Sethoxydim synergizes biocontrol of green foxtail by Pyricularia setariae

The sethoxydim herbicide at reduced rates substantially improved the biocontrol of green foxtail (GFT) by the mycoherbicide agent Pyricularia setariae. Reference transcriptomes of herbicide sensitive (HS) and herbicide-resistant (HR) GFT biotypes were constructed via de novo assembly of RNA-seq data using a mixture of RNA samples from several growth stages of GFT. Transcriptome profiles of GFT under the treatments of herbicide alone (0.1X rate), fungus alone, and herbicide plus fungus were analyzed. The herbicide treatment induced ABA-activated signaling pathways, as well as a bZIP transcription factor 60 (TF bZIP60) in HS plants only, which coincided with enhanced biocontrol efficacy. On HR plants, the herbicide failed to increase these activities and the biocontrol was not improved. An exogenous application of ABA to HS plants enhanced bZIP60 expression and improved the weed biocontrol, indicating the involvement of ABA and bZIP60 in weakening the defense system of HS-GFT against the mycoherbicide agent. The transcriptomics helped decipher molecular mechanisms of synergized biocontrol on HS GFT involving a sublethal-dosed sethoxydim herbicide and P. setariae via the activation of ABA signaling pathways and TF bZIP60 in GFT plants. This study also shows a new way to explore host-mycoherbicide interactions for improved weed biocontrol.