Breeding for climate change : genetics and physiology of seed vigor, seedling vigor and early drought resistance in winter oilseed rape (Brassica napus L.)
In the face of climate change, it seems crucial to increase crop resistance in terms of improved vigor and stress adaptability. To achieve this aim, new screening tools must be developed which allow a reliable selection for beneficial trait or gene combinations contributing to enhanced seed vigor and stable seedling development. A major aim of the present work was the identification of physiological, anatomic and genetic markers associated with improved seed germination and stable seedling development under optimal and suboptimal water conditions in rapeseed.A considerable potential for the improvement of seed vigor could be demonstrated within a genomics screening approach, in which several quantitative trait loci (QTL) could be identified throughout the rapeseed genome underlying seed germination and early seedling growth. Promising candidate genes for seed germination and seedling growth were found in co-localization with the identified QTL, such as Bna.SCO1, Bna.ATE1 and Bna.ARR4. Genomic SNP markers were identified which are anchored in the genomic regions associated with seed vigor. These markers are now available for genomics-based selection for improved seed vigor. Within two independent physiological experiments, osmotic stress responses of rapeseed genotypes differing in their drought resistance were investigated with regard to the seedling shoot and root. For a controlled application of osmotic stress, a novel hydroponic cultivation system was developed. In response to the osmotic stress treatment genotypes reacted with a shift in their shoot metabolite and hormone patterns. An accumulation of osmotically active compounds, such as proline or sugars, suggest that osmotic adjustment is an important factor in the adaptation of rapeseed to drought. However, osmotic adjustment was more distinct in homozygous lines than in hybrids, while the latter showed better growth performance under osmotic stress. It is therefore assumed that enhanced drought compatibility can be at least partially, and possibly mainly attributed to heterosis. For the characterization of root responses to osmotic stress, a new phenotyping tool was established, basing on the principles of Sholl analysis , a neuroscientific method applied for neural network analysis. The results showed that Sholl analysis captures interactive root properties which are normally not captured by conventional root phenotyping software. Under osmotic stress, rapeseed seedlings reacted with altered root architecture, due to enhanced lateral root growth at the expense of the number of lateral roots. A stronger reaction was observed in the resistant genotype. This suggests that the observed changes in root architecture contribute to a better water acquisition during soil desiccation in the field.
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