Morphology and Anatomy of "Stunted" Roots in Rice Plants

Abstract

"Stunted" roots of rice plants (roots less than 5 cm in full length) were investigated morphologically and anatomically, with materials taken from an actual paddy field. "Stunted" roots were identified as crown roots which stop growing soon after their emergence from the stems. According to their tip structures, "stunted" roots were classified into the following types : (1) tapering type; (2) cessation type; (3) deterioration type; (4) swelling type; and (5) other teratological types, respectively. Each type includes roots of various branching habits and also of different lengths. Anatomical investigations of "stunted" roots revealed the following anomalous behavior, as compared with the normally elongated ones : (1) a decrease in the number of cortical cell layers and also in the diameter of the stele (tapering type); (2) eccentricity of the stele in cross-sections and excessive development of the hypodermal sclerenchyma (cessation type); (3) necrotic symptoms in the cortex (deterioration type); (4) hypertrophy of the cortical cells (swelling type); and so on. Some possible relationships between the "stunted" root formation and the physical or physiological condition of the plants were discussed. Further, agricultural practices, such as nitrogen top-dressing and herbicide application, were suggested to be closely related to the formation of some types of "stunted" roots.