bluuebunny/crossref_metadata_2025 huggingface dataset:
Pathogenesis of Alfalfa mosaic virus in Soybean (Glycine max) and Expression of Chimeric Rabies Peptide in Virus-Infected Soybean Plants
Authors: Fleysh Nina , Deka Deepali , Drath Maria , Koprowski Hilary , Yusibov Vidadi
Published: May 2007

Infection of soybean (Glycine max) plants inoculated with particles of Alfalfa mosaic virus (AlMV) isolate 425 at 12 days after germination was monitored throughout the life cycle of the plant (vegetative growth, flowering, seed formation, and seed maturation) by western blot analysis of tissue samples. At 8 to 10 days after inoculation, the upper uninoculated leaves showed symptoms of virus infection and accumulation of viral coat protein (CP). Virus CP was detectable in leaves, stem, roots, seedpods, and seed coat up to 45 days postinoculation (dpi), but only in the seedpod and seed coat at 65 dpi. No virus accumulation was detected in embryos and cotyledons at any time during infection, and no seed transmission of virus was observed. Soybean plants inoculated with recombinant AlMV passaged from upper uninoculated leaves of infected plants showed accumulation of full-length chimeric AlMV CP containing rabies antigen in systemically infected leaves and seed coat. These results suggest the potential usefulness of plants and plant viruses as vehicles for producing proteins of biomedical importance in a safe and inexpensive manner. Moreover, even the soybean seed coat, treated as waste tissue during conventional processing for oil and other products, may be utilized for the expression of value-added proteins.
Pathogenic and Nonpathogenic Lifestyles in Colletotrichum acutatum from Strawberry and Other Plants
Authors: Freeman Stanley , Horowitz Sigal , Sharon Amir
Published: May 2007

Anthracnose is one of the major fungal diseases of strawberry occurring worldwide. In Israel, the disease is caused primarily by the species Colletotrichum acutatum. The pathogen causes black spot on fruit, root necrosis, and crown rot resulting in mortality of transplants in the field. The host range and specificity of C. acutatum from strawberry was examined on pepper, eggplant, tomato, bean, and strawberry under greenhouse conditions. The fungus was recovered from all plant species over a 3-month period but caused disease symptoms only on strawberry. Epiphytic and endophytic (colonization) fungal growth in the different plant species was confirmed by reisolation from leaf tissues and by polymerase chain reaction (PCR)-specific primer amplification. C. acutatum was also isolated from healthy looking, asymptomatic plants of the weed genera Vicia and Conyza. Isolates that were recovered from the weeds caused disease symptoms on strawberry and were positively identified as C. acutatum by PCR. The habitation of a large number of plant species, including weeds, by C. acutatum suggests that, although it causes disease only on strawberry and anemone in Israel, this fungus can persist on many other plant species. Therefore, plants that are not considered hosts of C. acutatum may serve as a potential inoculum source for strawberry infection and permit survival of the pathogen between seasons.
Characterization of a New Subgroup of Rhizoctonia solani Anastomosis Group 1 (AG-1-ID), Causal Agent of a Necrotic Leaf Spot on Coffee
Authors: Priyatmojo Achmadi , Escopalao Verma E. , Tangonan Naomi G. , Pascual Cecilia B. , Suga Haruhisa , Kageyama Koji , Hyakumachi Mitsuro
Published: May 2007

A new foliar disease on coffee leaves was observed in Mindanao, Philippines, in 1996. The symptoms appeared as large circular or irregularly shaped necrotic areas with small circular necrotic spots (1 mm or less in diameter) usually found around the periphery of the large necrotic areas. Rhizoctonia solani was consistently isolated from these diseased coffee leaves. Isolates obtained were multinucleate (3 to 12 nuclei per hyphal cell), had an optimum temperature for hyphal growth at 25°C, prototrophic for thiamine, and anastomosed with tester isolates belonging to R. solani anastomosis group 1 (AG-1). Mature cultures on potato dextrose agar (PDA) were light to dark brown. Sclerotia, light brown to brown, were formed on the surface of PDA and covered the whole mature colony culture. Individual sclerotia often aggregated into large clumps (3 to 8 mm in diameter) and their color was brown to dark brown. In pathogenicity tests, isolates from coffee caused necrotic symptoms on coffee leaves, whereas isolates of AG-1-IA (not isolated from coffee), 1-IB, and 1-IC did not. The results of analyses of restriction fragment length polymorphism of ribosomal DNA internal transcribed spacer, random amplified polymorphism DNA, and fatty acid profiles showed that R. solani isolates from coffee are a population of AG-1 different from AG-1-IA, 1-IB, and 1-IC. These results suggest that R. solani isolates from coffee represent a new subgroup distinct from AG-1-IA, 1-IB, and 1-IC. A new subgroup ID (AG-1-ID) is proposed.
Isolation and Characterization of a Cold-Tolerant Strain of Fusarium proliferatum, a Biocontrol Agent of Grape Downy Mildew
Authors: Bakshi Shlomo , Sztejnberg Abraham , Yarden Oded
Published: May 2007

A cold-tolerant strain of the mycoparasite Fusarium proliferatum was isolated following UV mutagenesis of the G6 strain, which is a biocontrol agent of grape downy mildew. The isolated strain (designated 1505) exhibited radial growth two to threefold that of the parent strain when grown at 13°C, which is generally suboptimal for growth of Fusarium spp., but desirable for its host, Plasmopara viticola. This rapid growth was correlated with improved biological control of P. viticola, determined by a detached-leaf assay. Even though radial growth of strain 1505 at higher temperatures was slower than that of G6 and the strain failed to conidiate, there was no reduction in biocontrol efficacy. Significantly higher levels of extracellular β-glucosidase and endo-1,4-β-glucanase activity were measured in the culture filtrate of strain 1505 relative to that of strain G6. A DNA-mediated transformation procedure that included the introduction of antibiotic resistance and a GUS reporter gene system was adapted for F. proliferatum. Using the GUS-engineered strains, we demonstrated that both G6 and 1505 exhibit the characteristic coiling and penetration of host structures.
Recessive Resistance to Septoria Stem Canker of Hybrid Poplar
Authors: Newcombe George , Ostry Mike
Published: May 2007

Stem canker, caused by Septoria musiva, is the most serious disease limiting intensive hybrid poplar culture in eastern North America. Populus deltoides (D) is itself resistant, but the susceptibility of western black cottonwood, P. trichocarpa (T) is apparently dominant in the F1 generation. To test a hypothesis of recessive inheritance of canker resistance, a three-generation T × D pedigree was deployed in the field in Iowa and Minnesota. In both sites and in keeping with expectations, P. trichocarpa and its F1 hybrids were susceptible to canker, whereas the P. deltoides parent was resistant. In Iowa, 10 of 70 F2 (TD × TD) individuals were free of canker, suggesting that a single recessive gene might control resistance. In the third year in Minnesota, more resistant individuals than expected were seen in the F2 generation and in TD × D and T × TD backcross progenies due to disease escape. By the fifth year, this was no longer an issue, but winter injury may have eliminated many clones. Qualitatively, however, evidence for recessive inheritance of resistance was still obtained. The only canker-free clones were in the TD × D backcross and the F2 generation, the two progenies in which they were expected. However, conclusive evidence that recessive canker resistance is conferred by a single gene was not obtained in this field study.
Rapid and Sensitive Detection of Apple stem pitting virus in Apple Trees Through RNA Amplification and Probing with Fluorescent Molecular Beacons
Authors: Klerks M. M. , Leone G. , Lindner J. L. , Schoen C. D. , van den Heuvel J. F. J. M.
Published: May 2007

Currently, detection of Apple stem pitting virus (ASPV; genus Foveavirus) in apple trees for certification purposes occurs by woody indexing. This method requires a minimum of 12 to 24 weeks in greenhouse testing to up to 2 years in field testing. In this paper, the development of a single tube AmpliDet RNA system for the rapid gel-free detection of ASPV in apple tree tissues is described. The system relies on the specific amplification of the viral RNA by nucleic acid sequence-based amplification and the simultaneous fluorescent detection of the amplification product through molecular beacons. A sensitivity of a minimum of 100 molecules of transcript RNA was obtained by the ASPV-specific AmpliDet RNA. All biologically characterized ASPV isolates from a field trial and 12 of 14 isolates from a plant virus collection were readily detected with this AmpliDet RNA system. In addition, the efficiency of this method for detecting ASPV in ‘Golden Delicious’ and ‘Gravenstein’ apple trees was compared throughout the year with mechanical inoculation onto Nicotiana occidentalis 37B, a candidate indicator for ASPV. This revealed that only AmpliDet RNA consistently detected the virus in bark tissue, irrespective of the season. Season-specific tissues such as buds, petals, and fruits, but not leaves, also were reliable sources for detection of ASPV by the AmpliDet RNA system.
Effect of Host Plant Resistance to Tomato yellow leaf curl virus (TYLCV) on Virus Acquisition and Transmission by Its Whitefly Vector
Authors: Lapidot Moshe , Friedmann Michael , Pilowsky Meir , Ben-Joseph Rachel , Cohen Shlomo
Published: May 2007

The effect that Tomato yellow leaf curl virus (TYLCV)-infected resistant tomato plants may have on virus epidemiology was studied. Four tomato genotypes that exhibit different levels of viral resistance, ranging from fully susceptible to highly resistant, served as TYLCV-infected source plants. Viral acquisition and transmission rates by white-flies following feeding on the different source plants were evaluated. TYLCV transmission rate by whiteflies that had fed on infected source plants 21 days postinoculation (DPI), shortly after the appearance of TYLCV symptoms, was negatively correlated with the level of resistance displayed by the source plant. Therefore, the higher the resistance, the lower the transmission rate. In addition, TYLCV DNA accumulation was shown to be lower in the resistant source plants compared with the susceptible plants. Whitefly survival rate, following feeding on source plants 21 DPI, was similar for all the cultivars tested. Significant differences in whitefly survival were found, however, following feeding on the infected source plants at 35 DPI; here, whitefly survival rate increased with higher levels of resistance displayed by the source plant. At 35 DPI, the susceptible plants had developed severe TYLCV disease symptoms, and transmission rates from these plants were the lowest, presumably due to the poor condition of these plants. Transmission rates from source plants displaying a medium level of resistance level were highest, with rates declining following feeding on source plants displaying higher levels of TYLCV resistance. TYLCV DNA accumulation in whiteflies following feeding on infected source plants at both 21 and 35 DPI was directly correlated with viral DNA accumulation in source plants. Results show that, in essence, the higher the resistance expressed, the less suitable the plant was as a viral source. Consequently, following acquisition from a highly resistant plant, TYLCV transmission by whiteflies will be less efficient.
Spatial Analysis of Lettuce Downy Mildew Using Geostatistics and Geographic Information Systems
Authors: Wu B. M. , van Bruggen A. H. C. , Subbarao K. V. , Pennings G. G. H.
Published: May 2007

The epidemiology of lettuce downy mildew has been investigated extensively in coastal California. However, the spatial patterns of the disease and the distance that Bremia lactucae spores can be transported have not been determined. During 1995 to 1998, we conducted several field- and valley-scale surveys to determine spatial patterns of this disease in the Salinas valley. Geostatistical analyses of the survey data at both scales showed that the influence range of downy mildew incidence at one location on incidence at other locations was between 80 and 3,000 m. A linear relationship was detected between semivariance and lag distance at the field scale, although no single statistical model could fit the semi-variograms at the valley scale. Spatial interpolation by the inverse distance weighting method with a power of 2 resulted in plausible estimates of incidence throughout the valley. Cluster analysis in geographic information systems on the interpolated disease incidence from different dates demonstrated that the Salinas valley could be divided into two areas, north and south of Salinas City, with high and low disease pressure, respectively. Seasonal and spatial trends along the valley suggested that the distinction between the downy mildew conducive and nonconducive areas might be determined by environmental factors.
Agrobacterium-Mediated Transformation of Fusarium oxysporum: An Efficient Tool for Insertional Mutagenesis and Gene Transfer
Authors: Mullins E. D. , Chen X. , Romaine P. , Raina R. , Geiser D. M. , Kang S.
Published: May 2007

Agrobacterium tumefaciens-mediated transformation (ATMT) has long been used to transfer genes to a wide variety of plants and has also served as an efficient tool for insertional mutagenesis. In this paper, we report the construction of four novel binary vectors for fungal transformation and the optimization of an ATMT protocol for insertional mutagenesis, which permits an efficient genetic manipulation of Fusarium oxysporum and other phytopathogenic fungi to be achieved. Employing the binary vectors, carrying the bacterial hygromycin B phosphotrans-ferase gene (hph) under the control of the Aspergillus nidulans trpC promoter as a selectable marker, led to the production of 300 to 500 hygromycin B resistant transformants per 1 × 106 conidia of F. oxysporum, which is at least an order of magnitude higher than that previously accomplished. Transformation efficiency correlated strongly with the duration of cocultivation of fungal spores with Agrobacterium tumefaciens cells and significantly with the number of Agrobacteruium tumefaciens cells present during the cocultivation period (r = 0.996; n = 3; P < 0.01). All transformants tested remained mitotically stable, maintaining their hygromycin B resistance. Growing Agrobacterium tumefaciens cells in the presence of acetosyringone (AS) prior to cocultivation shortened the time required for the formation of transformants but decreased to 53% the percentage of transformants containing a single T-DNA insert per genome. This increased to over 80% when Agrobacterium tumefaciens cells grown in the absence of AS were used. There was no correlation between the average copy number of T-DNA per genome and the colony diameter of the transformants, the period of cocultivation or the quantity of Agrobacterium tumefaciens cells present during cocultivation. To isolate the host sequences flanking the inserted T-DNA, we employed a modified thermal asymmetric interlaced PCR (TAIL-PCR) technique. Utilizing just one arbitrary primer resulted in the successful amplification of desired products in 90% of those transformants analyzed. The insertion event appeared to be a random process with truncation of the inserted T-DNA, ranging from 1 to 14 bp in size, occurring on both the right and left border sequences. Considering the size and design of the vectors described here, coupled with the efficiency and flexibility of this ATMT protocol, it is suggested that ATMT should be regarded as a highly efficient alternative to other DNA transfer procedures in characterizing those genes important for the pathogenicity of F. oxysporum and potentially those of other fungal pathogens.
Antimicrobial Activity of Culture Filtrate of Bacillus amyloliquefaciens RC-2 Isolated from Mulberry Leaves
Authors: Yoshida S. , Hiradate S. , Tsukamoto T. , Hatakeda K. , Shirata A.
Published: May 2007

A potential antagonist, Bacillus amyloliquefaciens strain RC-2, against Colletotrichum dematium, mulberry anthracnose fungus, was obtained from healthy mulberry leaves by in vitro and in vivo screening techniques. Application of culture filtrate of RC-2 inhibited disease on mulberry leaves, indicating that suppression was due to antifungal compounds in the filtrate. Development of mulberry anthracnose on mulberry leaves was inhibited only when the culture filtrate was applied before fungal inoculation, and it was not inhibited by application after inoculation. These results suggest that the antifungal compounds in the filtrate exhibit a preventive effect on the disease. Peptone significantly increased production of the antifungal compounds. The culture filtrate of RC-2 also inhibited the growth of several other phytopathogenic fungi and bacteria, such as Rosellinia necatrix, Pyricularia oryzae, Agrobacterium tumefaciens, and Xanthomonas campestris pv. campestris, in vitro. From the culture filtrate of RC-2, seven kinds of antifungal compounds were isolated by high performance liquid chromatography analysis, and one of the compounds was determined as iturin A2, a cyclic peptide, by nuclear magnetic resonance and fast atom bombardment mass analysis.
Differential Accumulation of Potato virus A and Expression of Pathogenesis-Related Genes in Resistant Potato cv. Shepody upon Graft Inoculation
Authors: Nie Xianzhou , Singh Rudra P.
Published: May 2007

Potato (Solanum tuberosum L.) cv. Shepody is highly resistant to Potato virus A (PVA), yielding no visible symptoms after rub inoculation. In ‘Shepody’ rootstocks graft-inoculated by PVA-infected scions from a susceptible host, we found a resistance consisting of traces of necrosis (necrotic streaks) in stems and chlorosis in newly emerged leaves. The response was temperature dependent, appearing at 15 to 18°C but not at 28 to 31°C. Necrosis was also observed in tubers, appearing first in the bud end and spreading randomly throughout the majority of the tuber. Trace amounts of PVA in plant tissues were detected by a combination of reverse transcription polymerase chain reaction and Southern blot procedures. The virus concentration was significantly higher in visibly necrotic areas than in nonnecrotic areas, suggesting that presence of the necrosis may be concentration dependent. Pathogenesis-related gene expression showed that chitinase A and B, glucanase B, and PR-10a were associated with chlorotic or necrotic symptoms in leaves, stems, and tubers. Gene expression was markedly more evident in tuber tissues than in leaves and stems. Furthermore, generation of oxidants was also observed within the necrotic areas. Although PVA was detected in necrotic areas of tubers, newly emerged plants from the same tubers were PVA-free.
The Effects of Rust and Anthracnose on the Photosynthetic Competence of Diseased Bean Leaves
Authors: Lopes Daniela B. , Berger Richard D.
Published: May 2007

The effects of rust (caused by Uromyces appendiculatus) and anthracnose (caused by Colletotrichum lindemuthianum) and their interaction on the photosynthetic rates of healthy and diseased bean (Phaseolus vulgaris) leaves were determined by gas-exchange analysis, in plants with each disease, grown under controlled conditions. The equation Px/P0= (1 - x)βwas used to relate relative photosynthetic rate (Px/P0) to proportional disease severity (x), where β represents the ratio between virtual and visual lesion. The β values obtained for rust were near one, indicating that the effect of the pathogen on the remaining green leaf area was minimal. The high values of β obtained for anthracnose (8.46 and 12.18) indicated that the photosynthesis in the green area beyond the necrotic symptoms of anthracnose was severely impaired. The impact of anthracnose on bean leaf photosynthesis should be considered in assessments of the proportion of healthy tissue in diseased leaves. The accurate assessment of the healthy portion of the leaf could improve the use of concepts such as healthy leaf area duration and healthy leaf area absorption, which are valuable predictors of crop yield. The equation used to analyze the interaction between rust and anthracnose on the same leaf was Pz= P0(1 - x)βx× (1 - y)βy, where Pzis the relative photosynthetic rate of any given leaf, P0is the maximum relative photosynthetic rate, x is anthracnose severity, y is rust severity, βx is the β value for anthracnose in the presence of rust, and βy is the β value for rust in the presence of anthracnose. From the resulting response surface, no interaction of the two diseases was observed. Dark respiration rate increased on diseased leaves compared with control leaves. The remaining green leaf area of leaves with both diseases was not a good source to estimate net photosynthetic rate because the effect of anthracnose extended far beyond the visual lesions, whereas the effect of rust on photosynthesis was essentially limited to the pustule plus halo.
Infection of Winter Wheat by a β-Glucuronidase-Transformed Isolate of Cephalosporium gramineum
Authors: Douhan G. W. , Murray T. D.
Published: May 2007

Field-grown winter wheat was inoculated with a β-glucuronidase-transformed isolate of Cephalosporium gramineum in two field seasons to elucidate the mode of infection in resistant and susceptible cultivars. Colonization of viable root epidermis and cortical cells occurred as soon as 15 days postinoculation and the pathogen was found in the vascular tissues by 20 days postinoculation, well before freezing soil temperatures occurred. Penetration occurred directly through the root epidermis and through wounds adjacent to emerging secondary roots. The pathogen also penetrated through root cap cells and colonized meristematic tissues near root tips to gain access to the vascular system. Lower stem base colonization was observed where the pathogen penetrated directly through the epidermis, wounds, or senescent tissues. Appressorium-like structures, which appeared to aid penetration of cell walls, were often found within cells of both roots and stems after initial colonization. The mechanisms of resistance were not apparent, but less colonization occurred in resistant than in susceptible cultivars.
Molecular and Physiological Analysis of the Powdery Mildew Antagonist Pseudozyma flocculosa and Related Fungi
Authors: Avis T. J. , Caron S. J. , Boekhout T. , Hamelin R. C. , Bélanger R. R.
Published: May 2007

A number of phenotypic and genotypic characteristics were used to ascertain the identity and diversity of Pseudozyma flocculosa, a natural antagonist of powdery mildews that has received little attention in terms of taxonomy. To this end, several putative isolates of P. flocculosa as well as several closely related species were analyzed. Ribosomal DNA sequences distinguished P. flocculosa from other Pseudozyma spp. and identified two previously unknown Pseudozyma isolates as P. flocculosa. Random amplified microsatellites revealed three distinct P. flocculosa strains among the tested isolates. Biocontrol properties and antifungal metabolite production were limited to the P. flocculosa spp. Results produced useful molecular markers to (i) distinguish P. flocculosa from other related fungi, (ii) identify different strains within this species, and (iii) aid in the construction of isolate-specific molecular tools that will assist in research and development of P. flocculosa as a biocontrol agent of powdery mildew fungi.
Partial Genome Organization, Identification of the Coat Protein Gene, and Detection ofGrapevine leafroll-associated virus-5
Authors: Good Xin , Monis Judit
Published: May 2007

The genome of Grapevine leafroll-associated virus-5 (GLRaV-5) was cloned, and the sequence of 4766 nt was determined. Degenerate oligonucleotide primers designed from the conserved closterovirus heat shock 70 protein (HSP 70) homologue were used to obtain viral-specific sequences to anchor the cloning of the viral RNA with a genomic walking approach. The partial nucleotide (nt) sequence of GLRaV-5 showed the presence of four open reading frames (ORF A through D), potentially coding for the HSP 70 homologue (ORF A); a 51-kDa protein of unknown function with similarity to GLRaV-3 p55 (ORF B); the viral capsid protein (ORF C); and a diverged viral duplicate capsid protein (ORF D). The ORF C was identified as GLRaV-5 viral capsid protein based on sequence analyses and the reactivity of the recombinant protein to GLRaV-5 specific antibodies by western blot analyses. The antiserum produced with the in vitro-expressed GLRaV-5 ORF C protein product specifically reacted with a 36-kDa polypeptide from GLRaV-5 infected vines but did not react with protein extracts from vines infected with other GLRaVs or uninfected vines. Furthermore, specific primers were designed for the sensitive detection of GLRaV-1 and GLRaV-5 by polymerase chain reaction.
Bacterial Populations Associated with Rice Seed in the Tropical Environment
Authors: Cottyn B. , Regalado E. , Lanoot B. , De Cleene M. , Mew T. W. , Swings J.
Published: May 2007

During the 1995 wet season, harvested rice seed was collected from farmers' fields at different locations in Iloilo, Philippines. Bacterial isolations from crushed seed yielded 428 isolates. The isolates were characterized by BOX-polymerase chain reaction fingerprinting of total genomic DNA and represented 151 fingerprint types (FPT). Most FPTs were found on a single occasion, although matching fingerprints for isolates from different samples also were found. Identifications were made by cellular fatty acid methyl ester analysis and additional use of Biolog GN/GP MicroPlates and API 20E/50CHE systems. The predominant bacteria were Enterobacteriaceae (25%), Bacillus spp. (22%), and Pseu-domonas spp. (14%). Other bacteria regularly present were identified as Xanthomonas spp., Cellulomonas flavigena, and Clavibacter michiganense. Of the total number of isolated bacteria, 4% exhibited in vitro antifungal activity against Rhizoctonia solani or Pyricularia grisea. Two percent of isolates were pathogens identified as Burkholderia glumae and Burkholderia gladioli. Five percent of isolates induced sheath necrosis on only 50 to 90% of inoculated plants and were related to Bacillus pumilus, Paenibacillus spp., Pseudomonas spp., and Pantoea spp.
Virulence and Molecular Diversity in Cochliobolus sativus
Authors: Zhong Shaobin , Steffenson Brian J.
Published: May 2007

Spot blotch, caused by the fungal pathogen Cochliobolus sativus, is an important disease of barley in many production areas of the world. To assess genetic diversity in this pathogen, a worldwide collection of C. sativus isolates was evaluated for virulence on barley and DNA polymorphism. Three pathotypes (0, 1, and 2) were identified among the 22 isolates tested in this study and the 36 isolates characterized previously on three barley differentials (ND5883, Bowman, and NDB112) that differ in their resistance to C. sativus. Pathotype 2, which exhibits high virulence on cv. Bowman, was only found in North Dakota, whereas the other two pathotypes occurred in many other regions of the world. Genetic diversity of the 58 C. sativus isolates, together with isolates of three related pathogenic Cochliobolus spp. (C. heterostrophus, C. carbonum, and C. victoriae) was analyzed using amplified fragment length polymorphism (AFLP) markers. A total of 577 polymorphic AFLP markers were recorded among the 70 isolates of the four Cochliobolus spp. using eight primer combinations. Cluster analysis revealed distinct groups corresponding to the four different species, except in one case where race 0 of C. carbonum was placed in an outgroup that may belong to a different species. In C. sativus, 95 polymorphic AFLP markers were detected with the eight primer pairs used, and each isolate exhibited a unique AFLP pattern. Allelic diversity in the pathotype 2 group was lower (0.10) than in the pathotype 0 (0.23) and pathotype 1 (0.15) groups, indicating that pathotype 2 may have arisen more recently. Cluster analysis did not reveal a close correlation between pathotypes and AFLP groups, although two AFLP markers unique to pathotype 2 isolates were identified. This low correlation suggests that genetic exchange may have occurred through parasexual recombination in the fungal population. Some isolates collected from different regions of the world were clustered into the same AFLP group, suggesting that migration of the fungal pathogen around these regions has occurred.
Probabilities for Profitable Fungicide Use Against Gray Leaf Spot in Hybrid Maize
Authors: Munkvold G. P. , Martinson C. A. , Shriver J. M. , Dixon P. M.
Published: May 2007

Gray leaf spot, caused by the fungus Cercospora zeae-maydis, causes considerable yield losses in hybrid maize grown in the north-central United States and elsewhere. Nonchemical management tactics have not adequately prevented these losses. The probability of profitably using fungicide application as a management tool for gray leaf spot was evaluated in 10 field experiments under conditions of natural inoculum in Iowa. Gray leaf spot severity in untreated control plots ranged from 2.6 to 72.8% for the ear leaf and from 3.0 to 7.7 (1 to 9 scale) for whole-plot ratings. In each experiment, fungicide applications with propiconazole or mancozeb significantly reduced gray leaf spot severity. Fungicide treatment significantly (P ≤ 0.05) increased yield by as much as 1.65 t/ha with a single propiconazole application. There were significant (P < 0.05) correlations between gray leaf spot severity and yield. We used a Bayesian inference method to calculate for each experiment the probability of achieving a positive net return with one or two propiconazole applications, based on the mean yields and standard deviations for treated and untreated plots, the price of grain, and the costs of the fungicide applications. For one application, the probability ranged from approximately 0.06 to more than 0.99, and exceeded 0.50 in six of nine scenarios (specific experiment/hybrid). The highest probabilities occurred in the 1995 experiments with the most susceptible hybrid. Probabilities were almost always higher for a single application of propiconazole than for two applications. These results indicate that a single application of propiconazole frequently can be profitable for gray leaf spot management in Iowa, but the probability of a profitable application is strongly influenced by hybrid susceptibility. The calculation of probabilities for positive net returns was more informative than mean separation in terms of assessing the economic success of the fungicide applications.
Role of Iron in Rhizobacteria-Mediated Induced Systemic Resistance of Cucumber
Authors: Press C. M. , Loper J. E. , Kloepper J. W.
Published: May 2007

Seed treatment with the rhizosphere bacterium Serratia marcescens strain 90-166 suppressed anthracnose of cucumber, caused by Colleto-trichum orbiculare, through induced systemic resistance (ISR). When the iron concentration of a planting mix was decreased by addition of an iron chelator, suppression of cucumber anthracnose by strain 90-166 was significantly improved. Strain 90-166 produced 465 ± 70 mg/liter of catechol siderophore, as determined by the Rioux assay in deferrated King's medium B. The hypothesis that a catechol siderophore produced by strain 90-166 may be responsible for induction of systemic resistance by this strain was tested by evaluating disease suppression by a mini-Tn5-phoA mutant deficient in siderophore production. Sequence analysis of genomic DNA flanking the mini-Tn5-phoA insertion identified the target gene as entA, which encodes an enzyme in the catechol siderophore biosynthetic pathways of several bacteria. Severity of anthracnose of cucumbers treated with the entA mutant was not significantly different (P = 0.05) from the control, whereas plants treated with wild-type 90-166 had significantly less disease (P = 0.05) than the control. Total (internal and external) population sizes of 90-166 and the entA mutant on roots did not differ significantly (P = 0.05) at any sample time, whereas internal population sizes of the entA mutant were significantly lower (P = 0.05) than those of the wild-type strain at two sampling times. These data suggest that catechol siderophore biosynthesis genes in Serratia marcescens 90-166 are associated with ISR but that this role may be indirect via a reduction in internal root populations.
Phylogenetic Analysis of Cercospora and Mycosphaerella Based on the Internal Transcribed Spacer Region of Ribosomal DNA
Authors: Goodwin Stephen B. , Dunkle Larry D. , Zismann Victoria L.
Published: May 2007

Most of the 3,000 named species in the genus Cercospora have no known sexual stage, although a Mycosphaerella teleomorph has been identified for a few. Mycosphaerella is an extremely large and important genus of plant pathogens, with more than 1,800 named species and at least 43 associated anamorph genera. The goal of this research was to perform a large-scale phylogenetic analysis to test hypotheses about the past evolutionary history of Cercospora and Mycosphaerella. Based on the phylogenetic analysis of internal transcribed spacer (ITS) sequence data (ITS1, 5.8S rRNA gene, ITS2), the genus Mycosphaerella is monophyletic. In contrast, many anamorph genera within Mycosphaerella were polyphyletic and were not useful for grouping species. One exception was Cercospora, which formed a highly supported monophyletic group. Most Cercospora species from cereal crops formed a subgroup within the main Cercospora cluster. Only species within the Cercospora cluster produced the toxin cercosporin, suggesting that the ability to produce this compound had a single evolutionary origin. Intraspecific variation for 25 taxa in the Mycosphaerella clade averaged 1.7 nucleotides (nts) in the ITS region. Thus, isolates with ITS sequences that differ by two or more nucleotides may be distinct species. ITS sequences of groups I and II of the gray leaf spot pathogen Cercospora zeae-maydis differed by 7 nts and clearly represent different species. There were 6.5 nt differences on average between the ITS sequences of the sorghum pathogen Cercospora sorghi and the maize pathogen Cercospora sorghi var. maydis, indicating that the latter is a separate species and not simply a variety of Cercospora sorghi. The large monophyletic Mycosphaerella cluster contained a number of anamorph genera with no known teleomorph associations. Therefore, the number of anamorph genera related to Mycosphaerella may be much larger than suspected previously.
Biological Control of the Root-Knot Nematode Meloidogyne javanica by Trichoderma harzianum
Authors: Sharon E. , Bar-Eyal M. , Chet I. , Herrera-Estrella A. , Kleifeld O. , Spiegel Y.
Published: May 2007

The fungal biocontrol agent, Trichoderma harzianum, was evaluated for its potential to control the root-knot nematode Meloidogyne javanica. In greenhouse experiments, root galling was reduced and top fresh weight increased in nematode-infected tomatoes following soil pretreatment with Trichoderma peat-bran preparations. The use of a proteinase Prb1-transformed line (P-2) that contains multiple copies of this gene improved biocontrol activity in the greenhouse experiments compared with the nontransformed wild-type strain (WT). All the Trichoderma strains showed the ability to colonize M. javanica-separated eggs and second-stage juveniles (J2) in sterile in vitro assays, whereas P-2 also penetrated the egg masses. This protease-transformed line presented the same nematicidal and overall proteolytic activity as the WT in in vitro tests in which concentrated soil extracts from Trichoderma-treated soils immobilized the infective J2. However, the J2 immobilization and proteolytic activities of both P-2 and the WT were higher than those obtained with strain T-203. Characterization of the activity of all Trichoderma strains soil extracts on J2 showed that it was heat resistant and restricted to the low-molecular-weight fraction (less than 3 kDa). It is suggested that improved proteolytic activity of the antagonist may be important for the biological control of the nematodes.
Steps in Predicting the Relationship of Yield on Fungicide Dose
Authors: Paveley N. D. , Sylvester-Bradley R. , Scott R. K. , Craigon J. , Day W.
Published: May 2007

A set of hypothetical steps has been defined, which links fungicide dose to marketable yield, whereby (i) increasing dose decreases symptom area, according to a dose-response curve, (ii) decreased symptom area increases crop green area index (GAI), (iii) increasing GAI increases fractional interception of photosynthetically active radiation, (iv) increased fractional interception increases crop dry matter accumulation, and (v) yield increases, depending on the partitioning of dry matter to the marketable fraction. One equation represented all five steps. By integrating this equation for light interception during the yield forming period and differentiating with respect to the ratio of fungicide cost over yield value, an analytical solution was obtained for the economic optimum dose. Taking published ranges of parameter values for the Septoria tritici wheat pathosystem as an example, yield-response curves and optimum doses were biologically plausible when compared with data from four field experiments. The analytical and empirical results imply that the dose required to optimize economic return will vary substantially between sites, seasons, and cultivars. Sensitivity analyses identified parameters describing specific facets of disease severity, fungicide efficacy, and assimilate partitioning as most influential in determining the dose optimum.
Simultaneous Temporal Progress of Sorghum Anthracnose and Leaf Blight in Crop Mixtures with Disparate Patterns
Authors: Ngugi H. K. , King S. B. , Holt J. , Julian A. M.
Published: May 2007

Field studies were conducted at Alupe in western Kenya in 1995 and 1996 to evaluate the efficacy of crop and species mixtures for the management of sorghum anthracnose (caused by Colletotrichum sublineolum) and leaf blight (caused by Exserohilum turcicum). The progress of these diseases developing simultaneously on a susceptible sorghum cultivar planted in inter- or intra-row mixtures of varying proportions with either maize or resistant sorghum was monitored. The effects of host type and mixture patterns on disease progress were compared by parameter estimates derived from fitted Lotka-Volterra competition equations and nonlinear logistic models. Competition coefficients were not significant and their confidence intervals included zero in most cases, suggesting that interactions between C. sublineolum and E. turcicum did not occur. Mixtures of the susceptible sorghum with either the nonhost maize or the resistant sorghum delayed the time when disease is first observed and reduced the rate of disease progress and carrying capacity for both anthracnose and leaf blight, with a more pronounced effect on the latter disease. The lower efficacy of mixtures in reducing anthracnose was attributed to an aggregated spatial pattern, coupled with higher rates of progress for this disease. Intra-row mixtures were more efficient than inter-row mixtures in reducing disease development in all years. The implications of these observations for the management of sorghum diseases under small-scale farming systems are discussed.
Variation in Transmission Efficiency Among Barley yellow dwarf virus-RMV Isolates and Clones of the Normally Inefficient Aphid Vector, Rhopalosiphum padi
Authors: Lucio-Zavaleta E. , Smith D. M. , Gray S. M.
Published: May 2007

The RMV strain of Barley yellow dwarf virus (BYDV-RMV) is an unassigned member of the Luteoviridae that causes barley yellow dwarf in various cereal crops. The virus is most efficiently vectored by the aphid Rhopalosiphum maidis, but can also be vectored with varying efficiency by R. padi and Schizaphis graminum. Field collections of alate aphids migrating into the emerging winter wheat crop in the fall of 1994 in central New York identified a high proportion of R. padi transmitting BYDV-RMV. This prompted a comparison of the BYDV-RMV isolates and the R. padi populations found in the field with type virus and aphid species maintained in the laboratory. A majority of the field isolates of BYDV-RMV were similar to each other and to the type BYDV-RMV isolate in disease severity on oat and in transmission by the laboratory-maintained population of R. maidis and a field-collected population of R. maidis. However, several field populations of R. padi differed in their ability to transmit the various BYDV-RMV isolates. The transmission efficiency of the R. padi clones was increased if acquisition and inoculation feeding periods were allowed at higher temperatures. In addition, the transmission efficiency of BYDV-RMV was significantly influenced by the aphid that inoculated the virus source tissue. In general, BYDV-RMV transmission by R. padi was higher when R. padi was the aphid that inoculated the source tissue than when R. maidis was the inoculating aphid. The magnitude of the change varied among virus isolates and R. padi clones. These results indicate that, under certain environmental conditions, R. padi can play a significant role in the epidemiology of BYDV-RMV. This may be especially significant in regions where corn is a major source of virus and of aphids that can carry virus into a fall-planted wheat crop.
Influence of Temperature and Inoculum Density of Fusarium oxysporum f. sp. ciceris on Suppression of Fusarium Wilt of Chickpea by Rhizosphere Bacteria
Authors: Landa Blanca B. , Navas-Cortés Juan A. , Hervás Ana , Jiménez-Díaz Rafael M.
Published: May 2007

The effects of temperature and inoculum density of Fusarium oxysporum f. sp. ciceris race 5 on suppression of Fusarium wilt in chickpea (Cicer arietinum) cv. PV 61 by seed and soil treatments with rhizobacteria isolated from the chickpea rhizosphere were studied in a model system. Disease development over a range of temperatures (20, 25, and 30°C) and inoculum densities (25 to 1,000 chlamydospores per gram of soil) was described by the Gompertz model. The Gompertz relative rate of disease progress and final amount of disease increased exponentially and monomolecularly, respectively, with increasing inoculum densities. Disease development was greater at 25°C compared with 20 and 30°C. At 20 and 30°C, disease development was greater at 250 to 1,000 chlamydospores per gram of soil compared with 25 to 100 chlamydospores per gram of soil. At 25°C, increasing inoculum densities of the pathogen did not influence disease. Nineteen Bacillus, Paenibacillus, Pseudomonas, and Stenotrophomonas spp. out of 23 bacterial isolates tested inhibited F. oxysporum f. sp. ciceris in vitro. Pseudomonas fluorescens RGAF 19 and RG 26, which did not inhibit the pathogen, showed the greatest Fusarium wilt suppression. Disease was suppressed only at 20 or 30°C and at inoculum densities below 250 chlamydospores per gram of soil. Bacterial treatments increased the time to initial symptoms, reduced the Gompertz relative rate of disease progress, and reduced the overall amount of disease developed.
Effects of Cellulytic Enzymes on Phytophthora cinnamomi
Authors: Downer A. J. , Menge J. A. , Pond E.
Published: May 2007

Two enzyme systems, cellulase (β-1,4-glucanase) and laminarinase (β-1,3-glucanase), were added to soil extracts to simulate (in vitro) lytic components found in mulches suppressive to Phytophthora cinnamomi. Concentration ranges of each enzyme were incubated with Phytophthora cinnamomi mycelium, zoospores, zoospores cysts, and zoospore-infected excised roots to evaluate the roles of each enzyme in potential control of avocado root rot disease. Cellulase significantly retarded the development of zoosporangia and chlamydospores when mycelia were incubated in soil extract containing the enzyme at concentrations greater than 10 units/ml. Zoospore production was also reduced by cellulase but not by laminarinase. Laminarinase had little effect on zoosporangia or chlamydospore formation. At high concentrations, laminarinase was consistently more effective at preventing encystment than cellulase. Chlamydospores preformed in root tips were immune to the lytic effects of all treatments except cellulase at 100 units/ml. Zoospores placed in enzyme solutions and plated on a selective medium survived high cellulase concentrations and formed colonies, but there were fewer surviving zoospores when laminarinase was present at greater than 10 units/ml. Low concentrations of cellulase stimulated infection of excised roots, however, low concentrations of laminarinase prevented infection. Cellulase and laminarinase have different effects on the structures of the Phytophthora cinnamomi life history, however, each enzyme may have a role in reduction of inoculum.
Aspergillus flavus and Aflatoxin Contamination of Leguminous Trees of the Sonoran Desert in Arizona
Authors: Boyd María L. , Cotty Peter J.
Published: May 2007

Aspergillus spp. in section Flavi were frequently associated with desert tree legumes in uncultivated areas of the Sonoran Desert. Of 270 samples of debris and fruits of mesquite (Prosopis spp.), ironwood (Olneya tesota), acacia (Acacia spp.), and palo verde (Cercidium and Parkinsonia spp.), 87% were positive for A. flavus (S and L strains) and A. tamarii. A. flavus was the most common species (87%) among the 3,763 isolates examined. Mesquite pods were both the substrate from which A. flavus was recovered most frequently and the substrate from native habitats with the greatest aflatoxin content. In vitro, most desert legumes supported significant growth, reproduction, and aflatoxin production by A. flavus, with mesquite pods yielding 1 × 1010 propagules/g and 5,000 μg/kg of aflatoxin B1. Twenty percent of legume pods collected in the desert contained measurable quantities of aflatoxin, ranging from 1 to >2,500 μg/kg. Insect-damaged mesquite pods had significantly higher aflatoxin than intact pods. Legumes are apparently important reservoirs of aflatoxin-producing fungi and significant sources of aflatoxin contamination in the native Sonoran Desert habitats of Arizona.
Sources and Origin of Resistance toXanthomonas campestrispv.campestrisinBrassicaGenomes
Authors: Taylor J. D. , Conway J. , Roberts S. J. , Astley D. , Vicente J. G.
Published: May 2007

Two hundred and seventy-six accessions of mainly Brassica spp. were screened for resistance to Xanthomonas campestris pv. campestris races. In Brassica oleracea (C genome), the majority of accessions were susceptible to all races, but 43% showed resistance to one or more of the rare races (2, 3, 5, and 6) and a single accession showed partial resistance to races 1, 3, 5, and 6. Further searches for resistance to races 1 and 4, currently the most important races worldwide, and race 6, the race with the widest host range, were made in accessions representing the A and B genomes. Strong resistance to race 4 was frequent in B. rapa (A genome) and B. napus (AC genome), indicating an A genome origin. Resistance to races 1 and 4 was present in a high proportion of B. nigra (B genome) and B. carinata (BC genome) accessions, indicating a B genome origin. B. juncea (AB genome) was the most resistant species, showing either strong resistance to races 1 and 4 or quantitative resistance to all races. Potentially race-nonspecific resistance was also found, but at a lower frequency, in B. rapa, B. nigra, and B. carinata. The combination of race-specific and race-nonspecific resistance could provide durable control of black rot of crucifers.