What is the key characteristic of plant pathogenic viruses?

The key characteristic of plant pathogenic viruses is that they rely on a host plant's nucleic acid for reproduction. Viruses are non-cellular infectious agents that lack the machinery necessary for replication. Instead, they hijack the cellular machinery of a host plant once they infect it. The viral genetic material, which can be either DNA or RNA, is introduced into the host plant cells where it takes over the host's cellular processes to produce new virus particles.

This reliance on the host's nucleic acid highlights the symbiotic relationship between the virus and the plant, as the virus cannot complete its life cycle without penetrating the host and using its resources. The other choices do not accurately describe the nature of plant pathogenic viruses. They do not have an independent reproduction capability, are more complex than just simple proteins, and do not survive in soil like sclerotia, which are structures formed by certain fungi for survival.