HYB: Limited Fertility -- Quarterbreds
From: Sharon McAllister <73372.1745@compuserve.com>
Message text written by Dennis Kramb
>
I'm really baffled by this phenomenon of "sometimes you get pollen,
sometimes you don't". From what I've been told, quarterbred arilbreds
usually do not give good pollen. But 4 out of 7 in my garden have given me
some.
<
There are two factors at work here: genetic potential and growing
conditions. The genetic potential must be there, but under adverse growing
conditions pollen may not form. Here in southern New Mexico, that usually
means hot, dry weather.
Let's start with the "pollen sterile" ones. TBs that have aborted anthers
can pass this trait on to their quarterbred offspring. Not even the most
favorable growing conditions will promote pollen production in one of
those. They are the exception, but perhaps they have given the entire class
a bad rep.
In my experience, MOST quarterbreds have the potential to produce pollen.
How much a given one produces is highly dependent on the weather. I've
made a lot of crosses involving quarterbreds, and have found this usually
just means fewer viable seeds per pod. Compared to TBs or halfbreds,
quarterbreds are relatively infertile -- but that does NOT mean that they
are "sterile".
Some, like JOINT VENTURE and PIXILATED, produce as much pollen as halfbreds
but not all of it is viable. Both of these can produce full pods on
halfbreds, but the percentage of viable seedlings is significantly less
than that produced by halfbreds crossed onto those same cultivars.
If you want lots of seedlings and a certain amount of predictability, work
within the fertile family of halfbreds.
If you have limited space and like surprises in the seedling patch, cross
quarterbreds with one of the fertile families in their ancestry.
Now, for your specific examples:
>
GREEN EYED SHEBA produced lots of fluffy pollen on all her blooms. She
seems pollen fertile because a number of those crosses have formed nice big
fat pods. She also has 2 or 3 pods of her own, so she appears to be pod
fertile too.
<
Look at her complex pedigree. She was registered as a quarterbred under
the quantum system, but could be anything from an SDB to a fully fertile
halfbred in today's system. I haven't grown this one, so can't guess her
true nature.
> OMAR'S TORCH bloomed twice, the first flower was barren, the second had
some scroungy looking pollen on it.
<
Conventional quarterbred, typical performance -- though I haven't grown
this one to confirm the observation.
> SATAN'S MISTRESS produces copious quantities of fluffy pollen on all her
blooms, without fail so far.
<
I wouldn't have used the term "copious", but SM certainly produces pollen
for me -- more than some TBs that are supposedly "pollen fertile".
> Wouldn't that be nice if quarterbreds are so happy in my garden that
they
can't help but be fertile?? Or maybe it's that Viagra soil amendment I've
been using. <grin!>
It would be one thing to occasionally find scroungy pollen on these
quarterbreds, but to consistently get anthers loaded with fluffy pollen
just baffles me about their reputation for limited fertility.
<
O.K. Time for a simplified <G> lecture on chromosome conjugation....
Most people work with halfbreds because they are fully fertile and
predictable. They can be described as AABB-type tetraploids and because
like sets pair on meiosis they produce AB-type gametes. Life is simple,
because
AB + AB = AABB.
Quarterbreds, however, are ABBB, ABBD, or ABDD-type tetraploids. For
simplicity's sake, I'll stick to the ABBB type and let you chart the others
if you're interested.
These are capable of producing two types of viable gametes: AB and BB.
On meiosis, two sets of B chromosomes pair, but the A set and the other B
set are not homologous. Most gametes will thus have one complete set of B
chromosomes and one mixed set -- and depending on the nature of the
mixture, most will not be viable. In some cases, though, all of the A
chromosomes will go to one daughter cell while all of the third B set will
go to the other. The result; a viable pair, one AB and one BB.
So when you harvest quarterbred pollen, you can expect some nonviable
grains, some ABs and some BBs. Crossed onto TBs, you may get TBs or
quarterbreds. Crossed onto halfbreds, you may get quarterbreds or
halfbreds. Crossed onto tetraploid arils, you may get halfbreds or
three-quarterbreds.
Note how I skipped the 1/4-bred by 3/4-bred cross? That's because I've
tried it and raised a few seedlings - very few -- none of which have
bloomed. THEORETICALLY, you could get quarterbreds, halfbreds, or
three-quarterbreds. [Go ahead -- chart it!]
To return to the original observation, the simple answer is thus that
quarterbred pollen tends not to be as good as it looks. Some grains are
viable, but many are not.
Although some dismiss them, I happen to think quarterbreds are worth
working with.
Sharon McAllister
73372.1745@compuserve.com
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