Systematic production techniques for high quality of Japanese radish cv.Gensuke under summer-sown culture

日本萝卜品种玄助因其风味而在石川县大量种植。然而，当在7月播种时，它经常在中央花柱中形成纵向中空的空隙，从而降低了根的质量。本研究的目的是在夏播栽培条件下生产高质量的‘玄助’块根。在高温条件下，木质素形成于根中部与细胞间隙相邻的薄壁细胞上，同时空心化现象明显.生长中期高温和生长素处理时，由于薄壁细胞不能增殖，细胞间的气隙形成一个大的空洞，与气隙相邻的薄壁细胞上形成活跃的木质素，阻碍了细胞向气隙的侵入.细胞分裂素CPPU {N-（2-氯-4-吡啶基）-N '-苯基脲}处理抑制了木质素的形成和空心化的发展，这是因为即使在高温下，根中心区域的薄壁细胞也能活跃地增殖.当植物在低平板密度下生长时，根的生长加速，并且根中出现空洞。在高密度条件下，根系生长受到抑制，不产生中空现象，因此，根中心区细胞间气隙的形成和与气隙相邻的薄壁细胞壁中木质素的形成是根中空现象产生的必要条件。因此，有理由认为，叶面喷施CPPU是夏播栽培条件下生产高质量‘玄助’根的最实用手段之一。

The Japanese radish cv.Gensuke has been largely cultivated in Ishikawa Prefecture for its flavor. When sown in July, however, it often develops a longitudinal hollow gap in the central style, thus lowering t he quality of the root. This study aimed to produce 'Gensuke' root of high quality under summer-sown culture.1. Under high soil temperature lignin formation was recognized on parenchymatous cells abutting on the intercellular air space in the central region of the root, and hollowing was clearly observed developing.2. When the plant was treated with high soil temperature and auxin during the middle growing stage intercellular air spaces coalesce into a large hollowing for want of proliferation of large parenchymatous c ells, which prevents the cells intruding into the air space as a result of active lignin formation on parenchymatous cells abutting on the air space.3. Lignin formation and hollowing development was repressed by the treatment of a kind of cytokinins, CPPU {N-(2-chloro-4-pyridyl)-N'-phenylurea} due to active proliferation of parenchymatous cells in the central region of the root even under high soil temperature.4. When plants were grown under low plating density, root growth was accelerated and hollowing developed in the root. When plants were grown under high planting density, root growth was sup-pressed and no hollowing developed.Therefore, genesis of intercellular air space in the central region of the root and lignin formation in the walls of parenchymatous cells abutting on the space are necessary for the development of hollowing in the root. From these results, it is reasonable to consider that foliar spraying of CPPU is one of the most practical means to produce 'Gensuke' root of high quality under summer-sown culture.