A consequence of the recent warm weather in the northeastern United States is the emergence of crocuses, an event that I documented at the TWiV Facebook page. A reader replied that it reminded her of the highly valued tulips with beautiful variegations produced by viruses.
In 17th-century Holland patterned tulips such as the Semper Augustus (image) were of enormous value, with single bulbs selling for 3000 guilders or more (about $1600 US today). The intricate lines and flame-like streaks produced stunning effects. We now know that these colorful patterns are caused by infection with potyviruses, which are filamentous plant viruses with positive-strand RNA genomes. The specific viruses involved are tulip-breaking virus, tulip top-breaking virus, tulip bandbreaking virus, and Rembrandt tulip-breaking virus. Lilies may also be patterned by infection with Lily mottle virus. These viruses infect the bulb and cause the single color to break, leading to bars, stripes, streaks, featherings or flame-like effects of different colors on the petals. These effects are caused by altered distribution of pigments in the petal caused by virus replication.
Unfortunately, infection with tulip-breaking viruses is not benign: with successive generations the bulb shrinks until it can no longer flower. For this reason most of the lines of broken tulips, including Semper Augustus, no longer exist. These viruses still circulate globally, transmitted by aphids. Because infection can cause costly damage to tulips, precautions must be taken to minimize spread. Contemporary variegated tulips such as Rem’s Sensation are produced by breeding, not virus infection.