Phytoprotective behaviour of compost extracts against aerial pathogenic fungi after rhizosphere application

This work describes an in-depth study of the microbiological and functional characterization of compost extracts. The main objective was to analyze the influence of different extraction protocols and raw materials on the functional diversity of compost extracts, as well as on their ability to suppress plant diseases and improve plant health. To obtain the extracts, different composts based on agri-food waste, sewage sludge, olive oil mill waste and vegetable waste were used, applying four different extraction protocols depending on temperature and incubation time. The results showed that extracts obtained with longer extraction times at mild temperatures presented higher functional diversity and microbial abundance, while samples extracted during shorter time at higher temperatures showed lower biological activity. In addition, compost extracts with higher functional diversity were more effective in controlling damage caused by the fungi Botrytis cinerea and Alternaria alternata on cucumber plants, achieving a 65–80 % reduction in plant damage. Consequently, this research suggests that the development of appropriate extraction protocols could improve the phytostimulant and phytoprotective capacity of compost extracts, serving as a sustainable alternative or complement to other agrochemical products. • Extraction conditions influence the functionality of compost extracts. • Mild temperatures guarantee the preservation of microbial functionality. • Protocols based on high temperatures reduce the abundance of microbial communities. • Extraction conditions may reduce heterogeneity when using different compost sources • Compost extracts mitigate foliar disease symptoms in cucumber plants.