Bøger af Manuela Nagel

Against the background of 7.4 million accessions stored in genebanks, long-term survival of stored seeds is an important trait. This study intended to elucidate genetic and biochemical mechanisms underlying barley (Hordeum vulgare L.) seed deterioration with respect to genetic diversity at different storage treatments ranging from cold storage with low seed moisture content (smc) to experimental seed ageing with high smc.On the basis of an assumed genetic impact on seed deterioration quantitative genetic analyses using four mapping populations were applied. Seeds of three bi-parental barley mapping populations were experimentally aged. Subsequent quantitative trait locus (QTL) analyses revealed 4 major loci on chromosomes 2H, 5H and 7H explaining a phenotypic variation up to 54%. Detected loci were confirmed by the fourth population that compromises a collection of independent barley accessions. These genotypes, multiplied in two field plots and experimentally aged were analysed by a genome-wide association approach which resulted in 105 marker-trait associations (MTAs) at 32 loci. Putative functions of MTAs and closely linked QTLs revealed predominantly biotic and abiotic stress affect seed longevity.

Conservation of biodiversity including plant genetic resources are fundamental for the future life on Earth. To safe-guard crop wild relatives, locally adapted landraces and varieties, ex situ genebanks were established at the beginning of the 20th century; primarily to store seeds. However, as any other material on Earth, seeds age and lose viability when stored for prolonged periods. The main factors determining deterioration processes are the genotype, the environmental conditions during seed development and the storage conditions including relative humidity, temperature, gas composition and pressure. To understand physiological, biochemical and genetic changes during seed deterioration in genetic resources of wheat, barley and oilseed rape, fundamental processes of germination, dormancy and seed viability loss are discussed in this book based on 13 scientific publications. Here, the loss of seed viability was investigated depending on seed moisture contents (MCs) between 5 % and >25 , storage temperatures between 0°C and 45°C and a modified atmosphere with increased O2 concentration (75) or increased atmospheric pressure (18 MPa). Although, the response to the different conditions varied among species, overall, elevating seed MCs and storage temperatures led to a gradual change of biochemical mechanisms during seed deterioration. Under dry seed storage conditions, glutathione (GSH) and tocochromanols functioned as low-molecular-weight antioxidants and were degraded. Lipids were oxidised or hydrolysed, the pH decreased, whereas organic radicals accumulated over time and correlated negatively with seed viability. At high seed MCs (>13 %) and storage temperatures (>40 °C), membrane damages, changes of pH or organic radicals were absent. Furthermore, GSH and GSSG depleted whereas tocochromanols remained stable or increased. Therefore, seeds stored under high MCs and temperatures were exposed to a different environment than seeds exposed to lower MCs and temperatures where water activity and deterioration rate were reduced and the cytoplasm was assumed to be glassy. As a consequence, quantitative trait loci (QTLs) varied between ageing treatments; thus to understand genetic mechanisms of seeds deterioration in seedbanks, studies must be carried out on dry-stored seeds. Overall, our plant genetic resources are safely preserved in genebanks. However, to avoid genetic drift and to prolong the life of the seed, the conditions for pre-storage and storage should be further optimised and improved for each individual species.