Effects of soil temperature on hollowness in Japanese radish ( Raphanus sativus L. cv. ‘Gensuke’)

Abstract

To examine the effect of high soil temperature on the development of hollowing 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 °C during the middle of the growth period. Root weight was reduced and hollowness occurred in roots from the July sowing. Roots of the July sowing had the greatest concentration of vessels in the central region. Lignin formed in walls surrounding 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 heating cables to increase soil temperature. Heating from the 16th day after sowing (DAS) to the 30th DAS and from the 31st to the 45th DAS slowed root growth, and produced some hollow cavities, caused more vessels to form in the central area, and promoted lignification near the central cavity. In contrast, heating from the 10th to the 15th DAS or from 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 central 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 growth period.