To detect ROS production on the rice flower organs during U. virens infection, spikelets from infected panicles and uninfected control panicles were stained with 3, 3’- Diaminobenzidine tetrahydrochloride solution (1 mg of DAB-HCl per 1mL of water) for 3 h at room temperature. The samples were destained in ethanol:chloroform (4:1) and then kept in the dark in 60% glycerol until examination by light microscopy.