Moderate drought stress increases resistance of Brassica napus to subsequent infection by Leptosphaeria maculans

Plants have developed adaptive strategies to cope with environmental stresses, but mechanisms effective under one stress may be counterproductive under others. This study investigates the effect of moderate drought stress pretreatment on the resistance of Brassica napus to Leptosphaeria maculans, the pathogen causing blackleg disease. B. napus plants were exposed to varying durations of drought stress, followed by a 24-h recovery period before inoculation with L. maculans. The results demonstrate a priming effect of the drought pretreatment, with a reduction in necrotic lesions in cotyledons compared to non-stressed controls. The most pronounced effect was observed in plants that underwent a 68-h drought pretreatment, resulting in a 45% reduction in disease symptoms. The transcriptions of 17 genes involved in B. napus defence against pathogen infection and drought stress were monitored. This revealed the involvement of the salicylic acid signaling pathway, indicated by increased expression of PR1 and PR2 marker genes. Additionally, drought stress marker genes were upregulated. These findings provide insight into the mechanisms of plant adaptation to combined biotic and abiotic stresses, which is essential for sustainable agriculture in a changing environment.