Having a lot of apple varieties gives me a chance to make some observations. One of those observations is which varieties show signs of apple mosaic virus and which do not. I can make this observation because I have a tree with many varieties that is infected with the virus. The disease virus is systemic, so any variety grafted to that tree has it. However, only a certain percentage will actually show it. I went through the whole collection and observed which varieties show symptom of the disease.
Of approximately 150 different apple varieties on !Frankentree!, the following are those that show visible signs of the mottling effect on the leaves that can be induced by the virus, also noted is the degree to which they are affected this year:
- Rubinette, Medium
- Katherine, High
- Red Astrachan, High
- Sam Young, Medium
- Cherry Cox, Low
- Sweet Sixteen, Medium
- Lyman's Summer, Low
- Pitmaston Pineapple, Medium
- Hudson's Golden Gem, Medium
- Pink Parfait, Medium
- Kandil Sinap, Medium
- Whitney Crab, Low
- Bullock's Pippin, Low
- Mollie's Delicious, High
- Ribston Pippin, Low
- Cox's Orange Pippin, Low
There are also 3 or more varieties on the tree which are unlabeled, but affected. All information considered, it would appear from the limited data I have that something in the neighborhood of 15% of varieties show signs of infection. Walking around the rest of the property, I see no other trees that show any sign of infection, including the the varieties that are on the above list, but which are also growing as separate trees or cordons. Most of those duplicates were either grafted a long time ago, or I went out of my way to source scions from elsewhere. Also, there is none of the disease in my apple seedlings, which is expected, since the virus is not transmitted in the seed.
I don't know a lot about the pathology of the disease. The only way I can tell a tree has it is if the leaves turn partly white or cream colored and some leaves will turn partially brown and crispy as well, possibly from sunburning on the white parts? I have seen branches affected pretty strongly, but over all Frankentree seems healthy and vigorous and bears well on good years. Apparently, it also affects other species.
I think that the free trading of scions by fruit enthusiasts must be contributing to the spread of Apple Mosaic Virus. I don't send out scions of anything that I know is infected unless it's so rare that it can't be obtained anywhere else, and the receiver is aware of the disease status of the material. I would suggest that others do the same. Even so, since something like over 80% of varieties show no sign of infection, it is likely that we will end up trading scions that are infected anyway. it is possible to graft a very susceptible variety onto a tree to see if it shows signs, but I would let it grow for more than one season before assuming the host tree is clean. Other than that, it is probably going to continue to proliferate among fruit collectors.
