bluuebunny/crossref_metadata_2025 huggingface dataset:
Evolution of Fusarium oxysporum f. sp. vasinfectum Races Inferred from Multigene Genealogies
Authors: Skovgaard Kerstin , Nirenberg Helgard I. , O'Donnell Kerry , Rosendahl Søren
Published: May 2007

Fusarium wilt of cotton is a serious fungal disease responsible for significant yield losses throughout the world. Evolution of the causal organism Fusarium oxysporum f. sp. vasinfectum, including the eight races described for this specialized form, was studied using multigene genealogies. Partial sequences of translation elongation factor (EF-1α), nitrate reductase (NIR), phosphate permase (PHO), and the mitochondrial small subunit (mtSSU) rDNA were sequenced in 28 isolates of F. oxysporum f. sp. vasinfectum selected to represent the global genetic diversity of this forma specialis. Results of a Wilcoxon Signed-Ranks Templeton test indicated that sequences of the four genes could be combined. In addition, using combined data from EF-1α and mtSSU rDNA, the phylogenetic origin of F. oxysporum f. sp. vasinfectum within the F. oxysporum complex was evaluated by the Kishino-Hasegawa likelihood test. Results of this test indicated the eight races of F. oxysporum f. sp. vasinfectum appeared to be nonmonophyletic, having at least two independent, or polyphyletic, evolutionary origins. Races 3 and 5 formed a strongly supported clade separate from the other six races. The combined EF-1α, NIR, PHO, and mtSSU rDNA sequence data from the 28 isolates of F. oxysporum f. sp. vasinfectum recovered four lineages that correlated with differences in virulence and geographic origin: lineage I contained race 3, mostly from Egypt, and race 5 from Sudan; lineage II contained races 1, 2, and 6 from North and South America and Africa; lineage III contained race 8 from China; and lineage IV contained isolates of races 4 and 7 from India and China, respectively.
Development of Colletotrichum gloeosporioides Restriction Enzyme-Mediated Integration Mutants as Biocontrol Agents Against Anthracnose Disease in Avocado Fruits
Authors: Yakoby N. , Zhou R. , Kobiler I. , Dinoor A. , Prusky D.
Published: May 2007

Reduced-pathogenicity mutants of the avocado fruit pathogen Colletotrichum gloeosporioides isolate Cg-14 (teleomorph: Glomerella cingulata) were generated by insertional mutagenesis by restriction enzyme-mediated integration (REMI) transformation. Following seven transformations, 3,500 hygromycin-resistant isolates were subjected to a virulence assay by inoculation on mesocarp and pericarp of cv. Fuerte avocado fruits. Fourteen isolates showed a reduced degree of virulence relative compared with wild-type Cg-14. Two isolates, Cg-M-142 and Cg-M-1150, were further characterized. Cg-M-142 produced appressoria on avocado pericarp similar to Cg-14, but caused reduced symptom development on the fruit's pericarp and mesocarp. Isolate Cg-M-1150 did not produce appressoria; it caused much reduced maceration on the mesocarp and no symptoms on the pericarp. Southern blot analysis of Cg-M-142 and Cg-M-1150 showed REMI at different XbaI sites of the fungal genome. Pre-inoculation of avocado fruit with Cg-M-142 delayed symptom development by the wild-type isolate. Induced resistance was accompanied by an increase in the levels of preformed antifungal diene, from 760 to 1,200 μg/g fresh weight 9 days after inoculation, whereas pre-inoculation with Cg-M-1150 did not affect the level of antifungal diene, nor did it delay the appearance of decay symptoms. The results presented here show that reduced-pathogenicity isolates can be used for the biological control of anthracnose caused by C. gloeosporioides attack.
A Model of the Effect of Pseudothecia on Genetic Recombination and Epidemic Development in Populations of Mycosphaerella graminicola
Authors: Eriksen L. , Shaw M. W. , Østergård H.
Published: May 2007

It is generally agreed that ascospores are the origin of primary infections for the disease septoria tritici blotch of wheat caused by the fungus Mycosphaerella graminicola (anamorph Septoria tritici). The epidemic during the growing season was previously ascribed to the asexual pycni-diospores dispersed over short distances by rain splash, but recent observations suggest that the airborne ascospores also may play a role. As a consequence, the composition of the pathogen population over the growing season may change through genetic recombination. In an attempt to resolve the relative importance of the two spore types to the epidemic over the growing season, a model simulating disease caused by both types of spores was constructed and analyzed. The conclusion from the analysis of this model is that sexual recombination will affect the genetic composition of the population during a growing season. A considerable proportion of spores released at the end of the growing season may be sexual descendants of the initial population. However, ascospores are unlikely to affect the severity of the epidemic during the growing season. This is due to the much longer latent period for pseudothecia compared with pycnidia, resulting in ascospores being produced too late to influence the epidemic.
Cytological Karyotyping of Three Cochliobolus spp. by the Germ Tube Burst Method
Authors: Tsuchiya Dai , Taga Masatoki
Published: May 2007

Cytological karyotypes with mitotic metaphase chromosomes were analyzed for Cochliobolus heterostrophus, C. carbonum, and C. sativus by the germ tube burst method (GTBM). Prior to karyotyping, procedures of GTBM suitable to Cochliobolus were established by examining several crucial conditions such as incubation period of conidia. The estimated chromosome numbers of C. heterostrophus and C. carbonum were n = 15 or 16 and n = 13 or 15 depending on the strains, respectively. In C. sativus, n = 15 was estimated. Morphological information of chromosomes including chromosome size and a threadlike-specific structure representing the nucleolar organizing region was also obtained. Our results for some standard strains are in agreement with previous estimates by pulsed field gel electrophoresis (PFGE) or PFGE coupled with restriction fragment length polymorphism genetic linkage analysis, but inconsistent with the previous estimates for other strains by conventional light microscopic cytology. Additionally, PFGE analysis of C. heterostro-phus strains indicated that chromosome number was not determinable solely by PFGE, which is hampered by comigration and clumping of DNA bands.
A Molecular Marker Correlated with Selected Virulence Against the Tomato Resistance Gene Mi in Meloidogyne incognita, M. javanica, and M. arenaria
Authors: Xu Jianhua , Narabu Takashi , Mizukubo Takayuki , Hibi Tadaaki
Published: May 2007

Root-knot nematodes of the genus Meloidogyne are economically important pathogens of a wide range of crops. The tomato resistance gene Mi typically confers resistance to the three major species, M. incognita, M. javanica, and M. arenaria. However, virulent populations completely overcoming the Mi resistance still occur. In an attempt to develop molecular markers for virulence against Mi and gain insights into the genetic relationships among virulent populations of different species and origins, random amplified polymorphic DNA (RAPD) analyses of laboratory-selected virulent, field virulent, and avirulent populations of M. incognita, M. javanica, and M. arenaria were carried out. A RAPD marker, specific for selected virulent populations, was identified, and subsequently, converted to a sequence characterized amplified region (SCAR). Sequence characterization of the SCAR locus showed that alleles from laboratory- and field-selected virulent populations were highly similar to each other and clearly different from alleles from natural virulent and avirulent populations. This result suggests that the genetic mechanism for virulence against Mi may be similar among selected virulent populations of the three Meloidogyne spp., but different between selected and natural virulent populations. Based on the nucleotide polymorphisms at the SCAR locus, codominant and dominant polymerase chain reaction-based markers were developed enabling rapid diagnosis of selected virulent genotypes in M. incognita, M. javanica, and M. arenaria.
Postinfection Biological Control of Oomycete Pathogens of Pea by Burkholderia cepacia AMMDR1
Authors: Heungens K. , Parke J. L.
Published: May 2007

Burkholderia cepacia AMMDR1 is a biocontrol agent that reduces Pythium damping-off and Aphanomyces root rot severity on peas in the field. We studied the effect of B. cepacia AMMDR1 on post-infection stages in the life cycles of these pathogens, including mycelial colonization of the host, production of oogonia, and production of secondary zoospore inoculum. We used Burkholderia cepacia 1324, a seed and rootcolonizing but antibiosis-deficient Tn5 mutant of B. cepacia AMMDR1, to study mechanisms of biological control other than antibiosis. B. cepacia AMMDR1 significantly reduced Pythium aphanidermatum postinfection colonization and damping-off of pea seeds, even when the bacteria were applied 12 h after zoospore inoculation. B. cepacia AMMDR1 also significantly reduced colonization of taproots by Aphanomyces euteiches mycelium, but only when the bacteria were applied at high population densities at the site of zoospore inoculation. The antibiosisdeficient mutant, B. cepacia 1324, had no effect on mycelial colonization of seeds or roots by Pythium aphanidermatum nor A. euteiches, suggesting that antibiosis is the primary mechanism of biological control. B. cepacia AMMDR1, but not B. cepacia 1324, reduced production of A. euteiches oogonia. This effect occurred even when the population size of B. cepacia AMMDR1 was too small to cause a reduction in lesion length early on in the infection process and may result from in situ antibiotic production. B. cepacia AMMDR1 had no effect on the production of secondary zoospores of A. euteiches from infected roots. The main effects of B. cepacia AMMDR1 on postinfection stages in the life cycles of these pathogens therefore were reductions in mycelial colonization by Pythium aphanidermatum and in formation of oogonia by A. euteiches. No mechanism other than antibiosis could be identified.
Universally Primed Polymerase Chain Reaction Alleles and Internal Transcribed Spacer Restriction Fragment Length Polymorphisms Distinguish Two Subgroups in Botrytis aclada Distinct from B. byssoidea
Authors: Nielsen K. , Justesen A. F. , Jensen D. Funck , Yohalem D. S.
Published: May 2007

Fifty-one isolates representing the four Botrytis spp. associated with onion neck rot were clustered by unweighted pair group method with arithmetic mean based on universal-primed polymerase chain reaction (UP-PCR) fingerprints. Bootstrap analysis of the consensus phenogram clearly demonstrated five strong clusters among the four Botrytis spp.: B. cinerea (C), B. squamosa (S), B. byssoidea (B), and B. aclada (AI and AII). Subdivision of the 30 B. aclada isolates, AI (14) and AII (16), from Europe, Egypt, North America, and Japan was further supported by restriction analysis of the internal transcribed spacer of the ribosomal genes and spore size measurements. Gene diversities (H) among AI and AII isolates were very low (0.007 and 0.043, respectively). A likelihood ratio chi-square test (G2) of Nei's coefficient of genetic differentiation (GST) showed that both B. aclada subgroups, AI and AII, were significantly different from B. byssoidea (P < 0.001), and that B. aclada subgroups AI and AII were significantly different from each other (P < 0.001). No UP-PCR alleles were shared by AI and B. byssoidea isolates, whereas 10 and 12 alleles were shared by AI:AII and AII:B. byssoidea, respectively. The hypothesis that AII may be a hybrid between AI and B. byssoidea is discussed.
Relationships Between Tillage and Spatial Patterns of Heterodera glycines
Authors: Gavassoni Walber L. , Tylka Gregory L. , Munkvold Gary P.
Published: May 2007

The dynamics of Heterodera glycines spatial patterns were studied under different tillage systems in two naturally infested soybean fields in Iowa from 1994 to 1997. At each location, there were four different tillage treatments (conventional tillage, reduced tillage, ridge tillage, and no tillage). Soil samples were taken from 98 contiguous quadrats (5.2 m2) per plot in the fall of 1994, before any tillage was performed, and in the spring of the following 3 years shortly after planting. Cysts were extracted from soil samples by elutriation and counted, and eggs were extracted from cysts and enumerated. Spatial patterns of H. glycines populations were characterized by geostatistical analysis and variance-to-mean (VM) ratios. Semivariance values were calculated for cyst and egg densities and semivariograms were constructed. In general, there was greater spatial dependence among cyst populations than egg populations. In one field with a strongly aggregated initial H. glycines population, tillage practices resulted in changes in spatial patterns of H. glycines populations, characterized by spherical-model semivariogram parameters (sill, nugget effect, and range of spatial dependence). These parameters indicated increasing aggregation over time in no tillage and ridge tillage treatments, but decreasing aggregation in reduced and conventional tillage treatments. There was an increase of 350% in sill values (maximum semivariance) for cyst populations after 3 years of no tillage, but in the conventional tillage treatment, sill values remained unchanged or decreased over time as tillage was implemented. Semivariograms for cyst and egg population densities revealed strong anisotropy (directional spatial dependence) along soybean rows, coincident with the direction of tillage practices. VM ratios for cyst counts increased each year in the no tillage and ridge tillage treatments, but decreased for 2 years in reduced tillage and conventional tillage treatments. Final VM ratios for cyst and egg counts were highest in the no tillage treatment. In a second field, with low initial aggregation of H. glycines populations, there was little measurable change in semivariogram parameters after 3 years of no tillage, but in the conventional tillage treatment, populations became less aggregated, as the range, sill, and the proportion of the sill explained by spatial dependence decreased for cyst population densities. Our results indicated that in soybean fields with initially aggregated populations of H. glycines, no tillage and ridge tillage systems promoted aggregation of the nematode population, whereas conventional and reduced tillage systems resulted in a less aggregated spatial pattern.
Biological and Molecular Characterization of a New Cucurbit-Infecting Tobamovirus
Authors: Antignus Y. , Wang Y. , Pearlsman M. , Lachman O. , Lavi N. , Gal-On A.
Published: May 2007

An uncharacterized virus was isolated from greenhouse-grown cucumber plants. Biological and serological data described in the present study indicated that the virus belonged in the genus Tobamovirus. The host range of the virus included several plant species within the family Cucurbitaceae. The virus designated Cucumber fruit mottle mosaic virus (CFMMV) causes severe mottling or mosaic on cucumber fruits, and its fast spread within greenhouses could lead to significant economic losses in cucumber crops. The genome of CFMMV has been completely sequenced and its genome organization was typical of a Tobamovirus. However, its sequence was distinct from other described viruses within the group of cucurbit-infecting Tobamoviruses. Comparisons of sequences and phylogenetic analysis suggested that the cucurbit-infecting Tobamoviruses be separated into two subgroups: subgroup I comprising the strains and isolates referred to in the literature as Cucumber green mottle mosaic virus (CGMMV) (CV3, CV4, CGMMV-W, CGMMV-SH, and CGMMV-Is) and subgroup II comprising CFMMV, Kyuri green mottle mosaic virus (KGMMV), and the Yodo strain of CGMMV, which is closely related to KGMMV and may be considered a strain of it.
Classification, Nomenclature, and Plant Pathogenic Bacteria - A Clarification
Authors: Young J. M. , Bull C. T. , De Boer S. H. , Firrao G. , Gardan L. , Saddler G. E. , Stead D. E. , Takikawa Y.
Published: May 2007

In a recent Letter to the Editor of Phytopathology, proposals were made for endorsement and for rejection of selected names of plant pathogenic Pseudomonas spp. and Xanthomonas spp. We believe that support for, and rejection of, several names was based on misconceptions concerning the Approved Lists of Bacterial Names and entails misinterpretations of several Rules of the International Code of Nomenclature of Bacteria. This letter aims to clarify those misconceptions and misinterpretations.
Molecular Identification of a Sexual Interloper: The Pear Pathogen, Venturia pirina, has Sex on Apple
Authors: Stehmann Christiane , Pennycook Shaun , Plummer Kim M.
Published: May 2007

Venturia pirina (the pear scab pathogen) and V. inaequalis (the apple scab pathogen) were detected as ascospores discharged from apple leaf litter in New Zealand (spring 1998). Pseudothecia of both species were located on dead apple leaves; however, only those of V. inaequalis were associated with scab lesions. V. pirina was identified by rDNA sequence analyses, because morphological characters could not distinguish this fungus from V. asperata (a rare saprophyte on apple) and other Venturia spp. pathogenic on rosaceous fruit trees. Species-specific polymerase chain reaction primers designed to the 18S end of the internal transcribed spacer 1 region differentiated Venturia fruit tree pathogens reliably. V. pirina field isolates were pathogenic on pear, but only weak saprophytes on apple. In rare instances, when appressoria of V. pirina appeared to penetrate the cuticle of apple leaves, epidermal cells responded with a localized hypersensitive response (HR). To our knowledge, this is the first report of induction of HR-like events by V. pirina on its nonhost, apple, and also the first record of sexual reproduction of V. pirina on apple. It is assumed that V. pirina pseudothecia formed from saprophytic lesions in senescing apple leaves when active defense mechanisms such as HR were no longer induced.
Foci of Stagonospora Nodorum Blotch in Winter Wheat Before Canopy Development
Authors: Shah Denis A. , Bergstrom Gary C. , Ueng Peter P.
Published: May 2007

Stagonospora nodorum blotch (SNB) often develops explosively on upper leaves and glumes of wheat. Inoculum for late season infections may arise from early disease foci in the lower canopy or from recent immigration of wind-dispersed ascospores. Research was conducted to determine if foci of SNB are present and secondary spread has occurred in fields before tiller elongation. We determined the incidence of infection by Stagonospora nodorum for plants sampled at the mid-tillering stage in 96 1-m2 quadrats in each of two fields. Isolates of S. nodorum were recovered from 32 quadrats, one per infected plant where possible. Multilocus restriction fragment length polymorphism haplotypes were determined for each isolate. Of 55 isolates collected from one field, there were 22 distinct haplotypes. Diseased plants were aggregated in both fields; aggregates sometimes extended to adjacent quadrats. Plants within aggregates were often infected by the same haplotype, suggesting that secondary spread had occurred. Foci overlapped because some aggregates were infected by more than one haplotype. Our results show that genetically diverse populations of S. nodorum were already established in fields before canopy development and were comprised of sometimes overlapping foci undergoing clonal expansion.
Germination and Sporulation ofColletotrichum acutatumon Symptomless Strawberry Leaves
Authors: Leandro L. F. S. , Gleason M. L. , Nutter F. W. , Wegulo S. N. , Dixon P. M.
Published: May 2007

The germination and sporulation of Colletotrichum acutatum were characterized over time on strawberry leaves (cv. Tristar) and plastic coverslips incubated at 26°C under continuous wetness. Conidia germinated within 3 h after inoculation and formed melanized appressoria with pores by 9 h after inoculation. Host penetration was not observed up to 7 days after inoculation. Production of secondary conidia on conidial and hyphal phialides began within 6 h after inoculation. Secondary conidiation was responsible for up to a threefold increase in the total number of conidia within 7 days after inoculation. Primary conidia and hyphae began to collapse 48 h after inoculation, whereas melanized appressoria remained intact. These findings suggest that appressoria and secondary conidia of C. acutatum produced on symptomless strawberry foliage may be significant sources of inoculum for fruit infections.
Transgressive Segregation, Heritability, and Number of Genes Controlling Durable Resistance to Stripe Rust in One Chinese and Two Italian Wheat Cultivars
Authors: Zhang Z. J. , Yang G. H. , Li G. H. , Jin S. L. , Yang X. B.
Published: May 2007

Wheat (Triticum aestivum) cvs. Libellula (LB), San Pastore (SP), and Xian Nong 4 (XN4) possess durable resistance to stripe rust, caused by Puccinia striiformis f. sp. tritici, and cv. Ming Xian 169 (MX169) is highly susceptible to the rust. Inheritance of stripe rust resistance was studied by crossing the four cultivars and evaluating the resistance of parental, F1, F2, backcross, and F3 plants in the fields. Transgressive segregation for resistance was observed in the resistant by resistant crosses of LB × XN4 and XN4 × SP, but not in cross LB × SP. These results indicate that (i) the resistance genes in XN4 are different from those in LB and SP, and (ii) LB and SP share common resistance genes. The number of genes segregating for the resistance was estimated by quantitative methods from the data of F2, backcross, and F3 populations. LB and XN4 appear to have two to three resistance genes, and SP appears to have two to four resistance genes when crossed with MX169. The resistance gene number in resistant by resistant cross LB × XN4 was four to five, approximately equal to the sum of the genes in LB and XN4. Similarly, the resistance gene number in cross XN4 × SP was approximately equal to the sum of the genes in XN4 and SP. Broad-sense heritability was high in all crosses except LB × SP. Compared with the three MX169-involved crosses, narrow-sense heritability was higher in LB × MX169 and SP × MX169 crosses than in the XN4 × MX169 cross. The LB × XN4 and XN4 × SP crosses showed moderate narrow-sense heritability.
Detection of Phytoplasma by Polymerase Chain Reaction of Insect Feeding Medium and Its Use in Determining Vectoring Ability
Authors: Tanne E. , Boudon-Padieu E. , Clair D. , Davidovich M. , Melamed S. , Klein Meir
Published: May 2007

A polymerase chain reaction (PCR)-based method was developed for the detection of phytoplasma in insect feeding medium (sucrose). A correlation was established between the transmissibility of Flavescence dorée phytoplasma in the experimental leafhopper vector Euscelidius variegatus and its detection by PCR in the insect feeding medium. However, phytoplasma were detected in the insects' bodies 3 weeks before they began to transmit. Hence, PCR assays of the sucrose medium reflected phytoplasma vectoring ability probably by detecting it in the insect saliva, whereas detection of phytoplasma in the insect's body did not identify it as a vector. The assay was applied to two field-collected leafhoppers suspected of being phytoplasma vectors in Israel (Orosius albicinctus and Anaceratagallia laevis). The presence of phytoplasma in the body of specimens of the latter species was assayed by PCR in 1999. Phytoplasmas were detected in insects' bodies throughout the year, with no specific seasonal pattern. In the saliva, however, no phytoplasma could be detected in the autumn. This seasonal pattern supported the validity of the feeding-medium tests and their correlation to the insect's ability to transmit phytoplasma. Transmission assays indicated, to our knowledge for the first time, that O. albicinctus and A. laevis are vectors of phytoplasma in Israel. A simple PCR-based assay is thus provided, circumventing the need for tedious biological assays and enabling epidemiological studies of phytoplasma transmissibility on a large scale.
Risk Analysis of Brown Rot Blossom Blight of Prune Caused by Monilinia fructicola
Authors: Luo Y. , Morgan D. P. , Michailides T. J.
Published: May 2007

Experiments under controlled environmental conditions were conducted during bloom of prune (Prunus domestica, L.) in 1999 and 2000 to assess the effects of inoculum concentration (IC), wetness duration (WD), temperature, and bloom stages on development of brown rot blossom blight of prunes. Branches from trees of a prune orchard were inoculated with Monilinia fructicola at different bloom stages and incubated at different temperatures with different periods of WD. The proportion of blighted blossoms (PBB) for each inoculated branch was determined. Bloom stage, IC, temperature, and WD significantly affected blossom blight of prunes. PBB at popcorn and full bloom stages was significantly greater than PBB at later bloom stages (P ≤0.05). The optimal temperatures for blossom blight development were 22 to 26°C, and Gaussian functions were used to describe the relationship between PBB and temperature. PBB linearly increased with increased IC. Linear regressions of PBB on WD were obtained for each combination of bloom stage, IC, and temperature. The parameters of these regressions were used in a computer program to produce the possible maximum PBB with 90% probability (PBB90) using stochastic simulations. Early bloom stages with a higher IC at temperatures from 20 to 25°C were associated with more severe blossom blight than late stages with a lower IC at nonoptimal temperatures. Blossom blight did not occur at <10 or >30°C and less than 4-h WD. However, longer than 4-h WD linearly increased incidence of blossom blight. A risk assessment table of blossom blight was produced for different environmental conditions to guide the control of prune brown rot.
Effect of Microsphaeropsis sp. Strain P130A on Germination and Production of Sclerotia of Rhizoctonia solani and Interaction Between the Antagonist and the Pathogen
Authors: Carisse Odile , El Bassam Souad , Benhamou Nicole
Published: May 2007

Microsphaeropsis sp. strain P130A was evaluated for the control of tuber-borne inoculum of Rhizoctonia solani based on the viability of sclerotia produced in vitro and on both the viability and production of tuber-borne sclerotia. The interactions between the antagonist and the pathogen, as well as the effect of the toxins produced by the antagonist on mycelial growth of R. solani were studied using transmission electron microscopy. On sclerotia produced in vitro, for all incubation periods (1 to 42 days), Microsphaeropsis sp. significantly reduced germination. Percent germination of sclerotia treated with Microsphaeropsis sp. decreased with increasing incubation period from an average of 82.0% after 1 day to stabilize at an average of 5.8% after 35 days. Similarly, percent germination of tuber-borne sclerotia was significantly lower when tubers were treated with Microsphaeropsis sp. Both 2% formaldehyde and Microsphaeropsis sp. treatments significantly reduced sclerotia germination to approximately 10% after 42 days of incubation at 4°C. Furthermore, on tubers treated with the antagonist, the number of sclerotia per square centimeter decreased from 1.6 to 0.5 during the 8 months of storage at 4°C, whereas an increase from 1.2 to 7.8 sclerotia per square centimeter was observed on untreated tubers. Microsphaeropsis sp. (strain P130A) colonized hyphae of R. solani within 4 days after contact on culture media. Transmission electron microscopic observations showed that the antagonist induced a rupture of the pathogen plasma membrane and that a chitin-enriched matrix was deposited at sites of potential antagonist penetration. Host penetration was not associated with pathogen cell wall alterations, which occurred at the time of progress of the antagonist in the pathogen cytoplasm. In the presence of a crude extract of Microsphaeropsis sp., cells of R. solani showed cytoplasm disorganization and breakdown of plasma membranes. Antibiosis and mycoparasitism were involved in the antagonism of R. solani by Microsphaeropsis sp., but the sequence by which these events occur, as well as the significance of wall appositions produced by R. solani, is yet to be established.
Resistance toBean pod mottle virusin Transgenic Soybean Lines Expressing the Capsid Polyprotein
Authors: Reddy M. S. Srinivasa , Ghabrial Said A. , Redmond Carl T. , Dinkins Randy D. , Collins Glenn B.
Published: May 2007

Transgenic fertile soybean plants were generated from somatic embryos of soybean (Glycine max) cv. Jack transformed via particle bombardment with the capsid polyprotein (pCP) gene of Bean pod mottle virus(BPMV). The plant transformation vector (pHIG/BPMV-pCP) utilized in these experiments contained the BPMV-pCP coding sequence, an intron-containing GUS gene, and the hygromycin phosphotransferase gene. Southern blot hybridization analysis showed that 19 transgenic soybean plants selected for resistance to hygromycin contained the genes for GUS and BPMV-pCP. The progeny of five of these transgenic soybean plants (plants 137, 139, 157, 183, and 186) were characterized in detail. An additional transgenic plant (plant 200) contained the intron-GUS and hygromycin resistance genes, but lacked the BPMV-pCP gene and was used as a negative control. Southern blot hybridization analysis of the five transgenic plants showed the presence of three copies of the T-DNA in a similar banding pattern suggesting that they were derived from a single transformation event. Western and northern blot analyses showed that the expression levels of BPMV-pCP and pCP transcript were high in these five pCP plants. Infectivity assays with detached leaves demonstrated that all five pCP plants exhibited resistance to virus infection because they accumulated lower levels of BPMV compared with plant 200 and nontransformed controls. Unlike the T2progeny of line 183-1 that segregated with respect to the pCP gene and, consequently, to BPMV resistance, the T2progeny of the homozygous line 183-2 showed little or no symptoms in response to rub-inoculation with virions of a severe strain of BPMV. Although BPMV accumulation was evident in leaves on which viruliferous beetles were allowed a 72-h inoculation access period, the upper noninoculated leaves of the T2progeny of line 183-2 plants were symptomless and accumulated little or no virus. Because the progeny of this homozygous transgenic line exhibited systemic resistance, they could potentially be useful in generating commercial cultivars resistant to BPMV.
Overwintering ofFrankliniella fusca(Thysanoptera: Thripidae) on Winter Annual Weeds Infected withTomato spotted wilt virusand Patterns of Virus Movement Between Susceptible Weed Hosts
Authors: Groves R. L. , Walgenbach J. F. , Moyer J. W. , Kennedy G. G.
Published: May 2007

Overwintering of tobacco thrips, Frankliniella fusca, was investigated on common winter annual host plants infected with Tomato spotted wilt virus (TSWV). Populations of tobacco thrips produced on TSWV-infected plants did not differ from those produced on healthy plants, whereas populations varied greatly among host plant species. The mean per plant populations of F. fusca averaged 401, 162, and 10 thrips per plant on Stellaria media, Scleranthus annuus, and Sonchus asper, respectively, during peak abundance in May. Adult F. fusca collected from plant hosts were predominately brachypterous throughout the winter and early spring, but macropterous forms predominated in late spring. Weed hosts varied in their ability to serve as overwintering sources of TSWV inoculum. Following the initial infection by TSWV in October 1997, 75% of Scleranthus annuus and Stellaria media retained infection over the winter and spring season, whereas only 17% of Sonchus asper plants remained infected throughout the same interval. Mortality of TSWV-infected Sonchus asper plants exceeded 25%, but mortality of infected Stellaria media and Scleranthus annuus did not exceed 8%. TSWV transmission by thrips produced on infected plants was greatest on Stellaria media (18%), intermediate on Scleranthus annuus (6%), and lowest on Sonchus asper (2%). Very few viruliferous F. fusca were recovered from soil samples collected below infected wild host plants. Vegetative growth stages of Stellaria media, Sonchus asper, and Ranunculus sardous were more susceptible to F. fusca transmission of TSWV than flowering growth stages, whereas both growth stages of Scleranthus annuus were equally susceptible. In a field study to monitor the spatial and temporal patterns of virus movement from a central source of TSWV-infected Stellaria media to adjacent plots of R. sardous, the incidence of infection in R. sardous plots increased from <1% in March to >42% in June 1999. Infection levels in the Stellaria media inoculum source remained high throughout the experiment, averaging nearly 80% until June 1999 when all Stellaria media plants had senesced. Dispersal of TSWV from the inoculum source extended to the limits of the experimental plot (>37 m). Significant directional patterns of TSWV spread to the R. sardous plots were detected in April and May but not in June. R. sardous infections were detected as early as March and April, suggesting that overwintering inoculum levels in an area can increase rapidly during the spring in susceptible weed hosts prior to planting of susceptible crops. This increase in the abundance of TSWV inoculum sources occurs at a time when vector populations are increasing rapidly. The spread of TSWV among weeds in the spring serves to bridge the period when overwintered inoculum sources decline and susceptible crops are planted.
Specific Polymerase Chain Reaction Identification of Venturia nashicola Using Internally Transcribed Spacer Region in the Ribosomal DNA
Authors: Le Cam Bruno , Devaux Martine , Parisi Luciana
Published: May 2007

A technique based on the polymerase chain reaction (PCR) was developed for the identification of Venturia nashicola using nucleotide sequence information of the ribosomal DNA region. The complete internal transcribed spacer (ITS) region of V. nashicola strains and phylo-genetically related species was amplified with the two universal ITS1 and ITS4 primers, sequenced, and digested with five restriction enzymes. The alignment of nucleotide sequences and analyses of digestion patterns indicated constant polymorphisms between V. nashicola and related species at nucleotides 126 and 127, which overlapped a TaqI restriction site. An oligonucleotide primer named A126 was designed for identifying this variable region. A primer set (A126 and ITS4) that allowed the amplification of a 391-bp DNA fragment within the ITS region by PCR was specific to V. nashicola when it was checked against fungal genomic DNAs of related fungi. This primer set was a good candidate for a species-specific reagent in a procedure for identification of V. nashicola by PCR.
Molecular Phylogenetic Analyses of Verticillium fungicola and Related Species Causing Dry Bubble Disease of the Cultivated Button Mushroom, Agaricus bisporus
Authors: Collopy P. D. , Largeteau-Mamoun M. L. , Romaine C. P. , Royse D. J.
Published: May 2007

Molecular phylogenetic analyses were performed on 40 isolates of Verticillium fungicola collected from various Pennsylvania mushroom farms in 1999 and 28 isolates of Verticillium spp. collected during the last 50 years from various geographic locations. Sequence analysis of internal transcribed spacers 1 and 2 (ITS1 and ITS2) and 5.8S regions of the nuclear ribosomal DNA (rDNA) transcriptional unit and analysis of random amplified polymorphic DNA (RAPD) data were performed for the 68 isolates of Verticillium spp. Identical rDNA sequences were obtained for all 40 Pennsylvania isolates collected during 1999, 13 North American isolates collected during the last 50 years, and the ex-type strain of V. fungicola var. aleophilum. Sequence analysis of European isolates revealed a close relationship to the ex-type strain V. fungicola var. fungicola. No European-like isolates of V. fungicola var. fungicola were detected in the collection of North American isolates examined. Results from six decamer RAPD primers strongly indicate the presence of a clonal population of V. fungicola among Pennsylvania isolates. In addition, RAPD data delineated a Korean isolate (DC130) and ex-type strain V. fungicola var. aleophilum from the North American group. Virulence assays, based on spore inoculation of mushroom pilei, revealed variation corresponding to each neighbor-joining and RAPD grouping. All isolates with rDNA sequence and RAPD grouping similarity to ex-type strains V. fungicola var. aleophilum and V. fungicola var. fungicola displayed the highest level of virulence. Based on rDNA sequence and RAPD analyses, isolates displaying reduced or no virulence were distantly related to these two varieties. All results obtained for the analyses of ex-type strain V. fungicola var. flavidum suggested that this fungal isolate should not be considered a variety of V. fungicola, but rather a distinct species.
A Point Mutation in the Two-Component Histidine KinaseBcOS-1Gene Confers Dicarboximide Resistance in Field Isolates ofBotrytis cinerea
Authors: Oshima Michiyo , Fujimura Makoto , Banno Shinpei , Hashimoto Chigusa , Motoyama Takayuki , Ichiishi Akihiko , Yamaguchi Isamu
Published: May 2007

Partial DNA fragments of Botrytis cinerea field isolates encoding the putative osmosensor histidine kinase gene (BcOS1) were cloned by polymerase chain reaction amplification and the predicted amino acid sequences were compared between dicarboximide-sensitive and resistant field isolates. The predicted BcOS1p is highly homologous to osmosensor histidine kinase OS1p from Neurospora crassa including the N-terminal six tandem repeats of approximately 90 amino acids. Four dicarboximide-resistant isolates of B. cinerea (Bc-19, Bc-45, Bc-682, and Bc-RKR) contained a single base pair mutation in their BcOS1 gene that resulted in an amino acid substitution in the predicted protein. In these resistant isolates, codon 86 of the second repeat, which encodes an isoleucine residue in sensitive strains, was converted to a codon for serine. The mutation of Botrytis field resistant isolates was located on the second unit of tandem amino acid repeats of BcOS1p, whereas the point mutations of the fifth repeat of OS1p confer resistance to both dicarboximides and phenylpyrroles and also osmotic sensitivity in Neurospora crassa. These results suggest that an amino acid substitution within the second repeat of BcOS1p is responsible for phenotypes of field resistant isolates (resistant to dicarboximides but sensitive to phenylpyrroles, and normal osmotic sensitivity) in B. cinerea.
AnthracnoseTracer: A Spatiotemporal Model for Simulating the Spread of Anthracnose in a Lupin Field
Authors: Diggle A. J. , Salam M. U. , Thomas G. J. , Yang H. A. , O'Connell M. , Sweetingham M. W.
Published: May 2007

A spatiotemporal model has been developed to simulate the spread of anthracnose, initiated by infected seed, in a lupin field. The model quantifies the loss of healthy growing points of lupin in all 1-m2subunits of a field throughout a growing season. The development of growing points is modeled as a function of temperature using a 1-day time step, and disease-induced compensatory growth is accounted for. Dispersal of spores is simulated explicitly using Monte Carlo techniques. Spread of spores occurs during rainfall events on a 1-h time step. The distance traveled by spores is partially dependent on wind speed and is generated by adding the values selected from half-Cauchy distributions. The direction of travel of the spores is influenced by wind direction. The model has been employed to produce a theoretical assessment of damage from disease in two environments at five levels of seed infection. It was calculated that in a susceptible lupin cultivar with a 0.01% initial seed infection, anthracnose would cause approximately 15% loss of healthy growing points in a high rainfall environment in Western Australia. In a low rainfall environment, similar damage would be unlikely even with a much higher (1%) level of seed infection.
New Avirulence Genes in the Phytopathogenic Fungus Leptosphaeria maculans
Authors: Balesdent M. H. , Attard A. , Kühn M. L. , Rouxel T.
Published: May 2007

Leptosphaeria maculans, the causal agent of stem canker of oilseed rape (Brassica napus), develops gene-for-gene interactions with oilseed rape, and four L. maculans avirulence (AVR) genes (AvrLm1, AvrLm2, AvrLm4, and alm1) were previously genetically characterized. Based on the analysis of progeny of numerous in vitro crosses between L. maculans isolates showing either already characterized or new differential interactions, this work aims to provide an overview of the AVR genes that may specify incompatibility toward B. napus and the related species B. juncea and B. rapa. Two novel differential interactions were thus identified between L. maculans and B. napus genotypes, one of them corresponding to a complete resistance to European races of L. maculans. In both cases, a single gene control of avirulence was established (genes AvrLm3 and AvrLm7). Similarly, a single gene control of avirulence toward a B. rapa genotype, also resistant to European L. maculans isolates, was demonstrated (gene AvrLm8). Finally, a digenic control of avirulence toward B. juncea was established (genes AvrLm5 and AvrLm6). Linkage analyses demonstrated that at least four unlinked L. maculans genomic regions, including at least one AVR gene cluster (AvrLm1-AvrLm2-AvrLm6), are involved in host specificity. The AvrLm3-AvrLm4-AvrLm7 region may correspond either to a second AVR gene cluster or to a multiallelic AVR gene.
Frequency of Sexual Reproduction byMycosphaerella graminicolaon Partially Resistant Wheat Cultivars
Authors: Cowger Christina , McDonald Bruce A. , Mundt Christopher C.
Published: May 2007

The frequency of sexual reproduction has a profound effect on the population structure and the adaptive potential of a facultatively sexual parasite. Little is known about the relationship of quantitative host resistance to the frequency of sex in pathogens. We sampled over 5,000 fungal fruiting bodies from eight different wheat cultivars over a 3-year period. The cultivars possessed varying degrees of susceptibility to Mycosphaerella graminicola, a facultatively sexual pathogen that is hetero-thallic and bipolar. The fruiting bodies were classified as M. graminicola pycnidia or ascocarps (asexual and sexual fruiting bodies, respectively), other identifiable fungi, or unidentified. In all 3 years, area under the disease progress curve (AUDPC) explained a significant proportion of the variation in ascocarps as a percentage of M. graminicola fruiting bodies (P < 0.0005). The mean percentage of M. graminicola ascocarps from all cultivars was 63% in 1998, when the epidemic was intense, and 14% in 1999, a year of low disease levels. In 2000, samples were taken at 7-day intervals from 6 June to 27 June from two cultivars with substantially different AUDPCs (788 and 2,185 percentage-days). The less diseased cultivar yielded its first M. graminicola ascocarps 1 week later than the more diseased cultivar, and respective means of ascocarps as a percentage of M. graminicola fruiting bodies across sampling dates were 20.2 and 59.3%. The ratio of sexual to asexual reproduction by M. graminicola is likely to be strongly conditioned by infection density.
The Analysis of Fruit Protection Mechanisms Provided by Reduced-Pathogenicity Mutants ofColletotrichum gloeosporioidesObtained by Restriction Enzyme Mediated Integration
Authors: Yakoby N. , Beno-Moualem D. , Kobiler I. , Prusky D.
Published: May 2007

Colletotrichum gloeosporioides is an important postharvest pathogen that attacks ripe avocado fruit. Two reduced-pathogenicity mutants, Cg-M-142 and Cg-M-1150, previously obtained by restriction enzyme mediated integration, were used for the sequential analysis of the induction of biocontrol in avocado fruit. Plant biochemical indicators, such as H+-ATPase activity and levels of reactive oxygen species, phenylalanine ammonia lyase, epicatechin, and an antifungal diene, were investigated. The main difference between Cg-M-142 and Cg-M-1150 was the lack of appressorium formation by the latter. Preinoculation of avocado fruit with Cg-M-142 enhanced H+-ATPase activity and the production of reactive oxygen species. These early signaling events were followed by higher phenylalanine ammonia lyase activity and higher levels of epicatechin and the antifungal diene, and decay was delayed. Unlike Cg-M-142, Cg-M-1150 did not activate early signaling events related to fruit resistance. We suggest that the initiation of early signaling events affecting fruit resistance is determined by the capability of the pathogen to interact with the fruit during appressorium formation. Furthermore, the intensity of the fruit defense response determines the level of resistance during fruit storage.
Development of Contamination-Free Restriction Fragment Length Polymorphism Probes for the Obligate Biotroph Peronospora tabacina, an Oomycete Causing Blue Mold of Tobacco
Authors: Sukno Serenella A. , Taylor Amy M. , Farman Mark
Published: May 2007

Peronospora tabacina is an obligately parasitic oomycete that causes blue mold, a devastating disease of tobacco. Genetic studies of this pathogen have been hampered by the lack of molecular markers. We generated a set of molecular markers for P. tabacina by collecting sporangiospores from infected tobacco leaves, extracting spore DNA, and cloning it in a plasmid vector. The resulting clones were then used to probe DNA from a collection of P. tabacina isolates to survey for polymorphisms. Most probes gave unexpected hybridization patterns with signal intensities that varied significantly from one DNA sample to another or between different DNA preparations of the same isolate. These results indicated that certain DNA preparations contained DNA from a source other than P. tabacina, which in turn suggested that some probes might have been derived from contaminating organisms present in the spore suspensions. Therefore, we characterized the inserts of several recombinant plasmids to determine their origins. Sequence analysis revealed that several of the inserts encoded peptides with similarity to bacterial proteins, suggesting that they were derived from bacterial contaminants. Of the remaining clones, five exhibited similarity to retroelements, one resembled eukaryotic helicase genes, and nine had no similarity to sequences in the databases. These were postulated to be true P. tabacina DNA clones. Verification of the origin of each probe was achieved by filtering a spore suspension, extracting DNA from the retentate and filtrate, and probing Southern blots of these DNA samples. These experiments confirmed the probe origins predicted by sequence analysis, resulting in the generation of 20 different restriction fragment length polymorphism probes that are specific for P. tabacina DNA. These probes should enable identification of reliable genetic markers for population studies of the blue mold organism.