Evolution characteristics of population quality during genetic improvement in early season indica rice cultivars

Sixteen cultivars released during 1934~2006 and ever since widely planted in South China were classified into four rice types under conventional cultivation conditions according to evolution stages. The types include tall cultivar (TC), dwarf cultivar (DC), dwarf and resistant cultivar (DRC), and good-quality and super rice cultivar (QSC). A total of eight crop population quality indices were investigated in this study. The results indicate that photosynthetic ability and accumulated dry matter of rice population in post anthesis are reinforced with the evolution of early season indica rice cultivars. Total spikelet number at full heading stage increases, effective leaf area and spikelet-bleeding intensity slightly decrease, effective leaf area and ear-bearing tiller change slightly and single stem and sheath weight initially decreases but subsequently increases. To further improve population quality of early season indica rice it is important to enhance root activity facilitating absorption of water and mineral nutrients by root and root materials transformation to grains. Increasing effective leaf area rate, photosynthetic products in post-anthesis and total spikelet number are also the most effective ways of improving early season indica rice cultivars. This increases grain-to-leaf ratio and enhances coordinated source-sink balance.