Si-modified biochar mediated tomato resistance to bacterial wilt by increasing soil silicon availability and inducing...

Although both silicon (Si) and biochar enhance plant defense responses, their effectiveness is often constrained by low silicon bioavailability and inconsistent impacts on rhizosphere microbiota. The mechanisms by which Si-modified biochar (MSC) enhances plant disease resistance through improved Si bioavailability, microbial modulation, and immune activation remain largely unknown. In this study, we developed Si-modified biochar and evaluated its effects on soil silicon availability, plant silicon uptake, and tomato resistance to bacterial wilt caused by Ralstonia solanacearum. The application of 1 % MSC significantly increased soil Si availability, promoting higher silicon uptake by plant roots and its subsequent translocation to the stems and leaves. This improvement in silicon nutrition contributed to a 74.8 % reduction in disease incidence compared to treatments with single silicon (SN) or unmodified biochar (SC), demonstrating MSC's superior wilt-suppressing efficiency. MSC significantly increased lignin deposition and soluble phenol levels, and enhanced the activities of plant defense-related enzymes, including polyphenol oxidase, peroxidase, phenylalanine ammonia-lyase, and lipoxygenase in leaves. MSC treatment also strengthened hormonal signaling pathways by increasing abscisic acid (ABA), salicylic acid (SA), and jasmonic acid (JA) levels. Furthermore, MSC upregulated resistance-related genes (PAL, PR-5, PDF1.2, LOX, PR-1), reinforcing plant immunity. Moreover, MSC increased photosynthetic efficiency and promoted tomato root growth, improved nutrient uptake, and enhanced overall plant health. Our findings reveal a mechanistic link between Si-modified biochar and plant immunity, providing a sustainable solution for disease management and contributing to agricultural resilience and global food security.