North American Fruit Explorers mailing list at ibiblio

[Philip Stewart <philstewart24@yahoo.com>]

While I can't really say what mechanism caused it, I
would think that the reason hexaploid plums evolved as
self-fertile is that those that somehow became
self-fertile are the only ones that managed to
reproduce.  Supposedly Prunus domestica is a union
between a tetraploid (P. spinosa) and diploid (P.
cerasifera) species, via either spontaneous doubling
in a triploid seedling or the magic of unreduced
gametes.  Once the hexaploid plant has grown, though,
what's it going to do for pollination?  It's now
producing triploid gametes.  In all likely, the only
source of triploid pollen anywhere remotely nearby is
itself. There's really no realistic way I can think of
for a diploid or a tetraploid to produce triploid
pollen...and if somehow the hexaploid managed to cross
with the tetraploid or diploid, the result would not
be a hexaploid anymore. So although there may well
have been self-incompatible hexaploid plums formed,
only the compatible ones made it to today.

I think this is frequently the
case...self-incompatibility often goes away in the
polyploids (note in your example with the cherries,
that sweet cherries are diploid while sour are
tetraploid.)

Oddly, dioceousness tends (I think) to be a bit more
common in polyploids (vs. their diploid progenitors). 
The Fragaria are all happily perfect flowered as
diploids, but most of the wild octoploids and
hexaploids (and maybe the tetraploids...I honestly
don't know anything about them) are male or female,
not both.  I suspect this may be a way of returning to
outcrossing to assure diversity after the formation of
the polyploid necessitated the original end to the
self-incompatibility.

(This is just idle speculation at 2am...I'm not at my
sharpest and could be completely wrong (not that I
couldn't be if I was wide awake, too)).

I suspect the problem with the lower nutritional value
(if is indeed the case) is the fault of the breeding
of hybrid corn, not the lack of homozygosity.  In the
neverending quest for higher yields, agronomic crop
breeders have at times lost sight of other important
traits.  (Really the same story, one way or another,
with all crops...we just grow a heck of a lot of corn).


                
__________________________________ 
Do you Yahoo!? 
Yahoo! Mail - 250MB free storage. Do more. Manage less. 
http://info.mail.yahoo.com/mail_250