Exploring the abiotic resistance traits of the local wild wheat relative, Thinopyrum distichum

Date
2024-12
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Stellenbosch University
Abstract
The phenotypic and genetic diversity in plants is crucial for adapting to environmental changes, yet most breeding programs often prioritize producer and end-user preferences over genetic diversity, leading to the erosion of this resource. Evaluating both phenotypic and genetic diversity of germplasm is vital for maintaining healthy crops, especially with the growing need for improved cultivars amid rising global populations and climate change. Bread wheat (Triticum aestivum L. (AABBDD)) is derived from hybridisation with its crop wild relatives (CWRs): Triticum urartu (AA), Aegilops speltoides (BB), and Aegilops tauschii (DD). As one of the world's staple foods, with a forecast global harvest of around 800 million tonnes for 2024, improving wheat is critical for maintaining food security, as the global population is projected to reach 9.8 billion by 2050. Climate change exacerbates challenges in agriculture through increased greenhouse gas emissions resulting in rising temperatures, which lead to disruptions in precipitation patterns, and soil salinization. Halophytic plants, which can tolerate high salinity levels, through a combination of osmotic adjustment, ion homeostasis, and reactive oxygen species (ROS) management, survive in saline environments. While saline soil is not widespread in South Africa, its current distribution threatens the main wheat production areas. Thinopyrum distichum, a native CWR of wheat known for its salt tolerance ability, was collected from 42 coastal locations in the Western Cape province. Genetic diversity was assessed through PCR with 12 unique chloroplast markers, leading to the construction of a phylogenetic tree. Unexpectedly, the genetic relationships among the collected entries were unresolved (polytomy), raising questions about Th. distichum's historical indigenous status. A salinity tolerance trial was also conducted to assess phenotypic responses to increasing salt concentrations. Eleven morpho-physiological parameters were measured to identify individuals with greater salt tolerance. A Principal component analysis, and hierarchical cluster analysis highlighted a group of five genotypes that performed well under high salt stress, suggesting a level of diversity not captured by the markers used in the genetic diversity study section. These top performing genotypes showed reduced salt accumulation in comparison to wheat under salt stress, as confirmed by inductively coupled plasma atomic emission spectroscopy (ICP-AES) analysis. However, they accumulated more salt than wheat under non-stressed conditions. Further investigation into HKT7 gene expression, a key player in the salt-overly stressed pathway, which maintains ion homeostasis, revealed significant downregulation in the root tissue of salt exposed plants, under increasing durations of the salt stress. This, with the ICP-AES results confirmed Th. distichum as a salt-accumulating halophyte. This project was able to identify five potential crossing parents to be included in a wheat pre-breeding programme, for further investigation into their salt tolerance mechanisms and eventual transfer of tolerance to wheat.
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