bluuebunny/crossref_metadata_2025 huggingface dataset:
Depth Distribution of Rotylenchulus reniformis Under Different Tillage and Crop Sequence Systems
Authors: Westphal A. , Smart J. R.
Published: May 2007

The population density of the reniform nematode, Rotylenchulus reniformis, was monitored at depths of 0 to 30, 30 to 60, 60 to 90, and 90 to 120 cm in a tillage and crop sequence trial in south Texas in 2000 and 2001. Main plots were subjected to three different tillage systems: conventional tillage (moldboard plowing and disking), ridge tillage, and no-tillage. Subplots were planted with three different crop sequences: spring cotton and fall corn every year; spring cotton and fall corn in one year, followed by corn for two years; and cotton followed by corn and then grain sorghum, one spring crop per year. The population density of R. reniformis on corn and grain sorghum was low throughout the soil profile. In plots planted with spring cotton and fall corn every year, fewer nematodes were found at depths of 60 to 120 cm in the no-tillage and ridge tillage systems than in the conventional tillage system. Population densities were lower at depths of 0 to 60 cm than at 60 to 120 cm. Soil moisture and cotton root length did not affect nematode population densities in the field. When soil was placed in pots and planted with cotton in the greenhouse, lower population densities developed in soil taken from depths of 0 to 60 cm than in soil from depths of 60 to 120 cm. Final nematode populations were similar in size in soil from the different tillage systems, but reproductive factors were higher in soil from plots with reduced-tillage systems than in soil from plots with conventional tillage. Reduced-tillage practices lowered the risk of increases in R. reniformis populations and reduced population densities following 2 years of non-hosts throughout soil depths, but population densities resurged to the same high levels as in soil planted with cotton every year during one season of cotton.
A Chitinase from Tex6 Maize Kernels Inhibits Growth of Aspergillus flavus
Authors: Moore Kenneth G. , Price Michael S. , Boston Rebecca S. , Weissinger Arthur K. , Payne Gary A.
Published: May 2007

The maize inbred Tex6 has resistance to colonization and aflatoxin accumulation by Aspergillus flavus. A protein inhibitory to growth of A. flavus has been identified from aqueous extracts of mature Tex6 seeds. This study reports the purification of a chitinase associated with this inhibitory activity to electrophoretic homogeneity and the further characterization of its properties. The inhibitory protein, which has an Mr of 29,000, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, is an endochitinase that is also capable of exochitinase activity. The enzyme has an optimal pH of 5.5 and a temperature optimum of 45°C. Chitinase activity in maize kernels peaked approximately 36 days after pollination. The Tex6 chitinase purified in this study is capable of inhibiting the growth of A. flavus by 50% at a concentration of 20 μg/ml. Our data indicate that chitinase activity in Tex6 kernels makes a major contribution to the antifungal activity in this maize genotype. Partial peptide sequence of the chitinase showed it to differ from previously reported chitinases.
Quantitative Trait Loci Analysis and Mapping of Seedling Resistance to Stagonospora nodorum Leaf Blotch in Wheat
Authors: Liu Z. H. , Friesen T. L. , Rasmussen J. B. , Ali S. , Meinhardt S. W. , Faris J. D.
Published: May 2007

Stagonospora nodorum leaf blotch is an economically important foliar disease in the major wheat-growing areas of the world. In related work, we identified a host-selective toxin (HST) produced by the S. nodorum isolate Sn2000 and determined the chromosomal location of the host gene (Snn1) conditioning sensitivity to the toxin using the International Triticeae Mapping Initiative mapping population and cytogenetic stocks. In this study, we used the same plant materials to identify quantitative trait loci (QTL) associated with resistance to fungal inoculations of Sn2000 and investigate the role of the toxin in causing disease. Disease reactions were scored at 5, 7, and 10 days postinoculation to evaluate changes in the degree of effectiveness of individual QTL. A major QTL was identified on the short arm of chromosome 1B, which coincided with the snn1 toxin-insensitivity gene. This locus explained 58% of the phenotypic variation for the 5-day reading but decreased to 27% for the 10-day reading, indicating that the toxin is most effective in the early stages of the interaction. In addition, relatively minor QTL were identified on chromosomes 3AS, 3DL, 4AL, 4BL, 5DL, 6AL, and 7BL, but not all minor QTL were significant for all readings and their effects varied. Multiple regression models explained from 68% of the phenotypic variation for the 5-day reading to 36% for the 10-day reading. The Chinese Spring nullisomic 1B tetrasomic 1D line and the Chinese Spring-Triticum dicoccoides disomic 1B chromosome substitution line, which were insensitive to SnTox1, were more resistant to the fungus than the rest of the nullisomictetrasomic and disomic chromosome substitution lines. Our results indicate that the toxin produced by isolate Sn2000 is a major virulence factor.
Spatial Pattern Analysis of Hop Powdery Mildew in the Pacific Northwest: Implications for Sampling
Authors: Turechek William W. , Mahaffee Walter F.
Published: May 2007

The spatial pattern of hop powdery mildew was characterized using 3 years of disease incidence data collected in commercial hop yards in the Pacific Northwest. Yards were selected randomly from yards with a history of powdery mildew, and two to five rows were selected for sampling within each yard. The proportion of symptomatic leaves out of 10 was determined from each of N sampling units in a row. The binomial and the beta-binomial frequency distributions were fit to the N sampling units observed in each row and to ΣN sampling units observed in each yard. Distributional analyses indicated that disease incidence was better characterized by the beta-binomial than the binomial distribution in 25 and 47% of the data sets at the row and yard scales, respectively, according to a log-likelihood ratio test. Median values of the beta-binomial parameter θ, a measure of small-scale aggregation, were near 0 at both sampling scales, indicating that disease incidence was close to being randomly distributed. The variability in disease incidence among rows sampled in the same yard generally increased with mean incidence at the yard scale. Spatial autocorrelation analysis, used to measure large-scale patterns of aggregation, indicated that disease incidence was not correlated between sampling units over several lag distances. Results of a covariance analysis showed that heterogeneity of disease incidence was not dependent upon cultivar, region, or time of year when sampling was conducted. A hierarchical analysis showed that disease incidence at the sampling unit scale (proportion of sampling units with one or more diseased leaves) increased as a saturation-type curve with respect to incidence at the leaf level and could be described by a binomial function modified to account for the effects of heterogeneity through an effective sample size. Use of these models permits sampling at the sampling unit scale while allowing inferences to be made at the leaf scale. Taken together, hop powdery mildew was nearly randomly distributed with no discernable foci, suggesting epidemics are initiated from a well-distributed or readily dispersible overwintering population. Implications for sampling are discussed.
Analysis of the Spatial Patterns of Pierce's Disease Incidence in the Lower San Joaquin Valley in California
Authors: Tubajika K. M. , Civerolo E. L. , Ciomperlik M. A. , Luvisi D. A. , Hashim J. M.
Published: May 2007

The incidence of Pierce's disease (PD), caused by Xylella fastidiosa, was monitored in 11 naturally infested commercial vineyards to determine the presence of an X. fastidiosa vector, Homalodisca coagulata (glassy-winged sharpshooter [GWSS]), to examine the spatial patterns of the disease and elucidate possible influences of surrounding environments. Disease incidence ranged from <1 to 65% among vineyards in 2001. Our efforts to trap or capture potential disease vectors have indicated that the GWSS is the most likely vector. Disease incidence doubled in most vineyards during the 2002 production season. Spatial patterns of symptomatic vines in 2001 and 2002, as determined by ordinary runs analysis, showed strong evidence for within- and across-row aggregation of infected vines. In most fields, they were no disease gradients observed relative to GWSS source (e.g., citrus). Within fields, however, disease incidence displayed strong spatial dependence and a high degree of anisotropy, indicating strongly aggregated patterns of disease with distinct directional orientation. The within-row (0°) and across-row (90°) orientations generally were the predominant directions of increased disease incidence, consistent with vine-to-vine spread of X. fastidiosa. We concluded that the distribution of PD in vineyards reflected the feeding pattern of vectors carrying X. fastidiosa. Based on these results, effective PD management is likely to be based on practices that reduce significant insect vector populations and remove infected vines as soon as identified and on the use of resistant cultivars.
Indole-3-Acetic Acid-Producing Bacteria Are Associated with Cranberry Stem Gall
Authors: Vasanthakumar Archana , McManus Patricia S.
Published: May 2007

Cranberry stem gall is characterized by tumors that girdle stems, thereby killing all distal leaves, flowers, and fruit. Among bacteria isolated from galls, all 11 isolates that were identified as members of the family Enterobacteriaceae caused galls on 50 to 100% of micropropagated cranberry plants that were inoculated. Four of fifteen isolates identified as Pseudomonas spp. caused galls on 10 to 83% of plants inoculated. Twelve of fifteen isolates identified as either Agrobacterium spp. or Rhizobium spp. caused galls on 10 to 50% of plants inoculated, but the galls were smaller than those caused by members of the family Enterobacteriaceae or Pseudomonas spp. There was a positive correlation between the ability of bacteria to produce IAA in vitro and cause galls. In 2002 and 2003, bacteria were isolated from plant and soil samples collected from beds where stem gall had been observed in the past 2 years and beds where stem gall had never been observed. IAA-producing bacteria were common in all samples, although trends were different across years. The results of this study support the hypothesis that IAA-producing bacteria cause cranberry stem gall and suggest that rather than one bacterial species being the cause, multiple strains of bacteria that produce IAA may be responsible for gall formation.
Polygenic Inheritance of Partial Resistance to Fusarium oxysporum f. sp. melonis Race 1.2 in Melon
Authors: Perchepied L. , Pitrat M.
Published: May 2007

Fusarium oxysporum f. sp. melonis is responsible for Fusarium wilt of melon. Race 1.2 strains overcome two dominant resistance genes (Fom-1 and Fom-2) and are further divided into two types depending on the symptoms they cause, yellowing or wilting. Partial resistance to F. oxysporum f. sp. melonis race 1.2 was studied by using a recombinant inbred line (RIL) population that was developed by single seed descent from an F1 hybrid between ‘Isabelle’, a partially resistant line, and a susceptible line, ‘Védrantais’. Artificial inoculations were performed with a yellowing strain (TST) and a wilting strain (D'Oléon 8) and replicated in six locations. Disease reactions of the parental lines, controls, and RILs were scored using a 1-to-5 scale and by using the area under the disease progress curve (AUDPC). Phenotypic correlations were highly significant between the different locations and experiments. The heritability of the resistance was high, from 0.72 to 0.96, and 4 to 14 genetic factors were estimated to confer resistance to F. oxysporum f. sp. melonis race 1.2. Thirteen other strains were tested with an RILs subset. Some small strainspecific effects may be involved. These results contribute to a better understanding of the polygenic inheritance of the partial resistance to F. oxysporum f. sp. melonis race 1.2.
Interactions Between Trichoderma harzianum Strain T22 and Maize Inbred Line Mo17 and Effects of These Interactions on Diseases Caused by Pythium ultimum and Colletotrichum graminicola
Authors: Harman Gary E. , Petzoldt Rixana , Comis Alfio , Chen Jie
Published: May 2007

Seed treatment with Trichoderma harzianum strain T22, which results in colonization of plant roots but little or no colonization of shoots or leaves, had substantial effects on growth of and disease expression in maize inbred line Mo17. Shoots and roots of 10-day-old seedlings grown in a sandy loam field soil were larger (roots were nearly twice as long) in the presence of T22 than in its absence. Both main and secondary roots were increased in size and area and the root hair area was greater with T22. However, root hair area per unit of root length was greater in control plants. Increased growth probably was due to direct stimulation of plant growth in addition to effects from biological control of deleterious microflora. Seedlings of Mo17 grown in autoclaved or mefenoxamtreated sandy loam field soil were larger than those produced in untreated soil. However, seedlings grown in the presence of T22, either in treated or untreated soil, were larger than those produced in its absence. Infestation of soil with Pythium ultimum had little effect upon growth of Mo17. The presence of T22 increased protein levels and activities of β-1,3 glucanase, exochitinase, and endochitinase in both roots and shoots, even though T22 colonized roots well but colonized shoots hardly at all. With some enzymes, the combination of T22 plus P. ultimum gave the greatest activity. Plants grown from T22-treated seed had reduced symptoms of anthracnose following inoculation of leaves with Colletotrichum graminicola, which indicates that root colonization by T22 induces systemic resistance in maize.
Silicon Enhances the Accumulation of Diterpenoid Phytoalexins in Rice: A Potential Mechanism for Blast Resistance
Authors: Rodrigues Fabrício Á. , McNally David J. , Datnoff Lawrence E. , Jones Jeffrey B. , Labbé Caroline , Benhamou Nicole , Menzies James G. , Bélanger Richard R.
Published: May 2007

Although several reports underscore the importance of silicon (Si) in controlling Magnaporthe grisea on rice, no study has associated this beneficial effect with specific mechanisms of host defense responses against this fungal attack. In this study, however, we provide evidence that higher levels of momilactone phytoalexins were found in leaf extracts from plants inoculated with M. grisea and amended with silicon (Si+) than in leaf extracts from inoculated plants not amended with silicon (Si- ) or noninoculated Si+ and Si- plants. On this basis, the more efficient stimulation of the terpenoid pathway in Si+ plants and, consequently, the increase in the levels of momilactones appears to be a factor contributing to enhanced rice resistance to blast. This may explain the lower level of blast severity observed on leaves of Si+ plants at 96 h after inoculation with M. grisea. The results of this study strongly suggest that Si plays an active role in the resistance of rice to blast rather than the formation of a physical barrier to penetration by M. grisea.
In Planta Dynamic Analysis of Onion Yellows Phytoplasma Using Localized Inoculation by Insect Transmission
Authors: Wei Wei , Kakizawa Shigeyuki , Suzuki Shiho , Jung Hee-Young , Nishigawa Hisashi , Miyata Shin-ichi , Oshima Kenro , Ugaki Masashi , Hibi Tadaaki , Namba Shigetou
Published: May 2007

Due to the lack of a means to inoculate plants mechanically, the histological dynamics and in planta spread of phytoplasmas have been studied very little. We analyzed the dynamics of plant infection by phytoplasmas, using a technique to infect a limited area of a leaf, nested polymerase chain reaction (PCR), real-time PCR, and immunohistochemical visualization. Following localized inoculation of a leaf of garland chrysanthemum (Chrysanthemum coronarium) by the vector leafhopper Macrosteles striifrons, the onion yellows (OY) phytoplasma spread within the plant from the inoculated leaf to the main stem (1 day postinoculation [dpi]), to the roots and the top leaf (2 dpi), and to other leaves from top to bottom (from 7 to 21 dpi). The populations of the OY phytoplasmas in inoculated leaves and roots increased approximately sixfold each week from 14 to 28 dpi. At 14 dpi, the OY phytoplasmas colonized limited regions of the phloem tissue in both the root and stem and then spread throughout the phloem by 21 dpi. This information should form the basis for elucidating the mechanisms of phytoplasma multiplication and migration within a plant host.
Sources of Resistance to Fumonisin Accumulation in Grain and Fusarium Ear and Kernel Rot of Corn
Authors: Clements M. J. , Maragos C. M. , Pataky J. K. , White D. G.
Published: May 2007

Fumonisin is a group of homologous mycotoxins produced by several species of Fusarium. Fumonisin has been associated with Fusarium ear and kernel rot of corn (Zea mays) and several toxicoses of animals and humans. Corn inbreds with a high level of resistance to fumonisin production and accumulation in grain have not been identified. The objective of this study was to evaluate a genetically diverse collection of inbreds as potential sources of resistance to fumonisin production and accumulation in grain and Fusarium ear and kernel rot when crossed with a commercial “B73-type” line. F1hybrids developed with the inbred FR1064 and 1,589 and 1,030 inbreds were evaluated in inoculated and naturally infected trials, respectively, in 2000. Thirty-five F1hybrids with fumonisin concentration in grain of ≤5 μg/g in both trials were selected. Inbreds from which these 35 F1hybrids were produced included yellow-, white-, and red-kernelled lines; flint and dent lines; and early- through late-maturing lines. In 2001, low fumonisin concentration in grain and low ear rot severity were associated with several of the F1hybrids and their distinct F2, and backcross to FR1064 generations. This suggests that several dominant genes are involved in resistance and that alleles for resistance from these inbreds can be transferred to FR1064.
Development of Co-Dominant Amplified Polymorphic Sequence Markers in Rice that Flank the Magnaporthe grisea Resistance Gene Pi7(t) in Recombinant Inbred Line 29
Authors: Campbell M. A. , Chen D. , Ronald P. C.
Published: May 2007

Pi7(t), a dominant blast resistance gene derived from the rice cultivar Moroberekan, confers complete resistance against the fungal pathogen Magnaporthe grisea. Pi7(t) previously was positioned on chromosome 11 by restriction fragment length polymorphism (RFLP) mapping of a recombinant inbred line population. One derivative of this population, recombinant inbred line (RIL)29, was designated as the representative line for Pi7(t). A segregating F2 population was created from RIL29 in order to determine the location of Pi7(t). The new mapping data indicate a position for Pi7(t) 30 centimorgans distal to the original location. Pi7(t) shares a common position with the previously mapped Pi1 M. grisea resistance gene. RIL29 carries DNA not derived from either parent used to create the RIL population at the newly assigned Pi7(t) locus. RFLP analysis has identified a possible donor source.
Generation and Molecular Mapping of a Sequence Characterized Amplified Region Marker Linked with theBctGene for Resistance toBeet curly top virusin Common Bean
Authors: Larsen Richard C. , Miklas Phillip N.
Published: May 2007

A random amplified polymorphic DNA (RAPD) marker directly linked (0.0 cM) with a resistance gene was identified in a snap bean recombinant inbred population (Moncayo × Primo) consisting of 94 F5:7recombinant inbred lines that had uniform segregation for disease reaction to Beet curly top virus (BCTV) across three field locations. Resistance was conditioned by a single dominant allele tentatively designated Bct. Seven hundred and fifty decamer primers were screened to obtain the linked RAPD marker that was then converted to a sequence characterized amplified region (SCAR) marker SAS8.1550. The SCAR mapped within a cluster of resistance genes on linkage group B7 of the core map. A survey of 103 BCTV-resistant and -susceptible snap and dry bean genotypes was conducted using SAS8.1550. Results showed that the SCAR would be highly useful for marker-assisted selection of Bct in snap and dry bean originating from the Andean gene pool. Marker-assisted selection for Bct will expedite the development of BCTV-resistant cultivars and minimize the need for cumbersome pathogen tests.
Detection of Nitric Oxide in Plants by Electron Spin Resonance
Authors: Xu Yang Cang , Cao Yuan Lin , Guo Ping , Tao Yi , Zhao Bao Lu
Published: May 2007

Three methods to detect nitric oxide (NO•) are reported here. The first method was determining NO• in extracted plant tissue. NO• was trapped by spin trapping reagent containing diethyldithiocarbamate (DETC) and FeSO4, extracted by ethyl acetate, and determined with an electron spin resonance (ESR) spectrometer. The second method was indirectly determining NO• in live wheat leaves. Seedlings were cultured in a medium containing FeSO4, and the leaves were brushed by DETC. Then, the leaves were ground and the complex of (DETC)2-Fe2+-NO was extracted and determined with an ESR spectrometer. The third method was directly determining NO• in live wheat leaves. After treating plant materials as in the second method, part of the water in leaves was transpired, and the leaf disks were inserted directly into quartz tubes to determine NO• with an ESR spectrometer. The NO• scavenger 2-phenyl-4,4,5,5,-tetramethylimidazoline- 1-oxyl 3-oxide (PTIO) decreased NO• signal detected either by an indirect or a direct method. This result indicates that both methods could detect NO• in the live plant. Using the first methods, we detected NO• change in wheat infected by Puccinia striiformis race CY22-2 pathogen (incompatible interaction) at different inoculation times, and it was found that the NO• content dramatically increased at 24 h postinoculation, quickly decreased at 48 h, and increased again at 96 h.
Control of Verticillium Yellows in Chinese Cabbage by the Dark Septate Endophytic Fungus LtVB3
Authors: Narisawa K. , Usuki F. , Hashiba T.
Published: May 2007

Three hundred forty-nine fungal endophytes were obtained from a total of 1,214 root segments of eggplant, melon, barley, and Chinese cabbage grown as bait plants in a mixed soil made up of samples from different forest soils in Alberta and British Columbia, Canada. Three of the 349 isolates, when inoculated in axenically reared Chinese cabbage seedlings grown in petri dishes, almost completely suppressed the effects of a postinoculated and virulent strain of Verticillium longisporum. Two isolates effective against the pathogen were Phialocephala fortinii, which had been obtained from the roots of eggplant and Chinese cabbage. The third isolate was a dark septate endophytic (DSE) fungus obtained from barley roots. Hyphae of P. fortinii grew along the surface of the root and formed microsclerotia on or in the epidermal layer. Hyphae of the DSE fungus heavily colonized root cells of the cortex. Seedlings grown for 1 week in the presence of the endophytes were then challenged with the Verticillium pathogen. In DSE-treated roots, some of cell walls in the epidermal and cortical layers showed cell wall appositions and thickenings, which appeared to limit the ingress of the pathogen into adjacent cells. Such marked host reactions were not observed in the root cells colonized by P. fortinii. Chinese cabbage preinoculated with the above endophytes and, for comparison, a previously reported disease-suppressive fungal endophyte, Heteroconium chaetospira, were transplanted into the field and disease symptoms were assessed. The DSE could most effectively inhibit the development of Verticillium yellows, with reductions in the percentages of external and internal disease symptoms of 84 and 88%, respectively. The protective values against the disease are extremely high compared with those of other isolates. Most of the DSE-treated plants in the plots achieved marketable quality.
Identification and Characterization of a New Blast Resistance Gene Located on Rice Chromosome 1 Through Linkage and Differential Analyses
Authors: Zhu Menglan , Wang Ling , Pan Qinghua
Published: May 2007

The Chinese native cv. Q14 expresses a high level of resistance to many isolates of Pyricularia grisea collected from Japan, Thailand, and China. Q14 was crossed to an indica-susceptible cultivar, Q61. To rapidly determine the chromosomal location of the major resistance gene present in the cultivar, a linkage analysis using microsatellite markers was performed in the F2 population segregating 3R:1S (resistant/susceptible) through bulked-segregant analysis (BSA) in combination with recessiveclass analysis (RCA). A total of 189 microsatellite markers selected from each chromosome equally (with ≈10 centimorgans) were tested with the BSA approach. Only two markers, RM151 and RM259, located on chromosome 1 showed positive and negative polymorphisms, respectively, for a resistance gene segregating in the population. To confirm the polymorphic markers, a total of 155 viable susceptible individuals were tested with the RCA approach. The markers RM151 and RM259 were found to link to the resistance gene with recombination frequencies of 11.9 ± 2.8% and 9.7 ± 8.0%, respectively. For further characterization of the resistance gene, 3 resistance genes mapped on chromosome 1, as well as 15 major resistance genes that might be employed in the breeding program, were selected for differential tests with 85 Chinese isolates. The resistance gene identified in this research conveys reactions distinct from those conditioned by the 18 resistance genes. This new resistance gene tentatively was designated Pi27(t).
Genetic Mapping of Pathogenicity and Aggressiveness of Gibberella zeae (Fusarium graminearum) Toward Wheat
Authors: Cumagun Christian Joseph R. , Bowden Robert L. , Jurgenson James E. , Leslie John F. , Miedaner Thomas
Published: May 2007

Gibberella zeae is the major fungal pathogen of Fusarium head blight of wheat and produces several mycotoxins that are harmful to humans and domesticated animals. We identified loci associated with pathogenicity and aggressiveness on an amplified fragment length polymorphism based genetic map of G. zeae in a cross between a lineage 6 nivalenol producer from Japan and a lineage 7 deoxynivalenol producer from Kansas. Ninety-nine progeny and the parents were tested in the greenhouse for 2 years. Progeny segregated qualitatively (61:38) for pathogenicity:nonpathogenicity, respectively. The trait maps to linkage group IV, which is adjacent to loci that affect colony pigmentation, perithecium production, and trichothecene toxin amount. Among the 61 pathogenic progeny, the amount of disease induced (aggressiveness) varied quantitatively. Two reproducible quantitative trait loci (QTL) for aggressiveness were detected on linkage group I using simple interval analysis. A QTL linked to the TRI5 locus (trichodiene synthase in the trichothecene pathway gene cluster) explained 51% of the variation observed, and a second QTL that was 50 centimorgans away explained 29% of the phenotypic variation. TRI5 is tightly linked to the locus controlling trichothecene toxin type. The two QTLs, however, were likely part of the same QTL using composite interval analysis. Progeny that produced deoxynivalenol were, on average, approximately twice as aggressive as those that produced nivalenol. No transgressive segregation for aggressiveness was detected. The rather simple inheritance of both traits in this interlineage cross suggests that relatively few loci for pathogenicity or aggressiveness differ between lineage 6 and 7.
Modeling and Analysis of Disease-Induced Host Growth in the Epidemiology of Take-All
Authors: Bailey D. J. , Gilligan C. A.
Published: May 2007

Epidemiological modeling, together with parameter estimation to experimental data, was used to examine the contribution of disease-induced root growth to the spread of take-all in wheat. Production of roots from plants grown in the absence of disease was compared with production of those grown in the presence of disease and the precise form of diseaseinduced growth was examined by fitting a mechanistic model to data describing change in the number of infected and susceptible roots over time from a low and a high density of inoculum. During the early phase of the epidemic, diseased plants produced more roots than their noninfected counterparts. However, as the epidemic progressed, the rate of root production for infected plants slowed so that by the end of the epidemic, and depending on inoculum density, infected plants had fewer roots than uninfected plants. The dynamical change in the numbers of infected and susceptible roots over time could only be explained by the mechanistic model when allowance was made for disease-induced root growth. Analysis of the effect of disease-induced root production on the spread of disease using the model suggests that additional roots produced early in the epidemic serve only to reduce the proportion of diseased roots. However, as the epidemic switches from primary to secondary infection, these roots perform an active role in the transmission of disease. Some consequence of disease-induced root growth for field epidemics is discussed.
Spatial and Genetic Analysis of a Flag Shoot Subpopulation ofErysiphe necatorin Italy
Authors: Cortesi Paolo , Ottaviani Marie-Paule , Milgroom Michael G.
Published: May 2007

Erysiphe necator overwinters as ascospores in cleistothecia and mycelium in dormant buds of grapevines. Shoots developing from infected buds early in the growing season are covered with dense mycelium and are known as “flag shoots”. Combining epidemiological and genetic analyses, the objective of this study was to analyze the spatial and genetic structure of a flag shoot subpopulation of E. necator as a way to assess the contribution of flag shoots as primary inoculum, and to determine if flag shoot subpopulations are clonal with only one mating type. One vineyard in Tuscany, Italy was surveyed intensively for flag shoots for 8 years; isolations of E. necator were made from flag shoots for 5 years. We observed distinct disease foci developing around flag shoots early in epidemics, demonstrating a steep dispersal gradient of conidia and the importance of flag shoots as primary inoculum sources. Flag shoots were spatially aggregated within and between years, most likely as a result of short-distance dispersal of conidia from flags early in the season when dormant buds for the next year's shoots are formed and are susceptible to infection. The two mating types were found in 1:1 ratios in this flag shoot subpopulation. Genotypic diversity, based on inter-simple sequence repeat markers, was high in all years with only two haplotypes occurring twice, and subpopulations were genetically differentiated between years. Similarities between haplotypes were not spatially autocorrelated. One multilocus analysis of population structure is consistent with the hypothesis of random mating but another is not. These results are not consistent with expectations for a strictly clonal or strictly randomly mating flag shoot subpopulation. Instead, the hypothesis that the flag shoot subpopulation of E. necator may reproduce clonally and sexually needs further testing.
A Cluster of Major Specific Resistance Genes to Leptosphaeria maculans in Brassica napus
Authors: Delourme R. , Pilet-Nayel M. L. , Archipiano M. , Horvais R. , Tanguy X. , Rouxel T. , Brun H. , Renard M. , Balesdent M. H.
Published: May 2007

Two types of genetic resistance to Leptosphaeria maculans usually are distinguished in Brassica napus: qualitative, total resistance expressed at the seedling stage and quantitative, partial resistance expressed at the adult plant stage. The latter is under the control of many genetic factors that have been mapped through quantitative trait loci (QTL) studies using ‘Darmor’ resistance. The former usually is ascribed to race-specific resistance controlled by single resistance to L. maculans (Rlm) genes. Three B. napus-originating specific Rlm genes (Rlm1, Rlm2, and Rlm4) previously were characterized. Here, we report on the genetic identification of two novel resistance genes, Rlm3 and Rlm7, corresponding to the avirulence genes AvrLm3 and AvrLm7. The identification of a novel L. maculans- B. napus specific interaction allowed the detection of another putative new specific resistance gene, Rlm9. The resistance genes were mapped in two genomic regions on LG10 and LG16 linkage groups. A cluster of five resistance genes (Rlm1, Rlm3, Rlm4, Rlm7, and Rlm9) was strongly suggested on LG10. The relation between all these specific resistance genes and their potential role in adult-plant field resistance is discussed. These two Rlm-carrying regions do not correspond to major QTL for Darmor quantitative resistance.
Genetic Variation and Virulence on Lr26 in Puccinia triticina
Authors: Kosman E. , Pardes E. , Anikster Y. , Manisterski J. , Yehuda P. Ben. , Szabo L. J. , Sharon A.
Published: May 2007

The genetic relationships between isolates of Puccinia triticina virulent on wheat with the Lr26 resistance gene were studied. The diversity within and between isolates of P. triticina from Israel, Europe, and the United States was determined by virulence on near-isogenic Thatcher lines and by random amplified polymorphic DNA. According to the molecular markers, isolates that were virulent on Lr26 had diversity levels similar to those of Lr26 nonpathogenic isolates. Distances between subpopulations of isolates virulent and avirulent on Lr26 varied and were unrelated to the Lr26 virulence phenotype. Cluster analysis suggested four groups, three of which were closely associated with the geographical origin of the isolates—Israel, the United States, and Europe. All four groups included both Lr26 virulent and avirulent pathotypes. The results showed that Lr26 virulent rust pathotypes are as genetically dissimilar as the rest of the population. The cluster analysis showed that the rust population in Israel includes at least two different subpopulations, both of which contain Lr26 virulent and Lr26 avirulent isolates.
Tomato spotted wilt virusInfection Improves Host Suitability for Its VectorFrankliniella occidentalis
Authors: Maris P. C. , Joosten N. N. , Goldbach R. W. , Peters D.
Published: May 2007

The effect of Tomato spotted wilt virus (TSWV) infection on plant attractiveness for the western flower thrips (Frankliniella occidentalis) was studied. Significantly more thrips were recovered on infected than were recovered on noninfected pepper (Capsicum annuum) plants in different preference tests. In addition, more offspring were produced on the virus-infected pepper plants, and this effect also was found for TSWV-infected Datura stramonium. Thrips behavior was minimally influenced by TSWV-infection of host plants with only a slight preference for feeding on infected plants. Offspring development was positively affected since larvae hatched earlier from eggs and subsequently pupated faster on TSWV-infected plants. These results show a mutualistic relationship between F. occidentalis and TSWV.
RNA Silencing of the Introduced Coat Protein Gene of Turnip mosaic virus Confers Broad-Spectrum Resistance in Transgenic Arabidopsis
Authors: Nomura Ken , Ohshima Kazusato , Anai Toyoaki , Uekusa Hidetoshi , Kita Nobuhiro
Published: May 2007

The coat protein (CP) gene derived from Turnip mosaic virus (TuMV) isolate JO was introduced into Arabidopsis thaliana and the resulting transgenic progenies were analyzed for resistance to TuMV. Transgenic Arabidopsis plants with no detectable transcripts of the introduced CP gene exhibited complete resistance to TuMV. There was no significant correlation between the resistance and the copy number of the transgene. Instead, small interfering RNAs (siRNAs) were detected in these resistant plants, indicating that the resistance is attributed to RNA silencing. The RNA-mediated resistance was not only inherited over successive generations but also effective against 17 worldwide TuMV isolates with different pathogenicity. Comparative analysis of the CP genes among the 17 TuMV isolates revealed that the 380-nt in the 3′ region is highly conserved, suggesting the importance of the 3′ conserved region for broad-spectrum resistance. These results indicate that introduction of the TuMV-CP gene into the target Brassicaceae plants followed by selecting transformants that show RNA silencing for the transgenes can be an effective and reliable strategy for developing crucifer crops with a broad spectrum of resistance to TuMV.
Virulence Gene Distribution and Dynamics of the White Pine Blister Rust Pathogen in Western North America
Authors: Kinloch Bohun B. , Sniezko Richard A. , Dupper Gayle E.
Published: May 2007

We assayed the distribution and frequency of two genes of the blisterpathogen with specific virulence to major resistance genes in sugar pine and western white pine in inoculum from extensive parts of the hosts' ranges. The genes, vcr1 and vcr2, differentially neutralize the cognate resistance alleles Cr1 and Cr2 of the two respective hosts and are clearly marked by their interaction phenotypes. Basidiospores from each inoculum source were cast over Cr1 and Cr2 host genotypes simultaneously, and interaction phenotypes scored when developed. vcr1 was confined to sites with high concentrations of Cr1 (mostly plantations) where frequencies tended toward fixation. vcr2 showed a similar tendency, except high frequencies were occasionally observed from natural and planted stands of western white pine with very low frequencies of Cr2. Otherwise, no pattern was evident for either allele: frequencies were very erratic from site to site within short distances (<1 to 7 km) of each other and oscillated with high amplitudes at the same sites measured in consecutive years. Intense selection for virulence by Cr alleles occurs locally, but spread of vcr alleles over the landscape is mitigated by remarkably low gene flow. Absence of heterozygotes among single telia inoculum on Cr2 genotypes indicated cytoplasmic inheritance of vcr2, similar to vcr1(previously reported).
Molecular Mapping of the Crown Rust Resistance Gene Rpc1 in Barley
Authors: Agrama H. A. , Dahleen L. , Wentz M. , Jin Y. , Steffenson B.
Published: May 2007

Crown rust of barley, caused by Puccinia coronata var. hordei, occurs sporadically and sometimes may cause yield and quality reductions in the Great Plains region of the United States and Canada. The incompletely dominant resistance allele Rpc1 confers resistance to P. coronata in barley. Two generations, F2 and F2:3, developed from a cross between the resistant line Hor2596 (CIho 1243) and the susceptible line Bowman (PI 483237), were used in this study. Bulked segregant analysis combined with random amplified polymorphic DNA (RAPD) primers were used to identify molecular markers linked to Rpc1. DNA genotypes produced by 500 RAPD primers, 200 microsatellites (SSRs), and 71 restriction fragment length polymorphism (RFLP) probes were applied to map Rpc1. Of these, 15 RAPD primers identified polymorphisms between resistant and susceptible bulks, and 62 SSR markers and 32 RFLP markers identified polymorphisms between the resistant and susceptible parents. The polymorphic markers were applied to 97 F2 individuals and F2:3 families. These markers identified 112 polymorphisms and were used for primary linkage mapping to Rpc1 using Map Manager QT. Two RFLP and five SSR markers spanning the centromere on chromosome 3H and one RAPD marker (OPO08-700) were linked with Rpc1 and, thus, used to construct a 30-centimorgan (cM) linkage map containing the Rpc1 locus. The genetic distance between Rpc1 and the closest marker, RAPD OPO08-700, was 2.5 cM. The linked markers will be useful for incorporating this crown rust resistance gene into barley breeding lines.
Identification and Mapping of Quantitative Trait Loci Conditioning Resistance to Southern Leaf Blight of Maize Caused by Cochliobolus heterostrophus Race O
Authors: Carson M. L. , Stuber C. W. , Senior M. L.
Published: May 2007

A random set of recombinant inbred (RI) lines (F2:7) derived from the cross of the inbred lines Mo17 (resistant) and B73 (susceptible) were evaluated for resistance to southern leaf blight (SLB) caused by Cochliobolus heterostrophus race O. The RI lines were genotyped at a total of 234 simple sequence repeat, restriction fragment length polymorphism, or isozyme loci. Field plots of the RI lines were inoculated artificially with an aggressive isolate of C. heterostrophus race O in each of two growing seasons in North Carolina. Lines were rated for percent SLB severity two (1996) or three (1995) times during the grain-filling period. Data also were converted to area under the disease progress curve (AUDPC) and analyzed using the composite interval mapping option of the PLABQTL program. When means of disease ratings over years were fitted to models, a total of 11 quantitative trait loci (QTLs) were found to condition resistance to SLB, depending upon which disease ratings were used in the analyses. When the AUDPC data were combined and analyzed over environments, seven QTLs, on chromosomes 1, 2, 3, 4, 7, and 10 were found to come from the resistant parent Mo17. An additional QTL for resistance on chromosome 1 came from the susceptible parent B73. The eight identified QTLs accounted for 46% of the phenotypic variation for resistance. QTL × environment interactions often were highly significant but, with one exception, were the result of differences in the magnitude of QTL effects between years and not due to changes in direction of effects. QTLs on the long arm of chromosome 1 and chromosomes 2 and 3 had the largest effects, were the most consistently detected, and accounted for most of the phenotypic variance. No significant additive × additive epistatic effects were detected. These data support earlier reports of the polygenic inheritance of resistance to SLB of maize.
Population Dynamics of Cucumber mosaic virus in Melon Crops and in Weeds in Central Spain
Authors: Sacristán Soledad , Fraile Aurora , García-Arenal Fernando
Published: May 2007

Understanding epidemiology and evolution of plant viruses requires knowledge of their ecology: obtaining information about the dynamics and genetic structure of viral populations in their various hosts is necessary to analyze host specialization and to identify reservoirs and inoculum sources. We present here a 3-year analysis of the population dynamics of Cucumber mosaic virus (CMV) in Central Spain in weed hosts and melon. CMV infection in weed hosts was detected throughout the year and showed a clear seasonality, with maximum incidence of 20 to 30% in summer and autumn. The dynamics of CMV incidence were different in various weed habitats (i.e., fallow fields, edges, and wastelands), which differed in stability due to the degree of human intervention. CMV incidence in weed habitats was correlated with the amount of vegetation, estimated both as biomass and as soil cover by plants. CMV population dynamics in melon crops was unrelated to that in weed habitats. Genetic characterization by ribonuclease protection assays and biological characterization on differential hosts showed no significant differences in the frequency of genotypes or biotypes for CMV isolates from weeds or melon. Hence, different population dynamics in various hosts and habitats has not resulted in population differentiation, suggesting that migration between hosts and habitats prevents fragmentation of the population.
New Applications of Statistical Tools in Plant Pathology
Authors: Garrett K. A. , Madden L. V. , Hughes G. , Pfender W. F.
Published: May 2007

The series of papers introduced by this one address a range of statistical applications in plant pathology, including survival analysis, nonparametric analysis of disease associations, multivariate analyses, neural networks, meta-analysis, and Bayesian statistics. Here we present an overview of additional applications of statistics in plant pathology. An analysis of variance based on the assumption of normally distributed responses with equal variances has been a standard approach in biology for decades. Advances in statistical theory and computation now make it convenient to appropriately deal with discrete responses using generalized linear models, with adjustments for overdispersion as needed. New nonparametric approaches are available for analysis of ordinal data such as disease ratings. Many experiments require the use of models with fixed and random effects for data analysis. New or expanded computing packages, such as SAS PROC MIXED, coupled with extensive advances in statistical theory, allow for appropriate analyses of normally distributed data using linear mixed models, and discrete data with generalized linear mixed models. Decision theory offers a framework in plant pathology for contexts such as the decision about whether to apply or withhold a treatment. Model selection can be performed using Akaike's information criterion. Plant pathologists studying pathogens at the population level have traditionally been the main consumers of statistical approaches in plant pathology, but new technologies such as microarrays supply estimates of gene expression for thousands of genes simultaneously and present challenges for statistical analysis. Applications to the study of the landscape of the field and of the genome share the risk of pseudoreplication, the problem of determining the appropriate scale of the experimental unit and of obtaining sufficient replication at that scale.
Overcoming opioid blockade from depot naltrexone (Prodetoxon®)
Authors: Kruptisky E. M. , Burakov A. M. , Tsoy M. V. , Egorova V. Y. , Slavina T. Y. , Grinenko A. Y. , Zvartau E. E. , Woody G. E.
Published: May 2007

Aim  To describe a situation in which an opioid‐dependent patient overcame naltrexone blockade.

Design, case report, setting  Addiction treatment center in St Petersburg, Russia.

Participant  Patient with naltrexone implant.

Intervention  Detoxification.

Measurements  Clinical observations.

Conclusions  It is possible, but very difficult, to overcome naltrexone blockade by using large doses of heroin.