Use of Virus-Induced Inclusions in Classification and Diagnosis

Abstract

Inclusions may consist almost entirely of aggregated virus particles, virus­ induced material, or cell components; inclusions may also consist of mix­ tures of these components. Plant virus inclusions have been reviewed by Goldin (43), McWhorter (87), Rubio-Huertos (118), Martelli & Russo (92), and Christie & Edwardson (15). A large body of cytological literature deals with the structure and composition of inclusions. In most cases develop­ mental stages of inclusion formation are not well understood, and the functions of plant virus inclusions are yet to be determined. Types and intracellular location of inclusion bodies are among 49 criteria listed for classifying plant viruses in groups (47). No single virus or group has been characterized by all of the criteria. Currently, 220 more or less well characterized plant viruses are assigned to 22 groups (31). Cytological studies have been conducted on tissues infected with 137 of these viruses. These cytological studies form the basis of this report. Proposing that certain inclusions be included as main characteristics of groups does not imply that the inclusions are necessarily diagnostic for infections at the group level, since there are cases where inclusions in one group appear similar to those in other groups. For instance, crystalline inclusions exist in a number of shapes in many groups. Although some of their shapes are different, others are similar. Many inclusions, however, are distinctive, and when they occur consistently within a group, they may be