Plant Extracts Induced Resistance to Fusarium Oxysporum F.sp. Lycopersici in Tomato

Tomato (Lycopersicon esculentum Mill.) is the most consumed vegetable in the world after potato. In Cameroon, the plant is cultivated in almost all agroecological areas, however, yields remain low due to attacks by various pathogens and insects. Among the pathogens, Fusarium oxysporum f.sp. lycopersici (FOL) is a phytopathogenic fungus responsible for Fusarium wilt, a disease responsible for enormous economic losses. To contribute to the control of this microbial pathogen, the stimulatory effect of the tomato defence system of extracts of some plants in the tomato/FOL interaction was evaluated. Tomato plants were treated with the aqueous extracts (AE) of Callistemon citrinus (C. citrinus), Cymbopogon citratus (C. citratus), and Oxalis barrelieri (O. barrelieri ). After 4 days of spraying with the extracts, the plants were inoculated with a virulent strain of Fusarium oxysporum f.sp. lycopersici (FOL) under controlled conditions. Tomato roots were used to determine the contents of hydrogen peroxide (H2O2), phenols and malondialdehyde (MDA). The activities of the main antioxidant enzymes were also evaluated in tomato roots: catalase (CAT), phenylalanine ammonia lyase (PAL), peroxidase (POX) and superoxide dismutase (SOD). The results showed that treatment of tomato plants with plant extracts and their infection with FOL induced an increase in the contents of H2O2, phenols and MDA in tomato roots; an increase in PAL, POX, SOD activities and a reduction in CAT activity. Our results suggest that the increase and reduction of enzymatic activities, and the increase in the synthesis of some metabolites could mitigate the oxidative damage that takes place during the expansion of the pathogen. Aqueous extracts of C. citrinus, C. citratus and O. barrelieri at 10% (W/V) could be used as natural products to stimulate the tomato defence system against FOL. These results could contribute to the development of natural products to induce tomato resistance against FOL, thus improving productivity, quantity and quality of production.