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Type: Thesis
Title: Understanding salinity tolerance of a bread wheat landrace Mocho de Espiga Branca
Author: Chana
Issue Date: 2019
School/Discipline: School of Agriculture, Food and Wine
Abstract: Salinity is one of the major abiotic stresses severely affecting cereal crop yields worldwide. Improving salinity tolerance of the most widely cultivated cereal, bread wheat (Triticum aestivum L.), is essential to increase grain yields on saline agricultural lands. Shoot sodium (Na⁺) exclusion is often reported as a major salinity tolerance mechanism in bread wheat. This process enables plants to reduce root-to-shoot Na⁺ transport by retrieving Na⁺ from the xylem and prevent toxic concentrations of Na⁺ from accumulating in the shoot. However, a Portuguese bread wheat landrace Mocho de Espiga Branca was recently identified with up to 10× higher leaf Na⁺ concentrations and yet maintained similar salinity tolerance compared to other bread wheat cultivars. The first focus of this PhD study was to understand how Mocho de Espiga Branca accumulates high concentrations of Na⁺ in the leaf compared to Gladius and Scout under salinity. DNA sequencing of a major Na⁺ exclusion gene TaHKT1;5-D revealed that a naturally occurring single nucleotide substitution resulted in a L190P amino acid residue change. This variation was found to disrupt the capability of TaHKT1;5-D to retrieve Na⁺ from the xylem and hence causing the high leaf Na⁺ accumulation in Mocho de Espiga Branca. A CAPS marker was developed to enable plant breeders to select for this allele in bread wheat. The second focus of this study was to identify novel genetic loci linked to salinity tolerance of Mocho de Espiga Branca. 19 salinity tolerance sub-traits were phenotyped in an F₂ population derived from Mocho de Espiga Branca and Gladius for quantitative trait loci (QTL) analysis. Genomic regions significantly associated with salinity tolerance were detected on chromosomes 1A, 1D, 4A, 4B and 5A for the sub-traits of plant growth, and on chromosome 2A, 2B, 4D and 5D for Na⁺, potassium (K⁺) and chloride (Cl⁻) accumulation. A number of candidate genes that encode proteins associated with plant salinity tolerance were identified. These include Na⁺/H⁺ antiporters, K⁺ channels, Na⁺/calcium (Ca²⁺) transporter, H⁺-ATPase, calcineurin B-like proteins (CBLs) and CBL-interacting protein kinases (CIPKs). The third focus of this study was to investigate whether any difference(s) in accumulation of five known compatible solutes (glycine betaine, proline, sucrose, glucose and fructose) associated with osmotic adjustment were present in Mocho de Espiga Branca compared to Gladius and Scout under salinity. The concentrations of the detected compatible solutes in Mocho de Espiga Branca were found to respond similarly compared to Gladius and Scout in response to salinity, suggesting these organic solutes are not contributing to the ability of Mocho de Espiga Branca to maintain growth while accumulating high concentration of leaf Na⁺ salinity. Overall, in this PhD study, a SNP linked to impairment of the Na⁺ transporter TaHKT1;5-D was identified and shown to be responsible for the increased shoot Na⁺ concentration in Mocho de Espiga Branca. The findings highlight the importance of other mechanisms that are independent from Na⁺ exclusion in salinity tolerance of bread wheat and the need to investigate these further in the future.
Advisor: Roy, Stuart
Pearson, Allison
Schilling, Rhiannon
Dissertation Note: Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food and Wine, 2020
Keywords: Salt tolerance
bread wheat
compatible solutes
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