Exploring wheat wild relatives as a source of traits for drought adaptation

Abstract

Crop domestication and subsequent breeding have significantly enhanced global food security. However, these processes have also created genetic bottlenecks, reducing crops' genetic diversity and making them more vulnerable to environmental stresses. Crop wild relatives offer a diverse range of valuable traits, including resistance to both biotic and abiotic stresses, which can play a crucial role in enhancing food security amidst future climate change. Wheat (Triticum aestivum L. and Triticum durum Desf.) is a crucial global staple crop, vital for food and energy supply, and thus plays a key role in food security. The Triticum gene pool of wheat includes diploid, tetraploid, and hexaploid forms. Wild wheats, which are exclusively diploid or tetraploid, serve as valuable genetic resources for wheat improvement due to their evolutionary relationships with domesticated wheat. Drought-induced wheat yield losses threaten global food security and are likely to increase with climate change. Drought stress impacts plant growth and development through morphological, physiological, and biochemical changes, ultimately reducing crop yield. To address the need for resilient crops in drought-prone regions, it is crucial to identify and develop varieties that exhibit drought tolerance traits. Although, wild wheat relatives harbor vast genetic diversity for drought tolerance traits, they have not been extensively explored. Therefore, the aim of this thesis was to explore and evaluate the drought-adaptive traits of wild Triticum taxa for use in breeding drought-tolerant wheat cultivars. To evaluate drought tolerance traits in wild wheats and landraces, 110 genotypes from diverse Triticum taxa (60 wild wheats, 44 landraces and 6 modern cultivars) were evaluated at a drought-prone location with sandy loam soil at the research station of University of Giessen in Gross-Gerau during the 2021/22 winter wheat growing season. Twenty selected genotypes were further evaluated for physiological and morphological drought-adaptive traits in the same field during the 2022/23 season, and results were assessed across both years. Genotypes were selected based on their relative grain yield performance and associated physiological traits. Subsequently, a greenhouse experiment was conducted on 17 of these selected genotypes (11 wild wheats, 3 landraces, and 3 modern cultivars). This was followed by another greenhouse study focusing on 3 potential drought-tolerant genotypes from a neglected species, T. araraticum, and 2 modern bread wheat cultivars to evaluate in-depth physiological and biochemical traits that differ from modern bread wheat cultivars. These experiments were conducted under two different moisture conditions: irrigated and rainfed conditions in the field, and well-watered and drought conditions in the greenhouse experiments. In both field and greenhouse experiments, a genotype-dependent response to drought stress was observed. The Triticum gene pool showed wide variations in morphological, physiological and biochemical traits. Wild wheats such as T. dicoccoides, T. urartu and T. boeoticum exhibited isohydric stomatal regulations, while landraces and modern cultivars demonstrated anisohydric stomatal regulations. Drought stress significantly increased the accumulation of osmoprotectants, such as proline and total soluble sugars, and enhanced antioxidant activity. Additionally, T. araraticum exhibited distinct drought tolerance via glutathione (GSH) redox balance, marked by enhanced enzymatic activities like monodehydroascorbate reductase (MDHAR) and glutathione reductase (GR). In contrast, modern bread wheat cultivars showed enhanced ascorbate (AsA) redox in response to drought stress. Four drought-tolerant candidates have been selected from this study across four different taxa: three from wild and one from a landrace. These candidates can be used as pre-breeding sources for wheat improvement. Modern breeding techniques could be employed to incorporate drought-tolerant candidates into breeding program.