Optimizing Tomato (Lycopersicon esculentum) Yield Under Salt Stress: The Physiological and Biochemical Effects of Foliar Thiourea Application

Abstract

A pot experiment was conducted to investigate the role of thiourea exogenous application (0 mg/L and 100 mg/L) on the morphological, physiological, and yield traits of two varieties of tomato (Naqeeb and Nadir) under different salt stress treatments (0, 60, and 120 mM) in completely randomized design (CRD). The imposition of salinity by rooting medium showed that salt stress reduced plant height by 20%, fresh shoot weight by 50%, dry shoot weight by 78%, fresh root weight by 43%, dry root weight by 84%, root length by 34%, shoot length by 32%, shoot K⁺ by 47%, Ca²⁺ by 70%, chlorophyll a by 30%, chlorophyll b by 67%, and the number of seeds per berry by 53%, while shoot Na⁺ ions were increased by 90% in comparison to those grown with control treatment. However, the exogenous application of thiourea significantly enhanced dry root weight by 25% and the number of seeds per berry by 20% in comparison to untreated plants with thiourea when grown under salt stress. Salt stress resulted in a reduction in the number of berries, weight per berry, number of seeds per berry, and seed weight in both varieties, while thiourea foliar application increased these yield parameters. On the other hand, the Nadir variety surpassed Naqeeb in plant height (+13%), root length (+31%) and shoot length (+11%), fresh shoot weight (+42%) and dry shoot weight (+11%), fresh root weight (+29%), dry root weight (+25%), area of leaf (+26%), chlorophyll a (+32%), and chlorophyll b (+24%). In conclusion, the exogenous application of thiourea can be used to mitigate salt stress in tomato plants since it can improve the growth, physiological, and yield traits of this strategic crop.

Keywords: antioxidant; plant bioregulators; salinity; thiourea; tomato; yield attributes.

Figure 1

Effects of different foliar applications of thiourea on shoot length (A), shoot fresh weight (B) and shoot dry weight (C) of two tomato varieties grown under salinity stress. Error bars = standard error (SE), and bars with different letters indicate significant differences (p ≤ 0.05).

Figure 2

Effects of different foliar applications of thiourea on root length (A), root fresh weight (B), and root dry weight (C) of two tomato varieties grown under salinity stress. Error bars = standard error (SE), and bars with different letters indicate significant differences (p ≤ 0.05).

Figure 3

Effects of different foliar applications of thiourea on plant height (A) and number of leaves (B) of two tomato varieties grown under salinity stress. Error bars = standard error (SE), and bars with different letters indicate significant differences (p ≤ 0.05).

Figure 4

Effects of different foliar applications of thiourea on chlorophyll a (A), chlorophyll b (B), and carotenoids (C) of tomato varieties grown under salinity stress. Error bars = standard error (SE), and bars with different letters indicate significant differences (p ≤ 0.05).

Figure 5

Effects of different foliar applications of thiourea on total chlorophyll (A) and chlorophyll a/b ratio (B) of two tomato varieties grown under salinity stress. Error bars = standard error (SE), and bars with different letters indicate significant differences (p ≤ 0.05).

Figure 6

Effects of different foliar applications of thiourea on SOD (A), POD (B), and CAT (C) of tomato varieties grown under salinity stress. Error bars = standard error (SE), and bars with different letters indicate significant differences (p ≤ 0.05).

Figure 7

Effects of different foliar applications of thiourea on sodium (A), potassium (B), and calcium ions (C) of tomato varieties grown under salinity stress with foliar application of thiourea. Error bars = standard error (SE), and bars with different letters indicate significant differences (p ≤ 0.05).

Figure 8

Effects of different foliar applications of thiourea on leaf area (A), specific leaf area (B), and leaf area index (C) of tomato varieties grown under salinity stress with foliar application of thiourea. Error bars = standard error (SE), and bars with different letters indicate significant differences (p ≤ 0.05).

Figure 9

Effects of different foliar applications of thiourea on the number of berries (A), number of seeds per berry (B), weight per berry (C), and seed weight (D) of tomato varieties grown under salinity stress. Error bars = standard error (SE), and bars with different letters indicate significant differences (p ≤ 0.05).

Figure 10

(a) Nadir variety; (b) Naqeeb variety. Pearson correlations of different morphophysiological and biochemical attributes of tomato (Nadir and Naqeeb). Morphological attributes: shoot dry weight (SDW), root dry weight (RDW), shoot fresh weight (SFW), root fresh weight (RFW), shoot length (SL), root length (RL), plant height (PH), number of leaves (NL), number of berries (NB), number of seed per berry (NSB), seed weight (SW), weight per berry (WB), leaf area (LA), leaf area index (LAI), and specific leaf area (SLA). Physiological attributes: chlorophyll a (Cha), chlorophyll b (Chb), carotenoids (CAR), chlorophyll a and b ratio (Cab), total chlorophyll (T.Ch), superoxide dismutase (SOD), peroxide (POD), and catalase (CAT). Biochemical attributes: sodium (Na⁺), potassium (K⁺), and calcium (Ca²⁺).

Figure 11

(a) Nadir variety; (b) Naqeeb variety. Clustered heatmap of different morphophysiological and biochemical attributes of tomato (Nadir and Naqib) under different levels of salt stress and with or without the application of thiourea. Morphological attributes: shoot dry weight (SDW), root dry weight (RDW), shoot fresh weight (SFW), root fresh weight (RFW), shoot length (SL), root length (RL), plant height (PH), number of leaves (NL), number of berries (NB), number of seed per berry (NSB), seed weight (SW), weight per berry (WB), leaf area (LA), leaf area index (LAI), and specific leaf area (SLA). Physiological attributes: chlorophyll a (Cha), chlorophyll b (Chb), carotenoids (CAR), chlorophyll a and b ratio (Cab), total chlorophyll (T.Ch), superoxide dismutase (SOD), peroxide (POD), and catalase (CAT). Biochemical attributes: sodium (Na⁺), potassium (K⁺), and calcium (Ca⁺²). Heatmap represents the separation of treatments into T₁ (salinity 0 mM + 0 ppm thiourea), T₂ (salinity 120 mM + 100 ppm thiourea), T₃ (salinity 60 mM + 0 ppm thiourea), T₄ (salinity 60 mM + 100 ppm thiourea), T₅ (salinity 120 mM + 0 ppm thiourea), and T₆ (salinity 120 mM + 100 ppm thiourea).