Characteristics of Dry Matter Production Process in High Yielding Rice Varieties

In order to clarify the characteristics of high yielding rice varieties, total dry matter production, yield and harvest index were compared in 1988 and 1989 among the two early and three medium varieties, which were used in the previous paper, with refference to dry matter accumulation in the panicle. Panicle dry weight increased rapidly after the heading time. The increase was resulted from translocation of the reserves from the stem and leaf (- δ S) to the panicle and of the assimilates produced after the heading (δW). Stem and leaf weight decreased after the heading (δS) and reincreased at the late stage of ripening (+ δS). The difference in the amount of - δS and + δS were observed among the five varieties. Both leaf sheath and culm dry weights decreased after the heading, but the dry weight reincreased only in the culm. These changes in the stem (leaf sheath and culm) dry weight conincided with the changes in total sugar and starch concentrations. In the early varieties, Nanjing 11 showed higher yield and harvest index (H. I.) as compared with Akihikari owing to larger sink size and larger - δS, in spite of a little smaller δW. In the medium varieties, higher yield and smaller H. I. in Musasikogane than those in Nipponbare were due to larger δW and larger + δS, respectively; higher yield and H. I. in Milyang 23 than those in Nipponbare were due to larger δW and the smallest reincrease in + δS; Milyang 23 showed the highest yield and H. I. among the three varieties because both reserves and assimilates were completely translocated to the panicle which has larger sink size.