Partitioning of photosynthates between growing panicle and vegetative parts before anthesis

Growth pattern and partitioning of photosynthates between growing panicles and vegetative organs during the development of young panicles were studied using two rice varieties differing in culm heights. 1) The growing panicle, leaf sheath of flag leaf, and culms grew simultaneously, but the culm displayed the highest growth rate. 2) Sink size of culm and leaf sheath was larger in the tall variety than in the short variety. 3) The proportion of 14C in the panicle was consistently greater in the short than in the tall variety under the condition where source capacity exceeded sink capacity. 4) The duration of panicle development was significantly longer in the tall than in the short variety. But the duration of the rapid elongation period was identical in the two varieties.