Bill,
There are examples from both fronts when crossing tets to dips.
Although it may be that using tet pollen on a diploid has fewer takes
statistically, we need to balance that out with the number of pollen
grains versus egg cells. A pod only has a limited amount of female
cells available and, if 1% are tet, then we will get less than one
viable seed per cross. If they are all tet and 1% of the pollen is as
well, we may see 5 or 6 seeds, as the number of pollen grains used may
be much higher. Non-compatable pollen simply dies, if it cannot
produce a viable zygote.
Although the math seems to speak for the dip pollen on the tet mother,
the number of Oncocyclus x Regelia crosses made with tet pollen on
diploid stigma seems to speak for another factor that we are unaware
of. Also, in the aril group, there are many triploid hybrids and more
are fertile than statistically should be.
In this particular group many of the hybrids are amphidiploids, which
are tetraploids made of doubled sets of diploid chromosomes from
differing karyotypes/chromosome numbers. Such as a cross between an
Onco (n=10) and a TB (n=12). The fertile tetraploid offspring have 44
chromosomes (10-10-12-12).
I do not wish to confuse the matter for you, simply make it clear that
Iris may behave differently than expected genetically. Also, the
Apogon and Pogon groups behave differently as well.
A book I found particularly interesting for laying a groundwork is The
World Of Irises. You can find a used copy in the internet.
Hope this helps ;-)
--
Jamie V.
_______________________
Köln (Cologne)
Germany
Zone 8
--- In iris-species@yahoogroups.com, Bill Chaney <billchaney@...> wrote:
Since I have not seen any posts for a couple days, thought I would
ask a question I have been pondering for some time. These winter days
give me time to poke around the web and do a little on-line library
research.
I am also cross posting to iris-photos and iris-species. If that is
not appropriate, my apologies. I am new to both groups. My
observation is that iris-photos seems to be mostly TB breeders and the
iris-species group has a somewhat wider interest. Is that accurate?
I know many of you will get this twice. Sorry.
So my question is: In making crosses of diploid and tetraploid
plants, my understanding is most people use the diploid pollen on
tetraploid pod parents because some of the pollen cells may be diploid
(unreduced) giving rise to viable tetraploid seed. There seems to be
some good evidence of this happening in the literature in a variety of
plant groups. (One of the advantages of being emeritus from the
University is that I still have electronic library access.) So what
happens to the all the reduced pollen? Does it germinate and produce
pollen tubes, but just not result in viable gametes? In some cases I
know triploid plants are produced, but these seem uncommon in iris.
Is that true? Any suggestions for some good cold night reading on the
subject?
Thanks
Bill
