Evaluation of Salicylic Acid and Proline Treatment on Tomato Plant Growth under Biotic Stress by Alternaria Alternata Fungus

Abstract

An experiment was conducted in 2024-2025 to examine the effects of treatment with different concentrations of salicylic acid SA and proline on pathogenic fungus Alternaria alternata on tomato plants. Seven fungal isolates of A. alternata fungi were obtained from tomato fruits showing symptoms of late blight infection, the pathogenicity of these isolates showed that two isolates (Ala2) and (Ala4) gave the highest percentage of pathogenicity, as the seedling death rate, and Ala4 isolate was chosen for the laboratory experiment and the greenhouse experiment. The results of the tested experiment also showed the inhibitory effect of SA on the growth of fungal mycelium on SDA medium, as the inhibition rate was 100% at all concentrations, As for proline, the concentration 0.5 recorded highest inhibition rate of 91.27%, Then the effect of spraying with five concentrations of resistance inducing agents (SA and proline) was tested, which are (0.5, 1, 1.5, 2, 2.5) ml. L-1 were sprayed on 40 day old tomato seedlings after treatment with the pathogenic fungus ,The results showed that superiority of spraying with SA in reducing the infection rate with early blight disease, the infection rate with the disease decreased with increasing the concentrations of spraying with salicylic acid. Accordingly, the lowest infection rate was in the spraying treatment with 2.5 ml. L-1 and was 1.96%. The results also show that spraying with proline had different results than spraying with SA, as the infection rate did not decrease with increasing concentration, and increasing the concentration of the treatment did not affect the pathogen. The results show that the treatment with SA and proline did not affect the average number of leaves or the leaf area of the plant compared to the control treatment without the pathogenic fungus, but it outperformed the control treatment with the pathogenic fungus.