Wednesday, 16 January 2008

Canna virus identified in 1928

Sydney Percy-Lancaster

"An Indian Garden", 1928

This is a quote from the book, "Cannas frequently show a wonderful streaking and striping on the petals, resembling the "broken" Tulips. If transplanted to fresh ground this variegation disappears and the bizarre effect is lost. As it has lately been discovered that breaking of Tulips and other flowers is due to a virus disease, Cannas probably are similarly affected. There does not appear to be any cure except changing the site and destroying the stock if the plant is badly diseased."

There we have it, Canna have suffered with virus for at least eighty years. So why has it suddenly grown out of control? Well, the use of the WWW has meant that more people around the world are now in contact with each other, and there has been a gigantic increase in the exchange of rhizomes. Could it be that over a period of time different varieties appeared that prospered in a given climate, and although the virus is present its effects are not noticeable. However, when grown in a different climate the effect is to make the virus more virulent? Purely speculation, of course.


  1. I have no doubt you are correct in your conclusion Malcolm. I believe that virus might have been the cause of cannas falling out of fashion around the 1920s. It does seem strange that there seems to be nothing on the subject during that era apart from Percy-Lancaster's comments.

    Here in Australia some cultivars exhibit virus-like symptoms on the first leaves of the season when cannas are stressed from the cool weather. They quickly shrug it off and appear quite normal as the weather warms up. We have been deluding ourselves here in Australia that this is climate stress. It is not. It is symptoms of viral infection. Time and time again I have obtained fresh replacement stock from a new source, of a troublesome cultivar and it has popped up in a cool spring without virus symptoms.

    I have just discovered an article in a 2004 Australian gardening magazine about our plant quarantine. A caption on a pic of potted young cherries under grow lights in a sealed room states: "At the Plant Quarantine Nursery, virus-infected cherry trees are grown in a heated room. The heat inhibits the virus, so the new tip growth will not be infected. Buds in the tip growth are removed and grafted onto healthy rootstocks."

    I have proven that cold has the same effect and have had success in cleaning cannas of virus by removing and growing on the extreme tip during our mildly frosty winters. It should be noted that in this country we do not need to lift and store our Canna rhizomes each winter. They remain in situ for years.

    The fact that heat also inhibits the spread of virus may well explain why our cannas here in Australia seem to outgrow their virus symptoms as summer arrives. By removing rhizome tip ghrowth during the hottest part of our summer, we could feasibly obtain unvirused stock. I assume that during autumn the virus gallops through undivided rhizomes and sits there all winter until it shows itself the following spring.

  2. While experimenting with various propagation methods a few years ago I did grow some tips about 3" long, one of the ten did not appear to have virus. I moved on to other techniques looking for better results. But this was a gardeners technique and not a laboratory technique. I bought some gel that is used for growing cuttings and just pushed them into that. Covered them with an air-tight lid and left them to it in a sunny position.Three grew roots, and when grown-on two displayed mottle virus symptoms.

  3. I don't think it's an autumn thing, because the new shoot foliage displays virus symptoms as well. My guess is that we are talking days before new growth joins in the festivities.

  4. My experiment with the winter rhizomes involved taking just the end centimetre of rhizome with no signs of any growth nodules for the foliage or roots. It took ages to throw out roots and growth buds after the warmer weather arrived. The trick was to keep it dry enough to prevent it rotting while it made roots and growth nodules and damp enough for it to live through the winter. The gel medium would have been ideal for my experiment.