Revalorization of olive waste as an alternative of biocontrol against the root rot caused by Phytophthora cinnamomi

Abstract: Dehesa ecosystems are seriously threatened by the oak root rot diseases triggered by the soilborne pathogen Phytophthora cinnamomi, being essential to develop control methods to mitigate this disease. On the other hand, between 13-65 % of total Spanish agriculture production are organic waste and by-products which are discarded due to their lack of economic value, but whose removal represents significant expenses. However, plants, including crop wastes, are a rich source of bioactive compounds and secondary metabolites with antifungal and biocide activity. The main goal of this work was to determine the biocide activity against P. cinnamomi of two organic extracts enriched in bioactive compounds which comes from organic waste of olive crops (Oliv 1 and Oliv 2). The effect of the bioactive phenolic compounds of these organic extracts were evaluated at two doses (0.15 and 0.10 %) on the mycelial growth and sporangial production of P. cinnamomi by in vitro experiments. The statistical analysis showed significant differences on the mycelial growth and sporangial
production between both olive-crop extracts at the two doses tested and unamended controls,
reaching percentages of sporangial production inhibition higher than 80 % with the organic
extracts. Moreover, both organic extracts did not affect seed germination regardless of the doses tested. In general, no phytotoxicity symptoms were observed, except for a plant yield reduction in the substrate treated with Oliv 1 at the highest dose (0.15 %). Additionally, in planta experiments using artificially infested substrate showed a significant reduction in plant mortality in substrate amended with Oliv 2. These results set the first steps to develop a
sustainable method to control the root disease based on the circular economy of agricultural
waste.