HYB: new notation for chromosome stuff

Just thought I'd throw this into the mix, and perhaps tie it in with some
thoughts about arilbred classification.

Chromosome information is extremely useful to hybridizers, especially those
working with various types of bearded and aril irises. The information is
usually given as a chromosome count, e.g., "48", or with a simple term,
e.g., "tetraploid". Such descriptions are convenient, but leave a lot of
ambiguity. An iris with 44 chromosomes, for example, could be an IB with 3
TB sets and 1 pumila set (12+12+12+8 = 44) or an amphidiploid arilbred with
2 TB sets and 2 aril sets (12+12+10+10 = 44). And of course there are many
different types of tetraploid irises, with different chromosome breakdown.

One can, of course, write 12+12+12+8 all the time. But this is a little
tedious and besides draws attention needless attention to the number of
chromosomes. What really matters for breeding is what kind of iris each set
came from; the numbers are an indirect way of conveying that information.

Arilbred breeders have long used a system of letters to represent the
different kinds of chromosome sets: A for an aril set, B for a bearded set.
(Actually, this was taken from a standard practice of geneticists, where A
and B are used just because they are the first two letters of the
alphabet...but the coincidence was too good to pass up!). So an
amphidiploid halfbred is AABB. Besides being easier to take in at a glance,
this system avoids the embarrassing problem of specifying whether the aril
set is oncocyclus (10 chromosomes), regelia (11 chromosomes), or a mixture
of both (10 or 11 chromosomes).

This is a great system, but it has one shortcoming: there is no standard
way to distinguish a dwarf bearded set from Iris pumila (8 chromosomes)
from a tall bearded set (12 chromosomes). I use "P" for a pumila set and
"T" for a TB set. With this modification, one can easily communicate about
the chromosome makeup of all irises with bearded and aril ancestry, and
describe the different types unambiguously.

A = aril (from oncocyclus or regelia; 10 or 11 chromosomes)
P = dwarf bearded (from pumila, attica, or pseudopumila; 8 chromosomes)
T = tall bearded (but also including the smaller species such as aphylla,
    variegata, reichenbachii, and suaveolens; 12 chromosomes)

Here's how the notation shakes down for some common types of garden irises:

TTTT   tall bearded and border bearded (plus tetraploid IBs and MTBs from
       aphylla breeding
TTTP   conventional IBs
TTPP   conventional SDBs (plus MDBs from SDB or aphylla/pumila breeding)
TPPP   conventional MDBs
PPPP   MDBs from pure pumila breeding

TT     conventional MTBs

AA     oncocycli, oncogelias, most regeliocycli, and diploid regelias
AAAA   tetraploid regelias and tetraploid regeliocycli
AAT    triploid 3/4-breds from diploid aril x halfbred breeding
AATT   halfbreds (CGWhite-type amphidiploid arilbreds)
ATTT   conventional quarterbreds)

APTT   conventional arilbred medians from SDB/halfbred breeding
APT    arilbred dwarfs and arilbred medians from SDB/aril breeding
AAPP   arilbred dwarfs from tet.aril/pumila breeding

There are other combinations, of course, many represented by real irises
that do not fit one of these categories. But the list probably covers more
than 95% of irises in commerce with aril or bearded ancestry.

I find this notation very useful, and I'd like to see it (or something
similar) become widespread. I even put this stuff on my garden labels!

I'll post some classification ideas in a separate message.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Tom Tadfor Little                   telp@Rt66.com
Iris-L list owner * USDA zone 5/6 * AIS region 23
Santa Fe, New Mexico (USA)
Telperion Productions  http://www.rt66.com/~telp/
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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