JI/SI cross techniques
- Subject: [sibrob] JI/SI cross techniques
- From: a*@toad.net
- Date: Sun, 19 Jan 2003 22:57:07 -0500
> Hi Christy, and robins,
> I would like to try some of the JI/SI crosses this year. Any hints or tricks to
> making it so? I do have frozen pollen to use. Have you tried tets? Thanks, Jim.
Jim,
Until Christy reported her success with JI/SI crosses, such a cross,
though theoretically possible, had yet to be reported. Among iris
aficionados, her claim has caused as much stir as the recent claim of a
successful human clone has caused among scientists.
My own experiences with JI/SI crosses have been nothing like Christy's.
I must admit that I first tried the crosses in 2002, but my "takes" were
scarce. I did crosses in both directions with fresh pollen between
diploid SI's and very early blooming JI's. All were diploid, since there
are no truly early JI tetraploids. I got no takes with the JI's as pod
parents. Of the 30+ crosses I did onto SI's (all the pollen I had), I
got only 3 pods.
Not wanting to risk traditional germination--and knowing techniques for
embryo rescue, I gathered the pods early, sterilized them using standard
techniques and excised the embryos. On visual examination, there were
only a dozen seed that appeared viable. When I cut open the seeds, there
was ABSOLUTELY NO ENDOSPERM, indicating that they would not have
germinated normally. Of course in angiosperms, the "dual fertilization"
is mandatory for successful formation of viable seed. The failure of the
endosperm to develop is typical in wide crosses, where the endosperm
fertilization is the "gatekeeper" for preserving the species.
Usually, when you excise an iris embryo, is is a delightfully smooth
little oblong form, slightly reminiscent of a "smoo" from Lil' Abner.
The embryos that I did excise from these crosses were malformed and
barely recognizable as embryos at all. I plated them out on agar and
most of them grew. However they only grew roots. There was absolutely no
apical growth. I tried stimulating a few of them with giberillic acid,
but ultimately, they all died.
I was quite encouraged by my results. The outcome is in keeping with
generally accepted theory of botany. If indeed, unquestioned JI/SI
crosses are to be made, I doubt that it will happen without use of some
technique such as embryo rescue. The lack of apical growth of the
embryos is perplexing, but may be explained by the condition of the
embryo when it was excised. In my part of the country, the 2002 growing
season was quite harsh and not particularly conducive to fertilization.
This year, I hope to make more crosses and hopefully get better pod set.
That will afford me the opportunity to stagger rescues, hopefully
harvesting a healthier embryo that will grow into a fully viable plant,
which then must meet the muster of the scientific community to determine
if it is a valid cross.
R. Dennis Hager
on Delmarva
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