Functional Study of <scp> <i>FgNiR</i> </scp> Gene in Pathogenicity and Utilisation Capacity of Nitrogen Sources of <i>Fusarium graminearum</i>

ABSTRACT Fusarium graminearum is the dominant pathogenic fungus of the Fusarium head blight (FHB) which seriously damages the yield and quality of wheat in China. The gene FgNiR encodes nitrite reductase (NiR) of the nitrogen reduction pathway in F. graminearum . However, the function and role of the FgNiR were unclear. In this study, FgNiR gene deletion mutants were compared with wild‐type strains and complementary mutants in terms of functional roles, including vegetative growth, tolerance to abiotic stress, sensitivity to fungicides, utilisation capacity of nitrogen sources, pathogenicity and the expression levels of Tris genes and nitrate reductase gene ( FgNR ). The results showed that FgNiR deletion significantly reduced the conidial germination rate and speed and pathogenicity of wheat coleoptile. The mycelial growth inhibition rates of deletion mutants were significantly decreased under osmotic stress but increased under oxidative stress. The inhibition rates of the deletion mutants treated with Congo red significantly increased. The EC 50 values of triazole fungicides and fluazinam of the deletion mutants were significantly higher, but the EC 50 values of phenamacril were significantly decreased. When FgNiR was absent, there were different degrees of difference in utilisation capacity of nitrogen in F. graminearum , and the expression level of FgNR was upregulated. The expression of Tris gene showed that the expression levels of Tri1 , Tri5 and Tri10 were significantly upregulated. These results are of crucial scientific significance for exploring the specific interaction mechanism of FgNR and FgNiR and developing efficient strategies for the prevention and control of FHB.