bluuebunny/crossref_metadata_2025 huggingface dataset:
Unraveling Evolutionary Relationships Among the Divergent Lineages of Colletotrichum Causing Anthracnose Disease in Turfgrass and Corn
Authors: Crouch Jo Anne , Clarke Bruce B. , Hillman Bradley I.
Published: May 2007

Colletotrichum species cause anthracnose diseases on a number of grass hosts and are common inhabitants of many others. They are divided into four species: C. sublineolum is pathogenic to Sorghum spp.; C. caudatum is found on C4 grasses such as indiangrass and big bluestem; C. falcatum causes red rot of sugarcane; and C. graminicola sensu lato is a broadly defined species including isolates that attack maize, wheat, oats, and many forage, turf, and amenity grasses of the subfamily Pooideae. In this paper, a combination of hierarchal- and nonhierarchal-based analyses were employed to examine evolutionary relationships among the grass-infecting Colletotrichum species, with special emphasis on isolates from turf and other grasses in the subfamily Pooideae. Reconstructions performed with data sets from over 100 Colletotrichum isolates at three variable loci using phylogenetic and network-based methodologies unambiguously supported the taxonomic separation of maize-infecting isolates of C. graminicola from the pooid-infecting strains of Colletotrichum. To reflect the evolutionary relationships that exist between these distinct lineages, we propose the resurrection of the species name C. cereale to describe the pooid-infecting isolates. There was also support for further subdivision of C. cereale, but the current data are insufficient to confidently subdivide the species, as there was some evidence of recombination between lineages of this species.
Identification of Differentially Expressed Genes by cDNA-Amplified Fragment Length Polymorphism in the Biocontrol Agent Pichia anomala (Strain Kh5)
Authors: Massart Sébastien , Jijakli M. Haissam
Published: May 2007

cDNA-amplified fragment length polymorphism (cDNA-AFLP) analysis was used to identify genes potentially involved in biological control, by strain Kh5 (Pichia anomala), of Botrytis cinerea, an important post-harvest pathogen on apples. Strain Kh5 was grown in yeast nitrogen base (YNB) plus glucose (G medium) or YNB plus cell walls of B. cinerea (B medium). Thirty-five primer pairs were used in AFLP amplifications, resulting in a total of more than 2,450 bands derived from the mRNA of strain Kh5 grown in B medium. Eighty-six bands (3.5%) corresponded to genes upregulated in B medium compared with G medium. Of these 86 bands, 28 were selected, cloned, sequenced, and subjected to real-time reverse transcription-polymerase chain reaction (RT-PCR) to confirm their differential expression. An appropriate housekeeping gene, G2, was selected and used to normalize the results of RT-PCR. Eleven genes presented an increased gene expression in the presence of B. cinerea cell walls (expression >1). Statistical analysis showed a significant increase for 5 of these 11 genes. The overexpressed genes show homologies to yeast genes with various functions, including β-glucosidase, transmembrane transport, citrate synthase, and external amino acid sensing and transport. Some of these functions could be related to cell wall metabolism and potentially involved in mycoparasitic properties.
Molecular Characterization, Phylogenetic Relationships, and Specific Detection of Peach mosaic virus
Authors: James D. , Varga A. , Croft H. , Rast H. , Thompson D. , Hayes S.
Published: May 2007

Peach mosaic virus (PcMV) and Cherry mottle leaf virus (CMLV) are serologically related viruses that cause distinct diseases, have a different host range, and are vectored by different eriophyid mites. Sequence analysis of the genome of PcMV indicates that it is closely related genetically to CMLV but distinct, with similar genome organization and a member of the genus Trichovirus. The genome of PcMV consists of 7,988 nucleotides, excluding a poly(A) tail at the 3′ end of the genome. Four putative open reading frames (ORF1 to 4) were identified coding for proteins of 216.3, 47.2, 21.7, and 15.7 kDa, respectively. Also, three noncoding regions were identified, including an intergenic region separating ORF3 and ORF4. The complete nucleotide sequence of PcMV shares 73% identity with CMLV. The CP amino acid sequence identity between isolates of PcMV ranged from 97 to 99% versus 83% identity when compared with the CP of CMLV. In vitro expression and subsequent western blot analysis confirmed ORF3 as encoding the CP gene of PcMV. Phylogenetic analysis supports classification of PcMV and CMLV as members of the genus Trichovirus. They are unique members of this genus with an extra ORF (ORF4). PcMV ORF4 appears to code for a putative nucleic acid-binding (NB) protein which has identity with the NB protein of CMLV and members of the genera Allexivirus, Carlavirus, and Vitivirus. PcMV and CMLV appear to be the products of recombination between members of the genus Trichovirus and a virus group containing the putative NB protein. Alternatively, PcMV and CMLV may represent the intact genome, with a deletion event producing members that lack ORF4. A reverse transcription-polymerase chain reaction procedure was developed for reliable and specific detection of PcMV. This will be an asset for stone fruit virus certification.
Epicuticular Wax and White Pine Blister Rust Resistance in Resistant and Susceptible Selections of Eastern White Pine (Pinus strobus)
Authors: Smith Jason A. , Blanchette Robert A. , Burnes Todd A. , Gillman Jeffrey H. , David Andrew J.
Published: May 2007

Epicuticular wax on needles was evaluated for its influence on Cronartium ribicola infection of resistant and susceptible selections of Pinus strobus. Environmental scanning electron microscopy comparisons revealed that needles from a resistant selection of eastern white pine, P327, had a significantly higher percentage of stomata that were occluded with wax, fewer basidiospores germinating at 48 h after inoculation, and fewer germ tubes penetrating stomata than needles from a susceptible selection H111. In addition, needles from seedlings that failed to develop symptoms 6 weeks after inoculation, from a cross between P327 and susceptible parent H109, had a significantly higher percentage of stomata occluded with wax compared with needles from seedlings that developed symptoms. In experiments where epicuticular waxes were removed from needles before seedlings were infected, resistant seedlings without wax developed approximately the same number of infection spots (as measured by spot index) as susceptible seedlings with wax intact. Gas chromatography/mass spectrometry comparisons of extracted epicuticular waxes revealed several peaks that were specific to P327 and not found in susceptible H111 suggesting biochemical differences in wax composition. These results implicate the role of epicuticular waxes as a resistance mechanism in P. strobus selection P327 and suggest a role for waxes in reducing spore germination and subsequent infection through stomatal openings.
Differential Sensitivity of Phytophthora parasitica var. nicotianae and Thielaviopsis basicola to Monomeric Aluminum Species
Authors: Fichtner E. J. , Hesterberg D. L. , Smyth T. J. , Shew H. D.
Published: May 2007

Aluminum (Al) is toxic to many plant pathogens, including Thielaviopsis basicola and Phytophthora parasitica var. nicotianae. Because fungi-toxicity of Al has been described in soils over a wide pH range, multiple species of Al may be responsible for pathogen suppression. The goals of this work were to determine the sensitivity of T. basicola and P. para-sitica var. nicotianae to Al over a range of pH values, quantify the toxicity of monomeric Al species to production of sporangia of P. parasitica var. nicotianae and chlamydospores of T. basicola, and detect the accumulation of Al in pathogen structures. A complete factorial treatment design was used with Al levels ranging from 0 to 100 μM and pH levels ranging from 4 to 6 in a minimal salts medium. The chemistry of test solutions was modeled using GEOCHEM-PC. Colonies were grown in 5% carrot broth, and after 1 or 2 days, the nutrient solution was removed, colonies were rinsed with water, and Al test solutions were added to each of four replicate plates. After 2 days, propagules were counted and colonies were stained with the Al-specific, fluorescent stain lumogallion. The oomycete P. parasitica var. nicotianae was sensitive to multiple monomeric Al species, whereas sensitivity of T. basicola to Al was pH-dependent, suggesting that only Al3+ is responsible for suppression of this fungal pathogen. Chlamydospore production by T. basicola was inhibited at pH values <5.0 and Al levels >20 μM, whereas sporangia production by P. parasitica was inhibited at Al levels as low as 2 μM across all pH values tested. The lumogallion stain was an effective technique for detection of Al in fungal tissues. Aluminum accumulated in sporangia and zoospores of P. parasitica var. nicotianae and in nonmelanized chlamy-dospores of T. basicola, but not in cell walls of either organism. The differential sensitivity of the two organisms may indicate that true fungi respond differently to Al than members of the oomycota, which are more closely related to plants.
The Frequencies and Spatial Distribution of Mating Types in Stagonospora nodorum Are Consistent with Recurring Sexual Reproduction
Authors: Sommerhalder Rubik J. , McDonald Bruce A. , Zhan Jiasui
Published: May 2007

To test the hypothesis that Stagonospora nodorum undergoes regular cycles of sexual recombination, a total of 1,207 isolates sampled from 18 fields in 12 geographical regions in six countries on five continents were analyzed for mating type frequency and distribution using polymerase chain reaction amplification of the mating type locus. Restriction fragment length polymorphism and random amplified polymorphic DNA fingerprints were used to clone-correct the data sets. Both mating types were often found on the smallest spatial scales tested, including within the same lesion, the same leaf, and the same 1-m2 plot. In only one case out of the 18 fields tested was there a significant departure from the expected 1:1 ratio. Combining this result with previous data on the population structure of S. nodorum, we conclude that this pathogen undergoes regular cycles of sexual recombination in all regions we examined.
Salicylic Acid Suppresses Potato virus Y Isolate N:O-Induced Symptoms in Tobacco Plants
Authors: Nie Xianzhou
Published: May 2007

The effects of salicylic acid (SA) and 1-aminocyclopropane-1-carboxylic acid (ACC) on the systemic development of symptoms induced by a severe isolate of Potato virus Y group N:O (PVYN:O) in tobacco were investigated. Upon inoculation, the systemic development of symptoms in tobacco plants could be divided into three stages: virus incubation stage, rapid symptom-progress stage, and partial recovery and symptom-shifting stage. Treatment of seedlings with SA delayed the virus-induced necrosis in stems by 1 to 2 days. SA, not ACC, also significantly suppressed the symptom severity in stems. However, neither SA nor ACC treatment affected the partial recovery phenotype exhibited in the latterly emerged upper parts of the plants. Further analysis indicated that the accumulation of PVY was retarded by SA at the early stage of infection, and the effects were more profound in stems than leaves. Peroxidase (POX) activity and pathogenesis-related (PR) genes PR-1a and PR-1b were enhanced by PVY infection. SA not only increased POX activity in stems and PR genes in stems and leaves of mock-inoculated plants, but also elevated the activity of POX in both leaves and stems and the expression of PR-1a in leaves of PVY-infected plants. Together, the results suggest that systemic acquired resistance plays a key role in suppressing PVYN:O-induced symptom development through SA-mediated and ethylene-independent pathways. The symptom suppression was correlated with reduced replication/ accumulation of virus at the early stage of infection. The results also suggest that neither SA nor ethylene plays a role in the recovery phenotype.
Disease Phenotype of Virus-Infected Helminthosporium victoriae Is Independent of Overexpression of the Cellular Alcohol Oxidase/RNA-Binding Protein Hv-p68
Authors: Zhao Tianyong , Havens Wendy M. , Ghabrial Said A.
Published: May 2007

The cellular protein Hv-p68 is a novel alcohol oxidase/RNA-binding protein that is overexpressed in virus-infected isolates of the plant-pathogenic fungus Helminthosporium victoriae (teleomorph: Cochliobolus victoriae). Overproduction of Hv-p68 has been hypothesized to lead to the accumulation of toxic aldehydes and to induce the disease phenotype associated with the virus-infected isolates. We overexpressed the Hv-p68 gene in virus-free isolates and evaluated the morphology of the resulting colonies. We cloned and sequenced the Hv-p68 genomic DNA, which contains five introns and the complete Hv-p68 coding sequence. Vectors for overexpression of the Hv-p68 gene were constructed with either Hv-p68 cDNA or the intron-containing Hv-p68 genomic DNA. Expression of Hv-p68 was significantly higher if the genomic sequence was used for transformation than if the cDNA sequence was used. The virus-free fungal transformants that overexpressed Hv-p68 gene did not exhibit the disease phenotype. In contrast, these transformants showed enhanced growth rates when compared with the nontransformed and empty vector controls. Interestingly, overexpression of Hv-p68 in a fungal isolate infected with both the totivirus Helminthosporium victoriae 190S virus (Hv190SV) and the chrysovirus Helminthosporium victoriae 145S virus (Hv145S) showed enhanced accumulation of the Hv145SV double-stranded (ds)RNA, but not of the Hv190SV. These results are consistent with an earlier report that Hv-p68 co-purified with viral dsRNA, mainly that of the Hv145SV. Elucidation of the role of Hv-p68 in disease induction is important for an understanding of host-virus interactions in this fungus-virus system.
Interference of Long-Distance Movement of Grapevine berry inner necrosis virus in Transgenic Plants Expressing a Defective Movement Protein of Apple chlorotic leaf spot virus
Authors: Yoshikawa N. , Saitou Y. , Kitajima A. , Chida T. , Sasaki N. , Isogai M.
Published: May 2007

Transgenic Nicotiana occidentalis plants expressing a movement protein (P50) and partially functional deletion mutants (ΔA and ΔC) of the Apple chlorotic leaf spot virus (ACLSV) showed resistance to Grapevine berry inner necrosis virus (GINV). The resistance is highly effective and GINV was below the level of detection in both inoculated and uninoculated upper leaves. In contrast, GINV accumulated in inoculated and uninoculated leaves of nontransgenic (NT) plants and transgenic plants expressing a dysfunctional mutant (ΔG). On the other hand, in some plants of a transgenic plant line expressing a deletion mutant (ΔA', deletion of the C-terminal 42 amino acids), GINV could spread in inoculated leaves, but not move into uninoculated leaves. In a tissue blot hybridization analysis of ΔA'-plants inoculated with GINV, virus could be detected in leaf blade, midribs, and petiole of inoculated leaves, but neither in stems immediately above inoculated leaves nor in any tissues of uninoculated leaves. Immunohistochemical analysis of GINV-inoculated leaves of ΔA'-plants showed that GINV could invade into phloem parenchyma cells through bundle sheath of minor veins, suggesting that the long-distance transport of GINV might be inhibited between the phloem cells and sieve element (and/or within sieve element) rather than bundle sheath-phloem interfaces. Immunogold electron microscopy using an anti-P50 antiserum showed that P50 accumulated on the parietal layer of sieve elements and on sieve plates. The results suggested that resistance in P50-transgenic plants to GINV is due to the interference of both long-distance and cell-to-cell movement of the virus.
Extracts of Inula viscosa Control Downy Mildew of Grapes Caused by Plasmopara viticola
Authors: Cohen Yigal , Wang Wenqiao , Ben-Daniel Bat-Hen , Ben-Daniel Yigal
Published: May 2007

The oily paste extracts of Inula viscosa leaves made with organic solvents were effective in controlling downy mildew caused by Plasmopara viticola in detached leaf tissues of grapes in growth chambers. Thin-layer chromatography of such extracts revealed the presence of 11 Rf regions of which four contained highly effective compounds against the disease. Two major inhibitory compounds, each comprising 10.6% of the total paste weight, were identified as tomentosin and costic acid. An emulsified concentrate formulation of the oily paste extracts provided excellent activity against the disease in the field. The effective dose (concentration) required for 90% control of the disease in treated shoots in the field was below 0.125% (paste in water). No seasonal fluctuations were observed in the control efficacy of six extracts made from I. viscosa leaves harvested during the period of May to July. In whole vines, treated and artificially inoculated, the paste concentration required for 90% control of the disease ranged between 0.30 to 0.37%, whereas in naturally infected vines it was 0.58%. It appears that I. viscosa is a valuable source for fungicidal preparations against downy mildew of grapes. This is the first report on the control of a disease with I. viscosa extracts under field conditions.
Introgression of a Tombusvirus Resistance Locus fromNicotiana edwardsoniivar. Columbia toN. clevelandii
Authors: Schoelz James E. , Wiggins B. Elizabeth , Wintermantel William M. , Ross Kathleen
Published: May 2007

A new variety of Nicotiana, N. edwardsonii var. Columbia, was evaluated for its capacity to serve as a new source for virus resistance genes. Columbia was developed from a hybridization between N. glutinosa and N. clevelandii, the same parents used for the formation of the original N. edwardsonii. However, in contrast to the original N. edwardsonii, crosses between Columbia and either of its parents are fertile. Thus, the inheritance of virus resistance genes present in N. glutinosa could be characterized by using Columbia as a bridge plant in crosses with the susceptible parent, N. clevelandii. To determine how virus resistance genes would segregate in interspecific crosses between Columbia and N. clevelandii, we followed the fate of the N gene, a single dominant gene that specifies resistance to Tobacco mosaic virus (TMV). Our genetic evidence indicated that the entire chromosome containing the N gene was introgressed into N. clevelandii to create an addition line, designated N. clevelandii line 19. Although line 19 was homozygous for resistance to TMV, it remained susceptible to Tomato bushy stunt virus (TBSV) and Cauliflower mosaic virus (CaMV) strain W260, indicating that resistance to these viruses must reside on other N. glutinosa chromosomes. We also developed a second addition line, N. clevelandii line 36, which was homozygous for resistance to TBSV. Line 36 was susceptible to TMV and CaMV strain W260, but was resistant to other tombusviruses, including Cucumber necrosis virus, Cymbidium ringspot virus, Lettuce necrotic stunt virus, and Carnation Italian ringspot virus.
Molecular Characterization of a Powdery Mildew Resistance Gene in Wheat Cultivar Suwon 92
Authors: Xu X.-Y. , Bai G.-H. , Carver B. F. , Shaner G. E. , Hunger R. M.
Published: May 2007

Powdery mildew, caused by Blumeria graminis f. sp tritici, is an important foliar disease of wheat worldwide. Pyramiding race-specific genes into a single cultivar and combining race-specific resistance genes with durable resistance genes are the preferred strategies to improve the durability of powdery mildew resistance. The objectives of this study were to characterize a powdery mildew resistance gene in Suwon 92 and identify gene-specific or tightly linked molecular markers for marker-assisted selection (MAS). A population of recombinant inbred lines (RILs) was derived by single seed descent from a cross between Suwon 92 and a susceptible cultivar, CI 13227. The RILs were screened for adult-plant infection type of powdery mildew and characterized with amplified fragment length polymorphism (AFLP) and simple sequence repeat (SSR) markers. The linked markers explained 41.3 to 69.2% of the phenotypic variances measured in 2 years. A morphological marker, hairy glume, was also associated with powdery mildew resistance in Suwon 92, and explained 43 to 51% of the phenotypic variance. The powdery mildew resistance gene in Suwon 92 was located on the short arm of chromosome 1A where Pm3 was located. Two gene-specific markers were developed based on the sequence of the cloned Pm3b gene. These two markers, which were mapped at the same locus in the peak region of the LOD score for the RIL population, explained most of the phenotypic variance for powdery mildew resistance in the RIL population. The powdery mildew resistance in Suwon 92 is most likely conditioned by the Pm3 locus. The gene markers developed herein can be directly used for MAS of some of the Pm3 alleles in breeding programs.
Spatial Relationships of Soil Texture and Crop Rotation to Aspergillus flavus Community Structure in South Texas
Authors: Jaime-Garcia Ramon , Cotty Peter J.
Published: May 2007

Aspergillus flavus, the causal agent of aflatoxin contamination of cottonseed, is a natural inhabitant of soils. A. flavus can be divided into the S and L strains, of which the S-strain isolates, on average, produce greater quantities of aflatoxins than the L-strain isolates. Aflatoxin contamination can be severe in several crops in South Texas. The structure of A. flavus communities residing in soils of South Texas was determined from 326 soil samples collected from 152 fields located from the Rio Grande Valley in the south to Fort Bend County in the north from 2001 through 2003. Analysis of variance indicated significant differences in the incidence of A. flavus isolates belonging to the S strain (percent S) among regions. The Coastal Bend (30.7%) and Upper Coast (25.5%) regions had significantly higher percent S incidence than the Rio Grande Valley (4.8%). No significant differences in percent S among years were detected. The CFU per gram of soil were not significantly different among regions. Strain S incidence was positively correlated with clay content and negatively correlated with sand content. Fields cropped to cotton the previous year had a higher S-strain incidence, whereas fields cropped to corn had greater total quantities of A. flavus propagules. Maps of S-strain patterns show that the S strain constitutes >30% of the overall A. flavus community in the area extending from the central Coastal Bend region to the central Upper Coast region. The west Rio Grande Valley had the lowest S-strain incidence (<10%). Geographic variation in S-strain incidence may influence the distribution of aflatoxin contamination in South Texas.
Fusarium-Induced Diseases of Tropical, Perennial Crops
Authors: Ploetz Randy C.
Published: May 2007

The world's oldest ecosystems are found in the tropics. They are diverse, highly evolved, but barely understood. This and subsequent papers describe diseases of tropical, perennial plants that are caused by Fusarium spp. Many of these are economically significant, difficult to manage, and of scientific interest. Some represent coevolved patho-systems (e.g., Panama disease, tracheomycosis of coffee, fusariosis of pineapple, and Fusarium wilt of oil palm), whereas others may be new-encounter diseases or are caused by generalist pathogens (cushion gall of cacao). New vector relationships are evident in other pathosystems (e.g., mango malformation), and two or more pathogens have been shown to cause some of the diseases (Panama disease and tracheomycosis of coffee). More work on these pathosystems is warranted as they could reveal much about the evolution of plant pathogens and the important diseases they cause.
Mango Malformation Disease and the Associated Fusarium Species
Authors: Marasas W. F. O. , Ploetz R. C. , Wingfield M. J. , Wingfield B. D. , Steenkamp E. T.
Published: May 2007

Mango malformation disease (MMD) occurs in Asia, Africa, and the Americas and was first reported in India in 1891. The vegetative form of MMD was first reproduced in 1966 with Fusarium moniliforme and the floral form with isolates of F. moniliforme var. subglutinans from both vegetative shoots and floral tissue. The fungi were subsequently recognized as F. subglutinans. In 2002, a new species, F. mangiferae, was established based on nuclear and mitochondrial DNA sequences; it included strains of F. subglutinans from Egypt, Florida, Israel, Malaysia, and South Africa, some of which had been shown to cause MMD by artificial inoculation. At least three additional taxa have been associated with MMD: F. sterilihyphosum from Brazil and South Africa, and Fusarium sp. nov. and F. proliferatum (teleomorph: Gibberella intermedia) from Malaysia. To date, Koch's postulates have not been completed with them. In the future, gene sequencing will be essential to identify the Fusarium spp. that are associated with MMD. Work remains to be done on the morphology, sexual compatibility, pathogenicity, and toxigenicity of these taxa.
Occurrence, Distribution, and Polymerase Chain Reaction-Based Detection of Resistance to Sterol Demethylation Inhibitor Fungicides in Populations of Blumeriella jaapii in Michigan
Authors: Proffer Tyre J. , Berardi Raffaele , Ma Zhonghua , Nugent James E. , Ehret Gail R. , McManus Patricia S. , Jones Alan L. , Sundin George W.
Published: May 2007

The intensive use of site-specific fungicides in agricultural production provides a potent selective mechanism for increasing the frequency of fungicide-resistant isolates in pathogen populations. Practical resistance occurs when the frequency and levels of resistance are great enough to limit the effectiveness of disease control in the field. Cherry leaf spot (CLS), caused by the fungus Blumeriella jaapii, is a major disease of cherry trees in the Great Lakes region. The site-specific sterol demethylation inhibitor fungicides (DMIs) have been used extensively in the region. In 2002, CLS control failed in a Michigan orchard that had used the DMI fenbuconazole exclusively for 8 years. That control failure and our observations from around the state suggested that practical resistance had developed in B. jaapii. Field trial data covering 1989 to 2005 for the DMIs fenbuconazole and tebuconazole supported observations of reduced efficacy of DMIs for controlling CLS. To verify the occurrence of fungicide-resistant B. jaapii, monoconidial isolates were collected in two surveys and tested using a fungicide-amended medium. In one survey, 137 isolates from sites with different DMI histories (no known history, mixed or alternated with other fungicides, and exclusive use) were tested against 12 concentrations of fenbuconazole, tebuconazole, myclobutanil, and fenarimol. Isolates from sites with no prior DMI use were DMI sensitive (DMIS = no colony growth at 0.2 μg/ml a.i.) whereas the isolates from the site with prior exclusive use showed growth at DMI concentrations 3 to >100 times higher, and were rated as DMI resistant (DMIR). A second survey examined 1,530 monoconidial isolates, including 1,143 from 62 orchard sites in Michigan, where DMIs had been used to control CLS. Resistance to fenbuconazole was detected in 99.7% of the orchard isolates. All isolates from wild cherry trees were sensitive and isolates from feral and dooryard trees showed a range of sensitivities. A polymerase chain reaction (PCR)-based detection method for identifying B. jaapii and DMIR was developed and tested. The species-specific primer pair (Bj-F and Bj-R) based on introns in the CYP51 gene of B. jaapii, and the DMIR-specific primer pair (DMI-R-Bj-F and DMI-R-Bj-R) based on an insert found upstream of CYP51 in all DMIR isolates, provided an accurate and rapid method for detecting DMIR B. jaapii. The PCR-based identification method will facilitate timely decision making and continued monitoring of DMIR subpopulations in response to management programs.
Induction of Beet-Cyst Nematode Suppressiveness by the Fungi Dactylella oviparasitica and Fusarium oxysporum in Field Microplots
Authors: Olatinwo Rabiu , Borneman James , Becker J. Ole
Published: May 2007

The ability of Dactylella oviparasitica and Fusarium oxysporum to suppress Heterodera schachtii numbers was examined in field microplots. Fungi were individually added to fumigated field soil that was seeded with sugar beet. Four weeks later, soils were infested with H. schachtii second-stage juveniles (J2). At two harvests, 11 weeks and 19 weeks (1,469 and 2,547 degree days (base 8°C), respectively) after nematode-infestation, H. schachtii cyst and egg numbers were assessed. At both time points, D. oviparasitica reduced H. schachtii population densities to those in the naturally suppressive soil, even when additional H. schachtii J2 were added to the microplots after the first harvest. Although F. oxy-sporum did not alter H. schachtii population densities after 11 weeks, significant reductions were detected after 19 weeks. The sustainability of the H. schachtii suppressiveness created by single applications of the fungi at the beginning of the microplot trials was further examined in a greenhouse study. Soil collected at the completion of the microplot trials was potted and seeded with sugar beet. Four weeks later, each pot was infested with H. schachtii J2. Approximately 16 weeks (1,389 degree days) after seeding, the D. oviparasitica-amended soil produced greater fresh root weights and considerably smaller nematode population densities than the nonamended control.
Dynamics of Xanthomonas oryzae pv. oryzae Populations in Korea and Their Relationship to Known Bacterial Blight Resistance Genes
Authors: Jeung J. U. , Heu S. G. , Shin M. S. , Vera Cruz C. M. , Jena K. K.
Published: May 2007

Developing resistant cultivars requires an understanding of the dynamics of the pathogen populations as well as the genetics of host resistance. Bacterial leaf blight (BB), caused by the vascular pathogen Xanthomonas oryzae pv. oryzae, has become one of the most devastating diseases of rice. We demonstrate here the quantitative analyses of responses of near-isogenic lines carrying various BB resistance (R) genes and R-gene combinations against 16 X. oryzae pv. oryzae isolates representing Korean BB pathotypes. The estimated main effects of each R gene against the 16 isolates identified prominent differences in BB pathotypes between Korea and other countries. Three major aspects of our quantitative observations and statistical analysis are (i) strong and broad resistance of xa5; (ii) independent and additive genetic actions of Xa4, xa5, and Xa21 under digenic or trigenic status; and (iii) a strong quantitative complementation effect contributed by the functional alleles of Xa4 and Xa21. We conclude that the pyramid line containing genes Xa4, xa5, and Xa21 would be the most promising and valuable genotype for improving Korean japonica cultivars for BB resistance.
Allium White Rot Suppression with Composts and Trichoderma viride in Relation to Sclerotia Viability
Authors: Coventry E. , Noble R. , Mead A. , Marin F. R. , Perez J. A. , Whipps J. M.
Published: May 2007

Allium white rot (AWR) is a serious disease of Allium spp. caused by the sclerotium-forming fungus Sclerotium cepivorum. This work has examined the effects of onion waste compost (OWC) and spent mushroom compost (SMC), with and without Trichoderma viride S17A, on sclerotia viability and AWR in glasshouse and field experiments. Incorporation of OWC into soil reduced the viability of sclerotia and the incidence of AWR on onion plants in glasshouse pot bioassays, whereas SMC or T. viride S17A only reduced incidence of AWR. In two field trials, OWC reduced sclerotia viability and was as effective in reducing AWR as a fungicide (Folicur, a.i. tebuconazole). Field application of SMC had no effect on sclerotia viability and did not control AWR. However, the addition of T. viride S17A to SMC facilitated proliferation of T. viride S17A in the soil and increased the healthy onion bulb yield. The results indicate two mechanisms for the suppression of AWR: (i) reduction in the soil population of viable sclerotia, which may be due to volatile sulfur compounds detected in OWC but absent in SMC, and (ii) prevention of infection of onion plants from sclerotia following amendment of soil with OWC, SMC, or T. viride S17A.
Inheritance and Heritability of Resistance to Citrus Leprosis
Authors: Bastianel Marinês , de Oliveira Antonio Carlos , Cristofani Mariângela , Filho Oliveiro Guerreiro , Freitas-Astúa Juliana , Rodrigues Vandeclei , Astúa-Monge Gustavo , Machado Marcos Antônio
Published: May 2007

The genetic inheritance of resistance to leprosis, the most important viral disease of citrus in Brazil, was characterized through the phenotypic assessment of 143 hybrids resulting from crosses between tangor ‘Murcott’ (Citrus sinensis × C. reticulata) and sweet orange ‘Pêra’ (C. sinensis), considered to be resistant and susceptible to the disease, respectively. All plants were grafted onto Rangpur lime (C. limonia) and inoculated with Citrus leprosis virus, cytoplasmic type through the infestation with viruliferous mites, Brevipalpus phoenicis. The experiments were arranged in a completely randomized block design with 10 replicates. Incidence and severity of the disease in leaves and stems as well as plant growth parameters (plant height and stem diameter) were recorded for 3 years after the infestation with the viruliferous mites. The average values of all variables were analyzed using principal component analysis, discriminant factorial analysis, estimation of the clonal repeatability coefficients, and frequency of the distributions of the average values for each measured variable. The principal component analysis resulted in the identification of at least two groups with resistance and susceptibility to leprosis, respectively. About 99% of all hybrids were correctly classified according to the discriminant factorial analysis. The broad-sense heritability coefficients for characteristics associated with incidence and severity of leprosis ranged from 0.88 to 0.96. The data suggest that the inheritance of resistance to leprosis may be controlled by only a few genes.
Hierarchical Analysis of Diversity, Selfing, and Genetic Differentiation in Populations of the Oomycete Aphanomyces euteiches
Authors: Grünwald Niklaus J. , Hoheisel Gwen-Alyn
Published: May 2007

Relatively little is known about the population biology of the legume pathogen Aphanomyces euteiches. A. euteiches is a soilborne pathogen causing Aphanomyces root rot of several legumes, including alfalfa, bean, lentil, and pea. Our objectives were to assess the degree of diversity, selfing, and population differentiation in A. euteiches. We contrasted populations within and among two geographically separated fields with a history of pea production. Molecular genotyping relied on amplified fragment length polymorphism analysis. Samples of A. euteiches recovered from two fields in northeast Oregon and western Washington confirmed previous reports of moderately high genetic diversity in populations of A. euteiches at the regional scale, but revealed higher-than-expected genotypic diversity within individual soil samples. Populations of A. euteiches were significantly differentiated at the soil sample, field, and regional level. The population structure appears to be patterned by regular selfing via oospores, a mixed reproductive system including both asexual and sexual reproduction, with occasional migration of novel genotypes or outcrossing.
Use of Bayesian Methods to Improve Prediction of Panicle and Shoot Blight Severity of Pistachio in California
Authors: Mila Asimina L. , Michailides Themis J.
Published: May 2007

Panicle and shoot blight, caused by a Fusicoccum sp., is one of the major aboveground diseases of pistachio in California. The effects of temperature, number of continuous rainy days in April and May, irrigation system, and incidence of latent infection of the Fusicoccum sp. on severity of panicle and shoot blight of pistachio leaves and fruit have been quantified previously, using data collected from 1999 through 2001. A predictive model for leaves and another model for fruit with good explanatory power were generated. In 2003 and 2004, newly collected data were used to evaluate the two models with non-Bayesian and Bayesian methods. The 95% credible (i.e., confidence) intervals of initial (before modification with non-Bayesian and Bayesian methods) and updated parameter estimates were used to investigate their prognostic validity. In 2003, the non-Bayesian analysis resulted in all parameter estimates, with the exception of cumulative daily mean temperature from 1 June until harvest, having different 95% confidence intervals than the parameter estimates of the original models. In addition, the parameter estimates for drip irrigation for the leaf infection and the parameter estimates for drip irrigation and number of continuous rainy days in April and May for fruit infection were not statistically significant. With Bayesian methods, the reestimated model parameters had overlapping 95% credible intervals with the initial estimated parameters, except for the number of continuous rainy days in April and May. When the two sets of modified parameter estimates were used to predict disease severity, statistically significant (α = 0.05) differences between observed and predicted disease severities were found with non-Bayesian analysis for leaf infection in three locations and with Bayesian analysis for fruit infection in one orchard. The parameter estimates were modified again at the end of the 2004 season and were all statistically significant with both non-Bayesian and Bayesian methods. Both sets of parameter estimates gave predictions that were not significantly different from observed disease severity on leaves and fruit in all monitored orchards in 2004. In summary, Bayesian methods gave more consistent results when used to update parameter estimates with new information and yielded predictions not statistically different from observed disease severity in more cases than the non-Bayesian analysis.
Phenotypic and Genetic Diversity in Strains of Common Blight Bacteria (Xanthomonas campestrispv.phaseoliandX. campestrispv.phaseolivar.fuscans) in a Secondary Center of Diversity of the Common Bean Host Suggests Multiple Introduction Events
Authors: López Ruth , Asensio Carmen , Gilbertson Robert L.
Published: May 2007

Common bacterial blight (CBB) disease of the common bean (Phaseolus vulgaris) is caused by Xanthomonas campestris pv. phaseoli and the brown-pigmented variant X. campestris pv. phaseoli var. fuscans. CBB first was described in Castilla y León County, Spain, in 1940, and is now a major constraint on common bean production. In this secondary center of diversity of the common bean, large-seeded Andean cultivars predominate, although medium-seeded Middle American cultivars also are grown. Xanthomonad-like bacteria associated with CBB in Castilla y León were characterized on the basis of carbohydrate metabolism, brown pigment production, genetic analyses (repetitive-element polymerase chain reaction [rep-PCR] and random amplified polymorphic DNA [RAPD]) and pathogenicity on cultivars representing the two common bean gene pools (Andean and Middle American). X. campestris pv. phaseoli was more prevalent (80%) than X. campestris pv. phaseoli var. fuscans (20%). Patterns of carbohydrate metabolism of Spanish CBB bacteria were similar to those of known strains; and only X. campestris pv. phaseoli var. fuscans strains utilized mannitol as a sole carbon source. rep-PCR and RAPD analyses revealed relatively little genetic diversity among Spanish X. campestris pv. phaseoli strains, and these strains were placed together with New World strains into a large cluster. Similar to other New World strains, representative Spanish X. campestris pv. phaseoli strains were highly pathogenic on bean cultivars of both gene pools, showing no gene pool specialization such as that found in certain East African strains. Genetic analyses and pathogenicity tests confirmed and extended previous results, indicating that these East African strains represent distinct xanthomonads that independently evolved to be pathogenic on common bean. X. campestris pv. phaseoli var. fuscans strains were more closely related and genetically distinct from X. campestris pv. phaseoli strains. However, two distinct clusters of X. campestris pv. phaseoli var. fuscans strains were identified, one having the most New World strains and the other having the most African strains. Spanish strains were placed in both clusters, but all strains tested were highly pathogenic on bean cultivars of both gene pools. Together, our results are consistent with multiple introductions of CBB bacteria into Spain. These findings are discussed in terms of breeding for CBB resistance and the overall understanding of the genetic diversity and evolution of CBB bacteria.
Identification, Characterization, and Molecular Detection of Alfalfa mosaic virus in Potato
Authors: Xu H. , Nie J.
Published: May 2007

Alfalfa mosaic virus (AMV) was detected in potato fields in several provinces in Canada and characterized by bioassay, enzyme-linked immunosorbent assay, and reverse-transcription polymerase chain reaction (RT-PCR). The identity of eight Canadian potato AMV isolates was confirmed by sequence analysis of their coat protein (CP) gene. Sequence and phylogenetic analysis indicated that these eight AMV potato isolates fell into one strain group, whereas a slight difference between Ca175 and the other Canadian AMV isolates was revealed. The Canadian AMV isolates, except Ca175, clustered together among other strains based on alignment of the CP gene sequence. To detect the virus, a pair of primers, AMV-F and AMV-R, specific to the AMV CP gene, was designed based on the nucleotide sequence alignment of known AMV strains. Evaluations showed that RT-PCR using this primer set was specific and sensitive for detecting AMV in potato leaf and tuber samples. AMV RNAs were easily detected in composite samples of 400 to 800 potato leaves or 200 to 400 tubers. Restriction analysis of PCR amplicons with SacI was a simple method for the confirmation of PCR tests. Thus, RT-PCR followed by restriction fragment length polymorphism analysis may be a useful approach for screening potato samples on a large scale for the presence of AMV.
Identification of Common Epitopes on a Conserved Region of NSs Proteins Among Tospoviruses of Watermelon silver mottle virus Serogroup
Authors: Chen Tsung-Chi , Huang Ching-Wen , Kuo Yan-Wen , Liu Fang-Lin , Yuan Chao-Hsiu Hsuan , Hsu Hei-Ti , Yeh Shyi-Dong
Published: May 2007

The NSs protein of Watermelon silver mottle virus (WSMoV) was expressed by a Zucchini yellow mosaic virus (ZYMV) vector in squash. The expressed NSs protein with a histidine tag and an additional NIa protease cleavage sequence was isolated by Ni2+-NTA resins as a free-form protein and further eluted after sodium dodecyl sulfate-polyacrylamide gel electrophoresis for production of rabbit antiserum and mouse monoclonal antibodies (MAbs). The rabbit antiserum strongly reacted with the NSs crude antigen of WSMoV and weakly reacted with that of a high-temperature-recovered gloxinia isolate (HT-1) of Capsicum chlorosis virus (CaCV), but not with that of Calla lily chlorotic spot virus (CCSV). In contrast, the MAbs reacted strongly with all crude NSs antigens of WSMoV, CaCV, and CCSV. Various deletions of the NSs open reading frame were constructed and expressed by ZYMV vector. Results indicate that all three MAbs target the 89- to 125-amino-acid (aa) region of WSMoV NSs protein. Two indispensable residues of cysteine and lysine were essential for MAbs recognition. Sequence comparison of the deduced MAbs-recognized region with the reported tospoviral NSs proteins revealed the presence of a consensus sequence VRKPGVKNTGCKFTMHNQIFNPN (denoted WNSscon), at the 98- to 120-aa position of NSs proteins, sharing 86 to 100% identities among those of WSMoV, CaCV, CCSV, and Peanut bud necrosis virus. A synthetic WNSscon peptide reacted with the MAbs and verified that the epitopes are present in the 98- to 120-aa region of WSMoV NSs protein. The WSMoV sero-group-specific NSs MAbs provide a means for reliable identification of tospoviruses in this large serogroup.
Development of Nested Polymerase Chain Reaction Detection ofMycosphaerellaspp. and Its Application to the Study of Leaf Disease inEucalyptusPlantations
Authors: Glen M. , Smith A. H. , Langrell S. R. H. , Mohammed C. L.
Published: May 2007

Mycosphaerella leaf disease (MLD) is a serious disease of two of the major eucalypt species grown in temperate regions worldwide, Eucalyptus globulus and E. nitens. More than 30 species of Mycosphaerella have been reported on eucalypts worldwide. Accurate, rapid, and early discrimination of Mycosphaerella spp. causing crown damage to E. globulus and E. nitens will assist the development of sustainable management strategies. This study describes the development, and incorporation in a nested polymerase chain reaction (PCR) approach, of specific primers for the detection and identification of Mycosphaerella spp. commonly reported from leaf lesions of E. globulus and E. nitens in Australia. Primer design was assisted by sequence alignment and phylogenetic analysis of 165 nonredundant sequences from the nuclear ribosomal DNA internal transcribed spacer regions of Mycosphaerella and related species. Phylo-genetic analysis revealed very high sequence similarity for two taxon groups, Mycosphaerella grandis and M. parva, and M. vespa, M. ambi phylla, and M. molleriana, and primers were designed to differentiate each of the two groups. Three other species, M. cryptica, M. nubilosa, and M. tasmaniensis, were distinct and distinguished by species-specific primers. In double-blind trials, the detection test accurately and rapidly identified Mycosphaerella spp. in cultures and discriminated against other pathogens that co-occur in or on Eucalyptus leaves, thereby verifying its reliability. The detection test has an internal amplification control in the first-round PCR with fungal-specific primers to raise confidence in test results, particularly to highlight negative results due to PCR inhibition. When applied to DNA extracted from leaf or stem samples either as multiple or single lesions, it detected and identified up to five Mycosphaerella spp. or taxon groups in both positively identified and in young (putative) MLD lesions. The samples were 20 mm2or larger in surface area and were collected while undertaking disease rating assessments in an experimental investigation of Eucalyptus plantations and regrowth forest. Using nested PCR detection, Mycosphaerella spp. were positively identified in 2 days, 1 to 5 months earlier than by classical methods, demonstrating the potential application of this detection test to the early discrimination of MLD components in ecological, epidemiological, and genetic investigations.