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HYB: Multiple Pollinations


From: Sharon McAllister <73372.1745@compuserve.com>

Lloyd Zurbrigg wrote:
>
I feel sure that one pollination, on one stigmatic lip, is enough to get a
pod full of seeds. I rarely have a pod that has only one double set of
seeds.  The purpose of multiple pollinations , I believe, was to increase
the chances of a fertilization taking place, and was used a lot in arilbred
crosses, because so many varieties had infertile pollen. 
<

More food for thought -- I certainly recognize the voice of experience when
I hear it.  This time, it leads me to the question of environment.   When
we experimented with pollen shipments, Lloyd had signficantly greater
success using pollen I sent than I had making the same types of crosses
myself.

In fact, I quit making TB x TB crosses some years ago -- mostly because it
was too difficult to get seeds.  In my experience, full pods were quite
rare.  At least one empty chamber was the rule, even when I pollinated all
three stigmatic lips.  

Now, what if the controlling factor is environmental?  We already know that
it takes some hours for the pollen tubes to grow down the style arm.  [I
think it was Dr. Werckmeister who recommended evening pollinations,
allowing the tubes to grow overnight before dissecting the flower -- but my
reference books are inaccessible right now].    Here, low humidity is the
rule and TB season coincides with hot winds from the west.  Perhaps the
side of the ovary exposed to the drying wind can't support seed production.
  

From dissecting flowers in varying stages of development, I do know that
the membrane separating the compartments is in place when the flower is
still in bud stage.  But it could be semi-permeable, in which case it is
possible that pollen tubes could penetrate to an adjacent compartment under
favorable conditions.

All of this is conjecture, of course -- which calls for an experiment.  
Any volunteers?

Stage 1 -- Research.    
Somebody with better library access than I have at the moment needs to find
and post the procedure for using a stain like methyl violet to make pollen
tube growth more visible.  

Stage 2 -- Testing.     
Preferably, this should be done by a number of different people in
different climates.   Select the sacrificial flower and pollinate one
stigmatic lip. Record time, temperature, relative humidity, and anything
else about the environmental conditions you consider important.   Allow
sufficient time for the pollen tubes to grow all the way into the ovary and
fertilize the waiting egg cells.  Record the elapsed time.  Dissect the
flower. Remove standards and falls to expose the connection of the style
arms to the ovary.   You can use an Exacto knife to cut it into segments
with minimal damage.  Peel each style arm apart to view the pollen tubes.
[Yes, even the two that aren't supposed to have any.]    Check to see if
any of the stained tubes have penetrated the adjacent compartments and , if
so, what path they took.

I've pulled apart many style arms in my quest to thoroughly understand the
process, but usually I'm examining the mass of pollen tubes, how many and
how quickly they've grown.  I don't think I could trace an unstained tube
down the style arm and into the ovary.  But if stained tubes show up in all
three compartments, an entry pattern should be discernable.

If you've never pollinated and dissected a flower, expect to have to do
quite a few before you master the timing. 

Sharon McAllister
73372.1745@compuserve.com 

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