Browsing by Subject "Marker assisted selection"

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    Phenotypic and genotypic evaluation of yield components and nitrogen use efficiency of triticale (× Triticosecale Wittmack)
    (2024) Neuweiler, Jan Eric; Würschum, Tobias
    Modern agricultural systems require the use of mineral or organic fertilization to keep up with the growing demand for food, feed and recently also to replace fossil energy sources. One of the most important macronutrients to increase yields is nitrogen, mostly applied in its mineral form nitrate and ammonium. However, the biggest disadvantage of mineral fertilization is the good water solubility of these ions, leading to a high rate of fertilizers being leached out by strong rain falls. This results in the eutrophication of aquatic ecosystems and thus the destruction of these habitats. Further critical points are the entry of nitrates into the groundwater, evaporation of gaseous nitrogen compounds from agricultural soils and canopies as well as high energy consumption for the production of mineral nitrogen fertilizers and in result an increased emission of greenhouse gases. This has led to an increasingly restrictive legislation regulating nitrogen fertilization. The solution to resolve this contradiction, where yields should be as high as possible and fertilizer inputs as low as possible is not trivial. A big part of the solution will be the breeding of new, resource efficient cultivars producing high yields under limited nitrogen availability as well as special purpose cultivars, having a chemical grain composition and grain shape characteristics as demanded by the market. Triticale (× Triticosecale Wittmack), is a man-made small-grain cereal created by the hybridization of wheat (Triticum spp.) as female parent and rye (Secale spp.) as male parent. Triticale can be considered as a multi-purpose crop as its grain is used as animal feed and for the production of bioethanol as well as the whole plant is used as substrate for the production of biogas. Therefore, triticale can be regarded as an ideal crop to develop breeding strategies to tackle future challenges and to study the genetic basis of traits related to resource efficiency, as these results might also be transferred to other crops. In order to contribute to the solution of these challenges, the objectives of this thesis were to: (i) evaluate the genetic architecture of grain yield and grain quality related traits as well as of traits related to nitrogen use efficiency (NUE), (ii) evaluate long-term genetic trends resulting from breeding progress for traits of agronomic importance, (iii) assess the potential of index-selection to simultaneously improve negatively correlated grain yield and grain protein content, (iv) develop strategies for the identification of nitrogen efficient triticale genotypes and (v) assess the usefulness of marker-based selection techniques to improve grain yield and grain quality related traits as well as traits related to NUE in triticale by breeding. For this purpose, we used two panels of diverse genotypes representing the variation present in the European winter triticale germplasm pool. The PredBreed panel, comprising 1,218 genotypes tested in 2014 and 2015 at five locations and the SENSELGO panel, comprising 450 genotypes tested in 2018 and 2019 at four locations. Grain yield and protein content were evaluated in all field trials. In addition, grain shape characteristics were evaluated in the PredBreed panel. The SENSELGO panel was tested under four different nitrogen fertilization levels representing 40%, 70% 100% and 130% of the legal, site-specific maximum amount of nitrogen to be applied according to the latest fertilizer regulation of Germany to test their reaction on different nitrogen fertilization rates and to assess their NUE. Additionally starch content was measured. Our results show, that there is a continuous annual increase of 0.5 dt/ha for grain yield over the last decades. Moreover, we found that modern cultivars were able to make better use of the available nitrogen. This indicates, that modern cultivars have a better NUE compared to old cultivars due to their higher overall grain yield potential. Besides grain yield, quality and grain shape related traits are of great importance for the subsequent use of the harvested grain. For these traits it was found that modern cultivars tend to have bigger and more spherical grains with the potential to produce higher protein contents from the available nitrogen. To simultaneously select for negatively correlated grain yield and the most important quality related trait protein content, we evaluated different indices accounting for both traits, revealing that the sum of the standardized grain yield and protein content (IndexEW) led to the most balanced selection, whereas the index grain protein deviation (GPD) led to the selection of mostly low-yielding genotypes with a high protein content. The genetic architecture of all traits under investigation was found to be complex with many small- and medium-effect quantitative trait loci (QTL) and a high level of pleiotropy. Moreover, the analysis of the SENSELGO panel revealed a nitrogen dependent effect for some quantitative trait loci and the use of indices does not lead to a reduction in the complexity of the genetic architecture. These findings suggest that marker-assisted selection (MAS) methods only have a limited potential for the improvement of traits related to resource efficiency and grain characteristics and we therefore suggest phenotypic selection as the method of choice. By calculating the genotype-by-nitrogen interaction variance of every single genotype, it is possible to identify genotypes deviating from normal behavior. These genotypes can be selected and used as parental components to start a new breeding cycle with the aim of breeding more nitrogen-efficient cultivars. However, our results show that the overall genotype-by-nitrogen interaction variance is rather low, with highest estimates under conventional nitrogen conditions, whereas the highest yielding genotype was always different for every nitrogen fertilization level. From these results we concluded that the selection under conventional nitrogen conditions in early generations followed by trials under the nitrogen condition of the target environment is the best approach to select the highest yielding and nitrogen efficient cultivars for all environments and markets. In conclusion, the breeding of resource efficient and special purpose triticale cultivars is of utmost importance to maintain our yields on a high level and take responsibility for the environment and future generations at the same time. It is a challenging but feasible task. The genetic architecture of these traits is too complex to make successful use of MAS but phenotypic selection methods offer sufficient tools as index selection and multi-stage selection under varying nitrogen fertilization levels, to improve these traits in order to fulfill the task of using the available resources responsibly and at the same time ensuring the supply for a growing world population under more and more extreme climatic conditions.