The Role of Sulfur, Tryptophan Acid, and Methyl Jasmonate in Vegetative Growth, Quality Indicators, and Total Yield of Lettuce Plants

The experiment was conducted in one of the agricultural fields of the College of Agriculture – University of Karbala during the agricultural growing season 2023-2024. The factorial experiment was designed according to the Randomized Complete Block Design (RCBD) with three factors: the first factor was the addition of agricultural sulfur at three levels (0, 15, and 25 kg ha-1), the second factor was spraying the amino acid tryptophan at three levels (0, 100, and 200 mg L-1), and the third factor was spraying methyl jasmonate at three levels (0, 75, and 150 mg L-1). The Least Significant Differences Test (L.S.D) was used to compare the means at a probability level of 0.05 for the growth and yield of lettuce plants (Lactuca sativa L.). The results indicated that the vegetative growth indicators (plant height, stem diameter, total number of leaves, and dry weight of the plant) increased in value when the factors were combined (addition of sulfur at 25 kg ha-1 + spraying tryptophan at 200 mg L-1 + spraying methyl jasmonate at 100 mg L-1). The recorded values were (35.84 cm plant-1, 3.89 cm plant-1, 44.36 leaves plant-1, and 48.30 g plant-1) respectively. In contrast, the treatment sprayed with distilled water only gave the lowest results (27.96 cm plant-1, 2.65 cm plant-1, 26.71 leaves plant-1, and 25.18 g plant-1) respectively. In addition, The results showed that the chemical indicators of the plant increased when the factors were combined (addition of sulfur at 25 kg ha-1 + spraying tryptophan at 200 mg L-1 + spraying methyl jasmonate at 100 mg L-1), with total soluble carbohydrates content in leaves (29.15 mg g-1 dry weight plant-1), the percentage of fiber in leaves (37.06%), nitrate concentration in leaves (797.41 mg kg-1), and oil estimation (3.46%,) In contrast, the control treatment recorded the lowest values, with 18.06 mg g-1 dry weight plant-1, 15.27%, 1824.03 mg kg-1, and 1.03%, respectively. The combination of the three factors at the levels (sulfur at 25 kg ha-1 + tryptophan at 200 mg L-1 + and methyl jasmonate at 100 mg L-1) resulted in the highest values in the studied yield indicators of the plant (average marketable head weight (were 753.42 g per plant), and total yield (33.904 tons ha-1). In contrast, the control treatment, where plants were only sprayed with distilled water, gave the lowest results, with 361.66 g per plant and 16.275 tons per hectare, respectively.