Effect of Shading on the Photosynthetic Characteristics and Yield at Later Growth Stage of Hybrid Rice Combination

Photosynthetic characteristics in shading treatment and adaptation mechanism under adverse conditions were studied using in six hybrid rice combinations with different photosensitivity.The results showed that the grain yield was significantly reduced under shading treatment(80% shading rate) at heading stage,then recovered to natural illumination;the chlorophyll(a+b) and chlorophyll b contents were increased,but failed to reach the normal level after the recovery period;low light reduced the photosynthetic rate of the functional leaves and the quantity of photosynthetic products transported to grain,meanwhile,the con-tent of malondialdehyde(MDA) and leaf area index were increased,the activity of SOD varied differently.There was a great difference in adaptability to low light environment among combinations.It is the physiological basis of rice tolerance to shading that the flag leaf under low light stress can maintain a higher net photosynthetic rate(Pn),quantum efficiency,chlorophyll content,and lower content of MDA and lower SOD activity.