Root System Development of Japonica-Indica Hybrid Rice Cultivars. 1. Number and elongation direction of primary roots.

Abstract

To characterize the root system of the Japonica-Indica hybrid rice cultivars (Milyang 23, Suweon 258), we compared the number and elongation direction of primary roots both per stem and shoot unit bases with the japonica type rice cultivars (Nipponbare, Koshihikari). The four cultivars were grown in 45-liter polyethylene containers with paddy field soil, and soil cores ( 15 cm in depth and 15 cm in diameter) were taken at the grain-filling stage. To estimate the number of primary roots of different elongation direction, soil cores were divided into four layers by different color markings. Stem numbers of the Japonica-Indica hybrids at the grain -filling stage were less than Japonica type cultivars, but the numbers of primary roots per stem were larger in the Japonica-Indica hybrid cultivars. In particular, the number of primary roots of Suweon 258 were the highest per shoot unit, per stem and per hill. The rate of primary roots of Japonica-Indica hybrid cultivars elongating deep into the soil were more than that of Japonica type cultivars. In the Japonica-Indica hybrid rice, the elongation direction of primary roots were very different between upper and lower roots in the higher shoot units of the main stem ; i.e. the upper roots elongate to the shallow layer, while the lower roots tend to elongate deep into the soil.