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Yellow Rust (yellow + rust)

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Life Sciences	100%

Selected Abstracts

Microsatellite marker for yellow rust resistance gene Yr5 in wheat introgressed from spelt wheat

PLANT BREEDING, Issue 6 2002
Q. Sun
Abstract Yellow rust of wheat caused by Puccinia striiformis f sp. tritici has been periodically epidemic and severely damaged wheat production in China and throughout the world. Breeding for resistant cultivars has been proved to be an effective way to resolve the problem. A yellow rust resistance gene, Yr5, derived from Triticum spelta shows immunity or high resistance to the most popular isolates Tiaozhong 30 and 31 in China. Establishment of DNA markers for the Yr5 gene will facilitate marker-assisted selection and gene pyramiding in the breeding programme. Since the Yr5 gene was cytologically located on the long arm of chromosome 2B, By33, the donor of Yr5, was crossed and backcrossed with the susceptible line 441, and BC3F2 and BC3F3 segregating populations were screened for polymorphism by using 11 microsatellite primers mapped on chromosome 2B. A marker, Xgwm501-195 bp/160 bp, was found to be linked to Yr5, with a genetic distance of 10.5-13.3 cM. [source]

Combination of resistance tests and molecular tests to postulate the yellow rust resistance gene Yr17 in bread wheat lines

PLANT BREEDING, Issue 6 2000
O. Robert
Abstract Yellow rust caused by Puccinia striiformis is a wheat disease of worldwide importance. The Yr17 resistance gene introgressed from Aegilops ventricosa was effective, in France, against all yellow rust isolates until 1998. The SC-Y15 marker is one of three molecular markers closely linked to Yr17. In this paper, results obtained are compared with the molecular marker SC-Y15 and with resistance tests performed at the seedling and adult plant stages on 31 lines from five populations derived from recurrent selection programmes. The resistance tests showed that Yr17 controlled the resistance in seven lines, but that others had additional resistance at the adult stage (18 lines). The molecular test corresponded well with the resistance test in most lines (98% of 156 plants tested), including individual plants that were resistant or susceptible in heterogeneous lines. It also indicated the presence of Yr17 in lines in which it could not be identified by the resistance test because of the presence of other genes. Three of the 156 plants tested appeared to have the gene Yr17 according to the resistance tests, but lacked the molecular marker. These could have resulted from breakage of the linkage, the number being consistent with the estimate of linkage already published. This indicated the need for a resistance test, at least in later stages of breeding programmes, if it is considered essential to have the Yr17 gene present. The use of the selected lines in breeding programmes is also discussed. [source]

Genetic Analysis of the Latent Period of Stripe Rust in Wheat Seedlings

JOURNAL OF PHYTOPATHOLOGY, Issue 6 2004
H. Dehghani
Abstract Genetics of slow-rusting resistance to yellow rust (Puccinia striiformis f.sp. tritici) was studied by a half-diallel design using six wheat varieties, Tiritea (susceptible), Tancred, Kotare, Otane, Karamu, and Briscard. The parents and 15 F1 progenies were evaluated in the greenhouse by three pathotypes 7E18A,, 38E0A+, and 134E134A+. The latent period was measured as the number of days from inoculation to the appearance of the first pustule. For each pathotype a randomized complete block design was used and data were analysed by methods of Griffing and Hayman. The range of average degree of dominance was from complete dominance to over-dominance. Positive and negative degrees of dominance were observed for each pathotype that showed the reversal of dominance. Analysis of variance showed the importance of both additive and dominance effects in controlling the latent period. Broad-sense heritabilities were 0.99 and narrow-sense heritabilities ranged from 0.85 to 0.94. Briscard and Karamu for the pathotypes 38E0A+ and 134E134A+, Kotare for the pathotype 7E18A, and Tancred for the pathotype 38E0A+ had significant and positive general combining ability (GCA) (more resistance) for latent period. The crosses of Kotare with Tancred, Briscard and Karamu indicated the highest and positive specific combining ability (SCA) for the pathotype 7E18A,. Significant additive genetic component and moderate narrow-sense heritability indicate the possibility of improving for longer latent period of stripe rust in breeding programmes. [source]

Combining ability and heterosis under pest epidemics in a broad-based global wheat-breeding population

PLANT BREEDING, Issue 3 2008
R. Ortiz
Abstract Wheat breeders rarely apply population improvement schemes or select parental sources according to combining ability and heterotic patterns. They rely on pedigree selection methods for breeding new cultivars. This experiment was undertaken to assess the advantages of using diallel crosses to define combining ability and understand heterosis in a broad-based wheat-breeding population across different environments affected by yellow rust. Sixty-four genotypes derived from a full diallel mating scheme were assessed for grain yield in two contrasting growing seasons at two locations for two consecutive years. Parental genotypes showed significant combining ability for grain yield that was affected by yellow rust and genotype-by-environment (GE) interactions, both of which affected heterosis for grain yield. Significant GE interactions suggested that decentralized selection for specific environments could maximize the use of this wheat germplasm. Cultivar effects and specific heterosis were the most important factors influencing grain yield. Some crosses capitalized on additive genetic variation for grain yield. This research shows the power of available quantitative breeding tools to help breeders choose parental sources in a population improvement programme. [source]

Combination of resistance tests and molecular tests to postulate the yellow rust resistance gene Yr17 in bread wheat lines

Mutants in wheat showing multipathogen resistance to biotrophic fungal pathogens

PLANT PATHOLOGY, Issue 4 2006
L. A. Boyd
Five fast-neutron-derived mutants were isolated from the wheat line Hobbit ,sib' that show enhanced field resistance towards Puccinia striiformis f.sp. tritici, the causal agent of yellow rust. Subsequent testing showed the yellow rust resistance phenotypes to differ between mutants, to be expressed at different growth stages and, in some cases, to show an isolate interaction. Three mutants, I3-48, I3-49 and I3-54, exhibited an enhanced yellow rust resistance phenotype from the third seedling leaf onwards, while mutants I3-27 and I3-30 did not show an altered yellow rust phenotype until later growth stages. Additional resistance for brown rust (causal agent Puccinia triticina) was identified in mutants I3-27, I3-30, I3-48 and I3-49, and for powdery mildew caused by Blumeria graminis f.sp. tritici in mutants I3-27, I3-30, I3-48 and I3-54, although in some cases the resistance was isolate-specific. [source]

Predicting effective fungicide doses through observation of leaf emergence

PLANT PATHOLOGY, Issue 6 2000
N. D. Paveley
Experimental data were used to test the hypothesis that the effective fungicide dose (ED) , the dose required to achieve a given level of disease suppression , varies in a predictable manner according to the pattern of development of the wheat canopy. Replicated and randomized field plots received a single systemic fungicide spray at either zero (control), 0·25, 0·5, 0·75 or 1·0 dose (the recommended dose), at one of eight timings from April to June. Wheat cultivars and locations for experiments were selected to promote epidemics of septoria tritici spot and yellow rust caused by Septoria tritici (anamorph of Mycosphaerella graminicola) and Puccinia striiformis, respectively. Logistic or exponential disease progress curves were fitted to disease severity data and used to estimate the date of disease onset (t0) and relative epidemic growth rate (r) on each leaf layer for each treatment. Area under the disease progress curve (AUDPC) values were used to construct fungicide dose by spray timing response surfaces for each of the upper four leaves. A parsimonious function, with an exponential form in the dose,response dimension and a normal distribution in the timing dimension described a high proportion of the variation in AUDPC (R2 values ranging from 0·73 to 0·97). Consistent patterns of treatment effect were noted across pathogen species, leaf layers, sites and seasons. Fungicide applications that coincided with full leaf emergence delayed t0 on that leaf layer. Treatments applied after full leaf emergence did not delay t0, but reduced r. Progressively earlier or later treatments, or lower doses, had decreasing effects. AUDPC was affected more by t0 than r. AUDPC response surface parameter estimates showed that curvature of the dose,response was not affected by spray timing, but appeared to be a characteristic of the fungicide,pathogen combination. However, the lower asymptote of the dose,response curve, and hence the ED, varied substantially with spray timing. The pattern of change in ED with spray timing was consistent across a range of leaf layers, pathosystems and seasons, and the spray timing at which the ED was minimized varied only within a small range, around the time of leaf emergence. In contrast, variation in untreated disease severity, resulting from variation in initial inoculum and weather, was large. It was concluded that the main value of disease forecasting schemes may be in their capacity to predict the level of untreated disease, to which the economic optimum, or ,appropriate', dose relates. Spray timing determines the part of the canopy where disease will be efficiently controlled and hence the green leaf area saved. Timing decisions should relate to observations of emergence of those leaf layers important to yield. [source]

Building anisotropic sampling schemes for the estimation of anisotropic dispersal

ANNALS OF APPLIED BIOLOGY, Issue 3 2009
S. Soubeyrand
Abstract Anisotropy, a structural property of dispersal, is observed in dispersal patterns occurring for a wide range of biological systems. While dispersal models more and more often incorporate anisotropy, the sampling schemes required to collect data for validation usually do not account for the anisotropy of dispersal data. Using a parametric model already published to describe the spatial spread of a plant disease, the wheat yellow rust, we carry out a study aimed at recommending an appropriate sampling scheme for anisotropic data. In a first step, we show with a simulation study that prior knowledge of dispersal anisotropy can be used to improve the sampling scheme. One of the main guidelines to be proposed is the orientation of the sampling grid around the main dispersal directions. In a second step, we propose a sequential sampling procedure (SSP) used to automatically build anisotropic sampling schemes adapted to the actual anisotropy of dispersal. The SSP is applied to simulated and real data. The proposed methodology is expected to be adapted easily to any kind of organisms with wind-borne propagule dispersal because it does not require the inclusion of biological features specific of the considered organism. [source]

A model of the effect of fungicides on disease-induced yield loss, for use in wheat disease management decision support systems

ANNALS OF APPLIED BIOLOGY, Issue 1 2007
A. Milne
Abstract A model of the effect of foliar-applied fungicides on disease-induced yield loss is described, parameterised and tested. The effects of fungicides on epidemics of Septoria tritici (leaf blotch), Puccinia striiformis (yellow rust), Blumeria graminis f.sp. tritici (powdery mildew) and Puccinia triticina (brown rust) on winter wheat were simulated using dose,response curve parameters. Where two or more active substances were applied together, their joint action was estimated using an additive dose model where the active substances had the same mode of action or a multiplicative survival model where the modes of action differed. By coupling the model with models of wheat canopy growth and foliar disease published previously, it was possible to estimate disease-induced yield loss for a prescribed fungicide programme. The difference in green canopy area and, hence, interception of photosynthetically active radiation between simulated undiseased and diseased (but treated) crop canopies was used to estimate yield loss. The model was tested against data from field experiments across a range of sites, seasons and wheat cultivars and was shown to predict the observed disease-induced yield loss with sufficient accuracy to support fungicide treatment decisions. A simple method of accounting for uncertainty in the predictions of yield loss is described. Fungicide product, dose and spray timing combinations selected using the coupled models responded appropriately to disease pressure and cultivar disease resistance. [source]

The importance of weather and agronomic factors for the overwinter survival of yellow rust (Puccinia striiformis) and subsequent disease risk in commercial wheat crops in England

ANNALS OF APPLIED BIOLOGY, Issue 3 2007
P. Gladders
Abstract Disease survey data from 4475 randomly selected crops of wheat from England and Wales during 1985,2000 showed that yellow rust was most prevalent in 1988, 1989, 1990, 1998 and 1999. Disease severity on the upper two leaves was low as >95% crops had received foliar fungicides. Factors affecting the presence or absence (incidence) of yellow rust were investigated using random effects logistic regression (general linear mixed model). This enabled crop management (risk) variables for individual crops to be combined with meteorological variables measured at the county level. Two models are presented that analysed the effect of host genotype on incidence either solely through yellow rust resistance rating (Model 1) or by including both resistance rating (fixed effect) and cultivar (fitted as a random term) (Model 2). In both models, the percentage of crops with yellow rust decreased with cultivar disease resistance ratings ,3, the occurrence of severe frosts (<,5°C), use of systemic seed treatment and application of foliar fungicide sprays. There were no significant effects (P < 0.05) of timing of fungicide sprays, previous cropping or summer weather. The use of risk variables associated with overwintering survival may help adjust fungicide inputs to seasonal risk. [source]