Varietal Difference in the Root of Rice Plant : I . Varietal difference in the morphology of crown root

The objectives of this series of papers are to elucidate the differences in the root morphology among rice varieties which belong to different ecotypes. and thus to contribute to analyse the morphological and functional relations between roots and aerial parts of rice plant. This paper reports the results of estimations on several morphological characters of crown roots for 53 rice varieties belonging to different ecotypes (Table 2). Examinations were carried in the experimental field (clay loam) located in Konosu city, Saitama prefecture. 1. The morphological characters were estimated in portion of 1∼5cm from the base of crown root. The third node counted from the highest rooting node was selected for the estimation, according to results of preliminary experiments. 2. The depth of tillage, the amount of applied fertilyzers or the climate of cultivation year did not affect greatly the morphological characters of crown roots (Tables 1 and 2), and accordingly the varietal orders in the characters were very close among the data obtained from experiments of different cultivation conditions or under different climatic conditions (Fig. 2). 3. The varieties used were divided into two groups, according to the thickness of crown root stele : the one group had a smaller transectional area of crown root steles (Group A in Fig. 3), and the other a larger one (Group B in Fig. 3). The former group included japonica, indica, Chincse indica, and some javanica lowland varieties. The latter included some javanica, American long grain lowland varieties and upland varieties (Fig. 3). 4. Japanese lowland varieties had thinner crown roots and thinner crown root steles, except that Hokkaido varieties and Tanginbozu had comparatively thicker ones in Group A (Fig. 3). 5. The transectional area of stele was highly correlated to the total transectional area of metaxylem II in the stele of a crown root among different varieties (Fig. 4). They were highly correlated also to number of metaxylem I (Fig. 5) and metaxylem II (Fig. 6) in the stele of a crown root. Varieties which had a comparatively small transectional area of crown root stele such as japonica or indica lowland generally had smaller and fewer vascular bundles in the crown root (Figs. 4 to 6). Some javanica varieties, however, had a thinner stele, but a larger number of vascular bundles (Figs. 5 and 6). 6. Varieties with thicker stele (Group B in Fig. 3) showed larger transectional area of metaxylem II per hill (that is, the product of the transectiolal area of metaxylem II per crown root and the number of crown root per hill). In varieties with thinn steles (Group B in Fig. 3), japonica lowland varieties showed smaller transectional area of metaxylem II per hill than indica lowland (Table 3). The ratio of the transectional area of metaxylem II to leaf area per hill, which is an index of the balance of water conductibility and transpiration, showed a similar order among varieties to total transectional area of metaxylem II per hill (Table 3). This order coincides with the order in transpiration ability reported by previous literature. These results stated above implies that the morphological analyses of rice roots in relation to the varieties will contribute to understand not only morphological characters of roots but also physiological or functional relations between aerial parts and roots, and ecotypical differences of them in rice plants.