Mycoplasma-like Organisms Associated with Little Leaf Disease of Eucalyptus microtheca Muell.

A little leaf disease has been observed in several plants of Eucalyptus microtheca Muell. grown in Wad Medani area, Sudan. The disease is characterized by general plant stunting, reduction in diameter and height of trunks of affected trees, yellowing and reduction in leaf size, shortening of internodes together with excessive proliferation of axillary shoots. Electron microscope observations on ultrathin sections have revealed the presence of pleomorphic bodies in the sieve elements of diseased but not of healthy plants. These bodies possess DNA strands, ribosome-like granules and a three-layered unit membrane well defined at high magnifications (> 100,000) suggesting a mollicute nature of these bodies. Studies using semi-thin sections revealed the absence of helical forms. Thus, a mycoplasma-like organism (MLO) is suspected to be the agent responsible for the disease. The results are discussed with reference to the economic and environmental importance of this tree species in the Sudanand, the possible threat of the disease to its cultivation.