Current world events have people thinking about viruses. There are a few similarities, and some major differences, between viruses in people and those in plants. Plants can carry viruses asymptomatically.
There are few, if any, treatments for viruses in plants- usually the recommendation for plants with virus issues is to destroy them. But occasionally, viruses in plants are considered so special and beautiful that we cultivate them on purpose. Fear not: people can’t catch plant viruses, although some studies suggest we may carry them and potentially spread them to other plants- tobacco mosaic virus, which affects several other plants besides tobacco, is one example.
Featured in numerous still-life paintings of Dutch-Flemish influence, “broken” tulips are those with variegated color streaking on the petals. Back in the 1500’s when broken tulips, in all their color- streaked glory, were first noticed, they were thought be a literal gift from god. It was not until many years later that the relationship between streaked tulips and root- feeding aphids was understood. Those aphids carried a virus, now called “tulip- breaking virus”, which caused the uniquely beautiful patterns of color on the petals. Nearly 500 years later, enthusiasts still pay extra for these diseased beauties, which are notoriously hard to propagate and keep healthy.
There are numerous viruses associated with strawberries. These often go unnoticed unless there is specific testing- strawberries can carry virus without expressing it. For this reason, strawberry producers must be careful to keep aphids, which carry the viruses, off their plants. In the eastern US, most strawberry growers buy their plants as small plugs or cuttings from Nova Scotia, Canada (similar plants for west coast growers are grown in the Klamath Basin). In 2014, an outbreak of virus in Canadian starter plants resulted in reduced yield in strawberries across the eastern US. Subsequent testing revealed that many strawberries carried one virus and had decreased yield, while those with two viruses had far more visible symptoms, and produced almost no berries at all.
Several viruses exist in PNW raspberries. Some are pollen-borne, and easily spread from plant to plant, while others are transmitted by aphids, and still more by tiny insects called thrips. One of the most common raspberry viruses seen in the Klamath County Master Gardener plant clinic is “crumbly fruit.” Sadly, the best treatment for these plants is removal, and replacement with a less susceptible plant in a new location. For a full explanation of raspberry viruses in the PNW, see: https://pnwhandbooks.org/plantdisease/host-disease/raspberry-rubus-spp-viruses.
Because of their ability to transmit viruses in potatoes, aphids are the nemesis of seed-potato producers seeking to sell disease free, certified potatoes for others to grow. Some of the aphids known to transmit a particularly challenging virus, “potato virus Y,” also feed on other plants. One important cultural control of the aphids used to reduce virus potential is reducing the number of alternate host plants (plants the aphids can feed on) near seed potato fields. Field borders planted with plants that don’t host potato virus Y helps control the disease- it’s carried on the outer mouthparts (stylets), and shed after several feeding events. Stylet oil is another tool against virus transmission. It does not kill the aphids, but interferes with the insects’ ability to transmit the disease, and is effective if used preventatively or at the first sign of an issue.
Bees and Cucumber Mosaic Virus
First found in cucumber and thusly named, CMV also affects tomatoes and some other vegetable plants. A 2016 study at Cambridge University found that the volatile oils component in virus- diseased plants attracted more bumblebees to diseased plants than healthy ones. This surprising result was in contrast to the expectation that bees would be most attracted to healthy plants.
Viruses in plants can be tricky in other ways. When plant virus symptoms are expressed, they often come in the form of unique leaf patterns: spots, concentric rings, variegations, and other patterns that are sometimes attractive to, and thus perpetuated by, people. With rare exceptions, however, plants with virus issues will not perform well. Starting with healthy plants, and reducing feeding by aphids and thrips, are the best ways to avoid this plant issue. Stay healthy, gardening friends!
Nicole Sanchez is horticulture faculty at OSU’s Klamath Basin Research and Extension Center. For more information on this or other gardening topics, contact Sanchez at 541-883-7131 or Nicole.email@example.com, or attend a “Garden Gab” session at Leap of Taste, fourth Friday of each month, 8:30 to 9:30 a.m.