Identification of Salt Tolerance Genes in Australian Wheat Breeding

Nasrin Sultana

Wheat is the most important crop in Australia, valued over A$5 billion annually. However, wheat production is affected by soil salinity and circumventing the adverse effect is yet to achieve. One of the sustainable approaches to combat the increase of soil salinity is to improve wheat salt tolerance level genetically. With an aim to doing genetic improvement of bread wheat, experiments were conducted twice in the year 2020 in hydroponics culture with 150 mM NaCl treatment to identify salt tolerance QTLs in Westonia x Kauz double haploid (DH) population consisting of 181 lines. Two major stable QTLs for Shoot Sodium (Na+) Content on chromosome 4D (qSNCS.4D) and Salt Tolerance Index of Shoot Dry Weight on chromosome 2A (qSDW_STI.2A) were identified, explaining up to 14.30% and 11.04% of phenotypic variation under salt condition, respectively. RNA-seq analysis was performed, for mining putative candidate genes from these major QTLs, using two contrasting DH lines for salt tolerance from the DH population for both shoot and root tissues in two time points of stress viz. 10 days and 25 days after salt stress imposition in a hydroponics culture where 5 replications were pooled. In transcriptome analysis, the significant gene ontology enrichment was obtained for Na+ transport, cell wall modification, apoplast, cell wall, ligand-gated ion channel activities, antiporter activities, oxidoreductase activities. The ABC transporter, photosynthesis, glycolysis pathways have been revealed to be enriched for salt tolerance. For the QTL qSDW_STI.2A, a plasma membrane intrinsic protein (PIP) aquaporin gene (TraesCS2A03G0130000) and a heavy metal associated iso-prenylated protein (HMA) metallo-chaperon gene (TraesCS2A03G0128600) were identified to be putative candidate genes. For the QTL qSNCS.4D, a Na+/H+ exchanger gene (TraesCS4D03G0305700) of a major NHX gene family and a HMA gene TraesCS4D03G0201600 were found to be potential candidate genes. Allele dynamics study of 155 Australian historical bread wheat cultivars from pre-1900s up to 2015 were performed concentrating upon salt tolerance gene-based microsatellite markers and phenotypic evaluation of salt tolerance level was carried out in hydroponics culture with 150 mM NaCl treatment by three replications. Allele percentage was found to be increased steeply from the breeding period 1970-80s but after the year 2000, it was in decreasing trend. The highest percentage of allele loss (15.79%) with respect to previous breeding period was found in the breeding period 1931-40s. One allele for cytosolic chaperone gene (TaClpB2) and one allele for jasmonate signalling allene oxide cyclase gene (TaAOC1) was found extinct since 1991 and 2001 respectively. One allele for the gene flavanone 3-hydroxylase (TaF3H1) was found newly since 1971. To conclude, the QTLs, salt tolerant DH lines, candidate genes and markers identified in this thesis are valuable materials and information to be used in salt tolerance wheat breeding programs.

Identification of Salt Tolerance Genes in Australian Wheat Breeding

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