Role of salicylic acid in growth of tomato seedlings infected by fusarium solani.

Abstract

The role of salicylic acid (SA) in inducing resistance of seedlings of tomato, Lycopersicon esculentum Mill., castle rock cultivar; against infection with the pathogenic fungus Fusarium solani through enhancing the growth, pathogen related (PR) protein and antioxidant system was studied. Tomato seeds were infected with lx106 spores / ml suspension of Fusarium solani for 12 hours, air dried, germinated in different concentrations of SA for 15 days and then transferred into growth chamber at 30-I- 2°C under 12 hr. light / day. Root rot disease parameter caused by the pathogenic fungus which including damping-off percentage and survival plants percentage and also other morphological criteria was recorded. Uniform seedlings from each treatment were used for measuring growth parameters and physiological studies which including the determination of pigments, carbohydrates, total soluble protein and enzyme activity of catalase, guaiacol peroxidase, ascorbate peroxidase and malondialdehyde content. Electrophoretic analysis was carried out and solubleTroteins of seedlings were determined. From this study it was found that the low conc of SA, 10 and 104 eleviate the pathogenic effect, significant increase in growth parameters ( radicle and hypocotyl length and fresh and dry weights )was observed. At high cone., 10'3 M, a negative elect and hence high damping-off percentage of seedlins; significant reduction in growth parameters was recorded. It was appeared also that SA at 10' M increased values of chlorophyll a, b and carotenoids. At 10° M of SA carbohydrate content was decreased gradually; 3.3, 20.0, 30.0 (rug glucose g'ID. wt) for.sucrose, polysaccharide and total carbohydrate respectively, while total soluble protein content was highly increased at 10-5 M of SA; (12.1 mg D.wt.). Gel electrophoretic patterns of soluble proteirfs of tomato seedlings showed that SA at the used conc produced new structural proteins with M.Wt 38.0, 33.0, 30.2, 27.0, 23.3, 20.4, 18.5 and 17.0 KDa in the infected seedlings. Finally it was found that catalase, peroxidase and ascorbate peroxidase activities were decreased gradually with increasing the conc. of SA and the inhibition of these enzymes would result in elevated levels of endogenous H202,. also, Lipid peroxidation was enhanced by SA reached maximum at 10'3 M of SA and respose to elevated H202 and may mediate signal transduction leading to (PR) protein, enhance disease resistance.