The season has begun, the cold and flu season that is. I can attest to that, having spent three days last week sneezing, freezing, and filling a trash can with enough Kleenex to cover Ohio, Pennsylvania, and most of Michigan. At some point after my attempt at breaking the world record for consecutive sneezes, I wondered why cold and flu viruses are named by numbers instead of real names like hurricanes. It certainly felt like I had been hit by one.
Of course, there are virus with names and not numbers. Ebola is one that obviously comes to mind. It was named for the Ebola River in Zaire where it first showed up back in 1976. We didn’t hear much about it back then, but another virus from Africa was making the news then, HIV, an acronym for Human Immunodeficiency Virus which is the way most viruses are named.
Viruses have been around a long, long time, and humans are not the only hosts. Plants are also the targets of these submicroscopic parasites. They often cause changes in the appearance of plants, which was the case with the Tulip Breaking Virus (TBV) whose symptoms, an attractive variegation in the flower, nearly brought down the whole Dutch economy in the 1600’s.
Tulips were not as readily available then, and the rare variegation caused by the TBV made them very valuable. Speculation in tulips caused a “tulip bubble” which of course burst, bankrupting many.
A newly described plant virus is the ominous sounding Hosta Virus X (HVX). First discovered by plant pathologists in Minnesota in the 1990’s, the symptoms can vary depending on the cultivar. They include color changes in the leaves that show up as mosaic patterns, ringspots, or lines running along the veins described as “inkbleeds”.. The leaves can also be puckered or twisted. Before this virus became widely known, some growers were tricked, like the old Dutch growers, into thinking the symptoms were new varieties.
It’s now thought that the characteristics exhibited by the hosta cultivars Breakdance, Eternal Father, Kiwi Watercolours, Leopard Frog, Lunacy, and Parkish Gold are a result of being infected by Hosta Virus X.
Unlike human viruses, plant viruses cannot be transmitted through the air because plant cells have a very thick wall that viruses cannot penetrate without help. Insects like aphids and thrips penetrate plant cell walls when they feed so viruses often use them to gain entry. Epidemiologists call these viral carriers vectors.
We can also become a vector for plant viruses. For example, Cannas, a tropical plant often used for summer color and vertical accents, have recently been exhibiting viral symptoms in gardens all over the country.
There is no insect vector, though. We are the vectors. When we propagate them, their fleshy rhizomes are cut up into smaller pieces. If the cutting utensils are not properly sanitized, cutting into a healthy plant with them will spread the virus if an infected plant had been cut up before. Hosta Virus X can also be mechanically distributed like that.
That is why anytime you prune or divide a plant, it is a good idea to sanitize your tools before moving on to the next plant. Soaking them in a 1:10 dilution of bleach is the most often recommended procedure, but I don’t usually have the time, so I use a propane torch.
Viruses don’t always adversely affect a plant. Infected cannas often look horrible at the beginning of the season, but will usually grow out of it enough to put on a show. Our dogs’ vet has a line of four Kousa dogwoods heavily mottled leaves which actually quite attractive, but it is so irregular it can’t be a natural variation. It has to be virus; yet, the trees are very healthy.
These are the exceptions though. Most plant viruses are very harmful, and plants infected by them should be destroyed. Given the cost of plants, they are a serious economic threat to growers and gardeners. Great strides have been made to exclude viruses from the plant production process, but the battle with viruses is never won. Be wary of plants that don’t look right, and make sure that you don’t become a viral vector. Good hygiene is not just for cold and flu season.
