Abstract
The effects of exogenously applied GA3 on rice seedling growth were analyzed by using 3 indica and 3 japonia varieties and the following results were obtained. (i) The increase of exogenously applied GA3 concentration reduced leaf and root growth of most test cultivars. GA3 increased the growth of sheath through enhanced partitioning of photosynthate to sheath. (ii) Increased NAR due to increased sink activity of sheath by the exogenous application of GA3 was one of the major factor for promoting initial growth of rice by GA3 treatment. (iii) Varietal difference in the initial growth in the control was positively related with leaf area developing ability. On the other hand, initial growth promotion by exogenous GA3 was due to increased NAR and not to increased leaf area. Thus, the difference in endogenous GA3 concentration might not be a major factor for controlling differential initial growth among rice varieties.
