Analyzing Fusarium graminearum strains for sensitivity to Tebuconazole fungicide and host responses by biochemical and molecular screening

Fusarium graminearum is the chief causal agent of Fusarium head blight (FHB) disease in cereal crops. The study aimed at identifying Tebuconazole-resistant and sensitive F. graminearum strains and host responses using Arabidopsis thaliana-F. graminearum interaction through biochemical and gene expression studies. Thirty-two fungal isolates isolated from FHB-infected wheat spikes were confirmed as F. graminearum members by molecular and phylogenetic analyses. All 32 strains were screened for sensitivity to Tebuconazole at the effective concentration (EC₅₀) of 2.5 ppm, determined using the control strain, Z-3639. Based on percent growth inhibition, the fungal strains were grouped into 5 highly resistant (HR), 7 resistant (R), 11 sensitive (S) and 9 highly sensitive (HS) strains. Assessing Tebuconazole effect on 8 strains, representing 2 from each group showed varying levels of mycelial and conidial malformation. Two strains– TN1-3 (HR) and TN3-4 (HS) and the control strain tested for the expression of Tebuconazole-responsive gene, CYP-51A showed up-regulation in fungicide-treated HR strain compared to fungicide-treated HS strain and the controls indicating it as the potential fungal target. Analysis of reactive oxygen species (ROS) accumulation by DAB (3,3′-diaminobenzidine) staining in plants challenged with fungicide treated HR and HS strains showed lesser accumulation compared to the plants challenged with Tebuconazole-untreated HR and HS strains revealing reduced fungal virulence due to fungicide treatment. Similarly the biochemical responses in terms of chlorophyll estimation, superoxide dismutase (SOD) and catalase assays also correlated with the defense gene expression in plants challenged with fungicide–treated F. graminearum strains highlighting defense activation against F. graminearum and the results are presented.