Hi list,

Can't seem to make a diagnosis on this one, so I thought I'd consult the
group. I have a phal that lost some roots a while back due to rot, and
I guess as a sequla, it's also losing some leaves. I never really
noticed before, but now it has become apparent that these leaves are not
'normal'. As a leaf turns yellow, there are these rings of green that
remain, though they eventually turn yellow as well. The rings are
irregular in shape, and are about 0.75 inches in diameter. As well, the
border of the rings is raised...if you feel the leaf at that point, it's
not too much different but one can notice that the leaf is thicker; it
still feels like normal leaf tissue. Also, if you hold it up to the
light, the area does look greener...though this could just be because
it's thicker. It's been like this ever since I bought it, and I have
not noticed these rings expanding or anything, and there's no necrosis,
or exudate...etc. It is growing a new leaf right now, and this new leaf
(about 3" long now) is smooth and normal, with no such rings structure.

So, here are my queries: is this plant infected with something, causing
the rings and the leaf drop? Could the leaf drop just be due to the
loss of the roots? Why is the new growth not affected? And the most
important question, should I get a replacement plant?

Cheers,
Xi

Diagnosis of viruses in plants is tricky at best. Although
typically suspicions are raised as a result of visual inspection of leaves
or other tissues, these are often misleading. Plants that appear healthy
may harbor one or more viruses, and signs and symptoms of infected plants
have fooled the best growers when they tested negative.

The first rule is that testing (usually ELISA or similar) is the
only definitive way to demonstrate a plant is infected with a given virus.
Of course, there are several viruses that infect phals, so each one would
have to be tested individually until either a positive hit is achieved, or
it becomes too expensive. Another way is to inoculate an indicator plant-
preferably one that is readily infected with any virus that comes its way-
and look for telltale signs of infection. Unfortunately, index plants have
become hard to find as many have intentionally been bred for virus
*resistance*. If you can find some wild type Cassia occidentalis, I hear
this is quite good for inducing non-systemic infection of a wide variety
of plant viruses.

Other'n that, I'd have to ask a couple of other things. How do the
flowers look? Any sign of flower break? How do the new leaves look?
Viruses appear more commonly on developing or developed leaves than those
that are senescing. Is there any chance you are confusing the latticework
of veins in dying leaves for virus infection? Normally, viral problems
result in sunken areas; raised areas would be most unusual for a plant
virus, far as I know.

So- don't panic. Set it aside where it can't drain on any other
plants. In fact, having ANY orchid where it can drain into another is a
bad idea. Test it, if desired, and see if it could be infected. To answer
your question, it is unlikely a grower would refund for a plant that
eventually proved to have virus, as it is not possible to determine when
the plant was infected. In this same vein (har har), virus testing should
be used only as an instantaneous snapshot as to the health of a plant; a
test indicates infection only at the time of testing, and is no guarantee
that it didn't get infected afterwards.

Making things yet worse is that the tests are not absolute. The
only way to tell if a virus is present through direct observation is with
an electron microscope; it is possible for viruses to be present at such a
low concentration that a skilled operator could search for days and never
find the virus in a plant. ELISA tests are not 100%, and I doubt anyone
has done serious studies as to the false positive and false negative rates
that these tests can produce. A recent PhD in plant pathology informed me
that it is suspected that orchids may tend to produce high false positive
rates; this would seem to jibe with some growers having their entire
collection tested, only to find that plants that are healthy and growing
just fine are "infected." Again- are they false positives, or infected
plants with a nasty case of the viruses waiting to manifest when the plant
is stressed?

Or, to paraphrase a conversation between myself and a doctoral
student at the university:

"You shouldn't cut multiple plants, using the same tool swirled
briefly in the same (ineffective) disinfectant."
"Why not?"
"You'll spread viruses."
"My plants aren't virused!"
(Surprised) "Oh! Good, you had them indexed, then?"
"What's indexing?"

That's when I knew we were in deep ka-ka. The disinfectant
solution was ineffective against plant viruses, so it was pretty much a
communal bath for the Swiss Family Rymovirus. To this day, I'm sure she's
confident none of her plants are virused, even though they belong to the
worst genus of all for plant viruses (Nicotiana) which has a rap sheet of
susceptibility longer than Robert Downey Jr.'s arrest record, and she's
never had a single one of them indexed for viruses despite using wild-type
plants.

The address in the header isn't valid. Send no e-mail there.

-AJHicks
Chandler, AZ

Hi Dr. Hicks,

Thanks for your response. To answer your questions, when the plant last
flowered, they seemed normal....actually, the flowers were great which
is why I really really really hope I don't lose this one. It's a really
nice harlequin Phal. Sogo Pearl, yellow with medium size plum blotches
evenly distributed, and the flowers are pretty flat. As far as I could
tell, there was no sign of anything wrong. It is currently growing a
new leaf, and the leaf is not showing anything resembling what I'm
seeing in the old and dying leaves. If it's a virus, it's not like
anything I've come across in my internet searches. I suppose I will
just leave it for now and see what happens.

PS. I don't think I will be doing any testing, as a new plant would
probably cost less!

Cheers,
Xi