Abstract: Twelve conventional japonica rice cultivars, which were newly bred in Zhejiang province, were planted， observed and measured. The structures of these rice cultivars were similar， such as plant height， blade angles， etc. While the control cultivar， an indica hybrid rice cultivar, had significant differences with japonica rice cultivars. The quadratic function was used to simulate and analyze the normilized blade shape. The shape was different between two genetic groups， and the size of the blades was different among rice cultivars， but the blade shape was similar when normalized. By quadratic model， it was found that in all the cultivars the largest width was close to leaf bottom in the upper leaf， and was close to leaf tip in the lower leaf. The leaf shape coefficients of all these cultivars were similar and could be set as 073， but there were still significant differences among different cultivars and different blade positions in the same cultivar. The p value was 1.95e-11 in positions and 4.89e-3 in cultivars.

Key words: rice breeding, blade shape, quadratic function model, leaf shape coefficient