An embodiment of the present invention takes the form of an IBH system that has two conduits, which are positioned close to a downstream end of a silencer section. The light source units are disposed around the light receiving unit discretely, and the light transmittance of the nonuniform filter is set so that a light intensity of at least one of the transmission light and the reflection light is uniform over an entire surface of the light receiving element. Methods for producing a maize plant that comprises crossing maize variety X7R417 with another maize plant.