Root System Development of Japonica-Indica Hybrid Cultivars. 2. Branching habit.

Abstract

Root system development of japonica-indica hybrid rice cultivars (J-IH : Milyang 23, Suwon 258) was compared with that of japonica-type cultivars (JT: Nipponbare, Koshihikari) with reference to branching habit from the viewpoint of developmental morphology. The four cultivars were grown in 45-liter polyethylene containers with paddy field soil and the plants with their root systems were carefully dug up at the grain-filling stage. After careful washing, the main stems of each cultivar were divided into each phytomer and the number, diameter and length of both crown and lateral roots were recorded together with their node position. From these data, the root dimensions (total number of lateral roots, total roots surface area and total root volume) were estimated for each crown root. The results indicated that lateral root development of J-IH was more vigorous than that of JT, especially in the higher phytomers formed after the panicle initiation stage. Such vigorous root branching in J-IH was mainly attributed to an increase in the number of second-order lateral roots. Detailed examination showed that the L-type first-order lateral roots were longer and the density of both L-type first-order and S-type second-order lateral roots were higher in J-IH than in JT. Thus, the root system of J-IH was characterized by long and dense L-type first-order lateral roots and large volume of S-type second-order lateral roots due to their high density. Results of this study suggest that the root system of J-IH increases the total length and surface area, by developing many S-type sedond order lateral roots, which may be related to their high-yield of J-IH.