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Unknown Virus Found in Tricyrtis
Chris Wilson, Hallson Gardens

Tricyrtis, commonly known as toad lilies, have been a passion of mine for several years and we have grown over thirteen varieties at our nursery. They are relatively easy to grow, multiply quickly, and bloom late in the season when most other shade perennials are already done for the year. Unfortunately this past fall we discovered that many of our Tricyrtis plants are actually infected with a virus. To make matters worse almost all of the new plants we have purchased in the past few years carry what may be the same virus.

In the spring of 2000 we started growing Tricyrtis maculata, as known as Tricyrtis hirta 'Miyazaki Hybrids'. Although we had Tricyrtis hirta and Tricyrtis hirta 'Alba' growing in our own gardens this was our first cultivated crop of toad lilies being grown for sale. The 'Miyazaki Hybrids' are similar to hirta but tend to be shorter and better branched. They bloom at the leaf axils in fall with pale purple spots on creamy flowers, as shown in the picture to the left.

In the spring of 2002 we started growing Tricyrtis 'Empress'. These plants have smooth, shiny leaves on tall stems and bloom in late summer. The blooms are white with irregular purple spotting. The dark spots are quite attractive, but I have always been curious about the random, dark purple spotting on the blooms. This seemed odd to me but the company we purchased them from assured me this was normal. 'Empress', which you can see in the photo to the right, has turned out to be very popular at our nursery and it is commonly grown and sold in many nurseries around the world. It boasts one of the largest toad lily blooms and some of the cleanest foliage. Unfortunately, as you will learn, something else may be lurking below the surface of these beautiful flowers.

In the fall of 2004 we discovered some plants of our original crop of the Tricyrtis 'Miyazaki Hybrids' developed purple mottling similar to the color on Tricyrtis 'Empress'. These two varieties were growing 10 to 15 feet away from each other in our growing areas. At first I was very excited and thought that perhaps we had some cross pollination going on here. The odd part about it, however, is that the dark purple mottling was very irregular and even varied from bloom to bloom on the same stem. Because of the variable amount of purple coloration and the extent of the mottling I became suspicious as to the cause. If it was a random seedling I would expect it to be more consistent and would have expected to see it on just one or two stems within the colony. But it was spread out in different areas and on several plants within the colony.

I contacted Terra Nova Nurseries and asked if they thought this odd coloration could be caused by a virus. In their return email I was told that they have all of their plants virus indexed by AGDIA prior to production, so no, they did not think this was a virus and they tended to believe these were random seedlings. An email to AGDIA generated the same response, that no, they did not think it possible for this coloration to be caused by a virus. I seemed fairly satisfied so simply removed the odd looking plants from the colony of T. 'Miyazaki Hybrids' and planted them about 100 feet from any other plants.

But this wasn't the end of the changing flowers. The very next fall I was presented with yet another strange occurrence which seemed to confirm that this could be a virus. An old clump of Tricyrtis hirta, with normal coloring pictured on the left side, suddenly bloomed an entirely different color, shown on the right. These plants had been in the same location for almost 5 years, growing approximately 50 feet from 'Empress' and the others, and its blooms had always been cream with pale purple spots. Now it had some flowers with nearly solid, raspberry red mottling. The odd flower color also only occurred on half of one plant with some of the flowers lower down on the same stem appearing normal. This newest flower change prompted me to contact Dr. Ben Lockhart of the plant pathology department at the University of Minnesota. Dr. Lockhart was intrigued by the findings and was interested in testing the plants.

We submitted the following Tricyrtis samples to Dr. Lockhart from our nursery: 'Blue Wonder', 'Dark Beauty', 'Empress', 'Hatatogisa', hirta, the raspberry red mottled hirta, hirta 'Alba', 'Lightning Strike', 'Miyazaki Hybrids' (normal colored and mottled), and 'Raspberry Mousse' (PPAF). 'Raspberry Mousse' is a newer cultivar from Holland that looks virtually identical to my raspberry red mottled Tricyrtis hirta, as you an see in the image to the right.

The results of Dr. Lockhart's testing certainly seemed to confirm my suspicions. The mottled plants did contain filamentous virus particles when viewed under the electron microscope. He had found similar-looking viruses in Tricyrtis on numerous occasions in the past, but since nobody has seemed particularly interested in identifying them he had never tried to do so. He indicated that morphologically the virus appeared similar to either Alstroemeria Mosaic or Bean Yellow Mosaic virus, but further tests would be needed to pinpoint the exact virus present.

Although he was not sure exactly which virus we were dealing with the specific results did seem to confirm that the odd coloration was caused by a virus. The normal colored Tricyrtis hirta was virus free. The mottled Tricyrtis hirta, the white variant Tricyrtis hirta 'Alba' and the Tricyrtis 'Lightning Strike' contained the highest concentration of virus. The latter two plants showed no mottling in the flowers, however, which may be because they do not contain the purple pigments that this virus seems to trigger. Tricyrtis 'Hatatogisa' was also virus free, which was actually quite interesting as I had been growing 'Hatatogisa' right next to 'Empress' for 3 years. This could mean that 'Hatatogisa' is immune to whichever virus this might be, but we would need further tests to prove that theory. 'Blue Wonder' was imported just 6 months earlier from Holland and was growing over 100 feet away from any other toad lily varieties. Since this cultivar was also infected it would appear that they arrived that way. 'Raspberry Mousse' was also growing over 100 feet away from any other Tricyrtis and because the coloration is virtually identical to that of our infected hirta plants, I believe it is safe to say that this variety not only arrived infected but is specifically named for its virus induced coloration. 'Dark Beauty' also has dark mottling in its flowers and it too contained the virus. The Tricyrtis 'Miyazaki Hybrids' all contained varying amount of the virus, although some didn't contain a high enough concentration of virus to trigger the flower mottling.

Based on the observations and on the virus testing done by Dr. Lockhart it is my opinion that an unknown virus is causing flower discoloration in several varieties of toad lilies on the market today. Tricyrtis 'Raspberry Mousse' appears to be named specifically for its virus induced flower color based on the fact that the plants were infected with a virus and the fact that this exact coloration occurred in the virus infected Tricyrtis hirta while the normal looking Tricyrtis hirta was virus free. 'Dark Beauty' and 'Empress' may also be named for their virus discoloration, although I would encourage other growers such as Terra Nova to have further tests performed in order to confirm this. Tricyrtis 'Hatatogisa' appears to be immune to the virus, but we will have further tests performed on this variety and on the varieties 'Gilt Edge' and 'Samurai', which we have in other parts of our growing areas, to back this up.

As we have seen with Hostas, when a virus gets deep into the supply chain it is very hard to eradicate, especially when the plants in question can be so attractive. This spring we will destroy all of our toad lily colonies that tested positive for virus and we will continue testing the remaining plants. Once we have eliminated the virus from our growing beds we will bring in new plants and have them virus indexed prior to planting and propagating. In time we hope to have a whole new crop of virus free plants. Hopefully other nurseries, especially wholesale growers, will also work to clean up their own crops to make sure that they grow and sell virus free plant stock. Whether or not most nurseries will stop selling these virus infected plants will remain to be seen. If you are concerned about your Tricyrtis flowers changing on you, especially in an older collection of specific species and cultivars, then you will want avoid growing toad lilies that display mottling in the flowers and be cautious bringing in other new plants. If you are a grower, ask your supplier if they have been virus testing their plants, and be cautious of plants changing their colors!