hort.net Seasonal photo, (c) 2006 Christopher P. Lindsey, All Rights Reserved: do not copy
articles | gallery of plants | blog | tech blog | plant profiles | patents | mailing lists | top stories | links | shorturl service | tom clothier's archive0
 Navigation
Articles
Gallery of Plants
Blog
Tech Blog
Plant Profiles
Patents
Mailing Lists
    FAQ
    Netiquette
    Search ALL lists
    Search help
    Subscription info
Top Stories
Links
sHORTurl service
Tom Clothier's Archive
 Top Stories
Disease could hit Britain's trees hard

Ten of the best snowdrop cultivars

Plant protein database helps identify plant gene functions

Dendroclimatologists record history through trees

Potato beetle could be thwarted through gene manipulation

Hawaii expands coffee farm quarantine

Study explains flower petal loss

Unauthorized use of a plant doesn't invalidate it's patent

RSS story archive

Hybridizing


There was a query on the list a few days ago about hybridizing techniques.
Hit the delete if this is too much stuff--below I'm copying the relevant
section from my book manuscript.  Please remember (before flaming) that the
audience for the book is the beginner.

THE BASICS OF HYBRIDIZING

With their large, simple flowers, irises are very easy for even a beginner
to hybridize.  But before rushing out to the garden to make some crosses,
consider carefully.  Planned crosses almost always provide better results
than ones made at random or impulsively.  Choose parents that already
exhibit qualities you would like to see in your seedlings, such as vigor,
disease resistance, form and habit typical for the kind of iris, and, of
course, attractive form and color.

Anticipation and Realization
But even with the most careful selection of parents, be prepared for some
of your seedlings to disappoint.  The genetics of irises are complex, and
the best qualities are not always passed on to offspring.  It is well to
remember the vegetable breeders who crossed radishes and cabbages (actually
quite closely related plants) hoping for radish-rooted plants that would
bear cabbages above ground.  They obtained, unfortunately, offspring with
cabbage roots and radish tops.

Geneticists have long been aware of a phenomonon called regression to the
mean, in which the offspring of outstanding parents have a tendency to drop
back in many of their characteristics to the average for the population as
a whole.   Premier iris breeder Ray Schreiner has been quoted as saying
that he selects from among 10,000 seedlings raised annually only 15 for
further testing, and of those, only two or three might eventually find
their way into catalogs.  Yet it is only through selecting outstanding
parents for crosses that the rare individual will be obtained that may
exceed them both in desirability.  Two inferior parents will rarely produce
a superior offspring.

It would be out of place in this book to launch into a long explication of
iris genetics.  An excellent introduction to the subject can be found in
the book The World of Irises, listed in the appendix on Further Reading.

The Hybridizer's Kit
You will also need to arm yourself with some basic equipment.  You will
appreciate having a box, tray, or other container to hold your equipment,
pencils, labels and notebook, to make it easy to carry them all into the
garden.  Some professionals prefer an apron with many commodious pockets of
various sizes, or a fisherman's vest.

A small pair of forceps or tweezers will be useful for collecting the
pollen-bearing anthers, as well as some small glass or plastic vials or
tubes in which to temporarily store the anthers.  Tie-on paper labels will
be needed in order to tag pollinated blooms to make sure they do not get
snapped off while cleaning up, and to connect the seed pod you hope will
form with the notes you have taken recording the parentage.

If you have now selected the first parents for your new hybridizing program
and have assembled the simple equipment needed, you are ready to go into
the garden and actually make the crosses.  Let's assume for now that you
are going to work with Tall Bearded Irises; later, we'll briefly discuss
some of the differences that need to be taken into account with other
types.

Pollination
Once in the garden, review the brief description and illustration in
Chapter 1 of an iris flower.  The two parts which you must be able to
distinguish are the pollen-bearing anthers and the stigmatic lip.  Both are
close together in the floral anatomy, the stigmatic lip being found near
the tip of the style arm, and the anther attached to the base of the bloom,
tucked in beneath the style arm.  The variety or species that will
contribute the pollen for the cross is called the pollen parent, while the
one that will develop the seeds is the seed parent.  For most kinds of
irises, a plant can play either role, but in a few cases, some may be
either pollen-sterile or seed-sterile, or both.  This can only be
ascertained through experience with the plants themselves.

Making the cross could not be simpler.  Examine the anthers of the pollen
paraent carefully; if they are mature and producing pollen, you will be
able to see a yellow, white, or bluish powder adhering to them.  It usually
requires at least a few hours after a flower first opens for the anthers to
mature, open, and show their pollen.

Using forceps or tweezers, remove one of the anthers from a bloom of the
pollen parent.  9-2 Select a bloom on the seed parent that has been open
for one day or less.  If the seed parent plant is nearby, you can simply
carry the anther there and, pulling back the crests of style arms with
thumb and forefinger to expose the stigmatic lip, wipe some of the pollen
from the anther on to the lip. 9-3

Again, it may take some hours after the bloom first opens for the stigmatic
lip to become receptive, but even if pollen is placed on a not-quite-ready
stigma, it will effect fertilization when the proper time comes.  Although
placing pollen on just one stigmatic lip is probably sufficient to produce
a full pod of seeds, it is wise to pollinate all three stigmas, as
insurance.

Keep Careful Records
Record the cross you just made in your notebook, by a code number you
assign.  For example, the first cross you make in 1998 might be called 98-1
in your notebook.  Opposite the code number, record the parents.  By
convention, the name of the seed parent comes first, followed by the name
of the pollen parent; the two names are separated by an "x" symbolizing the
hybridization.  As an example, perhaps cross 98-1 will be 'Stepping Out' x
'Victoria Falls.'  This tells us that pollen of 'Victoria Falls' was placed
on the stigma of 'Stepping Out.'

Not all attempted crosses will result in seeds (see below), so it may be
good to leave space in your notebook for recording if a pod formed or not,
and if so, how many seeds it contained.  When you plant any seeds that have
formed, write down that number as well, and in the spring make note of the
number of seedlings that appear.  Then each seedling can be assigned an
additional number, such as 98-1-7, the seventh seedling of the cross
described above.  Good record-keeping is extraordinarily important, even if
only a few crosses are made just for fun.

Attach a tag bearing the code number of the cross to the seed parent's
bloom stalk, just below the ovary.  Remember that this tag is going to be
exposed to the weather all summer, so select one that will last, and write
on it with pencil, not with a soluble or fading ink!

Did It Work?
Within about three days, if you used a fresh flower of the seed parent, the
ovary of the pollinated bloom will be slightly enlarged, indicating that
perhaps the cross was successful.  Be careful not to snap off any
pollinated flowers; the process of fertilization may take some time after
pollen transfer.  The pollen grains must sprout, and send a long, hollow
tube growing down through the stigmatic tissues.  These tubes eventually
reach the ovules, or potential seeds, in the ovary and fertilize them.
Only fertilized ovules will become seeds.  Warn garden visitors not to be
"helpful" in snapping off spent blooms!

After several more days have passed, the ovary containing developing seeds
will become noticeably larger; if the cross was unsuccessful, the ovary
will shrivel, turn yellow, and drop off.	 Successful pods will grow
larger through the summer, 9-4 eventually turning yellow or brown and
cracking open at the top.  If the exposed seeds are brown and glossy, they
are ready for harvest (rarely, a pod will be completely empty, what experts
call a balloon). 9-5 Collect them into an envelope which can be labelled
with the number you gave the cross in your notebook.  The seeds can be sown
and cared for as described above.

Helpful Hints
There are some other techniques involved in hybridizing that may prove
useful.  Often, pollen and seed parents do not bloom at the same time.  If
the pollen parent blooms first, anthers can be collected and stored in
small vials or tubes stoppered with cotton and stored in the refrigerator
until the seed parent blooms.

If the seed parent blooms first, an iris grower in a more southerly region
might have the pollen parent already in bloom.  Pollen can be shaken off
into an envelope and sent through the mails without evident harm.
[Cherilyn:  Yes, you are slow!  How else would one get the pollen from
North Carolina to Connecticut, for example?] In this case, a small
water-color brush can be used to collect the pollen from the envelope and
to transfer it to the seed parent's stigma.

Remember that pollen grains are microscopically small, and a few may adhere
to brushes or to vials used to transfer or store them.  Thoroughly wash
such implements before using them for another cross to avoid pollen from
the wrong parent effecting fertilization.  Some hybridizers use toothpicks
or matchsticks routinely to transfer pollen, and throw them away after use.

Volunteers
Sometimes pods full of seeds appear spontaneously in Tall Bearded Iris
plantings.  In such cases, insects have carried pollen from one flower to
another, or by some manner of means, pollen from the same flower has
reached the stigmatic lip.  Of course, the pollen parent is unknown for
such crosses, but it is up to you to decide to keep or discard the seeds.

 The appearance of these chance pods raises the question of insects
bringing additional pollen to a seed-parent bloom either just before or
just after you have pollinated it yourself.  Experience suggests that this
is not very likely, at least for Tall Bearded Irises.  Their blooms are so
large and so constructed that insect pollination can only be effected by
the largest bumblebees.

However, many professionals take the precaution of breaking off the fall
petals of pollinated flowers so that bumblebees will not have a landing
platform.  Others pop a small paper bag over the pollinated bloom until
they are sure the cross has taken.  The bags could be counter-productive on
windy days because the flower could be snapped off before fertilization
occurs.

Pollinating Beardless Irises
In contrast to the Tall Bearded Irises, many beardless forms, especially
the Sibrians, are readily self-pollinated or can easily be pollinated by
bees.  Left totally alone, almost every flower from a clump of Siberian
Irises will form a seed pod, usually as a result of visits from bees.

While crosses of all types of irises can be made by the same methods I've
already described, you must take precautions with beardless irises to avoid
unwanted pollination either before or after you make your cross.  The
method described by Currier McEwen for Siberians will work for all.  Select
as a seed parent a flower that is in the early stages of opening, and
carefully unfold the petals.  At this point, the pollen will be far from
mature, so the anthers can be safely removed and discarded.  Using a strip
of foliage, tie up the falls so that the flower remains inaccessible to
insects.  After some hours (or no more than a day), the stigmatic lips will
have become receptive and the bloom can be pollinated by hand.  Afterwards,
either remove the falls or re-tie them to deter insect visits.

The most difficult task of hybridizing comes when your seedlings bloom.
Unless you have unlimited space to preserve them all, you must ruthlessly
select only those that are improvements over their parents, allowing only
them to remain in your garden.  Perhaps you will be lucky enough to raise a
seedling that will achieve public acclaim, be introduced to commerce, and
win top awards from the American Iris Society (see box).   Or, like most of
us, you may only reap the satisfaction of having participated in an act of
artistic creation in which the medium is a living, growing plant.

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






 © 1995-2015 Mallorn Computing, Inc.All Rights Reserved.
Our Privacy Statement
Other Mailing lists | Author Index | Date Index | Subject Index | Thread Index