Abstract
Field-based trials are crucial for successfully achieving the goals of plant breeding programs aiming to screen and improve the salt tolerance of crop genotypes. In this study, simulated saline field growing conditions were designed using the subsurface water retention technique (SWRT) and three saline irrigation levels (control, 60, and 120 mM NaCl) to accurately appraise the suitability of a set of agro-physiological parameters including shoot biomass, grain yield, leaf water relations, gas exchange, chlorophyll fluorescence, and ion accumulation as screening criteria to establish the salt tolerance of the salt-tolerant (Sakha 93) and salt-sensitive (Sakha 61) wheat cultivars. Shoot dry weight and grain yield per hectare were substantially reduced by salinity, but the reduction was more pronounced in Sakha 61 than in Sakha 93. Increasing salinity stress caused a significant decrease in the net photosynthesis rate and stomatal conductance of both cultivars, although their leaf turgor pressure increased. The accumulation of toxic ions (Na+ and Cl-) was higher in Sakha 61, but the accumulation of essential cations (K+ and Ca2+) was higher in Sakha 93, which could be the reason for the observed maintenance of the higher leaf turgor of both cultivars in the salt treatments. The maximum quantum PSII photochemical efficiency (Fv/Fm) and the PSII quantum yield (ΦPSII) decreased with increasing salinity levels in Sakha 61, but they only started to decline at the moderate salinity condition in Sakha 93. The principle component analysis successfully identified the interrelationships between all parameters. The parameters of leaf water relations and toxic ion concentrations were significantly related to each other and could identify Sakha 61 at mild and moderate salinity levels, and, to a lesser extent, Sakha 93 at the moderate salinity level. Both cultivars under the control treatment and Sakha 93 at the mild salinity level were identified by most of the other parameters. The variability in the angle between the vectors of parameters explained which parameters could be used as individual, interchangeable, or supplementary screening criteria for evaluating wheat salt tolerance under simulated field conditions.
Highlights
Over 20% of the irrigated land and more than 6% of the world’s total land are within the ambit of the salt effects (Mickelbart et al, 2015)
Success in developing salt-tolerant wheat genotypes has remained limited so far. This is due to several factors, including but not limited to: (1) the lack of understanding of salt tolerance mechanisms; (2) the evaluation of salt tolerance being focused on the grain yield criterion, which reflects tolerance to salinity at the whole plant level only; (3) the majority of salinity experiments being done under tightly controlled conditions, using solutions and sand culture, which fail to express the complexity of saline soils that affect the soil–plant interactions under field conditions; and (4) the relatively infrequent use of physiological characteristics as selection criteria for salt tolerance, which can reflect the response to salt stress at the organ, tissue, and cellular levels (El-Hendawy et al, 2005a,b; Genc et al, 2010; Tavakkoli et al, 2010)
The objective of this study was to examine the efficiency of multivariable agro-physiological parameters, including leaf water relations, the photosynthetic efficiency apparatus, and ion concentrations as screening criteria to distinguish salt-tolerant wheat cultivars from salt-sensitive ones
Summary
Over 20% of the irrigated land and more than 6% of the world’s total land are within the ambit of the salt effects (Mickelbart et al, 2015). Water scarcity in arid and semiarid regions, where more than 40% of the world population resides, is leading toward an increase in the amount of saline or brackish water used for irrigating essential food crops, such as wheat All of these facts about salinity suggest that it is one of the most severe environmental stresses affecting human life. There are several agronomic management practices that can alleviate the adverse effects of salinity stress on the growth and yield of wheat: for example, the mixing of large quantities of gypsum into the soil, and the use of effective drainage schemes and leaching portion These practices are still prohibitively expensive, provide only a short-term solution, and are not feasible to apply on large scales. This is due to several factors, including but not limited to: (1) the lack of understanding of salt tolerance mechanisms; (2) the evaluation of salt tolerance being focused on the grain yield criterion, which reflects tolerance to salinity at the whole plant level only; (3) the majority of salinity experiments being done under tightly controlled conditions, using solutions and sand culture, which fail to express the complexity of saline soils that affect the soil–plant interactions under field conditions; and (4) the relatively infrequent use of physiological characteristics as selection criteria for salt tolerance, which can reflect the response to salt stress at the organ, tissue, and cellular levels (El-Hendawy et al, 2005a,b; Genc et al, 2010; Tavakkoli et al, 2010)
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