Examining the role of genetic variability for drought stress responses in wheat (Triticum aestivum L.) and sorghum (Sorghum bicolor L. Moench.) and its implications for water and nitrogen use efficiency

Abstract

In the present dissertation, an investigation of the physiological characteristics of traits related to drought stress resistance and a detailed analysis of the morphological and physiological responses to drought stress in wheat and sorghum were carried out. In addition, this dissertation provides an validation of the root growth-associated haplotypeblocks Hap-5B-RDMa and Hap-5B-RDMb in relation to nitrogen uptake, nitrogen remobilization and water use. In sorghum, the use of a modern gravimetric phenotyping platform showed the impact of early vegetative drought stress on morphological and physiological responses, such as plant development, biomass and flowering time. In wheat, a cost-effective phenotyping method was evaluated both in the field and under controlled conditions. Normalized difference vegetation index (NDVI) in the field as well as digital image analysis (PLA) under controlled conditions showed a significant (p < 0.05) influence of the second leaf on early plant development (early vigour). In addition, genome-wide association studies were performed to identify the genomic determination for Early Vigour, identifying 42 markers associated with NDVI and two markers associated with PLA. Furthermore, the gravimetric measurement in combination with the 15N tracer-based analysis showed significant (p < 0.05) effects for carriers of Hap-5B-RDMa and Hap-5B-RDMb on nitrogen uptake in the root. In addition, significantly (p < 0.1) lower transpiration rates were found for certain genotype-haplotypeblock interactions. In view of the changing climatic growing conditions and the goal of achieving more climate-neutral production systems, the development of new varieties is essential. These lines have to be more resilient to abiotic stress factors such as drought stress and must be able to meet food demand under lower input factors. This dissertation provides a significant contribution in understanding early vegetative drought stress on morphological and physiological growth parameters in sorghum. In addition, this work presents a cost-effective method for phenotyping early vigor and novel insights into the genetic influence of root-associated haplotypeblocks on nitrogen uptake in wheat. The findings presented here can be used as potential targets in pre-breeding to develop more efficient varieties.