Benzothiadiazole induces Pinus koraiensis to resist pine wilt disease

Benzothiadiazole (BTH) and methyl salicylate (MeSA) have been confirmed as effective inducers for numerous plant species, empowering them to fend off pathogens. In this research, we combined the relative tolerance index (RTI) and relative anti-nematode index (RAI) to assess how these two inducers influence Pinus koraiensis in resisting pine wood nematodes (PWNs). Additionally, we integrated transcriptome and metabolome analyses to uncover the underlying mechanism. The results indicated that BTH could stimulate P. koraiensis to resist PWNs, and the induction effects differed depending on the concentration. Among the tested concentrations, a 0.5 mM BTH solution yielded the most favorable induction outcome, and the spraying approach proved to be highly effective. Conversely, MeSA failed to trigger P. koraiensis to resist PWNs. The optimal induction protocol for BTH involved spraying a 0.5 mM BTH solution once a day, with a total of three sprays (Scheme 1). In P. koraiensis specimens that were inoculated with PWNs after being treated following Scheme 1, genes associated with plant disease resistance pathways, such as the flavonoid biosynthesis pathway, were activated. Simultaneously, the abundances of metabolites in the flavonoid biosynthesis pathway increased. The integrated transcriptome and metabolome analysis revealed that BTH regulates the expression of genes like chs, hct, ccoaomt, cyp75b1, fls, dfr, lar, ans, and anr in the flavonoid biosynthesis pathway of P. koraiensis. It channels upstream metabolites towards the synthesis pathways of epicatechin and taxifolin, resulting in the production and accumulation of these two substances. Consequently, the resistance of P. koraiensis to PWNs is enhanced.