ABSTRACT
Since the first report associating a new type of plant pathogen, the mycoplasma-like organism (MLO), with plant disease in 1967, awareness of the importance of these diseases to worldwide agricultural production has increased. Diseases of mycoplasmal etiology involve more than 600 plant species and include food, ornamental, forest, and fiber crops. Comprehensive reviews of MLOs and their associated diseases have been published. Certain nonanatomical information is necessary to enhance understanding of MLO-associated diseases and is essential to interpretation of the pathological anatomy associated with these pathogens. MLOs have pleomorphic cellular morphology. They can appear as small spherical or elongate polymorphic bodies in cross-section or as filamentous, many-branched, anastomosing bodies when serial sectioned. As seen in electron micrographs, MLOs are typically 60 to 1100 nm in diameter, bounded by a trilaminar unit membrane, electron dense, and slightly granular. Attempts have been made to classify or group MLOs by the type of symptoms they induce in their host plants.
