Abstract
Soil salinity is a worldwide issue that affects wheat production. A comprehensive understanding of salt-tolerance mechanisms and the selection of reliable screening indices are crucial for breeding salt-tolerant wheat cultivars. In this study, 30 wheat genotypes (obtained from a rapid selection of 96 original varieties) were chosen to investigate the existing screening methods and clarify the salinity tolerance mechanisms in wheat. Ten-day-old seedlings were treated with 150 mM NaCl. Eighteen agronomic and physiological parameters were measured. The results indicated that the effects of salinity on the agronomic and physiological traits were significant. Salinity stress significantly decreased K+ content and K+/Na+ ratio in the whole plant, while the leaf K+/Na+ ratio was the strongest determinant of salinity tolerance and had a significantly positive correlation with salt tolerance. In contrast, salinity stress significantly increased Na+ concentration and relative gene expression (TaHKT1;5, TaSOS1, and TaAKT1-like). The Na+ transporter gene (TaHKT1;5) showed a significantly greater increase in expression than the K+ transporter gene (TaAKT1-like). We concluded that Na+ exclusion rather than K+ retention contributed to an optimal leaf K+/Na+ ratio. Furthermore, the present exploration revealed that, under salt stress, tolerant accessions had higher shoot water content, shoot dry weight and lower stomatal density, leaf sap osmolality, and a significantly negative correlation was observed between salt tolerance and stomatal density. This indicated that changes in stomata density may represent a fundamental mechanism by which a plant may optimize water productivity and maintain growth under saline conditions. Taken together, the leaf K+/Na+ ratio and stomatal density can be used as reliable screening indices for salt tolerance in wheat at the seedling stage.
Highlights
Soil salinization is one of the main abiotic stress factors affecting crop yields worldwide; approximately 6% of the world’s total land area is threatened by salinity, including 20% of arable land and 33% of irrigated land (Shrivastava and Kumar, 2015; Kuang et al, 2019; Safdar et al, 2019)
Thirty wheat cultivars were obtained from the Wheat Research Centre of Yangzhou University and were used in this study
Salt tolerance index based on the total dry weight Chlorophyll content (SPAD values) Chlorophyll fluorescence Stomatal density Leaf sap osmolality Plant height Root length Shoot dry weight (g) Root dry weight (g) Shoot fresh weight (g) Root fresh weight (g) Shoot water content (%) Root water content (%) Leaf K+ content Leaf Na+ content Leaf K+/Na+ Ratio Root K+ content Root Na+ content Root K+/Na+ Ratio
Summary
Soil salinization is one of the main abiotic stress factors affecting crop yields worldwide; approximately 6% of the world’s total land area is threatened by salinity, including 20% of arable land and 33% of irrigated land (Shrivastava and Kumar, 2015; Kuang et al, 2019; Safdar et al, 2019). Salinity stress significantly decreases plant growth and productivity, which can substantially reduce yield production (Munns et al, 2019). Wheat (Triticum aestivum L.) is one of the most important crop plants worldwide and feeds a large number of people. Wheat is only moderately tolerant to salinity; the loss in its grain yield exceeds 60% under saline conditions (Khan et al, 2017). One of the most effective and feasible ways to minimize the detrimental effects of salinity on crop production is to enhance the salinity-tolerant ability (Sergey, 2013; Luo et al, 2019)
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