Effects and Physiological Mechanism of Planting Densities on Photosynthesis Characteristics of Flag Leaf and Grain Yield in Wheat Hybrid C6-38/Py85-1 PARENTAL COMBINAIION OF WHEAT HYERIDS IRRADIATED WITH γ-RAY Effect of Irrigation Times on the Photosynthetic Charcteristics of Flag Leaf and Grain Yield in Wheat Hybrid Ji’ai 1/ C6-38