Variation in Chitosan and Salicylic Acid Efficacy Towards Soil-borne and Air-borne Fungi and Their Suppressive Effect of Tomato Wilt Severity

Abstract

Two resistance inducers (RIs), chitosan and salicylic acid (SA), were assessed in vitro for their antifungal activity against ten tomato phytopathogenic fungi i.e. Fusarium oxysporum f. sp. lycopersici, F. oxysporum f. sp. radicislycopersici, F. solani, Verticillium dahliae, Rhizoctonia solani, Colletotrichum coccodes, Pythium aphanidermatum, Sclerotinia sclerotiorum, Botrytis cinerea, and Alternaria solani. The impact of these RIs, applied as soil drench, on Verticillium wilt, Fusarium wilt, and Fusarium Crown and Root Rot severity and on growth parameters of tomato cv. Rio Grande plants were also investigated. Chitosan (0.5-4 mg/ml) and SA (1-25 mM) inhibited mycelial growth of all pathogens in Potato Dextrose Agar (PDA) medium in a concentration-dependent manner, with the greatest inhibition achieved using the highest chitosan and SA concentrations. Inter specific variations in sensitivity to chitosan and SA were detected. P. aphanidermatum and S. Sclerotiorum were the most sensitive to both RIs. Single treatments with chitosan (4 mg/ml) and SA (10 mM) resulted in varied degree of protection against wilt diseases. Chitosan-and SA-based treatments resulted in 42.1-73.68, 60.86-78.26 and 45-50% reductions in wilt severity, as compared to VD-, FOL- and FORL-inoculated and untreated controls, respectively. All growth parameters noted were enhanced using RIs compared to pathogen-inoculated controls. In fact, SA-based treatment had significantly increased plant height, root and aerial part fresh weights by 17.94, 52.17 and 33.33%, by 23.01, 55.40 and 29.72%, and by 17.72, 50 and 46.84%, respectively, while compared to VD-, FOL- and FORL-inoculated and untreated plants. Chitosantreated plants showed increment in their height, root and aerial part fresh weights by 13.81, 62.16 and 38.97%, respectively, compared to FORL-inoculated and untreated control. Results from this investigation showed that SA and chitosan may be used as potential inducers of systemic acquired resistance for successfully controlling fungal tomato diseases in Tunisia.