Biochar nanoparticle-induced plant immunity and its application with the elicitor methoxyindole in Nicotiana benthamiana

The exogenous application of nanoscale biochar has great potential in agriculture to improve crop resistance to pathogens, although the mechanisms underlying this physiological response are unclear. We investigated the potential of nanoscale and conventional biochar amendment to induce resistance in Nicotiana benthamiana upon infection with the pathogen Phytophthora nicotianae. Nanoscale biochar synthesized at 350 degrees C (400 mg L-1) from corn straw with a particle size of similar to 160 nm had a beneficial role in the active immunity of N. benthamiana through the ethylene pathway to provide resistance to P. nicotianae infection; in leaf assays, lesion diameters were reduced by 9.26% as compared to controls. Mechanistically, a 20.3% increase in reactive oxygen species (ROS) from biochar NP amendment activated the ethylene pathway, followed by SA-induced systemic acquired resistance (SAR) expression. The SA-induced immunity increased over 10-fold in the two biochar NP treatments. In addition, the biochar NPs induced PR1-a to a significantly greater extent than did regular biochar particles. In an experiment with the plant elicitor 5-methoxyindole, biochar NPs served as a unique delivery platform to improve plant growth, over 105.3% in the shoot length and 41.2% in the root length after seed treatment with biochar NPs and 5-methoxyindole compared to the untreated controls. This study demonstrates the successful use of exogenous nanoscale biochar amendment to stimulate plant defense responses and subsequent resistance to the important pathogen P. nicotianae. This approach holds great promise as a new plant protection strategy in sustainable nano-enabled agriculture.