Characteristics of Dry Matter and Grain Production of Rice Cultivars in the Warmer Part of Japan : IV. Comparison between grain production of Japanese and new Korean cultivars

Abstract

In a previous paper, we suggested that the sink capacity, defined as the spikelet weight with the exclusion of grain per unit leaf area at harvest, was too low to allow further increase in grain yield of rice varieties cultivated in the warmer part of Japan. In this paper, we compare the characteristics of grain production among old and new types of cultivars growing in the warmer part of Japan and improved japonica-indica hybrid cultivars such as Milyang 23 and Yoo Sin. Milyang 23 showed higher yields, higher total dry matter production and higher harvest index in plots with standard and heavy nitrogen application (Fig. 1). In all cultivars used in this experiment the sink capacity and leaf area increased following heavy nitrogen application (Fig. 2). It was remarkable that both Korean cultivars had a larger number of spikelet per unit leaf area (49, 000/m2) as compared with the Japanese cultivars (37, 000/m2) (Table 1). This difference was ascribed to variations in the number of spikelets per ear between Japanese and Korean cultivars. The Korean cultivars showed a lower increase in leaf area and a higher increase in sink capacity in relation to nitrogen absorption during the period from transplanting to heading (Fig. 3). The sink/source ratio, representing the ratio of sink capacity to leaf area at heading, was much higher in both Korean cultivars than in the Japanese cultivars (Table 2). Among the Japanese cultivars the old types had a higher ratio because they had larger ear than the new types of cultivars (Table 2). Therefore, it is considered that the Korean cultivars can produce ears with higher sink capacity without displaying excessive leaf growth. As a result, the harvest index remained high when total dry weight increased following heavy nitrogen application (Fig. 1). The Korean cultivars, with short culm and large ears, showed two interesting feature, as follows; compared with the Japanese cultivars their sink/source ratio was higher than that of old types although they had the short culm of the new types of cultivars. However, since the Korean cultivars have several disadvantages related to taste and tolerance of disease and cold, it will be necessary to develop new cultivars showing with the advantages of the Korean cultivars, while minimaizing their shortcomings.