ROOT-SYSTEM DEVELOPMENT OF JAPONICA-INDICA HYBRID RICE CULTIVARS .1. NUMBER AND ELONGATION DIRECTION OF PRIMARY ROOTS

To characterize the root system of the Japonica-Indica hybrid rice cul tivars (Milyang 23, Suweon 258), we compared the number and elongation direction of primary roots both per stem and shoot unit bases with th e Japonica type rice cultivars (Nipponbare, Koshihikari). The four cul tivars were grown in 45-liter polyethylene containers with paddy field soil, and soil cores (15 cm in depth and 15 cm in diameter) were take n at the grain-filling stage. Td estimate the number of primary roots of different elongation direction, soil cores were divided into four l ayers by different color markings. Stem numbers of the Japonica-Indica hybrids at the grain filling stage were less than Japonica type culti vars, but the numbers of primary roots per stem were larger in the Jap onica-Indica hybrid cultivars. In particular, the number of primary ro ots of Suweon 258 were the highest per shoot unit, per stem and per hi ll. The rate of primary roots of Japonica-Indica hybrid cultivars elon gating deep into the soil, were more than that of Japonica type cultiv ars. In the Japonica-Indica hybrid rice, the elongation direction of p rimary 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 th e soil.