Reassessment of tissue Na⁺ concentration as a criterion for salinity tolerance in bread wheat

Abstract

Wheat is the most important crop grown on many of world's saline and sodic soils, and breeding for improved salinity tolerance (ST) is the only feasible way of improving yield and yield stability under these conditions. There are a number of possible mechanisms by which cereals can tolerate high levels of salinity, but these can be considered in terms of Na + exclusion and tissue tolerance. Na + exclusion has been the focus of much of the recent work in wheat, but with relatively little progress to date in developing highyielding, salt-tolerant genotypes. Using a diverse collection of bread wheat germplasm, the present study was conducted to assess the value of tissue Na + concentration as a criterion for ST, and to determine whether ST differs with growth stage. Two experiments were conducted, the first with 38 genotypes and the second with 21 genotypes.A wide range of Na + concentrations within the roots and shoots as well as in ST were observed in both experiments. However, maintenance of growth and yield when grown with 100 mM NaCl was not correlated with the ability of a genotype to exclude Na + either from an individual leaf blade or from the whole shoot. The K + : Na + ratio also showed a wide range among the genotypes, but it did not explain the variation in ST among the genotypes. The results suggested that Na + exclusion and tissue tolerance varied independently, and there was no significant relationship between Na + exclusion and ST in bread wheat. Consequently, similar levels of ST may be achieved through different combinations of exclusion and tissue tolerance. Breeding for improved ST in bread wheat needs to select for traits related to both exclusion and tissue tolerance.

Salinity tolerance and Na⁺ exclusion in wheat: variability, genetics, mapping populations and QTL analysis

“…Different species and sometimes different genotypes within one species can have different reactions to salinity stress. For example, a strong positive correlation between Na + exclusion and ST in durum wheats has been clearly demonstrated (Munns & James 2003), while in bread wheat, an ability to exclude Na + from the shoot does not play an important role in ST (Genc et al 2007) and perhaps tissue tolerance could be a more important component of ST.…”

Response of durum wheat (Triticum durum Desf.) growth to salt and drought stresses

“…Polyethylene glycol (PEG) widely used to induce water stress is a non-ionic water soluble polymer which is not expected to penetrate into the plant tissue rapidly (Kawasaki 1983). In contrast, Na + and Cl -penetrate into plant cells and can accumulate in the vacuole of tolerant plants or in the cytoplasm of sensitive cultivars (Genc 2007). One of the salt tolerance mechanisms depends on the capacity for osmotic adjustment which allows plant growth to continue under saline conditions.…”

Impact of ancestral wheat sodium exclusion genes Nax1 and Nax2 on grain yield of durum wheat on saline soils

“…Moderate correlations between grain yield and Na + exclusion from leaves have been shown in bread wheat in pot studies (Chhipa and Lal 1995;Ashraf and O'Leary 1996;Cuin et al 2009), but other studies have shown no correlation, e.g. Genc et al (2007). However, in that latter study the lack of correlation between yield and Na + exclusion was most likely due to the low stress applied (100 mM NaCl) and low concentrations of Na + in leaves and the relatively low genetic variation for Na + exclusion in the germplasm that was evaluated.…”