Browsing by Subject "Genetic variation"

Now showing 1 - 3 of 3
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    Genetische Variation für Resistenz gegen Mutterkorn (Claviceps purpurea [Fr.] Tul.) bei selbstinkompatiblen und selbstfertilen Roggenpopulationen
    (2006) Mirdita, Vilson; Miedaner, Thomas
    Ergot (Claviceps purpurea [Fr.] Tul.) is one of the most important diseases in rye. Infection during flowering results in the production of black, overwintering organs (sclerotia) instead of kernels, which contain harmful alcaloids. Three experiments were conducted to estimate quantitative-genetic parameters of the resistance of rye to ergot under the conditions of organic farming. The general aim was the estimation of genetic variation among and within self-incompatible rye populations and among CMS lines and their male-sterile testcrosses. In 2002 and 2004, genetic variation in resistance to ergot was tested among 65 rye populations at each of two locations (Experiment 1). Thirteen populations were registered rye varieties and the remaining 52 were genetic resources. To assess genetic variation within populations, 50 full-sib families (FSF) from each of five rye populations were developed and tested at four locations (Experiment 2). To test genetic differences in the susceptibility of ovaries towards fungal penetration in the absence of pollen, (i) 64 currently available CMS lines and (ii) their male-sterile crosses with three testers (=sets) were tested in 2003 and 2004, and in 2004, respectively. Inoculation was performed by spraying an aggressive mixture of isolates of Claviceps purpurea three times during the flowering period. The micro-plots were grown in a chess-board design separated by wheat plots to reduce the neighbouring effects. Traits of resistance were the proportion of infected spikes relative to the total number of spikes per plot, and the percentage by weight of ergot sclerotia in the grain. In Experiment 3, the weight of slcerotia per spike and per pair of spikelet were measured due to the absence of grain. Amount of pollen shedding was rated on the basis of the anther size and extrusion. Highly significant genotypic and genotype-environment interaction variances were found among rye populations in the percentage of ergot sclerotia in the grain. All genotypes were infected by ergot. No differences in mean among the registered rye varieties and genetic resources were detected. Because all populations were highly pollen shedding, the results indicate the existence of genetically determined resistance to ergot within the self-incompatible rye. Correlation between both resistance traits was significant (rp = 0.92). Genetic variation within populations was highly significant for all five populations. Individual progenies with resistance higher than the population mean were observed. The mean resistance of initial populations hardly differed from the mean of their progeny indicating a predominantly additive inheritance. Highly significant genetic variation in resistance to ergot was also detected among the currently available 64 CMS lines. Corresponding testcrosses mostly had a higher weight of sclerotia per spike than the lines. Considerable differences in the level of resistance were observed among testcrosses. Crosses with tester line 1 were substantially more susceptible, whereas those with tester 2 were hardly over the mean of the parental lines. The material showed a quantitative distribution of ergot resistance. Weak to medium-sized correlations (0.33 ? 0.47) between locations were detected among lines. The correlation between locations was even weaker in testcrosses. Weak correlations in ergot weight per spike were observed between CMS lines and their testcrosses in sets 2 and 3. In set 1, the estimated phenotypic correlation was higher (rp = 0.65). Estimates of error-corrected correlations were always higher than phenotypic correlations. No genetic difference was detected among the CMS lines for the amount of alkaloids in their sclerotia. This study shows that incompatible rye populations as well as self-fertile hybrid populations contain a substantial genetic variation for resistance to ergot that is inherited quantitatively. In both materials, mainly additive genetic variance was found. Because of a significant genotype-environment interaction, multi-environment trials are necessary to select for resistance. The results of this study nevertheless indicate good prospects to improve resistance to ergot in rye breeding in the long term.
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    High-resolution association mapping with libraries of immortalized lines from ancestral landraces
    (2021) Würschum, Tobias; Weiß, Thea M.; Renner, Juliane; Friedrich Utz, H.; Gierl, Alfons; Jonczyk, Rafal; Römisch-Margl, Lilla; Schipprack, Wolfgang; Schön, Chris-Carolin; Schrag, Tobias A.; Leiser, Willmar L.; Melchinger, Albrecht E.
    Landraces are traditional varieties of crops that present a valuable yet largely untapped reservoir of genetic variation to meet future challenges of agriculture. Here, we performed association mapping in a panel comprising 358 immortalized maize lines from six European Flint landraces. Linkage disequilibrium decayed much faster in the landraces than in the elite lines included for comparison, permitting a high mapping resolution. We demonstrate this by fine-mapping a quantitative trait locus (QTL) for oil content down to the phenylalanine insertion F469 in DGAT1-2 as the causal variant. For the metabolite allantoin, related to abiotic stress response, we identified promoter polymorphisms and differential expression of an allantoinase as putative cause of variation. Our results demonstrate the power of this approach to dissect QTL potentially down to the causal variants, toward the utilization of natural or engineered alleles in breeding. Moreover, we provide guidelines for studies using ancestral landraces for crop genetic research and breeding.
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    Inheritance of quantitative resistance and aggressiveness in the wheat/Fusarium pathosystem with emphasis on Rht dwarfing genes
    (2010) Voß, Hans-Henning; Miedaner, Thomas
    Fusarium head blight (FHB), or scab, is one of the most devastating fungal diseases affecting small-grain cereals and maize, causing severe yield losses and contamination of grain with mycotoxins such as deoxynivalenol (DON) worldwide. Fusarium graminearum (teleomorph Gibberella zeae) and Fusarium culmorum are the most prevalent Fusarium species in wheat production in Central and Northern Europe. Breeding for increased resistance to FHB in wheat is considered the most effective strategy for large scale disease management and mycotoxin reduction. Height reducing Rht genes are extensively used in wheat breeding programmes worldwide in order to improve lodging resistance and yield potential, with Rht-D1b being the most important Rht allele in Northern Europe. However, their individual effects on FHB resistance are yet unclear. Due to the incremental approach to increase host resistance the question arises whether the Fusarium pathogen has the capability to adapt by increased aggressiveness and/or increased mycotoxin production. Therefore, the objectives of the present study were to investigate the effects on FHB resistance of Rht-D1b and additional Rht alleles, the segregation variance for FHB resistance and identification of FHB resistance QTL in subsequent mapping analyses in three crossing populations segregating for the semi-dwarfing Rht-D1b allele and two sets of isogenic wheat lines. Regarding the pathogen, the study aims to determine the segregation variance in two F. graminearum crosses of highly aggressive parental isolates and to examine the stability of host FHB resistance, pathogen aggressiveness and the complex host-pathogen-environment interactions in a factorial field trial. All experiments were conducted on the basis of multienvironmental field trials including artificial inoculation of spores. The presence of Rht-D1b resulted in 7-18% reduction in plant height, but considerably increased FHB severity by 22-53% within progenies from three tested European elite winter wheat crosses. In the following QTL mapping analyses the QTL with the strongest additive effects was located at the Rht-D1 locus on chromosome arm 4DS and accordingly coincided with a major QTL for plant height in all three wheat populations. On total, a high number of 8 to 14 minor QTL for FHB reaction that were found in the three populations which emphasised the quantitative inheritance of FHB resistance in European winter wheat. The detected QTL mostly showed significant QTL-by-environment interactions and often coincided with QTL for plant height. By means of isogenic lines in the genetic background of the variety Mercia, Rht-D1b and Rht-B1d significantly increased mean FHB severity by 52 and 35%, respectively, compared to the wild-type (rht). Among the Maris Huntsman data set, the Rht alleles increased mean FHB severity by 22 up to 83%, but only the very short lines carrying Rht-B1c or Rht-B1b+Rht-D1b showed significance. The analyses of 120 progenies of the crosses from each of the highly aggressive parental F. graminearum isolates revealed significant genetic variation for aggressiveness, DON and fungal mycelium production following sexual recombination. This variation resulted in stable transgressive segregants towards increased aggressiveness in one of the two progeny. The factorial field trial, including eleven F. graminearum and F. culmorum isolates varying in aggressiveness and seven European elite winter wheat varieties, varying in their FHB resistance level, displayed no significant wheat variety × isolate interaction. Nevertheless, isolates possessing increased aggressiveness significantly increased FHB severity and DON production at a progressive rate on varieties with reduced FHB resistance. In conclusion, the analysed Rht alleles led to differently pronounced negative effects on FHB resistance that strongly depended on the genetic background. However, significant genetic variation for FHB resistance exists for selection and, thus, to largely counteract these effects by accumulating major and minor FHB resistance QTL. Significant genetic variation for aggressiveness among F. graminearum and the capability to increase its level of aggressiveness beyond yet known levels simply by sexual recombination may lead to long term erosion of FHB resistance. The rate at which increased aggressiveness develops will depend on the selection intensity and whether it is of constant, episodic or balanced nature. Consequently, the selection pressure imposed on the pathogen should be minimized by creating and maintaining a broad genetic base of FHB resistance that relies on more than one genetically unrelated resistance source by combining phenotypic and marker-assisted selection to achieve a sustainably improved FHB resistance in wheat breeding.