Evaluation of the optimal harvest time of rice (Oryza sativa L.) with different grain shapes grown in the Philippines

Abstract

Rice (Oryza sativa L.) grains are classified as long, medium, or short on the basis of their shapes. Long-grained rice cultivars belong to the indica subspecies, whereas short-grained rice cultivars are members of the japonica subspecies. Medium-grained cultivars may be members of either subspecies. Japonica cultivars are typically grown in temperate climates. The Grain Utilization Value Added Project, a collaborative effort between the International Rice Research Institute and the Rural Development Administration, Republic of Korea, has made efforts to develop japonica cultivars that are adaptable to the tropical climate. In this work, differences in grain filling characteristics (yield, head rice, and grain dimensions) among the three grain shape groups were identified. Moreover, the optimal harvest time of the tropically adapted japonica cultivars MS11, Japonica 1, Japonica 2, Japonica 6, and Japonica 7 grown in the Philippines during the 2019 wet season was determined. The optimal harvest time of long-grained indica cultivars was determined as 30–35 days after heading (DAH) on the basis of paddy rice and head rice yields. The optimal harvest time of long-grained cultivars was earlier than that of medium-grained and short-grained cultivars (35–40 DAH). The tropically adapted japonica cultivars investigated here retained the good yield traits and head rice ratio of its ancestor Jinmibyeo, a temperate japonica cultivar. These traits may be attributed to japonica’s dependence on longitudinal and latitudinal growth in contrast to the dependence of long-grained indica cultivars on longitudinal growth only.