerotiorum to five virulent isolates of S. minor. dsRNA and the hypovirulent phenotype were successfully transmitted to one of the five isolates, Sm10. Three putative converted isolates of Sm10 were slow growing and developed atypical colony morphologies characteristic of the hypovirulent phenotype. These isolates were assayed for virulence and produced significantly smaller lesions than isolate Sm10 on detached leaves of Romaine lettuce. One of these putative converted isolates, designated Sm10T, was tested to confirm interspecific transmission of dsRNA. In northern hybridizations, dsRNA isolated from Sm10T hybridized with a digoxigenin-labeled cDNA probe prepared from dsRNA isolated from Ss275. Random amplified polymorphic DNA analysis confirmed that isolate Sm10T was derived from Sm10 and not from Ss275 or a hybrid of the two species. The dsRNA and hypovirulent phenotype were subsequently transmitted intraspecifically from Sm10T to Sm8. To our knowledge, this is the first report of interspecific transmission of dsRNA and an associated hypovirulent phenotype between fungal plant pathogens by hyphal anastomosis.
Ultrastructural Characterization of Infection and Colonization of Maize Leaves byColletotrichum graminicola, and by aC. graminicolaPathogenicity Mutant
Authors: Mims C. W. , Vaillancourt L. J.
Published: May 2007

Observations were made of the ultrastructure of infection and colonization of leaves of a susceptible maize inbred by Colletotrichum graminicola and by a C. graminicola pathogenicity mutant. The mutant causes no symptoms on either maize leaves or stalks. Prior evidence suggested that it is deficient in production of signal peptidase, responsible for cleavage of signal peptides from proteins destined for transport through the endoplasmic reticulum. There was no significant difference in the process of infection or colonization by the mutant and wild-type strains up to 48 h after inoculation. Both the mutant and the wild type produced globose, melanized appressoria within 24 h after inoculation on the host surface. By 36 h, both strains had penetrated the host epidermal cells directly. The host cells frequently formed papillae in response to appressoria, but these were not usually successful in preventing fungal ingress in either case. Penetration was followed by formation of irregularly shaped, swollen infection hyphae. Infection hyphae of both strains grew biotrophically for a relatively short time (less than 12 h). One or more hyphal branches was produced from each infection hypha, and these invaded adjacent mesophyll cells. Both strains of the fungus grew cell-to-cell, setting up new biotrophic interactions in each cell, between 36 and 48 h after inoculation. Papillae were frequently formed by the mesophyll cells, but these were not successful in preventing fungal ingress. The first noticeable difference between the mutant and the wild type was related to their interaction with mesophyll cells. Cells invaded by the wild type died relatively quickly, whereas those infected by the mutant appeared to survive longer. The most dramatic difference between the mutant and wild type occurred when the mutant completely failed to make a transition to necrotrophic growth, while the wild type made that switch at 48 to 72 h after inoculation. The mutant may be unable to secrete sufficient quantities of one or more proteins that are necessary to support the switch between biotrophy and necrotrophy.
Quantification of Magnaporthe grisea During Infection of Rice Plants Using Real-Time Polymerase Chain Reaction and Northern Blot/Phosphoimaging Analyses
Authors: Qi Min , Yang Yinong
Published: May 2007

Rice blast, caused by Magnaporthe grisea, is a serious fungal disease of rice worldwide. Currently, evaluation of the fungal pathogenicity and host resistance is mainly based on a disease rating or measurement of blast lesion number and size. However, these methods only provide visual estimation rather than accurate measurement of fungal growth in rice plants. In this study, DNA-based real-time polymerase chain reaction (PCR) and RNA-based northern blot/phosphoimaging analyses were evaluated to quantify M. grisea. Both methods were sensitive, specific, and reproducible and could accurately measure the relative growth and absolute biomass of M. grisea. The real-time PCR analysis showed that the growth of M. grisea in seedling leaves of susceptible cultivars (M201 and Wells) was ≈46 to 80 times higher than that of a resistant cultivar (Drew) at 4 and 6 days after inoculation. The data obtained from the real-time PCR assays also were consistent with that from northern blot/ phosphoimaging analysis. However, the real-time PCR approach was much faster and more convenient in most cases. Therefore, it is an excellent tool for in planta quantification of M. grisea and can be used for reliable assessment of fungal pathogenicity and host resistance
Distribution of Pseudosclerotia of Monilinia vaccinii-corymbosi and Risk of Apothecial Emergence Following Mechanical Cultivation
Authors: Ngugi H. K. , Scherm H. , NeSmith D. S.
Published: May 2007

Pseudosclerotia (infected, mummified fruit) of Monilinia vacciniicorymbosi overwinter on the orchard floor and germinate to produce apothecia in early spring, providing the only source of primary inoculum for mummy berry disease of blueberry. Three experiments were carried out to develop a model for the relative efficacy of mechanical cultivation in reducing the risk associated with primary inoculum. In the first experiment, apothecial emergence from pseudosclerotia buried 0, 1.5, 3, 6, and 10 cm below the soil surface was monitored to determine the critical depth necessary to inhibit emergence. No apothecia emerged from pseudosclerotia buried at depths of ≥3 cm, and the critical depth of burial was determined at 2.6 cm by regression analysis. In the second experiment, pseudosclerotia or plastic beads (used as surrogates for pseudosclerotia) were placed on the soil surface of experimental plots before cultivation with an in-row rotary cultivator, a disc harrow, or a rotary cultivator with each implement operated in a single pass. Vertical distribution profiles of pseudosclerotia or beads in the topsoil were characterized after excavation with a custom-built sampling device. The proportion of pseudosclerotia placed below the critical depth of 2.6 cm was 20.9, 52.6, and 78.6% for the in-row rotary cultivator, the disc harrow, and the rotary cultivator, respectively. For all three implements, vertical distribution profiles of pseudosclerotia and plastic beads were very similar, allowing the latter to be used in subsequent experiments in commercial fields. In the third experiment, two blueberry plantings were surveyed to determine the horizontal distribution of pseudosclerotia on the orchard floor with distance from the crowns of the plants. The greatest frequency of pseudosclerotia occurred between 30 and 40 cm from the plants. Based on measurements of the distance from plants within which different implements can operate, the proportion of pseudosclerotia accessible by cultivation ranged from 58.7% for the disc harrow to 87.2% for the in-row rotary cultivator. Taken together, results from the three experiments indicated that cultivation with a single implement can reduce risk of apothecial emergence by about 50%. More effective risk reductions may be obtained by combining implements that result in deep burial of pseudosclerotia with those that have access to pseudosclerotia near the plants. This was demonstrated by a commercial cultivation method that utilized three passes of different implements and resulted in extensive reshaping of plant beds, placing 88.2% of beads below the critical depth of 2.6 cm.
Virus Transmission Phenotype Is Correlated with Host Adaptation Among Genetically Diverse Populations of the AphidSchizaphis graminum
Authors: Gray Stewart M. , Smith Dawn M. , Barbierri Lia , Burd John
Published: May 2007

Schizaphis graminum is an important insect pest of several grain crops and an efficient vector of cereal-infecting luteoviruses and poleroviruses. We examined the virus transmission characteristics of several distinct populations and various developmental stages of the aphid. Seven well-characterized S. graminum biotypes maintained at the USDA-ARS laboratory in Stillwater, OK, and two biotypes maintained in New York (one collected in Wisconsin and the other collected in South Carolina) were tested for their ability to transmit five viruses that cause barley yellow dwarf disease (BYD). Four of the Oklahoma biotypes, which do not commonly colonize agronomic crops, and the Wisconsin biotype, were efficient vectors of several viruses. The three other Oklahoma biotypes, which do colonize agronomic crops, and the South Carolina biotype, were poor vectors of all five viruses. Thus, the vector specificity long associated with viruses causing BYD is not limited to the level of aphid species; it clearly extends to populations within a single species. S. graminum nymphs are reported to be more efficient vectors of Barley yellow dwarf virus (BYDV-SGV) than are adults. This was confirmed only for the Wisconsin biotype, but not for the other eight S. graminum biotypes. Thus, there does not appear to be a generalized developmentally regulated barrier to the transmission of BYDV-SGV in S. graminum. Furthermore, the developmentally regulated vector competency observed in the Wisconsin biotype did not extend to other viruses. BYDV-PAV and Cereal yellow dwarf virus-RPV were transmitted with similar efficiency by all S. graminum biotypes when acquired by nymphs or adults.
Genetic and Morphological Characterization of Colletotrichum acutatum Causing Anthracnose of Lupins
Authors: Talhinhas Pedro , Sreenivasaprasad S. , Neves-Martins João , Oliveira Helena
Published: May 2007

Anthracnose, caused by Colletotrichum sp., is a serious problem of lupins (Lupinus spp.) worldwide. Morphological characters and molecular markers were used to characterize 43 Colletotrichum isolates from lupins, 8 isolates from other hosts, and 18 reference isolates representing related Colletotrichum spp., to assess the pathogen diversity and resolve its taxonomy. All lupin Colletotrichum isolates tested positive with C. acutatum-specific polymerase chain reaction (PCR) and did not test positive with C. gloeosporioides-specific PCR. Spore shape and colony diameter as well as insensitivity to benomyl grouped the lupin anthracnose isolates closer to C. acutatum than to C. gloeosporioides. Analysis of internal transcribed spacer (ITS) sequences of 57 Colletotrichum isolates grouped all lupin isolates with C. acutatum and distinct from C. gloeosporioides. Further, tub2 and his4 sequences revealed groups concordant with ITS, reducing the excessive dependence on the latter. Arbitrarily primed-PCR and amplified fragment length polymorphism analyses revealed intraspecific subgroups, but neither was useful to decipher species level relationships. ITS, tub2, and his4 results strongly support designating lupin anthracnose pathogen as C. acutatum or its subspecies. Most Colletotrichum isolates from lupins from worldwide locations are genetically homogeneous and form a distinct subgroup within C. acutatum. Present results also underline the potential of the C. acutatum-specific PCR for routine pathogen diagnosis.
Threshold Conditions That Lead Latent Infection to Prune Fruit Rot Caused by Monilinia fructicola
Authors: Luo Yong , Michailides Themis J.
Published: May 2007

Inoculations were performed six to eight times in each of 10 prune orchards located in nine counties of California. In each inoculation, branches that bore 40 to 60 blossoms or 30 to 40 fruit were inoculated with conidial suspensions of Monilinia fructicola. Three inoculum concentrations and 14 to 16 h of humidity were used for each inoculation. All inoculated fruit were maintained on trees and harvested separately 2 weeks before commercial harvest. The incidence of latent infection (ILI) and percentage of branches with fruit rot (PBFR) were determined for each inoculation in each orchard. As the ILI increased, the PBFR also increased linearly. Five conditions that lead latent infection to fruit rot include (i) latent infection level; (ii) fruit developmental stage; (iii) inoculum concentration; (iv) total hours of relative humidity greater than 90% (hRH); and (v) total hours of dew period (hDEW) from mid-July to mid-August. Three levels of PBFR, 1, 5, and 10% were assigned, and threshold conditions that lead to these levels were determined based on the experimental results. The relative probabilities that lead latent infection to fruit rot (r_PBFR) at different fruit developmental stages were calculated. A preliminary decision support model to guide fungicide application was developed based on the above results. One of the four recommendations, safe, wait, check historical weather as a reference, and apply a fungicide immediately, could be provided based on the level of latent infection and the decision process developed through this study.
Frequency, Diversity, and Activity of 2,4-Diacetylphloroglucinol-Producing Fluorescent Pseudomonas spp. in Dutch Take-all Decline Soils
Authors: de Souza Jorge T. , Weller David M. , Raaijmakers Jos M.
Published: May 2007

Natural suppressiveness of soils to take-all disease of wheat, referred to as take-all decline (TAD), occurs worldwide. It has been postulated that different microbial genera and mechanisms are responsible for TAD in soils from different geographical regions. In growth chamber experiments, we demonstrated that fluorescent Pseudomonas spp. that produce the antibiotic 2,4-diacetylphloroglucinol (2,4-DAPG) play a key role in the natural suppressiveness of two Dutch TAD soils. First, 2,4-DAPG-producing fluorescent Pseudomonas spp. were present on roots of wheat grown in both of the TAD soils at densities at or above the threshold density required to control take-all of wheat; in a complementary take-all conducive soil, population densities of 2,4-DAPG-producing Pseudomonas spp. were below this threshold level. Second, introduction of 2,4-DAPG-producing strain SSB17, a representative of the dominant geno-typic group found in the Dutch TAD soils, into the take-all conducive soil at population densities similar to the densities of indigenous 2,4-DAPG producers found in TAD soils provided control of take-all similar to that observed in the TAD soil. Third, a mutant of strain SSB17 deficient in 2,4-DAPG production was not able to control take-all of wheat, indicating that 2,4-DAPG is a key determinant in take-all suppression. These results show that in addition to the physicochemically different TAD soils from Washington State, 2,4-DAPG-producing fluorescent Pseudomonas spp. are also a key component of the natural suppressiveness found in Dutch TAD soils. Furthermore, it is the first time since the initial studies of Gerlagh (1968) that at least part of the mechanisms and microorganisms that operate in Dutch TAD soils are identified. Although quantitatively similar, the genotypic composition of 2,4-DAPG-producing Pseudomonas spp. varied between the Dutch TAD soils and the TAD soils from Washington State.
Diversity Among Strains of Xanthomonas campestris pv. vitians from Lettuce
Authors: Sahin F. , Abbasi P. A. , Ivey M. L. Lewis , Zhang J. , Miller S. A.
Published: May 2007

Diversity in host range, pathogenicity, phenotypic characteristics, repetitive extragenic palindromic polymerase chain reaction (rep-PCR) profiles, and sequence of the 16S-23S rDNA spacer region was examined among 44 Xanthomonas strains isolated from lettuce. Forty-two of the strains were divided into two groups, designated A and B. Seventy percent were Group A, and most of the remaining strains including a reference strain (LMG 938) were Group B. Group A strains induced both local and systemic symptoms, whereas Group B strains caused only distinct necrotic spots. Two strains, including the X. campestris pv. vitians type strain, were distinct from the Group A and B strains and were not pathogenic on lettuce. Analysis of fatty acid profiles, serotype, carbon substrate utilization patterns, and protein fingerprints confirmed this grouping. The Group A and B strains also formed two unique clusters (I and II) by rep-PCR profiling that corresponded to the two groups. Direct sequencing of a PCR-amplified DNA fragment (680 bp) from the 16S-23S rDNA spacer region of four representative strains, however, did not differentiate these groups. Serology and rep-PCR fingerprinting can be used to diagnose and identify X. campestris pv. vitians strains, while the other analyses evaluated are useful for strain characterization.
A Novel Mite-Transmitted Virus with a Divided RNA Genome Closely Associated with Pigeonpea Sterility Mosaic Disease
Authors: Kumar P. Lava , Jones A. Teifion , Reddy D. V. R.
Published: May 2007

The agent of sterility mosaic, a disease that is a major constraint on pigeonpea (Cajanus cajan) production in the Indian subcontinent, is transmitted by the eriophyid mite, Aceria cajani. This agent has remained elusive for decades despite intensive efforts but we report the isolation of highly flexuous filamentous virus-like particles (VLPs) of 3 to 10 nm in width and of undefined lengths from sterility mosaic disease (SMD)-affected pigeonpea plants. Purified VLP preparations from virus-infected pigeonpea and Nicotiana benthamiana had a buoyant density in cesium chloride of 1.22 to 1.23 g cm-3 and contained a major virus-specific protein species of ≈32 kDa and 5 to 7 RNA species of ≈6.8 to 1.1 kb. The sequence of some complementary DNA clones to RNA from purified VLP preparations had no significant matches in database searches. Two oligonucleotide primers derived from one such sequence, when used in reverse transcriptase-polymerase chain reaction assays, amplified a product of 321 bp specifically from SMD-affected pigeonpea plants. Purified VLP preparations were used to produce polyclonal antibodies that, in infected plants, detected the virus using enzyme-linked immuno-sorbent assay (ELISA) and the virus-specific 32-kDa protein in western immunoblotting (WIB). In such assays, the virus was detected consistently in all SMD-affected pigeonpea plant samples from several different locations in India, but not in samples from symptom-free pigeonpea plants from the same locations. In experimental studies, all pigeonpea plants inoculated with viruliferous A. cajani and those plants graft-inoculated with SMD-affected tissue were infected with the virus as assessed by ELISA and WIB, but not any uninfected pigeonpea plants. This virus, tentatively named Pigeonpea sterility mosaic virus (PPSMV), has some properties similar to virus species in the genera Tospovirus and Tenuivirus and with the eriophyid mite-transmitted High plains virus (HPV) but is distinct from these and from all other characterized viruses. The combination of novel properties shown by PPSMV and HPV suggest that they may constitute species in a new genus of plant viruses.
Calcium/Calmodulin-Dependent Signaling for Prepenetration Development inColletotrichum gloeosporioides
Authors: Uhm Kwang-Heum , Ahn Il-Pyung , Kim Soonok , Lee Yong-Hwan
Published: May 2007

Colletotrichum gloeosporioides forms a specialized infection structure, an appressorium, for host infection. Contacting hard surface induces appressorium formation in C. gloeosporioides, whereas hydrophobicity of the contact surface does not affect this infection-related differentiation. To determine if the calcium/calmodulin-dependent signaling system is involved in prepenetration morphogenesis in C. gloeosporioides pathogenic on red pepper, effects of calcium chelator (EGTA), phospholipase C inhibitor (neomycin), intracellular calcium modulators (TMB-8 and methoxy verampamil), and calmodulin antagonists (chloroproma-zine, phenoxy benzamine, and W-7) were tested on conidial germination and appressorium formation. Exogenous addition of Ca2+, regardless of concentration, augmented conidial germination, while appressorial differentiation decreased at higher concentrations. Inhibition of appressorium formation by EGTA was partly restored by the addition of calcium ionophore A23187 or CaCl2. Calcium channel blockers and calmodulin antagonists specifically reduced appressorium formation at micromolar levels. These results suggest that biochemical processes controlled by the calcium/calmodulin signaling system are involved in the induction of prepenetration morphogenesis in C. gloeosporioides pathogenic on red pepper.
Rhizobacteria-Mediated Growth Promotion of Tomato Leads to Protection AgainstCucumber mosaic virus
Authors: Murphy John F. , Reddy M. S. , Ryu Choong-Min , Kloepper Joseph W. , Li Ruhui
Published: May 2007

We evaluated combinations of two strains of plant growth-promoting rhizobacteria (PGPR) formulated with the carrier chitosan for the ability to induce growth promotion of tomato plants and resistance to infection by Cucumber mosaic virus (CMV). Each PGPR combination included GB03 (Bacillus subtilis) and one of the following PGPR strains: SE34 (B. pumilus), IN937a (B. amyloliquefaciens), IN937b (B. subtilis), INR7 (B. pumilus), or T4 (B. pumilus). The PGPR combinations formulated with chitosan are referred to as biopreparations. Tomato plants treated with each of the biopreparations appeared phenotypically and developmentally similar to nonbacterized control plants that were 10 days older (referred to as the older control). When plants were challenged with CMV, all plants in the biopreparation treatments and the older control treatment had significantly greater height, fresh weight, and flower and fruit numbers than that of plants in the CMV-inoculated same age control treatment. CMV disease severity ratings were significantly lower for biopreparation-treated and older control tomato plants than for that of same age control plants at 14 and 28 days postinoculation (dpi). CMV accumulation in young noninoculated leaves was significantly less for all biopreparation-treated plants and those in the older control than for the same age control plants at 14 dpi and for four of the five biopreparation treatments at 28 dpi. In those tomato plants shown to be infected, the amount of CMV in noninoculated leaves was significantly lower for three of the biopreparation treatments and the older control treatment at 14 dpi and biopreparation G/INR7 treatment at 28 dpi when compared with the control treatment. These data show that treatment of tomato plants with biopreparations results in significant enhancement of growth and protection against infection by CMV.
Cytological Characterization of Elicitin-Induced Protection in Tobacco Plants Infected by Phytophthora parasitica or Phytoplasma
Authors: Lherminier J. , Benhamou N. , Larrue J. , Milat M.-L. , Boudon-Padieu E. , Nicole M. , Blein J.-P.
Published: May 2007

Elicitins, small proteins secreted by Phytophthora and Pythium spp., display the ability to induce plant resistance toward pathogens. Ultrastructural investigations of cryptogein-treated tobacco plants evidenced host defense responses such as (i) formation of a calcium pectate gel in intercellular spaces of parenchymas, (ii) impregnation of pectin by phenolic compounds in intercellular spaces of phloem bundles, and (iii) accumulation of phloem proteins (P proteins) in the lumen of leaf sieve elements. These cytological modifications lead to the enhancement of physical barriers that prevent pathogen ingress and restrict host tissue colonization when cryptogein-treated tobacco plants were challenged with the pathogen Phytophthora parasitica. Wall appositions also were observed at most sites of penetration of hyphae. Moreover, growing hyphae exhibited severe morphological damages, suggesting a modified toxic environment. The same induction of P proteins in mature sieve tubes of tobacco leaves was obtained with oligandrin treatment, another elicitin. Cryptogein or oligandrin treatment prevented symptom expression in phytoplasma-infected tobacco plants in contrast with nontreated tobacco plants. Moreover, P protein plugs and occlusion of pore sites by callose were evidenced in sieve elements of treated plants. Both these phloem modifications might prevent the in planta movement of phloem-restricted microorganisms.
A Near-Isogenic Fusarium oxysporum f. sp. lycopersici Strain with a Novel Combination of Avirulence Characteristics
Authors: Teunissen Hedwich A. S. , Boer Yvonne , Verkooijen Jurgo , Cornelissen Ben J. C. , Haring Michel A.
Published: May 2007

A novel Fusarium oxysporum f. sp. lycopersici strain (F1-27) was obtained from protoplast fusions between race 1 Fol004 (putative avirulence genotype A1a2a3) and race 2 Fol007 (a1A2A3). Bioassays using different tomato cultivars revealed new virulence characteristics for F1-27 that were mitotically stable. The corresponding avirulence genotype for F1-27 was assigned a1A2a3. Despite their distinction in avirulence genotype, molecular analysis revealed that parent Fol007 and F1-27 were near-isogenic strains. The electrophoretic karyotype of F1-27 was identical to that observed for Fol007. Foxy-amplified fragment length polymorphism (AFLP) marker analysis showed that all Fol007-specific bands were present in F1-27. In addition, 11 new F1-27-specific Foxy insertions were identified. Segregation of both virulence and these new Foxy-AFLP markers was observed in a backcross between F1-27 and its parent Fol007. One marker was found to cosegregate with the a3 allele. The nature of the genetic change in this strain is discussed.