Anti-oomycete activity of asparagus and olive by-products with potential to control Phytophthora cinnamomi root rot

The development of environmentally friendly control methods to mitigate the severe damages caused by Phytophthora cinnamomi in the Mediterranean climate-type ecosystems is essential. In this way, crop waste and by-products which represent between 13 and 65% of agriculture production, are a rich source of bioactive compounds with antifungal and biocide activity. The main objective of this work was to determine the biocide activity against P. cinnamomi of three organic extracts. These extracts enriched in bioactive compounds come from residues of asparagus (Asp) and olive crops (Oliv and OH, from fruits and leaves respectively). They were evaluated at two doses (0.15 and 0.10%) on the mycelial growth and sporangial production of P. cinnamomi by in vitro experiments. Mycelial growth and sporangial production were significant reduced from the three plant extracts at the two doses tested, reaching a total inhibition with Asp at both doses. In general, no phytotoxicity symptoms were observed on seed germination and plant development, except for a plant yield reduction in the substrate treated with Oliv and Asp at the highest dose. In experiments performed in artificially infested soil, Asp induced a reduction of chlamydospores viability greater than 75% compared to unamended soil. Additionally, in planta experiments showed a significant reduction in plant mortality in substrate amended with OH. These results suggest that soil application of Asp and OH can limit P. cinnamomi infectivity and survival, setting the first steps to develop a sustainable method to control the root disease based on agricultural waste circular economy.