The structure of Eucalypt roots

Abstract

The two eucalypt species Eucalyptus obliqua and E. st johnii differ in their susceptibility to Phytophthora cinnamomi, which infects their roots. A comparative study of the anatomy of the root systems of 12-week-old intermediate seedlings was made, the material used ranging in size from the finest roots to first order laterals. The root anatomy of the two species was similar but the species could be distinguished by differences in cortex persistence and in the rate of polyphenol accumulation. However, it was recognized that such differences were dependent on the age and growth rates of the roots sampled and could not be correlated with the differing susceptibilities of the two eucalypt species to Phytophthora cinnamomi. The walls of the exodermis and endodermis in both species are suberized and the ultrastructure of these walls was examined. Broad bands of suberized lamellae completely lined the exodermal cells in the zone of differentiation. In mature root zones the external radial walls of the epidermis were thickened and contained polyphenols. The roots which had commenced secondary thickening developed a specialized periderm, a polyderm, which consisted of alternating layers of suberized and non-suberized cells.