Cause of High Yield in a Long Grain Japonica Rice

Abstract

In Kyushu National Agricultural Experiment Station, a high yielding long grain japonica rice cultivar was developed and named Saikai 187. In this study, the author analysed the cause of the high yield of Saikai 187 and examined the inherited factors related to its high yield traits . In yield trials conducted in 1987-1989 with two (low and high) nitrogen levelsl¹), Saikai 187 showed stable high yield in both nitrogen levels, and showed 8% higher yeild than two standard short grain cultivars raised in identical conditions. The plant type of Saikai 187 was medium type with short culms. When Saikai 187 was compared to standard short grain cultivars, Saikai 187 was found to have almost the sarne total weight including strow and grain as standard cultivars. However, Saikai 187 exhibited 1.0mm longer grain length and 6mg heavier 1-grain weight. In addition, Saikai 187 had a larger sink size (number of spikelets × 1-brown rice weight) because the ratio of sink size to hull weight (number of spikelets × 1-hull weight) was considerably higher although the hull weight was slightly smaller than standard cultivars. Since the ratio of sink size to hull weight is converted into 1-brown rice weight/1-hull weight²), the ratio correlates positively with the husking ratio of 1-brown rice weight to 1-grain weight³). Hence the Saikai 187 had higher husking ratio. In this sense, the larger sink size of Saikai 187 may also be attributed to a higher husking ratio.