Clonal breakdown- lily virus

Kenneth Hixson
Tue, 21 Nov 2006 17:13:20 PST
Dear members:
         This subject is a fascinating can of worms, probably because
we really do not understand exactly what is happening.  The term
'clonal breakdown' was used to describe an observable phenomenon,
which--rightly or wrongly--now would probably be ascribed to the
effects of virus.  It happens in other plants too--from fruit trees to
landscape junipers, etc.

>Hybrid vigor, while evident in plants raised from seed, does not last
>for ever if continued asexual reproduction of a plant is continued over
>many years.

Hybrid vigor is another term that can't really be explained--we can
observe that it happens and formulate theories about why, but it
is easy to confuse exactly why.  Plants raised from seed usually
do not carry a "burden" of virus, but as they accumulate virus, vigor
declines--so, are seedlings expressing 'hybrid vigor', or are they
simply not yet infected by viruses, and thus more vigorous?
Individual seedlings do vary in their inherited vigor, and hybridizing
may allow the expression of particularly favorable genetic expressions
of vigor.  The favorable combinations resulting in "vigor" are
selected, either by nature, or by man, and in turn pass on the
favorable genetic expression to their seedlings.

There are many viruses which can infect lilies.  The one many
people notice by the color changes and foliage distortions, is
tulip breaking virus.  There is also one called "lily symptomless
virus", which doesn't by itself seem to harm lilies.  When a
lily accumulates several--five or six-viruses, the "burden" causes
the plant to become less vigorous, and often it dies--but the
triploid tiger lily is widely known as a "typhoid mary" which
carries several viruses, but continues to grow and thrive, even
though the viruses it carries can/will kill other lilies.
Some lilies seem able to tolerate certain viruses or combinations
of viruses, while very susceptible  to other viruses, and this
is presumably a genetic characteristic.  L formosanum seems
to have little or no resistance to virus, and will quickly die.  The
easter lily, L. longiflorum, has some tolerance--it can carry a
virus that results in "flecking" or very small spots on the leaves,
without dying.

It is my understanding that plants have, in effect, three layers
of cells, and the somatic mutations, the things we usually see,
are confined to the outer layer.  This is a problem in things
like hostas, where variegated foliage is the thing of value.
When propagating hostas by tissue culture, for years the
variegations were lost and only "normal" green leaved plants
resulted from tissue culture.  It is now possible to propagate the
variegated leaves by tissue culture--just don't ask me how it's
done.  For one thing, some of the genetic variegations are used
in breeding, but that isn't the whole answer.
When growing plants from tissue culture, the resulting plantlets
need to be carefully monitored, because mutations often appear
among the cultured plantlets--reasonable if you assume that they
are propagated from a very small number of vigorously dividing cells,
where mutations could easily appear and be propagated.

The sexual organs--pollen and egg cells, arise from the third
or innermost layer, so they usually do not carry the somatic
mutations such as variegated foliage.  It is possible that
variegated foliage is genetic, and can be passed on, or a
somatic mutation, and can't be passed on.  Camellias are
an example of plants where both types of variegation are
possible.  It is possible to breed either variegated foliage,
or plain green leaved seedlings, depending on the parent
plant combinations.  I assume the same is true for other
plants such as hostas, though here my knowledge is

This is an area where much work in now being done, and
most or all of what I "know" is probably outdated.

For what it is worth, the cost of tissue culture has gone way
down in recent years.  I don't know about hippeastrum, but
for lilies there are laboratories that can provide thousands
or hundreds of thousands of plantlets for a miniscule price.
I don't know current prices, but wouldn't be surprised if it
were less than ten cents per plantlet per the hundred thousand.
Five years ago, the price of a flowering size lily bulb, to
produce a three to five flowered stem for forcing, ran about
forty cents per bulb in hundred thousand lots.  These were
imported from south america in pallet-boxes, about four feet
on a side.  The same bulbs in individual plastic bags, with
their own peatmoss packaging and color label, would retail for
about three to five dollars, depending more on the perceived
market demand than on  production costs.

Rodger W.'s comments on dutch bulb suppliers may seem
libelous, but unfortunately seem to match the experiences
of many people, including myself.  Orders arrive which turn
out to contain misnamed bulbs, or obviously diseased bulbs.
There is no doubt in my mind that there are reputable dutch
bulb growers.  Unfortunately, what I've received does not
represent honest business practice.  This is a practice the
dutch should deal with, and they do not seem willing to
do so, so the reputable growers suffer from the business
practices of others.  I've gotten to the point that I am reluctant
to order from suppliers of dutch bulbs.  Complaining about
several items on every order simply isn't a satisfactory way
of doing business.


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