Bacterial indicators for the disease suppressive effect of composts in three different plant-pathogen systems

Summary in the original language of the document

Composts can supress soil-borne diseases, although the effectiveness varies across plant-pathogen systems and composts. The underlaying mechanisms, likely driven by compost microorganisms, are yet unknown. Identification of microorganisms responsible for disease suppression in compost is crucial for its targeted use in plant protection. We tested 37 composts from commercial compost producers for their physicochemical properties, microbial activity and disease suppressive activity in the three plant-pathogen systems: cress-Globisporangium ultimum (GU), cucumber-GU and cucumber-Rhizoctonia solani (RS), and analyzed their bacterial communities using 16S metabarcoding. Of the tested 37 composts, 76%, 46% and 24% significantly increased disease suppression in the three pathogen – plant systems, respectively. A positive correlation of disease suppression was only found for GU – cress and GU – cucumber (rho = 0.63, p < 0.001). Furthermore, no significant correlation was detected for the abiotic properties and microbial activities of the composts with disease suppression. The bacterial community structure of the composts did not correlate with disease suppression. Indicator species analysis showed that a total of 317 bacterial amplicon sequence variants (ASVS), i.e., 137 for cress-GU, 146 for cucumber-GU and 80 for cucumber-RS, were significantly more abundant in the nine most suppressive compared to the nine least suppressive composts. Notably, for GU-suppression, bacteria from the genera Luteimonas, Sphingopyxis, and Algoriphagus emerged as promising indicators for disease-suppressive composts. These findings provide a foundation for targeted microbial isolation, aiming to elucidate the role of microorganisms in compost-mediated disease suppression, and to predict and optimize suppressive activity.