Abstract
In general, the new types of cultivars have a shorter culm and more ears than the old types. In a previous paper, it was demonstrated that the new types produced less dry matter before heading due to their short stature. In this paper, we compared the dry matter production of one of the new types of cultivars (Asominori) growing in the warmer part of Japan with that of the improved japonica-indica hybrid cultivar Milyang 23, which was released in Korea in 1975 and is well known for its high yielding capacity. There was no difference in culm length between Asominori and Milyang 23 but Milyang 23 was taller than Asominori in all stages of growth (Table 1). Milyang 23 produced more dry matter than Asominori during the period of growth from ear initiation to harvest (Fig. 1). Leaf area index (LAI) of both cultivars changed similarly in all stages except in the later ripening stage, and crop growth rate (CGR) and net assimilation rate (NAR) were higher in Milyang 23 during the growth period from ear initiation to harvest (Fig. 2 and 3). The values for the leaf area density were identical in both cultivars during the ear initiation stage, because Milyang 23 had a slightly higher LAI than Asominori (Fig. 4), but after heading, Milyang 23 had a lower leaf area density. Milyang 23 showed higher value in relative light intensity (I/Io) in the canopy, resulting in a lower extinction coefficient (k) since the canopy of Milyang 23 consisted of erect leaves as compared to that of Asominori, and Milyang 23 had a higher angle of inclination with the upper leaves (Fig. 4, 5 and 6, Table 3). There was no significant difference in the photosynthetic rates (p0) of the cultivars during the ear initiation stage.
