bluuebunny/crossref_metadata_2025 huggingface dataset:
Aerial Photography Used for Spatial Pattern Analysis of Late Blight Infection in Irrigated Potato Circles
Authors: Johnson Dennis A. , Alldredge J. Richard , Hamm Philip B. , Frazier Bruce E.
Published: May 2007

Spatial and temporal dynamics of late blight were investigated from color, infrared aerial photographs of five commercial potato fields in the Columbia Basin during epidemics in 1993, 1995, and 1998. Aerial photographs were taken one to four times at 6- to 21-day intervals. Photographs were scanned and pixels, representing approximately 1 m2in the field, were used in the analysis. Late blight-infected plants were aggregated as indicated by runs analysis. Significant z-tests were computed for four directions during each sampling date in each of the five fields. Absolute z-values for runs analysis increased, indicating increasing aggregation in the four directions, as disease incidence increased in the early and midphases of the epidemics in each field. Variograms indicated the existence of autocorrelation among infected plants in four directions; the range of influence increased as disease incidence increased except at the highest levels of disease. Late blight was observed to spread in fields as foci. Late blight foci enlarged in size, produced distinct daughter foci, and coalesced. A field where initial inoculum likely originated from infected seed tubers exhibited less initial aggregation than the other fields, perhaps due to a different source of primary inoculum. Aerial photography coupled with spatial analyses of late blight-infected plants was an effective technique to quantitatively assess disease patterns in relatively large fields and was useful in quantifying an intensification of aggregation during the epidemic process on a large scale.
Disease Development and Symptom Expression of Xanthomonas axonopodis pv. citri in Various Citrus Plant Tissues
Authors: Vernière C. J. , Gottwald T. R. , Pruvost O.
Published: May 2007

Experimental inoculations of Xanthomonas axonopodis pv. citri in different tissues of Tahiti lime and Pineapple sweet orange were conducted monthly under natural conditions on Réunion Island. The interactions between a set of environmental and epidemic variables associated with disease expression and 184 different factor combinations were investigated to determine the parameters needed to explain Asiatic citrus canker (ACC) disease expression. Area under the disease progress curve (AUDPC), inoculation date (Id), fruit and leaf age ratings (FAR and LAR), and number of days during the first 2 weeks postinoculation for which the temperature was less than 14°C (Tmin) or more than 28°C (Tmax) were retained by principal component analysis and canonical correlation analysis as the most meaningful epidemic and environmental variables, respectively. AUDPC as the strongest dependent variable and combinations of the environmental variables as independent variables were used in multiple regression analyses. Tissue age rating at the time of infection was a good predictor for disease resulting from spray inoculation on fruits and leaves and also on fruits following a wound inoculation. Temperature, as expressed by Tmin or Tmax, was also a significant factor in determining disease development described by AUDPC. Mature green stems were highly susceptible after wounding, similarly to leaves, but buds and leaf scars expressed the lowest susceptibility. These variations in disease expression according to the tissues will have different impacts on ACC epidemiology.
Quantitative Trait Loci Associated with Seedling Resistance to Isolates ofPuccinia coronatain Oat
Authors: Zhu Shuquan , Leonard Kurt J. , Kaeppler Heidi F.
Published: May 2007

In our previous report, quantitative trait loci (QTL) for field adult plant resistance to crown rust were identified in an oat population of 152 F5:6recombinant inbred lines from the cross of ‘Ogle’ (susceptible)/MAM17-5 (resistant). The objectives of the present study were to identify in the same population, the number, genomic location, and effect of QTL and digenic QTL epistasis associated with greenhouse seedling resistance to isolates of Puccinia coronata to determine if the QTL detected are isolate-specific and to compare them with previously detected QTL for field resistance. Reaction type was scored on greenhouse seedlings inoculated with three isolates. Composite interval mapping was conducted to identify genomic regions associated with resistance using a framework map of 272 molecular markers. Two QTL, Pcq1 and Pcq2, were identified for resistance to each of the three isolates. Pcq1, the major QTL controlling field resistance, did not confer detectable greenhouse seedling resistance when present singly; however, Pcq1 did serve as an enhancer of seedling resistance when it was combined with Pcq2. The final model explained 76.5, 77.9, and 79.3% of total phenotypic variation for resistance to isolates MNB248, MNB249, and MNB251, respectively. Race-specificity of quantitative resistance remains to be further examined.
Microsatellite Markers for Genes Lr34/Yr18 and Other Quantitative Trait Loci for Leaf Rust and Stripe Rust Resistance in Bread Wheat
Authors: Suenaga K. , Singh R. P. , Huerta-Espino J. , William H. M.
Published: May 2007

Leaf rust and stripe rust, caused by Puccinia triticina and P. striiformis, respectively, are important diseases of wheat in many countries. In this study we sought to identify molecular markers for adult plant resistance genes that could aid in incorporating such durable resistance into wheat. We used a doubled haploid population from a Japanese cv. Fukuho-komugi × Israeli wheat Oligoculm cross that had segregated for resistance to leaf rust and stripe rust in field trials. Joint and/or single-year analyses by composite interval mapping identified two quantitative trait loci (QTL) that reduced leaf rust severity and up to 11 and 7 QTLs that might have influenced stripe rust severity and infection type, respectively. Four common QTLs reduced stripe rust severity and infection type. Except for a QTL on chromosome 7DS, no common QTL for leaf rust and stripe rust was detected. QTL-7DS derived from ‘Fukuho-komugi’ had the largest effect on both leaf rust and stripe rust severities, possibly due to linked resistance genes Lr34/Yr18. The microsatellite locus Xgwm295.1, located almost at the peak of the likelihood ratio contours for both leaf and stripe rust severity, was closest to Lr34/Yr18. QTLs located on 1BL for leaf rust severity and 3BS for stripe rust infection type were derived from ‘Oligoculm’ and considered to be due to genes Lr46 and Yr30, respectively. Most of the remaining QTLs for stripe rust severity or infection type had smaller effects. Our results indicate there is significant diversity for genes that have minor effects on stripe rust resistance, and that successful detection of these QTLs by molecular markers should be helpful both for characterizing wheat genotypes effectively and combining such resistance genes.
Ultrastructural and Immunochemical Changes During the In Vitro Development of Plasmopara halstedii
Authors: Bouterige Sandrine , Tronchin Guy , Lesourd Maurice , Marot-Leblond Agnès , Molinéro Valérie , Bouchara Jean-Philippe , Robert Raymond
Published: May 2007

The asexual phase of the life cycle of Plasmopara halstedii, the causal agent of downy mildew of sunflower, plays a key role in the propagation of the disease. We investigated the morphological and ultrastructural changes that occur during the asexual development of the pathogen. Direct examination of infected cotyledons confirmed the presence of sporangiophores. In contact with water, important ultrastructural changes occurred, affecting the surface of zoosporangia, which became smoother, and their cytoplasm, which differentiated into flagellate zoospores. The subsequent encystment of zoospores was characterized by the synthesis of a cell wall and the loss of the flagella. In addition, two monoclonal antibodies (MAbs) specific for P. halstedii were used to analyze the immunochemical changes associated with these modifications. MAb 16A6, which bound to a 48-kDa glycoprotein, mainly labeled the surface of mobile or encysted zoospores and of mother cells of germ tubes. Conversely, MAb 2F9, which recognized highly glycosylated antigens, labeled the surface of zoosporangia and of flagellate zoospores, but not the encysted zoospores. These results provide new insights into the morphological and ultrastructural changes associated with the release and the encystment of zoospores which may be interesting targets for the development of new antimicrobial products.
Environmental Factors Affecting the Release and Dispersal of Ascospores of Mycosphaerella citri
Authors: Mondal S. N. , Gottwald T. R. , Timmer L. W.
Published: May 2007

Greasy spot, caused by Mycosphaerella citri, produces a leaf spot disease affecting all citrus species in Florida and the Caribbean Basin. M. citri produces pseudothecia and ascospores, which are considered the principal source of inoculum, in decomposing leaves on the grove floor. In studies using a computer-controlled environmental chamber, a single rain event triggered release of most mature ascospores beginning 30 to 60 min after the rain event. Additional rain events did not bring about further release. High relative humidity without rain triggered release of low numbers of ascospores, but vibration and red/infrared irradiation had little or no effect on ascospore release. After three to four cycles of wetting and drying of leaves, all pseudothecia had matured and released their ascospores. In the field, ascospores were detectable starting about 2 h after the beginning of a rain or irrigation and most ascospores were released within 16 h. Ascospore release was greatest following rain events and somewhat less following irrigations, and low numbers of ascospores were detectable on days without precipitation. Ascospore numbers declined linearly with horizontal distance from the source and as a function of the logarithm of ascospore numbers with vertical distance. Low numbers of ascospores were detected 7.5 m above the ground and 90 m downwind from the grove. Ascospore release can be advanced by irrigating frequently during dry, nonconducive conditions to stimulate ascospore release when environmental conditions are unfavorable for infection, but the eventual effects on disease severity are uncertain.
Dominating North American Forest Pathology Issues of the 20th Century
Authors: MacDonald William L.
Published: May 2007

The profession of forest pathology evolved in the early decades of the 20th century from a science describing microorganisms that infect trees to a discipline that was required to deal with numerous disease outbreaks. The foundations of the science were carried from Europe to the “New World” and initially dealt with decay and the resource losses it caused. The profession was forced to shift direction quickly because it was called upon to address major diseases caused by the introduction of pathogens from other continents; notably organisms inciting chestnut blight, Dutch elm disease, and white pine blister rust. Changes in natural ecosystems that resulted from a legacy of poor forest practice, land abuse, and an increase in plantation monocultures gave rise to other disease problems when host-pathogen balances in natural ecosystems were disturbed. Further, the need for large numbers of tree seedlings resulted in numerous nursery disease problems. Although many of the principles of general plant pathology had application to the study of forest diseases, the long-term nature of forests requires varied approaches to their study and management. Today, the science continues to evolve as the complexities of forest ecosystems unfold.
Perspectives and Challenges from the 20th Century
Authors: Tainter F. H.
Published: May 2007

The magnitude of change in our understanding of tree diseases during the past century is almost incomprehensible. This does not mean to imply that we know everything, but the science of forest pathology has come a long way in the past 100 years. This remarkable progress was driven by three events: (i) an investment in the early 1900s in federal and state experiment stations, which established the need for, and benefits of, research in tree diseases; (ii) veterans acquiring an education under the GI Bill, which created a pool of forest pathologists and students eager to solve the devastation caused by diseases such as chestnut blight, white pine blister rust, Dutch elm disease, and oak wilt; and (iii) the McIntire-Stennis Cooperative Forestry Program, which established a strategy for the federal government to assist the financing of forestry research in the universities. Although all three of these events are being drastically modified by a discontented tax-paying public, the threats of changing land use patterns, population pressures, and exotic pests on fragile forested ecosystems will certainly force a renaissance in our field that will dwarf progress of the past century and help assure an acceptable quality of life in the new century. The magnitude of what forest pathologists will accomplish, to a great extent, depends on what the public is willing to pay for.
Characterization of a Hydrophobic Amylase Inhibitor from Corn (Zea mays) Seeds with Activity Against Amylase from Fusarium verticillioides
Authors: Figueira Edson L. Z. , Hirooka Elisa Y. , Mendiola-Olaya Elizabeth , Blanco-Labra Alejandro
Published: May 2007

A hydrophobic 19.7-kDa amylase inhibitor (AI) was purified from corn kernels by 95% ethanol extraction and anionic exchange chromatography. The AI has an isoelectric point of 3.6 and was very stable at different pH values and high temperatures, maintaining 47.6% activity after heating to 94°C for 60 min. Amino acid analysis indicated high valine, leucine, glycine, alanine, and glutamic acid/glutamine content, and especially high valine content (41.2 mol%). This inhibitor is not a glycoprotein. It required 30-min preincubation to maximize complex enzyme-inhibitor formation when the amylase from Fusarium verticillioides was tested. The optimal pH of interaction was 6.5. It showed broad-spectrum activity including the following amylases: human saliva, porcine pancreas, F. verticillioides, as well as those from some insects of agricultural importance (Acanthoscelides obtectus, Zabrotes subfasciatus, Sitophilus zeamais, and Prostephanus truncatus). This novel hydrophobic protein not only inhibited the amylase from F. verticillioides but also decreased the conidia germination. Thus, this protein represents an approach to decrease the production of fumonisin in corn, either by using it as a molecular marker to detect fungal resistance or through genetic engineering.
Digital Image Analysis of Internal Light Spots of Appressoria ofColletotrichum acutatum
Authors: Diéguez-Uribeondo J. , Förster H. , Adaskaveg J. E.
Published: May 2007

The initial penetration process of appressoria of Colletotrichum acutatum on almond leaves was studied using digital image analysis of light micrographs and scanning electron microscopy. For image analysis, a series of sequential, partially focused digital micrographs of appressoria was analyzed to generate a single, completely focused montage image with a continuous in-focus depth of field. In studies on the development of the internal light spot (ILS), we observed that 50.4% of the appressoria formed an ILS after leaves were inoculated and incubated for 12 h at 20°C, and that this increased to 95.8% after 24 h. Comparative image analyses of appressoria with and without ILSs using depth relief mapping and line profile software options showed that the ILS had a depth relief that was below that of the leaf surface. Depth relief analysis in the ILS region during incubation revealed an increase in depth in this area of up to 1.8 μm in some of the appressoria. A comparative morphological study of the ILS in montage images and the penetration pore of appressoria in scanning electron micrographs showed similar shapes and dimensions of the two structures in the appressorium. Light micrographs of histological sections confirmed fungal penetration and internal vesicle formation in almond leaves within 36 h after inoculation and incubation at 20°C. This study represents the first direct evidence that the ILS in appressoria corresponds to the penetration pore and the developing penetration peg using a rapid, digital image analysis technique.
An Analysis of the Durability of Resistance to Plant Viruses
Authors: García-Arenal Fernando , McDonald Bruce A.
Published: May 2007

Genetic resistance often fails because a resistance-breaking (RB) pathogen genotype increases in frequency. On the basis of an analysis of cellular plant pathogens, it was recently proposed that the evolutionary potential of a pathogen is a major determinant of the durability of resistance. We test this hypothesis for plant viruses, which differ substantially from cellular pathogens in the nature, size, and expression of their genomes. Our analysis was based on 29 plant virus species that provide a good representation of the genetic and biological diversity of plant viruses. These 29 viruses were involved in 35 pathosystems, and 50 resistance factors deployed against them were analyzed. Resistance was found to be durable more often than not, in contrast with resistance to cellular plant pathogens. In a third of the analyzed pathosystems RB strains have not been reported, and in another third RB strains have been reported but have not become prevalent in the virus population. The evolutionary potential of the viruses in the 35 pathosystems was evaluated with a compound risk index based on three evolutionary factors: the population of the pathogen, the degree of recombination, and the amount of gene and genotype flow. Our analysis indicates that evolutionary potential may be an important determinant of the durability of resistance against plant viruses.
Changes in Carbohydrate Metabolism in Coconut Palms Infected with the Lethal Yellowing Phytoplasma
Authors: Maust B. E. , Espadas F. , Talavera C. , Aguilar M. , Santamaría J. M. , Oropeza C.
Published: May 2007

Lethal yellowing (LY), a disease caused by a phytoplasma, is the most devastating disease affecting coconut (Cocos nucifera) in Mexico. Thousands of coconut palm trees have died on the Yucatan peninsula while plantations in Central America and on the Pacific coast of Mexico are severely threatened. Polymerase chain reaction assays enable identification of incubating palm trees (stage 0+, phytoplasma detected but palm asymptomatic). With the development of LY, palm trees exhibit various visual symptoms such as premature nut fall (stage 1), inflorescence necrosis (stages 2 to 3), leaf chlorosis and senescence (stages 4 to 6), and finally palm death. However, physiological changes occur in the leaves and roots prior to onset of visual symptoms. Stomatal conductance, photosynthesis, and root respiration decreased in stages 0+ to 6. The number of active photosystem II (PSII) reaction centers decreased during stage 2, but maximum quantum use efficiency of PSII remained similar until stage 3 before declining. Sugar and starch concentrations in intermediate leaves (leaf 14) and upper leaves (leaf 4) increased from stage 0- (healthy) to stages 2 to 4, while root carbohydrate concentrations decreased rapidly from stage 0- to stage 0+ (incubating phytoplasma). Although photosynthetic rates and root carbohydrate concentrations decreased, leaf carbohydrate concentrations increased, suggesting inhibition of sugar transport in the phloem leading to stress in sink tissues and development of visual symptoms of LY.
Blackleg Sporacle: A Model for Predicting Onset of Pseudothecia Maturity and Seasonal Ascospore Showers in Relation to Blackleg of Canola
Authors: Salam M. U. , Khangura R. K. , Diggle A. J. , Barbetti M. J.
Published: May 2007

A simple model has been developed to predict the onset of pseudothecia maturity and seasonal ascospore showers in relation to blackleg disease in canola, caused by the fungus Leptosphaeria maculans. The model considers a combination of two weather factors, daily mean temperature and daily total rainfall, to drive progress of maturity of pseudothecia on the infested canola stubble left from past crops. Each day is categorized as suitable or not suitable for progress of the maturation process. The onset of pseudothecia maturity occurs when approximately 43 suitable days have occurred. Following the onset of maturity, ascospore showers are triggered when daily rainfall exceeds a threshold. The model satisfactorily predicted the timing of the onset of pseudothecia maturity when tested with 3 years of field observations at four locations in Western Australia, which characteristically has a Mediterranean climate. The model also agreed reasonably well with the daily pattern of ascospore release observed in two locations. Sensitivity analysis was performed to show the relative importance of the parameters that describe the onset of pseudothecia maturity.
Using Air Pressure Cells to Evaluate the Effect of Soil Environment on the Transmission of Soilborne Viruses of Wheat
Authors: Cadle-Davidson L. , Schindelbeck R. R. , van Es H. M. , Gray S. M. , Bergstrom G. C.
Published: May 2007

An air pressure cell, a laboratory tool that precisely controls soil matric potential, was utilized in a novel approach to investigate the epidemiology and management of soilborne disease. Matric potentials of −1, −5, −20, and −40 kPa were established in cores of field soil infested with Wheat soilborne mosaic virus (WSBMV) and its presumed vector Polymyxa graminis. Equilibrated soil cores were planted to wheat (Triticum aestivum), and after intervals of growth under controlled environment, virus transmission was assessed by serological detection of the virus in washed roots. Transmission occurred at all but the driest soil matric potential tested, −40 kPa, in which only pores with a diameter of 7.4 μm or less were water-filled, possibly obstructing movement of P. graminis zoospores. By starting plants at −40 kPa for 10.5 days and then watering them to conducive matric potential, we found that WSBMV transmission occurred between 12 to 24 h at 15°C, and within 36 h at 20°C. No significant transmission occurred within 96 h at 6.5°C. In contrast, transmission of Wheat spindle streak mosaic virus (WSSMV) did not occur at 15°C (the only transmission temperature tested), suggesting either that WSSMV is unable to establish infection at 15°C or that a different vector is involved. The air pressure cell is a novel tool with many potential applications in research on the epidemiology and management of soilborne pathogens. Applications of the precise environmental control attained through the use of air pressure cells range from assessing the effects of cultural practices on soilborne inoculum to standardized virulence assays for soilborne pathogens to preliminary screens of host resistance and pesticide efficacy.
Use of a Nitrate-Nonutilizing Mutant and Selective Media to Examine Population Dynamics of Fusarium oxysporum f. sp. spinaciae in Soil
Authors: Takehara Toshiaki , Kuniyasu Katsuto , Mori Mitsutaka , Hagiwara Hiroshi
Published: May 2007

Determining the population density of the spinach wilt pathogen Fusarium oxysporum f. sp. spinaciae in soil with conventional Fusarium-selective media is quite difficult because nonpathogenic strains of F. oxysporum also grow on those media and are indistinguishable from the pathogen. Therefore, a nitrate-nonutilizing (nit) mutant of the pathogen and corresponding selective media were tested in an experimental approach to determine the population density of the pathogen. Colony forming units of the pathogen were countable after soil-dilution plating onto nit mutant-selective media MMCPA, CMP, and CGMBP. Colony forming units of wild-type Fusarium spp. were countable using a wildtype Fusarium-selective medium, GMBP. By combining nit mutant- and wild-type-selective media, the population densities of pathogenic and nonpathogenic F. oxysporum in the same soil could be measured selectively. This method was useful in studying population dynamics of the pathogen after different soil treatments. Soil disinfested with hot water or chloropicrin was amended with the nit mutant pathogen, and subsequent changes in population densities of the pathogen were compared with those in nontreated field soil. The pathogen rapidly proliferated in disinfested soil and wilt developed faster than in nontreated soil. When a nonpathogenic isolate of F. oxysporum was added at high density to sterilized soil prior to the pathogen, growth of the pathogen was greatly suppressed. Nonpathogenic F. oxysporum could not, however, reduce the density of preexisting pathogen.
Aflatoxin Contamination of Commercial Cottonseed in South Texas
Authors: Jaime-Garcia Ramon , Cotty Peter J.
Published: May 2007

Aflatoxins are toxic fungal metabolites produced by several members of Aspergillus section Flavi. U.S. federal regulations limit the use of aflatoxin-contaminated cottonseed. Cottonseed with aflatoxin content of 20 ng/g or higher may not enter the profitable dairy market. Between 4,472 and 9,949 truckloads of cottonseed from 31 to 35 gins in South Texas were analyzed for aflatoxin content each year from 1997 to 2001 upon receipt at the Valley Co-op Oil Mill in Harlingen, TX. The highest levels of contamination occurred in 1999, with an average aflatoxin content of 112 ng/g and 66% of the cottonseed truckloads exceeding 20 ng/g. Years 1997 and 2000 had the lowest aflatoxin levels, averaging 24 ng/g, with the lowest incidence (16%) of the truckloads exceeding 20 ng/g in 1997. In general, aflatoxin contamination increased as the ginning season progressed. Rainfall after boll opening correlated highly with aflatoxin content, with rainfall in July explaining over 50% of the observed variability in aflatoxin content. South Texas was divided into four regions: Rio Grande Valley, Coastal Bend, Upper Coast, and Winter Garden. Geostatistical analyses revealed recurrent patterns of high and low contamination. The greatest contamination occurred from the central Coastal Bend region through the southern Upper Coast region. The Rio Grande Valley region experienced the least contamination during the study period.
Nonparametric Analysis of Ordinal Data in Designed Factorial Experiments
Authors: Shah D. A. , Madden L. V.
Published: May 2007

Plant disease severity often is assessed using an ordinal rating scale rather than a continuous scale of measurement. Although such data usually should be analyzed with nonparametric methods, and not with the typical parametric techniques (such as analysis of variance), limitations in the statistical methodology available had meant that experimental designs generally could not be more complicated than a one-way layout. Very recent advancements in the theoretical formulation of hypotheses and associated test statistics within a nonparametric framework, together with development of software for implementing the methods, have made it possible for plant pathologists to analyze properly ordinal data from more complicated designs using nonparametric techniques. In this paper, we illustrate the nonparametric analysis of ordinal data obtained from two-way factorial designs, including a repeated measures design, and show how to quantify the effects of experimental factors on ratings through estimated relative marginal effects.
Enumeration, Resuscitation, and Infectivity of the Sublethally Injured Erwinia Cells Induced by Mild Acid Treatment
Authors: Liao Ching-Hsing , Shollenberger Lisa M.
Published: May 2007

Current knowledge about microbial injury was derived mostly from studies with bacteria associated with processed foods. Demonstration of injury and repair in phytopathogenic bacteria and its implication on pathogen detection and disease ecology have not been reported. The objective of this study was to investigate the lethal and sublethal effects of acetic acid (AA) on soft-rot Erwinia spp. and the limitation of using selective media for isolation of injured cells. Following exposure to 0.3% AA for 6 min, 90 to 99% of E. carotovora subsp. carotovora, E. carotovora subsp. atroseptica, and E. chrysanthemi cells were killed. When AA-treated samples were plated on agar media, the number of bacteria recovered on nonselective media such as brain heart infusion agar was 3 log units higher than that recovered on selective media such as crystal violet pectate (CVP). Lethal and sublethal actions of AA on Erwinia spp. were affected greatly by acid concentration, exposure time, and bacterial strains tested. Injured Erwinia cells were able to repair and regain the ability to grow on CVP when placed in nutrient broth but not in selective broth containing crystal violet and sodium dodecyl sulfate. Injured cells also were able to resuscitate on cut surfaces of cucumber fruit and to induce soft rot on green bell pepper. Together, these results suggest that direct use of selective media for isolation of Erwinia spp. could limit the recovery of injured cells in samples that have been exposed to chemical or physical stresses. Enrichment of these samples in nutrient broth before plating on CVP is expected to improve the detection of injured Erwinia spp.
Leaf Rust onAegilops speltoidesCaused by a New Forma Specialis ofPuccinia triticina
Authors: Yehuda Pnina Ben , Eilam Tamar , Manisterski Jacob , Shimoni Ayelet , Anikster Yehoshua
Published: May 2007

A leaf rust attacking Aegilops speltoides in its natural habitat is reported for the first time. It was found in two locations in northern and central Israel. The two collections from A. speltoides resemble wheat leaf rust, Puccinia triticina, in most spore dimensions, in the morphology of the substomatal vesicle of the urediniospore, and in DNA content in pycniospore nuclei. Similarly to P. triticina isolates from wheat, isolates taken from A. speltoides are compatible with Thalictrum speciosissimum as an aecial host and they are crossed easily with wheat leaf rust isolates. However, isolates from A. speltoides differ from wheat leaf rust in their telial host range. They are avirulent to cultivated wheat cultivars, but attack hundreds of A. speltoides accessions that were immune to wheat leaf rust. This distinct host preference justifies delineation of the newly found leaf rust as a forma specialis (f. sp. speltoides) within P. triticina.
Molecular Mapping of the Stb4 Gene for Resistance to Septoria tritici Blotch in Wheat
Authors: Adhikari Tika B. , Cavaletto Jessica R. , Dubcovsky Jorge , Gieco Jorge Omar , Schlatter Ana Rosa , Goodwin Stephen B.
Published: May 2007

Breeding wheat for resistance is the most effective means to control Septoria tritici blotch (STB), caused by the ascomycete Mycosphaerella graminicola (anamorph Septoria tritici). At least eight genes that confer resistance to STB in wheat have been identified. Among them, the Stb4 locus from the wheat cv. Tadinia showed resistance to M. graminicola at both seedling and adult-plant stages. However, no attempt has been made to map the Stb4 locus in the wheat genome. A mapping population of 77 F10 recombinant-inbred lines (RILs) derived from a three-way cross between the resistant cv. Tadinia and the susceptible parent (Yecora Rojo × UC554) was evaluated for disease resistance and molecular mapping. The RILs were tested with Argentina isolate I 89 of M. graminicola for one greenhouse season in Brazil during 1999, with an isolate from Brazil (IPBr1) for one field season in Piracicaba (Brazil) during 2000, and with Indiana tester isolate IN95-Lafayette-1196-WW-1-4 in the greenhouse during 2000 and 2001. The ratio of resistant:susceptible RILs was 1:1 in all three tests, confirming the single-gene model for control of resistance to STB in Tadinia. However, the patterns of resistance and susceptibility were different between the Indiana isolate and those from South America. For example, the ratio of RILs resistant to both the Indiana and Argentina isolates, resistant to one but susceptible to the other, and susceptible to both isolates was approximately 1:1:1:1, indicating that Tadinia may contain at least two genes for resistance to STB. A similar pattern was observed between the Indiana and Brazil isolates. The gene identified with the Indiana tester isolate was assumed to be the same as Stb4, whereas that revealed by the South American isolates may be new. Bulked-segregant analysis was used to identify amplified fragment length polymorphism (AFLP) and microsatellite markers linked to the presumed Stb4 gene. The AFLP marker EcoRI-ACTG/MseI-CAAA5 and microsatellite Xgwm111 were closely linked to the Stb4 locus in coupling at distances of 2.1 and 0.7 centimorgans (cM), respectively. A flanking marker, AFLP EAGG/ M-CAT10, was 4 cM from Stb4. The Stb4 gene was in a potential supercluster of resistance genes near the centromere on the short arm of wheat chromosome 7D that also contained Stb5 plus five previously identified genes for resistance to Russian wheat aphid. The microsatellite marker Xgwm111 identified in this study may be useful for facilitating the transfer of Stb4 into improved cultivars of wheat.
Measuring Spatial Aggregation in Binary Epidemics: Correlative Analysis and the Advantage of Fractal-Based Sampling
Authors: Ferrandino Francis J.
Published: May 2007

The incomplete sampling of a binary epidemic is nothing more than the overlap of two spatial patterns: the pattern of diseased plants and the pattern of sampled points. Thus, the information on the spatial arrangement of diseased plants obtained from such a sampling explicitly depends on the geometric locations of the sampled points. A number of procedures for sampling disease incidence are examined. These include samples placed on a regular grid, spatially clustered samples, randomly selected samples, and samples specified by a nested fractal design. The performance of these various sampling schemes was examined using simulated binary epidemics with varying degrees of spatial aggregation over different length scales, generated using a Neyman-Scott cluster process. A modification of spatial correlation analysis specifically geared to binary epidemics is derived and shown to be equivalent to a X2test comparing the number of infected plant pairs to that expected from a spatially random epidemic. This analysis was applied to the data obtained using the various sampling schemes and the results are compared and contrasted. For the same number of sampling points, the fractal design is most efficient in the detection of contagion and provides spatial information over a larger range of distance scales than other sampling schemes. However, the regular grid sampling scheme consistently yielded an estimate of average disease incidence that had the smallest variance. Sampling patterns consisting of randomly selected points were intermediate in behavior between the two extremes.
Gene Cloning and Tissue Expression Analysis of a PR-5 Thaumatin-Like Protein in Phellinus weirii-Infected Douglas-Fir
Authors: Zamani Arezoo , Sturrock Rona N. , Ekramoddoullah Abul K. M. , Liu Jun Jun , Yu Xueshu
Published: May 2007

In western North America, Douglas-fir (Pseudotsuga menziesii) is the most economically important conifer species susceptible to laminated root rot caused by Phellinus weirii. While attempting to internally sequence an endochitinase found to be up-regulated in P. weirii-infected Douglas-fir roots, we obtained overlapping peptide fragments showing 28% similarity with a PR-5 thaumatin-like protein (TLP) designated PmTLP (Pm for Pseudotsuga menziesi). A rabbit polyclonal antibody was reared against a synthetic peptide composed of a 29-amino-acid-long, conserved, internal sequence of PmTLP and purified by immunoaffinity. Western immunoblot analysis of infected roots of 24-year-old coastalfir showed significantly higher amounts of PmTLP (P < 0.01) closest to the point of P. weirii inoculation and infection than in uninfected regions of the same root. The antibody was also used to screen for PmTLP in roots of 25-year-old interior Douglas-firs naturally infected with a related pathogen, Armillaria ostoyae, and results showed significantly higher levels of PmTLP in bark tissues adjacent to infection (P < 0.05) than in uninfected tissue. Using polymerase chain reaction (PCR)-based cloning, the cDNA of PmTLP was shown to have a 702-bp open reading frame with a signal peptide cleavage site at 155 bp corresponding to a 29-amino-acid-long residue prior to the start of the N-terminal. Based on the deduced amino acid sequence, the molecular mass of the putative PmTLP was calculated to be 21.0 kDa with an isoelectric point of 3.71. Alignment analysis of PmTLP cDNA with a representative genomic DNA PCR sequence showed presence of one intron of variable size, within the coding region. The induction of PmTLP at the site of root infection and its presence in needle tissue suggests a general role for this protein in adaptation to stress and may be part of an integrated defense response initiated by the host to impede further pathogen spread.
Structural Modifications and Programmed Cell Death of Chili Pepper Fruit Related to Resistance Responses toColletotrichum gloeosporioidesInfection
Authors: Kim Kwang-Hyung , Yoon Jae-Bok , Park Hyo-Guen , Park Eun Woo , Kim Young Ho
Published: May 2007

Postharvest (detached) and in planta (attached) fruits of pepper plants, Capsicum annuum cv. Jejujaerae (susceptible) and Capsicum baccatum cv. PBC80 (resistant), inoculated with the anthracnose pathogen Colletotrichum gloeosporioides were examined using light, confocal laser scanning, and electron microscopy to compare the cytological differences between the compatible and incompatible interactions. In nonwound inoculation of postharvest pepper fruit, resistant pepper tissues showed a significant increase in the thickness of the cuticle layer compared with that of the susceptible and noninoculated fruit. Cytological features of programmed cell death (PCD) were observed in the resistant pepper fruit with postharvest inoculation, and these were characterized by positive responses to terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling. The oligonucleosomal fragments of DNA were confirmed electrophoretically as DNA laddering. The PCD-positive responses occurred around the inoculation sites early in in planta wound inoculation in the resistant pepper. Nuclear modifications and structural changes of hypersensitivity were also observed in the resistant fruit, including separation of the plasma membrane from the cell wall, dilation of the endoplasmic reticulum, accumulation of electron-dense inclusions in vacuoles, and cytoplasmic vacuolization accompanying fragmentation of the cytoplasm. These structural changes may also implicate PCD-like host responses. In addition, in planta wound inoculation resulted in cell enlargement and cell division during the later stages of infection to form a periderm-like boundary layer around the inoculation site.
Characterization of Two Major Genetic Factors Controlling Quantitative Resistance toMelampsora larici-populinaLeaf Rust in Hybrid Poplars: Strain Specificity, Field Expression, Combined Effects, and Relationship with a Defeated Qualitative Resistance Gene
Authors: Dowkiw A. , Bastien C.
Published: May 2007

Two genetic factors explain a significant proportion of the variability for quantitative resistance to Melampsora larici-populina leaf rust in a Populus deltoides × P. trichocarpa F1progeny. One is inherited from P. deltoides and is associated with a defeated qualitative resistance gene R1, and the other, RUS, is inherited from P. trichocarpa. To assess the potential contribution of these two factors for durable resistance breeding, 284 genotypes from this F1progeny were studied in laboratory experiments with three M. larici-populina strains and in a field experiment under natural inoculum pressure. Results confirmed that both factors can have strong beneficial effects in the laboratory. These effects were strain specific, thus impairing their chances for durability. However, association of both factors led to synergistic effects in most situations. In accordance with good field-laboratory relationships, especially those involving uredinia-size laboratory measurements, field effects of both resistance factors were significant. RUSled to a significant reduction of rust colonization on the most infected leaf in the field, and its effect was significant both in the presence and the absence of R1. In contrast, the presence of R1was useful in the field only when RUSwas absent. The nature of the genetic relationship between both factors remains unknown, but benefits from their association should be quantified over a longer period to evaluate potential adaptation of the pathogen.
Use of Green Fluorescent Protein and Image Analysis to Quantify Proliferation of Trichoderma harzianum in Nonsterile Soil
Authors: Orr K. A. , Knudsen G. R.
Published: May 2007

One drawback of traditional methods for fungal biomass measurement is the inability to distinguish biomass of an introduced fungus from that of the indigenous microbial community in nonsterile soil. We quantified biomass of a specific fungal biological control agent in nonsterile soil using epifluorescence microscopy and image analysis of green fluorescent protein (GFP)-expressing Trichoderma harzianum (ThzID1-M3). Numbers of colony forming units on a semiselective medium were compared with biomass estimates from image analysis, after ThzID1-M3 was incubated in soil that either remained moist (-0.05 MPa) for 14 to 21 days or remained moist for approximately 5 days and then was allowed to dry to <-3.0 MPa. Recovery of significant numbers of ThzID1-M3 propagules lagged approximately 3 days behind initiation of hyphal growth. Reductions in both colony counts and biomass were observed over time when soil was allowed to dry. However, in soil that remained moist, colony counts increased over a 14- to 21-day period even though biomass declined after approximately 3 to 5 days. Our results confirm that use of GFP, along with epifluorescence microscopy, is a useful tool to distinguish active hyphal biomass, the form of the fungus that is functional for biological control, from inactive propagules such as conidia or chlamydospores that are enumerated by plate counts.
Factors Affecting the Spread ofPlum pox virusStrain M in Peach Orchards Subjected to Roguing in France
Authors: Dallot Sylvie , Gottwald Tim , Labonne Gérard , Quiot Jean-Bernard
Published: May 2007

We evaluated the impact of roguing on the spread and persistence of the aggressive Plum pox virus strain M (PPV-M) in 19 peach orchard blocks in Southern France. During a 7- to 10-year period, orchards were visually inspected for PPV symptoms, and symptomatic trees were removed every year. Disease incidence was low in all orchards at disease discovery and was <1% in 16 of the 19 orchard blocks. The spread of Sharka disease was limited in all 19 blocks, with an annual disease incidence between 2 and 6%. However, new symptomatic trees were continuously detected, even after 7 to 10 years of uninterrupted control measures. An extended Cox model was developed to evaluate to what extent tree location, orchard characteristics, environment, and disease status within the vicinity influenced the risk of infection through time. Eleven variables with potential effect on tree survival (i.e., maintenance of a tree in a disease- free status through time) were selected from survey data and databases created using a geographical information system. Area of the orchard, density of planting, distance of a tree from the edge of the orchard block sharing a boundary with another diseased orchard, and distance to the nearest previously detected symptomatic tree had a significant effect on the risk for a tree to become infected through time. The combined results of this study suggest that new PPV-M infections within orchards subjected to roguing resulted from exogenous sources of inoculum, disease development of latent infected trees, as well as infected trees overlooked within the orchards during visual surveys. A revision of the survey and the roguing procedures used for more effective removal of potential sources of inoculum within the orchards and in the vicinity of the orchards would improve disease control suppression of PPV.
Effect of Moisture on Thermal Inactivation of Soilborne Pathogens Under Structural Solarization
Authors: Shlevin Eli , Mahrer Yitzhak , Katan Jaacov
Published: May 2007

Structural solarization of greenhouses for sanitation by closing them involves dry heating to 60°C and higher with a consequent low relative humidity (RH) (≈15%), thus requiring an extended period for thermal inactivation of pathogens. In an attempt to enhance pathogen control by increasing moisture during the hot hours of the day, various regimes of inoculum moistening were studied. However, wetting inoculum of Fusarium oxysporum f. sp. melonis and F. oxysporum f. sp. radicis-lycopersici resulted in less effective pathogen control compared with that of dry heating. Fifty percent effective dose (ED50) values of thermal inactivation of wetted and dry inoculum for the former pathogen were 18 and 7 days, respectively, and for the latter, a respective 9 and 4 days. This was because wetting resulted in inoculum cooling due to evaporation, which eventually led to its drying. A model describing the drying of wet inoculum in a wetted greenhouse, based on the fact that there was an ≈10°C difference between greenhouse and ambient temperatures, was proposed. A double-tent system reduced this difference to 1 to 2°C, reduced moisture loss, and led to improved inoculum inactivation of F. oxysporum f. sp. radicis-lycopersici. Thus, the ED50 value of thermal inactivation was reduced from 15 days to 1 day, because this system provided both high temperature (≈60°C) and high RH (≈100%), resulting in effective wet heating.
Spiral Gradient Dilution, a Rapid Method for Determining Growth Responses and 50% Effective Concentration Values in Fungus-Fungicide Interactions
Authors: Förster Helga , Kanetis Loukas , Adaskaveg James E.
Published: May 2007

A new technique, the spiral gradient dilution method, was evaluated for determining 50% effective concentrations (EC50 values) of fungicides for the inhibition of mycelial growth and conidial germination of various fungi. In this method, an agar medium is plated with a fungicide solution by means of a spiral plater, which applies the fungicide in a 2.5-log dilution in a continuous radial concentration gradient. Fungal inoculum is then placed along radial lines across the gradient. After incubation of the plates, distinct growth shapes were observed in different fungus-fungicide interactions. Mycelial growth responses to increasing fungicide concentrations ranged from abrupt to gradual transitions. Conidial germination responses were similar; in addition, distinct zones of confluent growth, nonconfluent growth, and outlier colonies were also identified, depending on the fungus-fungicide interaction. The fungicide concentration at the radial distance at which 50% reduction of growth or spore germination occurred, compared with growth or germination on unamended media, was calculated by a computer program. EC50 values were obtained for mycelial growth in 22 fungus-fungicide interactions and for conidial germination in five interactions. The fungi evaluated were members of the Zygomycota, Ascomycota, Basidiomycota, and Deuteromycota. Nine fungicides, belonging to six different chemical classes, were tested. EC50 values were compared with those obtained by the traditional agar dilution method. In linear regression analyses of the two methods, the models were highly significant (P < 0.01), and coefficients of determination (r2) were 0.92 for the mycelial growth assays and 0.94 for the conidial germination assays. Regression slopes were not significantly different from 1 (P > 0.05) with optimal program settings in the software. Estimated bias, coefficients of variation, and actual confidence intervals for the regression slope were 13.5%, 6.5%, and 1.14 ± 0.14 for the mycelial growth assays and 7.5%, 14.5%, and 1.08 ± 0.37 for the conidial germination assays. These analyses indicate that the spiral gradient dilution method is accurate and precise compared with the agar dilution method for calculating EC50 values of fungicides in continuous growth responses to fungicide concentration gradients.