Cultivar-dependent efficacy and mode of action of plant resistance inducers in wheat against Septoria tritici leaf blotch

Abstract: The induction of plant resistance could be a helpful alternative to conventional fungicides in order to protect in a more durable manner wheat crop against Mycosphaerella graminicola, the causal agent of Septoria tritici leaf blotch (SLB). The aim of our study was to compare the efficacy and to investigate the mode of action of three distinct potential resistance inducers (referred as FSOV2, FSOV7 and FSOV10) on three distinct soft wheat cultivars (Alixan, Premio and Altigo) presenting varying resistance levels to SLB. Our study was carried out in the greenhouse on three-week old plants pretreated with each resistance inducer 48 h before inoculation with the T01193 strain of M. graminicola. Interestingly, protection levels conferred by the resistance inducers differed on the three cultivars. In addition, the fungal infection process, sporulation intensity as well as the level of the xylanase cell-wall degrading activity were also affected to different extents. Further in planta investigations showed that tested inducers have no direct effect against M. graminicola except FSOV10, and induce peroxidase (PO) activity involved in plant defense mechanisms. However, the PO activity level did not increase specifically when a significant protection efficacy was observed, thereby indicating that this enzyme could not be considered as a standard induced resistance marker in wheat against M. graminicola.