by Merry — What do stunted co­conut palms, mis­shapen potato tu­bers, and peach trees with necrotic branches have in com­mon? They are three of the nu­mer­ous crops stricken with dis­eases caused by vi­roids, an as­ton­ish­ing group of min­i­mal­ist plant pathogens. There isn't much to a vi­roid, just...