Potential of Seed Halopriming in the Mitigation of Salinity Stress during Germination and Seedling Establishment in Durum Wheat (Triticum durum Desf.)

Abstract

The salinity of soils and irrigation water is among the main factors that limit plant productivity worldwide. Several alternatives have been proposed to get around this problem. However, these alternatives have faced difficulties in their implementation. As an alternative, the adverse effects of salinity on crop yield can be minimized by selecting species and varieties better adapted to salinity and/or by finding priming agents that give plants a certain tolerance during the vegetative and reproductive stages. The latter are strictly dependent on germination and seedling establishment. For this purpose, a laboratory experiment was conducted on three Tunisian wheat cultivars (Karim, Razeg, and Maali) subjected to moderate salinity stress (MSS, 5 g L^-1 NaCl), severe salinity stress (SSS, 10 g L^-1 NaCl), or control (0 NaCl) after soaking the seeds in a solution of KNO₃ or ZnSO₄ (0.5 g L^-1). Salinity stress significantly decreased germination capacity (GC) and induced osmotic stress under MSS, which declined under SSS in favor of toxic stress. Pretreatment of seeds with KNO₃ or ZnSO₄ alleviated the toxic effect, and seedlings recovered initial vigor and GC even under SSS. The Karim cultivar showed better tolerance to salinity and a higher ability to react to priming agents. The calculated sensitivity tolerance index (STI) based on germination capacity, seedling growth, and initial vigor decreased in all cultivars under salt stress; however, this parameter clearly discriminated the studied cultivars. Karim was the most tolerant as compared to Razeg and Maali. We conclude that halopriming provides a benefit by alleviating the harmful effects of salt toxicity and that cultivars differ in their response to priming and extent of salt stress. KNO₃ and ZnSO₄ effectively alleviated the inhibitory effect of salt stress on seed germination and seedling establishment while significantly improving initial vigor.

Keywords: initial vigor; osmotic effect; seed pretreatment; seedling emergence; stress tolerance index; toxic effect.

Figure 1

Germination capacity (GC) of durum wheat seeds primed with ZnSO₄ (P ZnSO₄), KNO₃ (P KNO₃), or not primed (P0) and subjected to different salinity stress levels (1: 0 g L⁻¹ NaCl, 2: MSS = 5 g L⁻¹ NaCl, and 3: SSS = 10 g L⁻¹ NaCl). The significance of the differences is marked by the letters in the figures. Means with different letters are significantly different at α = 0.05 according to Fisher’s Least Significant Difference. The standard error of the mean of 100 seeds (five replicates of twenty seeds each) is represented by the bars on the columns.

Figure 2

Daily mean germination (DMG) of durum wheat seeds primed with ZnSO₄ (P ZnSO₄), KNO₃ (P KNO₃), or not primed (P0) and subjected to different salinity stress levels (1: 0 g L⁻¹ NaCl, 2: MSS = 5 g L⁻¹ NaCl, and 3: SSS = 10 g L⁻¹ NaCl). The significance of the differences is marked by the letters in the figures. Means with different letters are significantly different at α = 0.05 according to Fisher’s Least Significant Difference. The standard error of the mean of 100 seeds (five replicates of twenty seeds each) is represented by the bars on the columns.

Figure 3

Mean time germination (MTG) of durum wheat seeds primed with ZnSO₄ (P ZnSO₄), KNO₃ (P KNO₃), or not primed (P0) and subjected to different salinity stress levels (1: 0 g L⁻¹ NaCl, 2: MSS = 5 g L⁻¹ NaCl, and 3: SSS = 10 g L⁻¹ NaCl). The significance of the differences is marked by the letters in the figures. Means with different letters are significantly different at α = 0.05 according to Fisher’s Least Significant Difference. The standard error of the mean of 100 seeds (five replicates of twenty seeds each) is represented by the bars on the columns.

Figure 4

Velocity coefficient of durum wheat seeds primed with ZnSO₄ (P ZnSO₄), KNO₃ (P KNO₃), or not primed (P0) and subjected to different salinity stress levels (1: 0 g L⁻¹ NaCl, 2: MSS = 5 g L⁻¹ NaCl, and 3: SSS = 10 g L⁻¹ NaCl). The significance of the differences is marked by the letters in the figures. Means with different letters are significantly different at α = 0.05 according to Fisher’s Least Significant Difference. The standard error of the mean of 100 seeds (five replicates of twenty seeds each) is represented by the bars on the columns.

Figure 5

Germination recovery (GRec, (a)) and final germination capacity (FGC, (b)) of durum wheat seeds primed with ZnSO₄ (P ZnSO₄), KNO₃ (P KNO₃), or not primed (P0) and subjected to different levels of salinity stress (5 g L⁻¹ NaCl, and 10 g L⁻¹ NaCl). The significance of the differences is marked by the letters in the figures. Means with different letters are significantly different at α = 0.05 according to Fisher’s Least Significant Difference. The standard error of the mean of 100 seeds (five replicates of twenty seeds each) is represented by the bars on the columns. 1: Karim, 2: Razeg, 3: Maali.

Figure 6

Osmotic (OE) and toxic (TE) effects of salinity stress affecting durum wheat seed germination (5 and 10 g L⁻¹ NaCl) and when primed with ZnSO₄ or KNO₃ (P ZnSO₄, P KNO₃).

Figure 7

Potassium concentration in non-germinating durum wheat seeds subjected to different salinity stress levels (1: MSS = 5 g L⁻¹ NaCl, 2: SSS = 10 g L⁻¹ NaCl). The letters in the figure indicate the significance of the differences. Means with different letters are significantly different at α = 0.05 according to Fisher’s Least Significant Difference. The standard error of the mean of five replicates is represented by the bars on the columns. P0: non-primed seeds, P ZnSO₄: seeds primed with ZnSO₄, P KNO₃: seeds primed with KNO₃.

Figure 8

Sodium concentration in non-germinating durum wheat seeds subjected to different salinity stress levels (1: MSS = 5 g L⁻¹ NaCl, 2: SSS = 10 g L⁻¹ NaCl). The significance of the differences is marked by the letters in the figures. Means with different letters are significantly different at α = 0.05 according to Fisher’s Least Significant Difference. The standard error of the mean of five replicates is represented by the bars on the columns. P0: non-primed seeds, P ZnSO₄: seeds primed with ZnSO₄, P KNO₃: seeds primed with KNO₃.

Figure 9

Seedling length of durum wheat subjected to different salinity stress levels for 11 days (4 days for germination and an extra 7 days for emergence). Seeds were primed (or not, P0) with ZnSO₄ or KNO₃. The significance of the differences is marked by the letters in the figures. Means with different letters are significantly different at α = 0.05 according to Fisher’s Least Significant Difference. The standard error of the mean of 20 seedlings is represented by the bars on the columns. 1: 0 g L⁻¹ NaCl, 2: 5 g L⁻¹ NaCl, and 3: 10 g L⁻¹ NaCl.