Abstract
In the southern Great Plains of the United States, winter wheat grown for dual-purpose is often planted early, which puts it at risk for drought stress at the seedling stage in the autumn. To map quantitative trait loci (QTL) associated with seedling drought tolerance, a genome-wide association study (GWAS) was performed on a hard winter wheat association mapping panel. Two sets of plants were planted in the greenhouse initially under well-watered conditions. At the five-leaf stage, one set continued to receive the optimum amount of water, whereas watering was withdrawn from the other set (drought stress treatment) for 14 days to mimic drought stress. Large phenotypic variation was observed in leaf chlorophyll content, leaf chlorophyll fluorescence, shoot length, number of leaves per seedling, and seedling recovery. A mixed linear model analysis detected multiple significant QTL associated with seedling drought tolerance-related traits on chromosomes 1B, 2A, 2B, 2D, 3A, 3B, 3D, 4B, 5A, 5B, 6B, and 7B. Among those, 12 stable QTL responding to drought stress for various traits were identified. Shoot length and leaf chlorophyll fluorescence were good indicators in responding to drought stress because most of the drought responding QTL detected using means of these two traits were also detected in at least two experimental repeats. These stable QTL are more valuable for use in marker-assisted selection during wheat breeding. Moreover, different traits were mapped on several common chromosomes, such as 1B, 2B, 3B, and 6B, and two QTL clusters associated with three or more traits were located at 107–130 and 80–83 cM on chromosomes 2B and 6B, respectively. Furthermore, some QTL detected in this study co-localized with previously reported QTL for root and shoot traits at the seedling stage and canopy temperature at the grain-filling stage of wheat. In addition, several of the mapped chromosomes were also associated with drought tolerance during the flowering or grain-filling stage in wheat. Some significant single-nucleotide polymorphisms (SNPs) were aligned to candidate genes playing roles in plant abiotic stress responses. The SNP markers identified in this study will be further validated and used for marker-assisted breeding of seedling drought tolerance during dual-purpose wheat breeding.
Highlights
Winter wheat (Triticum aestivum L.) is the most important cereal crop grown for forage and grain production in the southern Great Plains of the United States (Kumssa et al, 2019)
The objectives of this study were to map quantitative trait loci (QTL) associated with seedling drought tolerance-related traits in winter wheat and to identify single-nucleotide polymorphism (SNP) markers that can be used for marker-assisted selection (MAS) of seedling drought tolerance during wheat breeding
In the southern Great Plains of the United States, wheat intended for winter grazing needs to be planted in early September for increased autumn–winter forage production (Kumssa et al, 2019)
Summary
Winter wheat (Triticum aestivum L.) is the most important cereal crop grown for forage and grain production in the southern Great Plains of the United States (Kumssa et al, 2019). In this region, when wheat is grown for winter pasture, it is often planted at least 2–3 weeks earlier than wheat grown for grainonly production. Significant attempts have been made to improve resilience against drought stress by conventional breeding in different crop species, including wheat. Improving drought tolerance using conventional approaches has been proven difficult because of the genetic complexity of the trait, which is contributed by multiple quantitative trait loci (QTL) (Edae et al, 2014; Gupta et al, 2017; Wang and Qin, 2017; Lehnert et al, 2018). It is difficult to phenotype drought tolerance under field conditions, especially when plants are at the seedling stage
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