The Viroid: A Tiny Emissary From the Ancient Past

Carl Zimmer in the New York Times:

In the early 1920s, farmers in New Jersey noticed their potatoes were shriveling, their leaves becoming deformed. The plants were sick with an illness that came to be known as potato spindle tuber disease. But it took almost five decades for someone to find the cause.

In 1971, Theodor O. Diener, a plant pathologist at the Department of Agriculture, discovered that the culprit is an inconceivably tiny pathogen — one-80th the size of a virus. Dr. Diener called it a viroid.

Since Dr. Diener’s initial discovery, scientists have identified nearly three dozen species of viroids that attack crops from tomatoes to coconuts, as well as flowers such as dahlias and chrysanthemums. In many cases, the only way to stop an outbreak is to destroy all the infected plants. These days many countries require that plants be certified viroid-free before being imported.

But viroids may be much more than agricultural pests. New research suggests that they existed at the earliest stages of life on Earth, enduring in their primitive state for billions of years. These are the pterodactyls of the microbial world — except that they are still very much with us. We just didn’t realize it.

More here.