Evaluating effect of Salicylic acid and Proline on inducing resistance in Tomato(Solanum lycopersicon L.) plants against Eearly blight caused by the Alternaria alternate fungus

Abstract

    A factorial experiment was conducted in the greenhouse during the 2024-2025 year to study the effect of spraying tomato plants with six concentrations (0.0, 0.5, 1.0, 1.5, 2, and 2.5 ml.L-1) of Salicylic acid and Proline on their resistance to infection by the fungus Alternaria alternate which caused early blight disease . The results showed decrease in the average number of flowers, fruits, and fruit weight with increasing concentrations of Salicylic acid and Proline. Conversely, the results showed an increase in defensive enzymes in the tomato plant, as recorded the activity of the phenylalanine ammonia-lyase (PAL) enzyme in plants treated with salicylic acid, with activity increasing with increasing concentration. The highest value was recorded at 2.5 ml. L-1 (3.978 g. L-1), while the lowest value was 2.953 g. L-1 at a concentration of 0.5 ml. L-1. Conversely, enzyme activity decreased with increasing proline concentration, reaching a peak of 3.286 at 0.5 ml. L-1 and a minimum of 0.879 at 2.5 ml. L-1. In contrast, the levels of PO, total protein, and lignin increased with increasing salicylic acid and proline concentrations, reaching peaks of 0.365, 1.839, and 31.13, respectively, at 2.5 ml. L-1, and minimums of 0.212, 1.489, and 16.40, respectively, at 0.5 mL/L. Salicylic acid coefficients were highest at 2.5 mL/L, at 0.290, 1.818, and 20.66, respectively, and lowest at 0.5 ml. L-1, at 0.153, 1.484, and 13.66, respectively. Regarding the salicylic acid content in the plant, its coefficients decreased with increasing concentration, reaching a high of 41.18 at 2.5 ml. L-1and a low of 16.47 at 0.5 ml. L-1. In contrast, the proline content in the plant increased with increasing concentration, reaching a high of 119.06 at 2.5 ml. L-1and a low of 93.50 at 0.5 ml. L-1. By exploiting the plants' innate resistance to pathogens, the use of resistance inducers may reduce the need for environmentally toxic chemicals in disease management. Therefore, we propose using proline and salicylic acid as unconventional and environmentally friendly alternatives for plant protection and promoting sustainable agriculture.