HYBRIDIZING WITH CONVERTED
TETRAPLOIDS II
Microscopic Identification
(MID)
Text and drawings
by Oscie B. Whatley, Missouri
Most of us, including myself, will procrastinate about using
microscopic identification and will resort to eyeballing the
plant parts because MID just seems to be too much trouble.
Usually, there are unaided visual differences between the diploid
and its conversion (tet) such as the following:
1. Tetraploid foliage will be more ridged.
2. The upper surface of tet foliage is warty.
3. Tet scapes ate usually shorter and heavier.
4. The tetraploid sepal tips ate thicker than the diploid
and tend to open prematurely.
5. A tet ovary may be shorter and larger in diameter.
6. Most tet flower segments are thicker.
7. Tetraploid flower styles are larger in diameter and may
twist or kink.
8. Scapes of tets ate more susceptible to vertical cracking.
9. Flowers ate usually larger on tets with the sepals proportionately
longer.
10. Color may change in value (darker more likely on the tet
flower).
A significant number of these characteristics can be seen
with the naked eye, but I have seen many good conversions
where only a few (sometimes none) were evident.
Tet GENTLE SHEPHERD easily could have been overlooked using
only unaided visual evaluation.
We should look for these conspicuous differences;
but if we depend entirely on the eyeball method, the chimera
zebras and jokers will have lots of fun at our expense.
To further confirm suspicions of conversion, we turn to making
test crosses to known tets. This practice could be the ultimate
of testing if we follow safe hybridizing rules and observe
carefully the resulting seedlings.
Unfortunately, there are natural barriers such as high temperatures,
incompatibility of parent, limited sterility, etc. The influence
of these barriers can be easily mistaken for a non-conversion.
I have seen good conversions discarded because successful crosses
could not be made in the first 10 or 20 tries. If the treated
plant had been MIDed, a lot more persistence would have taken
place, thus enlarging the possibility of ultimate success.
JUMBLE EDGE was the result of over 300 crosses that netted
only three pods. On the strength of microscopic identification,
I was convinced of the parent ZENAR's potential as a converted
tet.
Adding MID to eyeballing and test crossing will reinforce your
knowledge of where to concentrate your efforts. Becoming qualified
and efficient at MID will save you time and increase your success
rate.
It takes a microscope to do MID, but not necessarily an expensive
one. A grade level normally used in high schools is more than
adequate. You must have 10X and 43X power for checking both
pollen and stomata guard cells. A measuring device (optic micrometer)
installed in the eyepiece is beneficial. A good used microscope
with above features should cost less than $150.00. (Note: Any
measuring device should be calibrated to a standard by
the user.)
Determination of the conversion is by comparison. This can
be done two ways: (1) by comparing to a standard created by
the distribution charts in illustrations "A" and "B" or
(2) by comparing the treated plant to an untreated plant. The
treated plant should be about 40% larger on stomatas and
pollen sizes.
Refer to illustration "A" (above) for checking foliage
stomata guard cells. Tet foliage will increase strongly your
chances of tet pollen. However, even if the leaves check diploid,
you still may have a 2/4 conversion, which is usable. This
rare conversion has occurred only once for me, in tet GENTLE
SHEPHERD. Try to check all your treated plants before they
bloom on mature leaves (after leaf #3).
Refer to illustration "B" for checking pollen. Collect
pollen early to avoid contamination from other daylily flowers.
It should be dry and fluffy when preparing the specimens.
Hybridizing with some conversions can be a snap while others
may be next to
impossible. MID should make the difficult ones a little easier
to accomplish.
The next article will deal with the practice of "Safe
Hybridizing."
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