REPLY2: [pbs] Narcissus 'Quince'
Thu, 15 Apr 2004 09:45:43 PDT
In a message dated 14-Apr-04 1:42:34 PM Pacific Daylight Time, writes:

> Another way of cleaning up virus infected bulbs is by heat treatment.  It 
> undoubtedly varies by bulb species and pest species, but 55 C for an hour 
> is perhaps close to what you can do.  Rather than discard valuable but 
> virus infected bulbs, try heat treating them first.
> I don't know, does heat also kill mycoplasma?

Jim ~

This is a concept rather widely believed.  While it may be true in genera 
other than Narcissus, I stand by my statement that a plant, once infected with 
virus, is best destroyed or kept isolated.  I still isolate many narcissus 
thinking I would use them for their genetic material.  Now, however, I am 
questioning even that practice since there is evidence that daffodil viruses can be 
seed transmitted.  I think it fair to say that all clonally propagated plants 
will, sooner or later, contract one (or more) of the viruses known to infect 
their genus.

Bear in mind, there is no guarantee that virus spores won't survive any form 
of heat treatment only to re-infect when conditions are appropriate (the 
propagule must continually be ELSA tested for any degree of certainty).  In heat 
treatment of Narcissus, at best, all one can hope for is a diminution of 
symptomology, not a "cure."  I still stand by my belief that once infected, virus in 
a plant is incurable.  On the other hand, what often happens as a result of 
heat treatment is that viral activity is diminished for a year, or two, leading 
to healthier appearing plants and to the belief that a cure has taken place.

Heat treatment in the form of a circulating, hot water bath in an insulated 
tank kept at 114 deg F (45.6 C) for three hours is the recommended treatment 
for the occurrence of the bulb and stem nematode (Ditylenchus sp.), the 
absolutely worst event to befall a daffodil (or any tunicate bulb) grower!  At this 
temperature range, there is a very fine line between curing the infestation and 
the death of the bulb!  The colloquial name for such treatment is "cooking," 
and for sound reason!  I have heard that there exists in Holland a heat 
resistant form of this nematode that has (most likely) arisen from sloppy heat 
treatment practices over the years.  Woe to one who contracts this one!!!  Over the 
years, the best advice I have heard, has been (and not entirely 
tongue-in-cheek) to sell the place and move and start over!!

Formalin (formaldehyde) has long been the recommended additive to the hot 
water bath to combat fungus (e.g., fusarium) at the same time.  In many places, 
this is now a restricted chemical, if even available any longer, even though 
this is a naturally occurring substance.  There are some newer replacement 
chemicals that have come into the marketplace that have been shown effective 
against fusarium and the fungi infecting the outer scales of the bulb.

Dave Karnstedt
Cascade Daffodils
Silverton, OR  97381-0237

More information about the pbs mailing list