DECODING THE MECHANISMS THAT UNDERLIE DISEASE SUPPRESSION BY BIOCHAR AGAINST FUSARIUM CROWN AND ROOT ROT IN TOMATO

Biochar, a highly efficient means of carbon sequestration, which when applied to soil, simultaneously improves soil quality, crop performance, and surprisingly, reduces foliar and soilborne diseases in various crops. Nevertheless, the mechanisms associated with soilborne-disease suppression are not fully understood. This study tested the effects of two contrasting biochars at concentration of 0-3% (w:w) on Fusarium crown and root rot (FCRR) of tomato caused by Fusarium oxysporum f. sp. radicis-lycopersici (FORL), with emphasizing the mechanisms of disease suppression. We found that biochar has ability to suppress FCRR of tomato at higher concentration up to 79% as compared to the control. The mechanism of disease suppression could not explained by direct toxicity as no significant mycelia radial growth inhibition was detected by either biochar up to 3% in in vitro assay. Adsorption of pathogenic enzymes (cellulase and polygalacturonase) by biochar experiments showed the clear evidence that adsorption of enzymes may be the one of the disease suppression mechanism. Biochar amendment significantly increased the culturable counts of general bacteria, fluorescent Pseudomonas spp., Trichoderma spp. (a well-known biocontrol agents and PGPR) and other microbes. PCR-DGGE and Illumina sequencing analyses of 16S rRNA genes showed substantial differences in rhizosphere bacterial taxonomical composition between biochar-amended and control soils. Nevertheless, biochar amendment caused a significant increase in bacterial diversity and richness concurrent with disease suppression. The enrichment of bacterial abundance, bacterial diversity, and beneficial microorganisms may play a part in the overall effects of biochar on disease suppression either through direct antagonist effect towards pathogen or indirectly via induction of systemic resistance in plant.