Re: HYB:Diploid Irises with Arils and Arilbreds

>Bill Shear wrote:
>>
>> ....
>>
>> If diploid pure arils are used on diploid TBs, there should be a better
>> chance of seed set than if diploids were used with tetraploids in either
>> combination.

>And how about fertility? Do really wide crosses with at one diploid
>parent
>need an unreduced gamete from that parent (those parents) to be fertile?
>
>If so, would not the dip-dip crosses be much less likely to be fertile
>than dip-tet, needing two unreduced gametes rather than one?

Perhaps Sharon could answer this better than I, but no, unreduced gametes
are not required for fertility in diploid x diploid crosses.  Assuming you
mean by "fertility" seed set in the original cross, and not the ability of
the offspring to produce viable gametes.  The latter situation depends on
many other variables, including the number of chromosomes and the ability
of the chromosomes from the two parents to pair during meiosis.  The fact
is that such hybrids are usually sterile because either they have odd
numbers of total chromosomes (thus gametes wind up with extras or lack
some) or because the parental sets can't pair in meiosis.  This would be
the case with most of the early pure aril x diploid TB hybrids, such as
WILLIAM MOHR.  That latter variety was fertile only when an unreduced
gamete (that contained all the chromosomes) was produced.  Evidently this
happens with WM somewhat more frequently than with others.  WILLIAM MOHR x
IBMAC produced the tetraploid CAPITOLA, which does not set seed but has
very fertile pollen.  Most of the "classic" quarterbreds either came direct
from WILLIAM MOHR or IBMAC (which also was pollen fertile), or by use of
CAPITOLA pollen on tetraploid TBs.  The quarterbreds, though, are very
infertile (some have limited fertility and have proven useful) because of
unbalanced chromosome sets.

Yes, there might be something to be gained by experimenting with TB species
that have not been used before in crosses with arils, but the chances are
very low.  One assumes that you want to focus on something that would be
more likely to be productive.  If you can raise 10,000 seedlings, then you
might win the sweepstakes and find something useful, but if like most of us
you can only raise at most a few hundred each year, better to use the
information we already know and work where you are most likely to succeed.
I would be the last to try to dissuade anyone from experimenting, but you
should keep the odds in mind.


Bill Shear
Department of Biology
Hampden-Sydney College
Hampden-Sydney VA 23943
(804)223-6172
FAX (804)223-6374
email<wshear@email.hsc.edu>
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