I suspect that the apple tree that bears these fruit is infected with
the dapple apple/scar skin viroid. Copied below is an article about
the diseases caused by this viroid that I put into Scaffolds fruit
journal in September of 1994. I have photos very similar to yours
that I took in an old Empire orchard in the Hudson Valley in the late
1980's or early 1990's, but the scar-skin symptoms seem to be
relatively rare. I'm not certain if any more work has been done on
this viroid in the past 16 years. Following is the old article that
I wrote in 1994:
A fruit disorder known as "dapple apple" has appeared this
fall in several commercial orchards in the Hudson Valley. On
affected fruit, circular patches of the skin fail to develop red
color and remain green or faintly pink. The poorly colored circular
areas may overlap to produce irregular blotchy areas on the fruit.
As the fruit become fully mature, the green areas turn bright yellow,
giving the fruit a marbled appearance. A more severe manifestation
of the same disease is known as "scar skin". On apples affected by
scar skin, the sides and calyx ends of affected fruit develop a rough
skin in early summer. The roughened skin then develops numerous
small cracks as the fruit mature. Fruit with scar skin have the
appearance of fruit that received severe spray burn or had a limb rub.
I have seen dapple apple on Macoun four or five times over
the past 15 years, but symptoms this year are the most spectacular I
have ever seen. Other varieties may also show symptoms. In a mixed
planting of 15-20 year-old Macoun, Empire, and McIntosh, several
Empire trees showed severe scar skin while other Empire trees had
dapple apple or no symptoms at all. All of the Macoun trees and most
fruit on each tree showed distinct dapple apple symptoms. A few
dapple apple symptoms were found on McIntosh, but the proportion of
affected fruit was quite low and severity of symptoms was much less
than on Macoun.
Dapple apple was first reported in the United States in 1956
and was associated with trees propagated on Virginia crab rootstock
or stem pieces. The disorder was assumed to be a virus disease until
the early 1980's when Japanese researchers showed that dapple apple
and a related disorder called "scar skin" are both caused by viroids.
In general terms, a viroid can be described as a virus without a
protein coat. Many viruses can be eliminated from propagation
material by heat treatments which damages the viral protein and
thereby eliminates the virus. Because viroids have no coat protein,
they are very heat resistant and therefore more difficult to
eliminate from propagating material.
All reports in the literature (and there aren't many!)
suggest dapple apple is only transmitted by root grafting and by
using contaminated propagating materials. However, I would guess
that over a period of years, the disorder might move from one tree to
the next with an orchard by some means that has not yet been
identified. Movement within orchards is certainly very slow if it
occurs at all.
Why is the disorder evident this year in 15-20 year-old trees
that never showed symptoms before? No one knows, but the best guess
is that certain undefined weather conditions are required for symptom
development. The critical period for determining whether or not
symptoms appear may be the period during and shortly after bloom.
Because symptoms development is probably weather dependent, trees
with dapple apple symptoms this year may produce unblemished fruit
next year. Thus, I do not think that growers should necessarily
remove trees which produced fruit with dapple-apple for the first
time this year. Fruit from the same trees may show no symptoms next
year. However, growers may wish to mark affected trees for
observation next year and then remove those trees that are
consistently produced blemished fruit.
Can dapple apple survive in soil and affect trees replanted
into a site from which trees with dapple apple were removed?
Probably not, but there is a possibility that new trees could root
graft to living tree roots left in the soil after orchard renovation.
Thus, growers opting to remove severely affected trees should avoid
replanting with highly susceptible cultivars such as Macoun,
Delicious, Empire, and Spartan. Golden Delicious reportedly do not
develop symptoms when infected, and symptoms on infected McIntosh,
Mutsu, Idared and Jonathan are quite mild. Susceptibility of other
varieties is unknown.
Dear apple-croppers...
Last year at this time of the year, we had a fun thread on a mystery apple.
This year, I would propose one on a mystery disease... Hopefully it will
trigger just as much interesting discussion!
I have taken pictures showing the symptoms/damage. Please look here:
http://picasaweb.google.com/cjoliprsf/AppleDisease2010
Let me give you a little information on this:
- Pictures were taken on August 14 2010
- The size of the apples on the picture is about 1 inch across
- The apples didn't grow any bigger during fall
- All the apples show the same symptoms
- There is only one tree affected in the orchard (a small 1 acre orchard)
- Affected variety: Wealthy (there are other Wealthy trees around that are
normal)
- This appeared about 5 years ago and reappears every year on this
particular tree
- The affected apples ripen later than normal - actually, they don't really
ripen, but they stay attached on the tree until snow.
- The foliage is otherwise healthy and the tree normally vigorous
- Other trees about 20 feet away do not show any similar symptoms
Thanks for looking at this.
Claude Jolicoeur
Orchardist and cider maker
Zone 4, Quebec
--------------------------------------------------------------------------
The 'Apple-Crop' LISTSERV is sponsored by the Virtual Orchard
<http://www.virtualorchard.net> and managed by Win Cowgill and Jon
Clements <webmas...@virtualorchard.net>.
Apple-Crop is not moderated. Therefore, the statements do not represent
"official" opinions and the Virtual Orchard takes no responsibility for
the content.
--
**************************************************************
Dave Rosenberger
Professor of Plant Pathology Office: 845-691-7231
Cornell University's Hudson Valley Lab Fax: 845-691-2719
P.O. Box 727, Highland, NY 12528 Cell: 845-594-3060
http://www.nysaes.cornell.edu/pp/faculty/rosenberger/
