HYB: Fertility

Steve Rocha wrote:

>       Is there any way I can find out on my own if an iris or airlbred =
is
>  fertile or not?
>  I hope someone can point me in the right direction. It will save me a
lot
>  of time by not trying to hybridize infertile cultivars               =

                                        =

and Dennis Kramb added:

>  I have a similar question.  Is there any way to find out what % aril
content
>  is in the various arilbreds on the market?  Many are just listed as
>  "arilbred".  But I know that anything over 50% aril content is not
likely
>  to survive here in Cincinnati and I'd hate to spend upwards of $10 for=
 a
>  rhizome that's going to die before blooming.  :(

To address the last concern first,
Henry Danielson introduced a lot
of cultivars with more than 50% aril =

content when he was hybridizing
in Chicago.  The TYPE of aril ancestry
is as important as the amount.

Now for the fertility / % aril question....

Fertility is not an all or nothing matter.
The most fertile arilbreds are balanced
tetraploids, with two sets of bearded
chromosomes and two sets of aril
chromosomes.  Diploids, triploids, and
pentaploids often exhibit some fertility,
as do unbalanced tetraploids.  Actually,
I don't like to write off any cultivar as
"infertile" -- I prefer to think that it hasn't
yet found the right mate.  I've even =

obtained seedlings by crossing a
1/4-bred with a 3/4-bred.  But if your goal
is lots of fertile seedlings, you want to
intercross the balanced tetraploids.

So I'm guessing the real question is how
to identify balanced tetraploids without
making a lot of test crosses....

The answer is usually found in the
registration.  Balanced tetraploids
registered since 1990 are coded OB,
OGB, or RB.  These are defined as
halfbreds in the chromosome set
system.  A plus (+) or minus (-) after
the code indicates more or less than
50% aril chromosome sets and thus =

limited fertility.  [Of course, this means
you can overlook some good breeders
like WHIRLWIND ROMANCE....]

Those are the easy ones. From the =

mid-70s until 1990, exactly the
same codes were used under the =

quantum system -- but OB, OGB,
and OB simply meant that half of the
ancesters were aril, half nonaril.  The
cultivar itself could be diploid (relatively
infertile), a balanced tetraploid, or a =

triploid.  =


On the other hand, OB-, OGB-, and RB-
meant that less than half of the ancestors
were aril -- but when wide crosses had
been involved the cultivar itself might be
a balanced tetraploid.  For example,
BOLD SENTRY [ARAB DUSK x GENETIC
BURST] was registered as an OGB- =

because it was 5/16 aril by the quantum
system but it proved to be quite fertile and
was later counted as a chromosome-set
halfbred.

Similarly, OB+, OGB+, and RB+ meant that
more than half of the ancestors were aril --
but the individual cultivars might be fertile,
balanced tetraploids.  For example, =

KOKO KNOLL was registered as OGB+ =

because it was 11/16 aril by the quantum
system -- but its breeding characteristics
are those of a fully fertile halfbred.

To complicate matters further, the use of
these codes in registration was optional. =

Some hybridizers followed the spirit =

of the rules while others followed the letter.
When the codes were devised, C.G. White's
amphidiploidlike hybrids and their linebred
offspring were assumed to be OGBs.
Cultivars that proved to be compatible with
them -- even if they had resulted from complex
crosses -- were often registered as OGBs
even if they were computed as OGB- or OGB+.

In other words, there is NO easy answer.
If you're working with cultivars registered =

during that era, I strongly recommend =

learning to analyze pedigrees -- and if
you're working with things registered
before 1975, pedigree analysis is even
more important.   Although quantum codes
were provided in the ASI Checklist for
older cultivars, there were so many =

typographical errors that no hybridizer
should rely on them.

Fundamentals of pedigree analysis:

Progeny of an aril X arilbred cross usually
show limited fertility at best.

Progeny of an arilbred X arilbred cross
may or may not be fertile.

Progeny of an arilbred X bearded cross
usually show limited fertility at best.

Progeny of a tetraploid aril X tetraploid
bearded cross are often fertile.

Progeny of a diploid aril X tetraploid
bearded cross are rarely fertile.

Is this more or less than you wanted
to know?

Sharon McAllister
73372.1745@compuserve.com
Other Mailing lists | Author Index | Date Index | Subject Index | Thread Index