The natural infection process of U. virensremains unclear, which hampers studies on the disease. However, several research groups have reported that the artificial inoculation method can be used to evaluate disease index of fungal infection in greenhouse [9-11]. The artificial inoculation experiments demonstrated that the late booting stage is the critical period for U. virensinfection. The artificial inoculation method uses the mixture of conidia and hyphae produced in liquid culture to inject the leaf sheath of flag leaf at the latebooting stage, leading to a much higher disease index and even more reproducibility than the field trial.