LINKING THE BELOWGROUND MICROBIAL COMPOSITION, DIVERSITY AND ACTIVITY TO SOILBORNE DISEASE SUPPRESSION AND GROWTH PROMOTION OF TOMATO AMENDED WITH BIOCHAR

Amit K. Jaiswal ^1,2,3 Yigal Elad ¹ Ellen Graber ² Eddie Cytryn ² Omer Frenkel ¹

¹Department of Plant Pathology, Agricultural Research Organization, Volcani Center, Beit Dagan
²Department of Soil Sciences and Microbiology, Agricultural Research Organization, Volcani Center, Beit Dagan
³Department of Plant Pathology and Microbiology, Faculty of Agriculture, The Hebrew University of Jerusalem, Rehovot

Biochar, in addition to carbon sequestration, soil amelioration and improvement of plant performance, can significantly reduce plant diseases. Nevertheless, the mechanisms associated with soilborne-disease suppression are not fully understood. This study tested the effects of two biochars at concentration of 0-3% (w:w) on fusarium crown and root rot (FCRR) of tomato caused by Fusarium oxysporum f. sp. radices-lycopersici (FORL), with an emphasis on mechanisms of disease suppression. Biochar at higher concentrations suppressed FCRR of tomato by up to 79%. Furthermore, biochar significantly reduced the Fusarium root colonization and survival in soil. Yet, direct toxicity of biochar to FORL was not observed in in vitro assay. Biochar amendment significantly increased the culturable counts of general bacteria, fluorescent Pseudomonas spp., Trichoderma spp. (well-known biocontrol and plant growth promoting agents) and other microorganisms. Indeed, biochar-stimulated fluorescent Pseudomonas have antagonistic activity towards FORL. Illumina sequencing analyses of 16S rRNA gene showed substantial differences in bulk soil, rhizosphere and rhizoplane bacterial taxonomical composition between biochar-amended and control soils. Nevertheless, biochar amendment caused a significant increase in microbial taxon and functional diversity (Shannon’s diversity, richness), microbial activities (respiration rates, dehydrogenase and other enzymes activities) and an overall shift in carbon-source utilization by microbial communities (Biolog Microplates), concurrent with increased plant growth and disease suppression. High microbial diversity and activity in the rhizosphere has been previously associated with soilborne diseases suppression and growth promotion, and this may collectively explain the significant reduction of disease and increase in plant growth observed in the presence of biochar.