Response of Tomato to Salinity and Drought Stress

Abstract

Soil salinity and drought are major abiotic stresses that affect plant morpho-physiology and lead to decreased yield. The deleterious effect of salinity and drought on morpho-physiological attributes in tomato (Lycopersicon esculetum var. Rio Grande) and its amelioration by supplemental potash application was investigated. The growth, yield and physiological responses of tomato plant were investigated under different salinity levels and drought regime at Centre of Plant Biodiversity and Botanical Garden, University of Peshawar during 2011-12. Tomato plants were subjected to five salt treatments i.e. 0 (control), 50, 100, 150 and 200 mM NaCl and four drought regimes i.e. 0 (Control), 2 days, 4 days and 6 days drought stress at 4-5 true leaves stage to the harvesting stage. The root length (8.17 cm), shoot length (21.04), root fresh weight (10.57 g), shoot fresh weight (126 g), root dry weight (17.43%), shoot dry weight (19%), number of branches per plant (11.5), leaf area (9.47 cm2), chlorophyll content (62.63 spade reading) in control treatment declined with increasing salinity levels to the minimum 6.67 cm, 13.17 cm, 5.45 g, 34.0 g, 13.92%, 8.5%, 8.83, 6.99 cm2, 34.56 accordingly with the highest salt concentration of 200 mM. Similarly, droughts stress decreased root fresh weight (10.07 g), shoot fresh weight (117 g), root dry weight (25.19%), shoot dry weight (16.4%), number of branches per plant (10.67), leaf area (11.87 cm2), chlorophyll content (52.97 spade reading) in control treatment to the minimum 5.97 g, 43.0 g, 15.69%, 10.9%, 8.8, 4.54 cm2, 41.47 accordingly with the maximum drought stress. The number of flowers cluster (4.17), fruits per cluster (3.75) and number of fruits per plant (18.50), average fruit weight (83.60 g), yield (5.38 t.ha-1) in control treatment decreased to 3, 1.92, 5.50, 35.96 g and 1.30 t.ha-1 with 200 mM stress. By contrast, root moisture content (72.57%), shoot moisture content (80.90%), root fresh/dry weight ratio (3.74) and shoot fresh/dry weight ratio (5.29) in control plants increased to 86.07%, 91.50%, 7.36 and 12.16 respectively with increasing salinity stress to 6 days. The drought stress also significantly decline the number of flowers cluster (4.20), fruits per cluster (3.20) and number of fruits per plant (14.33), average fruit weight (74.28 g), yield (4.63 t.ha-1) in control treatment decreased to 3.33, 1.93, 6.60, 47.53 g and 1.55 t.ha-1 accordingly. The root moisture content (74.18%), shoot moisture content (83.60%), root fresh/dry weight ratio (4.70) and shoot fresh/dry weight ratio (6.88) increased to 84.31%, 89.0%, 6.60 and 10.71 accordingly with increasing drought stress to 6 days. The salinity and drought stress, however, improved the fruit firmness 3.66 kg.cm-2 and 3.99 kg.cm-2 and TSS content 4.31 and 3.94% enhanced to 5.01 and 4.76 kg.cm-2, and 5.18 and 5.45% with 200 mM and 6 days drought stress respectively. The shoot Na+ (3870 μM/g D.wt.) and root Na+ (2337 μM/g D.wt.) in control plants increased with increasing salinity levels to the maximum of 4955 and 3577 μM/g D.wt. at 200 mM stress. By contrast the K+ content of the shoot (8906 μM/g D.wt.) and root (5639 μM/g D.wt.) decreased to 5149 in shoot and 3826 μM/g D.wt. in the root resulting in increased Na+/K+ ratio so that it increased from 0439 to 0.992 in shoot and 0416 to 0930 in root with increasing salinity levels from 0 to 200 mM. By contrast, the Na+ content in control plant (4293 μM/g D.wt.) increased to the maximum of 5241 μM/g D.wt. with 4 days drought stress but then declined to 4421 μM/g D.wt. with increasing drought stress to 6days. The Na+ content of the root, however, continued to decline with increasing drought stress so that it declined from 3748 μM/g D.wt. to 2450 μM/g D.wt. with 6 days drought stress. The maximum K+ content of the shoot (7779 13 μM/g D.wt.) in control plant decreased to 6599 μM/g D.wt. but thereafter non significantly with increasing drought stress to 6 days. The K+ content of the root in control plants (4925 μM/g D.wt.) was not significant with 2 days drought stress but decreased significantly to 4588 and 4333 when drought stress was increased to 4 and 6 days. As a result the Na+/K+ ratio in shoot increased from 0.572 in control to the maximum of 0.879 with 4 days drought, while it declined from 0.804 in control to 0.597 with 6 days drought stress in roots. Both the salinity and drought stress increased proline content of the root and shoot. The proline content of the root (2.010 μM/g F.wt.) and shoot (3.713μM/g F.wt.) in control plants increased to 9.530 in the roots and 22.867 μM/g F.wt. in the shoot with 200 mM NaCl stress. Drought stress also resulted in significant increase in proline content so that root (3.526 μM/g F.wt.) and shoot proline content (8.833 μM/g F.wt.) increased to 5.935 with 4 days drought stress and 14.415 μM/g F.wt. with 6 days drought stress in root and shoot respectively. The interaction of salinity and drought stress significantly increased the Na+ content, Na+/K+ ratio and proline content of root and shoot, while decreased the K+ content of the root and shoot. The experiment on supplemental potash (220 kg ha-1) and its sources (MOP & SOP) on alleviation of salinity stress responses of tomato that fresh weight of roots (8.968 g) and shoot (217.4 g) in control plants decreased with increasing salinity levels and finally to the minimum of 3.632 and 69.71 g in root and shoot respectively with 200 mM NaCl. The dry weight of the roots (3.110 g) and shoot (46.35 g) in control plants decreased to 0.757 and 11.55 g respectively. The shoot/root ratio in control plants (24.56) and yield (7.32 t. h-1) decreased to 18.46 and 1.15 t. h-1 with the highest salinity (200 mM NaCl). The sodium (Na+) content of the shoot increased from 2193 to 4707 μM/g D.wt., while potassium (K+) content of the shoot decreased from 5695 to 2396 μM/g D.wt. resulting in increasing Na+/K+ ratio from 0.4006 to 2.200 with increasing NaCl treatment from 0 to 200 mM. The leaf proline content and ion leakage from leaf discs increased from 0.6320 μM/g F.wt. and 17.67% in control to 3.6020 μM/g F.wt and 29.56% in plants exposed to 0 and 200 mM NaCl stress respectively. While, potash application significantly affected the salinity induced changes in tomato plants, but the potash sources effect was variable on different parameters. The potassium source SOP was superior for fresh weight of root (6.737 g) and shoot (158.5 g), dry weight of root (2.171 g) and shoot (32.11 g), shoot root ratio (23.23), Na+/K+ ratio (0.822) and yield 4.61 than 4.932 g, 113.1 g, 1.316 g, 21.56 g, 21.58, 1.796 and 3.72 t. ha-1 in control treatment respectively. By contrast MOP was more effective in decreasing Na+ (3332 μM/g D.wt), increasing K+ (4384 μM/g D.wt) and retaining better Na+/K+ ratio (0.875) as well proline content (2.466 μM/g F.wt) but caused higher ion leakage (27%) as compared to 3955 μM/g D.wt, 2717 μM/g D.wt, 1.796, 2.006 μM/g F.wt. and 23.80% in control (No Potash supplement) treatment respectively. The interaction of salinity levels and potash application had no significant effect on root and shoot fresh weight, root and shoot dry weight, root/ shoot ratio and yield ha.-1 but significantly decreased the shoot Na content while increased the shoot K content and Na+/K+ ratio. The proline content of the shoot and ion leakage was higher than control with MOP source but lower than control with SOP application.