Abstract: The leaf area index (LAI) development, which is related to the capacity of light interception, and the maximum leaf photosynthetic rate (Pmax), which related to the efficiency of light energy conversion, are two key photosynthetic traits to increase the utilization efficiency of solar energy. Using the Guangdong rice "Qiguizao', which belongs to low light adapt-able ecotype and characterized by quick developing LAI, and the US rice "Lemont', which belongs to high light adaptable ecotype and characterized by higher light saturation point of photosynthesis, as parents to make a hybrid (Le/Qi) by means of chemical hybridizing agent, the authors successfully solved the contradiction between LAI and Prix. The hybrid Le/Qi not only showed quick developing LAI, but also higher Pmax, less or no midday depression of photosynthesis and less or no photooxidation under high light induced conditions. The photosynthetic productivity and adaptability of Le/Qi were increased over 20 % and improved a lot according to the growth analysis under different light and temperature conditions in growth chambers and field trials in flatlands, hilly land or mountain area. This study indicated that utilization of high light adaptable US elite rice as parent to make a hybrid with Guangdong low light adaptable local elite rice by means of chemical hybridizing agent is an effective and quick breeding approach to improve the adaptability of Guangdong rice to high light and to increase the photosynthetic productivity in turn the economic income.

Key words: Breeding for high photosynthetic efficiency, Hybrid rice, Chemical hybridizing agents, Leaf area index, Photosynthetic rate