Applying brassinolide (BL, a phytohormone) in combination with pyraclostrobin (Pyr, a fungicide) has shown effective disease control in field trials. However, the mechanism by which BL + Pyr control disease remains uncertain. This work compared the disease control and defense responses of three pretreatments (BL, Pyr, and BL + Pyr) in Arabidopsis thaliana. We found that BL + Pyr improved control against Pyr-sensitive Hyaloperonospora arabidopsidis and Botrytis cinerea by 19 and 17% over Pyr, respectively, and achieved 29% control against Pyr-resistant B. cinerea. Furthermore, BL + Pyr outperformed BL or Pyr in boosting transient H2O2 accumulation, and the activities of POD, APX, GST, and GPX. RNA-seq analysis revealed a more potent activation of defense genes elicited by BL + Pyr than by BL or Pyr. Overall, BL + Pyr controlled disease by integrating the elicitation of plant innate disease resistance with the fungicidal activity of Pyr.
Keywords: antioxidant system; brassinolide; defense; pyraclostrobin; transcriptome.