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. radicis-lycopersici, 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. Chitosan-treated 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.
Highlights
Tomato (Solanum lycopersicum L., formerly, Lycopersicon esculentum Mill.), is one of the most important vegetable crop worldwide after potato, regarding areas under cultivation and ranked second after eggplant in terms of production [1,2]
As compared to the untreated control, chitosan had inhibited fungal mycelial growth at variable rates depending on concentrations uses where the inhibition ranged between 47.71 and 100% using chitosan at 4 mg/ml compared to 0-24.19%, 2.15-36.97%, 10.92-79.21%, 11.27-83.87%, 21.03-100%, and 36.27-100% achieved using this resistance inducers (RIs) at 0.5, 1, 1.5, 2, 2.5 and 3 mg/ml, respectively
When treated with these increasing salicylic acid (SA) concentrations, mycelial growth of B. cinerea and A. solani was reduced by 1.79-48.93% and 20.93-63.57%, respectively, compared to inhibitions of 15-100% and 21.21-100% noted for S. sclerotiorum and P. aphanidermatum, respectively
Summary
Tomato (Solanum lycopersicum L., formerly, Lycopersicon esculentum Mill.), is one of the most important vegetable crop worldwide after potato, regarding areas under cultivation and ranked second after eggplant in terms of production [1,2]. Average areas of 29 000 ha/year are devoted to the growing of open field and protected tomatoes covering about 17% of areas cultivated with vegetables, with an average annual production of about 1.2 million tons representing about 39% of national production of vegetable crops [3]. Tomato is grown both on small- and large-scales commercial crop. Radicis-lycopersici (FORL) and Verticillium dahliae (VD) are highly destructive soil-borne pathogens causing wilt and root rot diseases in both greenhouse and field-grown tomatoes in warm producing areas. Grey mold caused by B. cinerea and early blight incited by A. solani are among the most important diseases of tomato aerial parts leading to lower quantity and quality of fruit yields [8,9]
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