Abstract
The growth irradiances in the primary habitats of newly popularised Chinese rice 'Gui-Chao 2' and modern U.S. rice varieties 'Bellemont' and 'Lemont' are quite different, with only 2-8 h sunshine per day in Guangzhou, China, and 8-12 h sunshine per day in Texas, U.S.A. The U.S. varieties Bellemont and Lemont adapted to higher photon irradiance, showing increase of photosynthesis and increase of leaf thickness under high photon irradiance (1000 �mol photons m-2 s-1). Bright light reduced leaf chlorophyll content less in Bellemont than in Gui-Chao 2. The Chinese variety Gui-Chao 2 seemed adapted to low photon irradiance, showed delayed leaf senescence and retained higher photosynthetic rate after 20 days shading treatment. Thus, the yield reduction under shading of Gui-Chao 2 was less than that of Bellemont. After treatment for 9 days at 1000 �mol photons m-2 s-1, the quantum yield and light- and CO2-saturated photosynthesis of Gui-Chao 2 was lower than that of Lemont, suggesting possible photoinhibition in Gui-Chao 2 under high irradiance. It was proposed that these varieties represent two light-intensity ecotypes of rice. The possible application of this research to rice breeding and agricultural cultivation is discussed.
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