SAKAGAMI, J., A. ISODA, H. NOJIMA and Y. TAKASAKI (Graduate School of Science and Technology, Chiba Univ., Matsudo 27l-8510, Japan)

Abstract : Ten cultivars of O. sativa (6 japonica, 2 indica, and 2 japonica x indica) and five cultivars of O. glaberrima were grown in pots. Half of each cultivar was cut at 10 cm above the ground at maturity, and the other half remained uncut. Both were grown under two different day-length conditions with a suitable temperature. The growth state at maturity, the changes in the number of living tillers after maturity, and the survival rate after maturity were examined. The starch content in the stem (stem+1eaf sheath) of O. sativa at maturity tended to be higher than that of O. glaberrima. The nodal root number and the total leaf length of the tiller bud from the node of a stem section at maturity were greater in O. sativa than in O. glaberrima. New tillers appeared in both O. sativa and O. glaberrima after maturity. The number of living tillers after maturity was always greater in O. sativa than in O. glaberrima, though the relation was reversed for some period in the long day uncut plot because of the appearance of new tillers from higher nodes. The long day and the uncut conditions enhanced the survival of tillers. In O. glaberrima, the survival rate of all cultivars at 250 days after maturity was nil. In O. sativa, japonica cultivars were higher than indica cultivars, including japonica x indica cultivars in the survival rate at 250 days after maturity. All plants of some indica cultivars had died before 250 days after maturity. The long-day condition favored the survival rate. The continued appearance of new tillers in both O. sativa and O. glaberrima after maturity suggested that both O. sativa and O. glaberrima had potential perennial ability. It was inferred that the perennial ability of O. glaberrima was very small compared with that of O. sativa. It was also inferred that varietal differences in the survival rate existed in O. sativa.

Key words : Annual, Nodal activity, Oryza glaberrima Steud., Oryza sativa L., Perennial, Starch content, Survival rate, Tiller appearance.