Factors Concerning the Difference of the Number of Shoot Units without Crown Roots among Rice Cultivars Having the Different Member of Leaves on the Main Stem

[摘要] In previous papers, the author made clear that the number of shoot units without crown roots differed among rice cultivars which had the different number of leaves on the main stem and that this difference closely related to the difference in the finishing time of crown roots elongation. Therefore, several investigations were conducted to elucidate the causal factors concerning the difference of the number of shoot units without crown roots among rice cultivars having the different number of leaves on the main stem. As is seen generally, no crown roots were observed in the shoot unit with an elongated internode. This was also true in the case that the shoot unit with an elongated internode was put deeply in soil by transplanting. As for the shoot unit with a non-elongated internode, however, crown roots appeared even in the case that it existed above the soil surface as well as in soil. From these results, it is considered that crown roots appearance is not affected by whether the shoot unit exists above the soil surface or in soil, but is determined by whether its internode is an elongated one or not. Reproductive growth did not seem to inhibit the appearance of crown roots so strongly as the internode elongation did. In every rice cultivar having the different number of leaves on the main stem, the reproductive growth phase took place when the fourth leaf, that was countered basipetally from the flag leaf, began to appear. On the other hand, the more the number of leaves or the main stem of the rice cultivar concerned were, the sooner the internode elongation began after the commencement of the reproductive growth phase and the more the number of elongated internodes were. So, such the difference in the number of elongated internodes as this is thought to concern the difference of the number of shoot units without crown roots among rice cultivars which have the different number of leaves on the main stem.

[学科分类] 农业科学（综合）