Green Alternatives for the Control of Fungal Diseases in Strawberry: In-Field Optimization of the Use of Elicitors, Botanical Extracts and Essential Oils

Finding, safe and reliable alternatives to fungicides is one of the most actual challenges in agriculture. In this regard, our experiment investigated the effectiveness of different elicitors, botanical extracts and essential oils to control grey mould (Botrytis cinerea) and powdery mildew (Podosphaera aphanis) on strawberry plants. Furthermore, the defence mechanisms activated in plants after treatments were investigated. The trial was conducted in field conditions under plastic tunnel with strawberry plants ‘Elsanta’. In the first experiment, a group of strawberry plants was treated before flowering with elicitors acibenzolar-S-Methyl – (BTH), chitosan, botanical extracts (seaweed extract, alfalfa hydrolysate) and essential oils (thyme and juniper) to evaluate their ability to reduce the incidence of grey mould infection on flowers. In the second experiment, another group of plants was treated before and after experimental inoculation with P. aphanis. Results indicated that the incidence of flower infected by B. cinerea was significantly reduced by thyme and juniper essential oils, showing values that were not significantly different from the commercial fungicide penconazole (positive control). As a consequence, final yield of essential oil-treated plants was +27% higher as compared to control. No significant differences emerged for other tested products against grey mould. However, gene expression analysis showed an up-regulation of FaEDS1, FaLOX and PR gene expression (FaPR1, FaPR5, FaPR10) in leaves treated with BTH. The other tested natural substances also elicited defence-related genes, however at a lower level than BTH. In the experiment, all treatments applied prior inoculation significantly reduced the incidence and severity of powdery mildew as compared to control. At 28 days after inoculation, chitosan and thyme essential oil applications performed similarly to their positive controls (BTH and penconazole, respectively), showing a significant reduction of disease incidence (by -84 and -92%) as compared to control. Post-inoculum application of essential oils showed similar effective action to fungicide (penconazole) in reducing incidence and severity of powdery mildew. These results indicate that the tested substances could be used as alternatives to fungicides for the control of grey mould and powdery mildew in strawberry, therefore representing a valuable tool for the control of these fungal diseases under the framework of the sustainable agriculture.