Re: Re: HYB: Inheritance of vigor

I'm going to toss out an idea that has been floating around in my imagination
for some years now, as I have observed what I think both Chris and Linda are
seeding.

Most crosses between almost any parents have seedlings that span the range
from extraordinarily vigorous to the other extreme--can hardly grow at all,
very slow to increase and show what looks like a struggle merely to survive,
if survive they do.

I'm wondering if part if not most of this range of behavior comes from the
complexity of chromosomes we have from the wide variety of species involved in
the origin of our modern garden varieties.

Not all of the chromosomes from the various sources will pair neatly and well
with those from others, and in some cases will not pair at all.  Those that
have close evolutionary origins in common are those most likely to have
homologous chromosomes or sections of chromosomes, can pair readily, and form
normal cross-overs, stirring the genetic pot deeply and well.

Less closely related species will probably have chromosomes that have
homologous sections that allow pairing, sort-of.  Hetero- rather than
homo-logous areas of chromosomes will arc away from each other if homologous
sections of chromosomes pair.  I would expect this to be the behavior between
early hybrids between any remote, distinctly different species.  When combined
in tetraploids all sorts of pairing behavior is observed, including un-paired
singletons, bivalent, trivalent and quadrivalent associations--meaning no
pair, one-on-one pairing, three paired up section by section in a daisy chain
arrangement, or four in a chain or round-robin sort of arrangement.  All of
these different possibilities stir the pot in different ways--and result in
varying chromosome counts in the cultivars varying up and down from 48.  As we
move farther and farther from species origins, the behavior settles down, it
seems, but we still get those variances in vigor you note.

Not only may incompatibilities in some chromosomes be at work, but there may
be differing, competing enzymes resulting from slight differences in the DNA
on those chromosomes, both trying to regulate the same step in the sequence of
growth determinants.  Two different, conflicting, sets of directions confuse
people--likewise they would confuse plants.  If a seedling ends up with
several such competing sets of enzymes resulting from conflicting blueprints
in the chromosomes that, in each case, cannot *both* occur, the seedling won't
thrive.  Rather than "hybrid vigor" we would have "hybrid confusion."

In a pair of crosses between EMPEROR'S CONCERTO and DIRECT FLIGHT, made both
directions, such behavior was especially evident.  Emperor's Concerto has
black, blue and pink ancestry.  Direct Flight is from several inbred
generations of pink x blue-bearded whites (Lady Blue Beard and Sweet Alice
Lee) crosses, so the mix in this cross is pretty wide in origin.  The vigor
and plant behavior ranged all over the map.  At one extreme were large, trifty
TB's with medium-sized blooms, not unlike what one would expect from the
parents.  At the other were some that refused to grow and one  SDB-sized plant
with lots of increase, few bloomstalks, but BB-sized bloom at 10" or so.  I
did save the best of these two extremes and discarded the rest.  My curiosity
was piqued, and I wanted to see if the apparent size and vigor continued.
What a strange mix!  Variances like this occur in many crosses.

At the other extreme, I have seen crosses where the vigor and behavior was so
nearly identical the seedlings could hardly be told apart.  In a cross many
years ago between ARABI PASHA, the English DM dark blue, and a blue primarily
from Hinkle breeding the seedlings looked like a row of the same iris lined
out---nearly identical color, height and vigor--which was high.  If my
speculation above represents anything that in fact does occur, this would be
said to be a cross that was virtually homologous across the board--every
chromosome mating with another so much like itself that no enzymatic arguments
ensued.  The results certainly suggested that.

Neil Mogensen  z 7  western NC

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