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

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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.