Cover photograph (Copyright © 2006, American Society for Microbiology. All Rights Reserved.): Schematic diagram of the distribution of virus diversity in a single plant host, with different colors of branches and leaves illustrating the diversity of haplotypes isolated from different locations on a single, chronically infected host tree. The results demonstrate that several distinct subpopulations of Plum pox virus differentiate and evolve independently in different locations of a single tree. Closely related colors represent closely related haplotypes. Photo provided by Michel Yvon, Chiraz Jridi, and Stéphane Blanc. (See related article in March 2006: vol. 80, issue 5, page 2349.)