Virused Bulbs

Nathan Lange
Mon, 07 Apr 2014 19:05:27 PDT

The implication of the dark pink-flowering Sparaxis photo posted 
below a title of "Virus" is that a virus is known to have caused the 
pattern seen on the petals in the photos and that this pattern 
represents a known symptom of viral infection. I do not believe this 
is the case. Finding a virus does not establish cause and effect, and 
is clearly not a definitive diagnosis for the cause of the observed 
color pattern. Many, if not most, plants are infected with viruses 
with no visible symptoms, as Mary Sue admits to finding out for 
herself. To correctly diagnose what is going on with this Sparaxis 
flower, the next logical step would have been to attempt to infect 
other Sparaxis and/or closely related genera to see if one can 
replicate the same pattern of speckled petals in a previously 
uninfected plant. Transposable elements are not transmissible. Also, 
one could attempt to grow out seeds from this plant. If the resulting 
seed grown plants also exhibited this trait, then that would strongly 
rule out virus. However, if no seed-grown plants exhibit this trait, 
neither possible cause is ruled out since we know nothing about the 
genetics of this hypothetical tranposon.
In this instance, I think the cause is far more likely to be a 
transposon than virus for four reasons:
1. The margins of the white sectors seem fairly well defined, not 
diffuse as is typical of viral infection, although this is difficult 
to say conclusively given the photo's limited focus.
2. The sectors seem to follow the developmental pattern within each 
petal as if the pigment machinery were turned off and back on very 
early during development along dividing cell lines.
3. The white sectors are white and not light pink, as if a transposon 
is completely turning off all anthocyanin production. A virus doesn't 
usually completely turn off all pigment production and would probably 
create lighter pink areas of varying intensity.
4. There are known, identified examples of transposons affecting 
petal color patterns which resemble the pattern seen with this Sparaxis flower.

I think this is an interesting photo but posting it under a title of 
"Virus" adds to the confusion encountered by home gardeners seeking 
answers and may lead someone to needlessly destroy a wonderful new 
cultivar. I recommend its removal from the "Virus" page.


At 04:38 PM 4/7/2014, you wrote:
>Many years ago I sent in some bulbs to a lab in Sacramento to test 
>them for virus. My experience proved that you can't tell for sure 
>whether something that looks virused is virused.  Some things I sent 
>in that looked virused were and some were not. Some I sent in that 
>didn't look virused were. Since most people don't wish to take the 
>trouble to do this, it seems safer just to toss plants that are 
>suspect even if you end up throwing out something that is suffering 
>from nutrient deficiencies.  But it is not so easy if the plant is 
>symptomless. I sent in Sparaxis  I had purchased because the petal 
>variation made me worry, but I also sent in some that did not have 
>those symptoms. They were all virused, even the ones that  looked 
>fine.  Nathan thinks the plants shown on the wiki were likely 
>misdiagnosed as virused but this is not so. It is possible that 
>plants with petal variation can be virused. It makes it very 
>challenging for the home gardener.
>Mary Sue
>pbs mailing list

More information about the pbs mailing list