ABSTRACT
Plant viruses are obligate parasites and depend on the host cell for their survival and replication. They have a great potential for genetic variation, rapid evolution, and adaptation. Broadly, the factors influencing the virus evolutionary process can be divided into macro and micro levels. This chapter provides updates on current understanding and future perspectives of evolution, adaptation, and host selection by plant viruses. Viruses adapt to their hosts by evading defense mechanisms and taking over cellular metabolism for their own benefit. Alterations in cell metabolism as well as side effects of antiviral responses contribute to symptoms development and virulence. Antagonistic pleiotropy is the first mechanism that results from opposite phenotypic effects of mutations across hosts. Mutation accumulation is another mechanism that results from the accumulation by drift of mutations that are neutral in one host, but deleterious in another one.
