A Physiological Disorder in Secondary Phloem of Carrot Roots (Daucus CarotaL.) in Japan

SummaryStudies were carried oui to elucidate the mechanism of the occurrence of the shiny white belt-like patches under the epidermis of carrot roots (designated as abnormal root). The specific gravity of secondary phloem of the abnormal root was less than that of the normal one. Many lysigenous intercellular spaces were found in the secondary phloem of the abnormal roots. Fourteen days after harvest, several lengthwise splits were observed on the surface of the abnormal root, with several hollows in the shiny white regions in cross-sections of the roots. The occurrence of the abnormal roots and the diameter of secondary xylem showed a positive correlation. The diameter of secondary xylem increased with increased root weight. The diameter of secondary xylem was small in the warm-season cultivar, and larger in the cool-season cultivars. The occurrence of abnormal roots was low in the warm-season cultivars, and high in the cool-season ones. It is concluded that shiny, white, belt-like patches occur in roots in which the growth of secondary xylem is greater than that of the secondary phloem, because the mechanical strength acts tangentially there, due to differential growth between the secondary phloem and xylem of the root.