Molecular and biochemical insight into biochar and Bacillus subtilis induced defense in tomatoes against Alternaria solani

Abstract

Abstract This study was aimed to elucidate the biochar induced resistance pathways in association with beneficial plant growth promoting rhizobacteria (PGPR) in the tomato (Solanum lycopersicum) – Alternaria solani pathosystem. To examine the impact of biochar on plant defense mechanisms at the molecular level, tomato plants were grown in two different biochars (wood and green waste biochar; 3 and 6% application level of each) both with and without Bacillus subtilis, (PGPR). Although, the reduction in disease index and disease incidence was significant in wood biochar amended soil but the resistant plant response against early blight was only recorded in the 6% green waste biochar amended treatment. Biochar application has induced the expression of defense associated genes including jasmonic acid related PI2, TomloxD, salicylic acid related PR1a, PR2 and ethylene responsive Pti4. Green waste biochar (6%) was more efficient in eliciting the expression level of TomloxD, PI2, PR1a and PR2 in tomatoes challenged by A. solani, while PGPR inoculation has enhanced the PR2 expression levels in comparison to tomatoes grown in wood biochar amended soil substrate. Moreover, phenolics, catalase and peroxidase production levels of plants grown in green waste biochar alone as well as in the presence of B. subtilis, contributed significantly in moderating infection induced damages. In conclusion, tomatoes response to invading A. solani was dependent on the type of biochar, while protection against early blight was better at higher application rate of biochar i.e. 6%. Different biochar types also differ with their ability to elicit the defense gene expression/signaling pathways. Our study revealed that biochar and PGPR induced protection against early blight of tomatoes involves both induced systemic resistance (ISR) and systemic acquired resistance (SAR) mechanisms.