Global mRNA profiling reveals the effect of boron as a crop protection tool against <i>Sclerotinia sclerotiorum</i>

<i>Sclerotinia sclerotiorum</i>, the causal agent of white mould, is a necrotrophic fungal pathogen responsible for extensive crop loss. Current control options rely heavily on the application of chemical fungicides that are becoming less effective and may lead to the development of fungal resistance. In the current study, we used a foliar application of boron to protect <i>Brassica napus</i> (canola) from <i>S. sclerotiorum</i> infection using whole-plant infection assays. Application of boron to aerial surfaces of the canola plant reduced the number of <i>S. sclerotiorum</i>-forming lesions by 87 % compared to an untreated control. Dual RNA sequencing revealed the effect of boron on both the host plant and fungal pathogen during the infection process. Differential gene expression analysis and gene ontology term enrichment further revealed the mode of action of a foliar boron spray at the mRNA level. A single foliar application of boron primed the plant defence response through the induction of genes associated with systemic acquired resistance while an application of boron followed by <i>S. sclerotiorum</i> infection-induced genes associated with defence response-related cellular signalling cascades. Additionally, in <i>S. sclerotiorum</i> inoculated on boron-treated <i>B. napus</i>, we uncovered gene activity in response to salicylic acid breakdown, consistent with salicylic acid-dependent systemic acquired resistance induction within the host plant. Taken together, this study demonstrates that a foliar application of boron results in priming of the <i>B. napus</i> plant defence response, likely through systemic acquired resistance, thereby contributing to increased tolerance to <i>S. sclerotiorum</i> infection.