EFFECTS OF SOIL-TEMPERATURE ON HOLLOWNESS IN JAPANESE RADISH (RAPHANUS-SATIVUS L CV GENSUKE)

To examine the effect of high soil temperature on the development of h ollowing in the root of radish, seeds were sown in the field on 27 May , 10 July and 16 August 1992. Plants of the July sowing were subjected to soil temperatures above 32 degrees C during the middle of the grow th period. Root weight was reduced and hollowness occurred in roots fr om the July sowing. Roots of the July sowing had the greatest concentr ation of vessels in the central region. Lignin formed in walls surroun ding the central cavity only in roots of the July sowing. In a second experiment, seeds were sown on 30 April 1991, in plastic pots with hea ting cables to increase soil temperature. Heating from the 16th day af ter sowing (DAS) to the 30th DAS and from the 31st to the 45th DAS slo wed root growth, and produced some hollow cavities, caused more vessel s to form in the central area, and promoted lignification near the cen tral cavity. In contrast, heating from the 10th to the 15th DAS or fro m the 46th to the 60th DAS produced roots with no hollow cavities, and resulted in the production of a smaller number of vessels in the cent ral region of the root. The heating during these periods had no effect on lignin formation. In conclusion, a large hollow cavity develops in the central region of the root as a result of active lignin formation in the surrounding cells induced by heating in the middle of the grow th period.