Varietal differences in tillering ability of fourteen Japonica and Indica rice varieties

Field experiments were conducted to clarify the relation between the tillering ability and morphological characters, dry matter production, or nitrogen absorption among 14 rice varieties including different ecospecies with different plant types, and about the same heading time. Tiller number varied widely among the varieties and the number of tillers per plant at the maximum tiller number stage ranged between 14.3 and 39.5 in 1995 and 12.2 and 34.6 in 1996. Among all the varieties, In 36 followed by Suweon 258 produced the highest maximum tiller number and Dawn produced the lowest maximum tiller number. The plant length and the specific leaf area, i.e, one of the indicators of leaf thickness, showed a strong negative and positive significant correlation, respectively, with the maximum tiller number. The varieties with a shorter plant length produced shorter and thinner leaves which would provide less competition for dry matter and nitrogen between mother stem and tillers and among tillers. This resulted in a higher efficiency of tiller production in the higher-tillering varieties for the same amount of dry matter production and nitrogen absorption. Percentage of productive tillers widely varied among the varieties, ranging from 42 to 73% in 1995 and from 50 to 81% in 1996, Semidwarf indica and japonica-indica varieties showed a lower percentage of productive tillers than the Japanese and tall indica varieties, and high-tillering varieties IR 36 and Suweon 258 produced the highest number of dead tillers, which resulted in the lowest percentage of productive tillers. The number of dead tillers depended mainly on the extent of competition for carbohydrates produced and nitrogen absorbed from the maximum tiller number stage to heading among tillers, although the increasing ratio of dead tillers was higher in indica varieties than in japonica varieties with a decrease in the amounts of these substances.