Effect of Salicylic acid and Silicon biostimulants on the induced resistance response in Strawberry plants against Phytophthora fragariae and cactorum

In strawberry production, plant diseases can affect plant yields if not treated efficiently and on time. However, pest management nowadays is increasingly complex due to issues associated with agrochemicals; the withdrawal of some active ingredients, restrictions on the use of some substances, and mitigation measures aimed at safeguarding the environment, human and animal health, have encouraged the adoption of alternative techniques to be used for the control of harmful pathogens. Environmentally friendly products, such as biostimulants, capable of increasing plant tolerance against pathogens or inducing plants own defence responses are becoming increasingly used. However, their efficiency should be strictly tested in different pathosystems to evaluate their real potential in plant protection. Phytophthora cactorum and P. fragariae are a group of filamentous plant pathogens responsible for roots and crown rots in strawberry plants, causing high economic losses in the production areas. These pathogens are oomycetes that overwinter through survival spores found in the soil and germinate when environmental conditions are suitable. Their spores can also remain inactive for years in the soil making it difficult to control them in the field and identify the source of contamination (Newton et al, 2010). In this thesis work, the possibility of using salicylic acid and silicon as biostimulants for the control P. cactorum and P. fragariae on strawberry plants was evaluated by testing the incidence of the disease in inoculated strawberry leaf, crown, and roots previously treated four times (one treatment per week) with salicylic acid or silicon. The salicylic acid biostimulant should enhance a hypersensitive response in the treated plants, by leading to programmed cell death that should restrict the growth and/or spread of biotrophic pathogens. The silicon biostimulant should accumulate in the tissues leading to a physical reinforcement of the cell walls and interfering with the pathogen penetration in the host. The experiments, performed on different varieties of strawberry plants (Clery, Polka, and Malling Centenary) with a similar sensibility, showed these biostimulants did not significantly reduce the incidence of P. cactorum and P. fragariae disease, while the reference chemical treatment with the synthetic fungicide fosetyl-Al proved to be the most effective control method for controlling these pathogens.