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nafex - Re: [NAFEX] Another strawberry question

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  • From: Philip Stewart <philstewart24@yahoo.com>
  • To: nafex@lists.ibiblio.org
  • Subject: Re: [NAFEX] Another strawberry question
  • Date: Wed, 31 May 2006 12:29:25 -0700 (PDT)

Jim,

Believe me, I HAVE counted strawberry chromosomes.
Many, many cells worth. From both anthers and root tip
preps (it's neither fun nor easy). I have also checked
ploidy levels with flow cytometry. All commercial
edible strawberries are octoploids with 56
chromosomes, with only a few very, very minor
exceptions:

- Very small amounts of Fragaria vesca and Fragaria
moschata, primarily produced in Europe for the gourmet
market
- A series of decaploid Fragaria x vescana cultivars
developed in Sweden. To my knowledge there is little
or no commerical production of these.
- The Fragaria-Potentilla ornamental hybrids such as
Pink Panda and Lipstick. I have heard varying reports
on the ploidy of these, from decaploid to octoploid
plus two chromosomes. I attempted to do a root tip
count from Lipstick at one point, but I had difficulty
getting a good prep, although I'm pretty sure I could
make out no less than 60 chromosomes in the best prep.

These combine for probably less than .01% of
strawberry acreage, and most strawberry growers have
never even seen any of these. Maybe you have been
growing non-octoploid strawberries (though I'm not
sure why you would aside from the novelty value), but
that would make you exceedingly rare, and entail a
fair amount of work, since there is no nursery source
for large numbers of non-octoploids.

The ploidy of cultivated strawberry is well
established, as are those for nearly all other
Fragaria species. Most of these were demonstrated as
early as the 1920's, and have been consistently
reconfirmed by later research. You might want to check
out the relevant chapter in the classic work on
strawberries by George Darrow:
http://www.nalusda.gov/pgdic/Strawberry/book/bokseve.htm

A reversion to lower ploidy level in vegetatively
produced plants would be almost unheard of, and
certainly not happening on any noticeable scale in
strawberry field. It would be more common, and still
exceedingly rare (if I recall, one study found 4
possible cases in roughly 10,000 flowers worth of
seeds) with seed propagated strawberries, but almost
nobody is growing strawberries that way, it's not even
relevant. Even then, changes to higher ploidy, while
still rare would be far, far more common (I have a 12x
seedling of an octoploid plant growing at home, for
example). I'm not saying it's impossible, but unless
you have chromosome counts or flow cytometry data I'd
be willing to bet against reversion to lower ploidy.
If it is happening, as far as I can tell it's never
been previous reported.

As for the fertility of triploid strawberries (from
Yarnell, 1930): "So far as is known, the triploids
have never spontaneously set fruit". They do set the
occasional fruit if artificially pollinated by
diploids or allowed to be open pollinated in the field
where surrounded by normal strawberries, but even then
the fruits are infrequent and have very few achenes.

Small berries and small leaves are not necessarily
indicators of lower ploidy...there are many
physiological factors that can result in the same
thing. When I grow strawberries in tissue culture,
many cultivars never develop leaves bigger than about
a quarter while in vitro, yet quickly revert to normal
phenotype when grown under normal conditions. It can
also be a result of mutations not involving ploidy
changes.

--Phil

> Message: 3
> Date: Wed, 31 May 2006 06:51:00 -0500
> From: Jim Fruth <jfruth@uslink.net>
> Subject: [NAFEX] Another Strawberry Question
> To: <nafex@lists.ibiblio.org>
> Message-ID: <C0A2ED53.2BFA%jfruth@uslink.net>
> Content-Type: text/plain; charset="US-ASCII"
>
> Philip,
> Maybe you ought to invest in a microscope and
> check a few strawberries
> at meiosis. Not just any plant but those that
> stopped growing large berries
> and have started producing small berries and small
> leaves. And, apparently
> your source of information is different from mine.
>
> Philip said: I think you're confused about this.
> Essentially all
> commercial strawberries are octoploid, and will stay
> octoploid forever. Changes in ploidy are very rare,
> --
>
> Jim Fruth
> Brambleberry Farm
> Pequot Lakes, MN
> www.bberryfarm.com
> Jams, Jellies and Syrups
> (218)568-8483 [Store]
> (218)831-7018 [My cell]
>
>

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