Water restriction technique for inoculation of Fusarium meridionale in wheat seeds

Fusarium head blight (FHB) is a disease of wheat caused by the Fusarium graminearum species complex in which Fusarium meridionale is included. The seed is an inoculum source and the use of inoculated seeds for this pathosystem studies can optimize the time of experimental tests. However early germination of seed during the inoculation process can make studies on the FHB pathosystem very challenging. Therefore, this study aimed to determine the optimal water restriction condition and time of exposure for inoculation of F. meridionale in wheat seeds without reducing seed germination, to define a reliable and rapid technique for inoculating FHB using wheat seeds. Mycelial discs of F. meridionale were placed in the center of Petri dishes containing potato dextrose agar (PDA) media with different quantities of mannitol to establish water potentials of −0.4, −0.6, −0.8, −1.0 or − 1.2 MPa. A control plate with only PDA had −0.36 MPa. Mycelial growth was measured for 178 hours post inoculation (hpi). Wheat seeds were placed in contact with the mycelium at 12, 24, 36, 48 or 60 hpi. Seed germination and seed pathology were evaluated. The greatest growth of the pathogen was at water potentials between −0.8 and − 1.06 MPa. Seed germination was not affected by the water potential at 12 hpi. It was verified that at −1.0 MPa the seeds did not germinate early, and the pathogen was detected in 100% of the inoculated seeds. Thus, the use of mannitol at water potential of −1.0 MPa and seed contact with the pathogen at 12 hpi is a method that can be used for inoculation of F. meridionale in wheat seeds.