a study on possible effect of using salicylic acid and some of its derivatives for inducing host resistance against tomato stem canker disease

abstract application of chemicals which activate plant defense mechanisms before pathogen attack without environmental side effects of protective chemical agents have stimulated great deal of researches in this area. one of the important crops in the world is tomato and recently recognized as a model plant for plant-pathogen interactions. tomato early blight is one of the most devastating disease worldwide, caused by alternaria alternata f. sp. lycopersici. in this study possible effect of using salicylic acid (sa) and some of it’s derivatives including 4-chloro salicylic acid, 5-chloro salicylic acid, 5-methoxy salicylic acid, 5-amino salicylic acid, 5-methyl salicylic acid and 3,5-dinitro salicylic acid in host resistance induction with different concentrations of 200 µm, 400 µm and 500 µm as leaf spray against tomato stem canker disease was investigated. the results demonstrated that application of 200 µm dosage of chemicals is insufficient dose. application of sa, 4-chloro salicylic acid and 5-methoxy salicylic acid in concentration 400 µm reduced disease index significantly comparing with infected control. 5-chloro salicylic acid and 3,5- dinitro salicylic acid were ineffective in this dose. all the chemicals have been tested with concentration of 500 µm were significantly effective in disease symptoms reduction but also made chlorosis in treated plants. htplc results showed highly correlation between increasing endogenous level of sa in treated plants and reduction of necrotic area (r2=0.59) and reduction of lesion number (r2=0.82).