Improvement of salt and waterlogging tolerance in wheat: comparative physiology of Hordeum marinum-Triticum aestivum amphiploids with their H. marinum and wheat parents

[Truncated] Wheat (Triticum aestivum L.) is one of the most important cereal grains, yet is sensitive to the combined salinity and waterlogging that often occurs on saline land. One way to improve the growth of crops on saline land might be to introduce genes from relevant adapted wild germplasm. Sea barleygrass (Hordeum marinum Huds.), a wild relative of wheat, can withstand the combined effects of salinity and waterlogging and might therefore be used to improve the tolerance of wheat via wide hybridisations. This PhD project aimed to identify physiological traits contributing to salt and waterlogging tolerance in H. marinum-wheat amphiploids in comparison to the parents, and for some of these traits examine the expression patterns of two candidate genes (HKT1;5-like and NHX1-like transcripts) involved in Na⁺ (and for one also K⁺) transport.

The physiology of salt and waterlogging tolerance was evaluated in 8 accessions of H. marinum. Overall, two of the H. marinum accessions (H109 and WA9) were identified as being relatively tolerant of the combined salinity and stagnant treatments, whereas H546 was identified as being the most sensitive accession. With the combination of salinity (400 mM NaCl) and stagnant treatments the most tolerant accessions had higher RGRs (4665% of control compared to 33% of control RGR for the sensitive accession), less accumulation of Na+ and Cl^- in the shoots (concentrations 56% and 20% lower than the sensitive accession, for Na⁺ and Cl^- respectively) and a lower proportion of dead leaves (5-14% of shoot DM, compared with 58% in the sensitive accession). In addition, the higher RGR of the tolerant accessions was associated with up to 52% higher K⁺ concentration in shoot, and therefore a 67% higher shoot K⁺/Na⁺ ratio than in the sensitive accession. Further studies on two of the H. marinum accessions suggested that decreased stomatal conductance was a major cause of the reduction in net photosynthesis of young leaves under saline or stagnant saline treatments.