Productivity of Upper Nodal Tillers of Rice Plants Compared to Those of Mother Stems under Low Establishment Density in Direct Sowing

In direct broadcast sowing cultivation of rice plants, the seedling density is naturally low from nonuniform distribution of the seed and there is an increased chance of developing upper nodal tillers (UNTs). In this experiment, 50 seedlings were established per square meter, and the emergence of UNTs was investigated. Then the productivity of UNT panicles was clarified and compared to that of mother stems. The appearance ratio of UNTs from the mother stem was 98.8% in 253 rice hills. We observed 59 eared UNTs in 22 rice hills we examined. All but one of them had two leaves. Almost all UNTs emerged from the axil of the upper second leaf of the mother stem. About half the number of the UNTs had one tiller, but no ears emerged from them. The number of spikelets per panicle (18.9), the percentage of ripened grains (55.8%), the 1000-grain weight of brown rice (17.0 g) and the weight of brown rice per panicle (0.211 g) on UNTs were to 20%, 71%, 84% and 14% respectively of the mother stems. Most rice grains of UNTs were immature grains, such as green immature grains. Thus, the weight of brown rice per panicle in UNTs was low compared with that on the mother stems and it was suggested that emergence of many UNTs does not contribute to increased yield and causes the deterioration of brown rice quality by producing numerous immature grains.