Eco-Friendly Resistance Inducers for Control of Pseudomonas Cichorii in Lettuce

During pathologic process, plant physiology undergoes substantial changes, including altered biomass accumulation and synthesis of photosynthetic pigments and proteins. These processes can be modulated by resistance-inducing compounds with immunomodulatory activity. In the present study, we evaluated the effects of salicylic acid (SA; C7H6O3), chitosan (C6H11NO4)n, and silicon dioxide (SiO2) on disease development, morphometric traits, and the pigment system of lettuce plants, Lactuca sativa L., cv. Lalik, infected with Pseudomonas cichorii (Swingle 1925) Stapp 1928. Plants were grown in a non-circulating deep water culture hydroponic system under controlled conditions. Thirty-four days after germination, test compounds were applied by foliar spraying, followed by inoculation with Pseudomonas cichorii strain Pch12 (105 CFU/mL) via leaf petiole injection. Symptoms were recorded daily for 10 days, after which shoot weight, leaf length, and photosynthetic pigment content were determined. Delayed symptom development and better preservation of growth parameters in infected plants were observed after SiO2 treatment at 2 mg/plant. Compared with the infected control, SiO2-treated infected plants showed substantially higher shoot fresh weight (21.18 vs. 8.9 g) and leaf length (10.8 vs. 7.8 cm). In the samples treated with chitosan (3.1 mg/plant) and with SA (0.7 mg/plant), total chlorophyll content exceeded the infected control by 42.9 and 37.1%, while carotenoid content was higher by 31.6 and 35.5%, respectively. SiO2 more effectively limited disease symptoms and reduced growth losses, whereas chitosan and salicylic acid better maintained the photosynthetic pigment system under infection.