Ecological Studies of Rice Variety : IV. Some studies on the internode elongation

Abstract

The authors have investigated and examined the internode elongation in relation to the process of the ear emergence of rice plant, continually from the last report. In general the number of elongated nodes of rice plant was found to increase with a individal which has produced many leaves on a main culm within a same variety grown under a same cultural condition. Also the number of elongated nodes varies with different varieties and cultural season. Especially, regarding to cultural season, the individuals which have many elongated nodes tend to increase in number in the case of late planting of late maturing variety. This appearance may be due to a multiple action of day-length and atmospheric temperature change caused by the transfer of cultural season, but may mostly be due to the influence of atmospheric temperature. Thus, the number of elongated nodes in early or late maturing variety as well as the time of initiation of internode elongation may be determined by these factors. As we had suggested in the last report that the limiting or optimum atmospheric temperature for the period of young panicle differentiation of rice plant was not the same for the maturing time, we now ascertained that the time of the young panicle differentiation was not same as the time of internode elongation in case of early maturing variety and that they were same in case of late maturing variety. In other words, we considered that the atmospheric temperature necessary for the young panicle differentiation is different with the one for the internode elongation in case of early maturing variety, but both are about same in case of very late maturing variety. Accordingly, the number of elongated nodes of late maturing variety which has more elongated nodes than early one depends upon the temperature circumstances. And generally, the upper elongated internodes (1st, 2nd, 3rd internode as counted from ear-neck) which occupy the large part of culm length among all elongated internodes may be controlled greatly by low temperature, and on the contrary, the lower elongated internodes (4th, 5th, 6th internode as counted from ear-neck) which occupy a small part of culm length will elongate even by a little higher temperature than the limiting temperature. Therefore, in case of very late maturing variety, which has many elongated internodes and a short range from optimum temperature for young panicle differentiation to one for internode elongation, variation of number of elongated internodes will be observed frequently. On the other hand, in case of early maturing variety, the optimum temperature for young panicle differentiation differs from the one for internode elongation, so that the increase or decrease in number of elongated internodes or in culm elongation is less than these of late maturing variety. Moreover it is presumed that this phenomena might be promoted to some extent by the other factor the response to day-length of varieties.