Re: HYB: Getting It Straight For the Simple Minded - RePost

In a message dated 5/8/05 10:20:03 PM Eastern Daylight Time, 
steve@familyszabo.com writes:

> Now, I've seen on this list that there are varieties of iris that are 
> called
> tetraploid when referring to their genetic make-up. This means that instead
> of having the one normal set of chromosomes, they have two sets. This,
> apparently, increases the varietal possibilities from those iris so far as
> bloom, color, growth, etc. are concerned, looking for some sort of "ideal"
> combination. Is this correct so far?
> 
> When dealing with tetraploids, there may be some fertility issues between
> various varieties, but, for the most part, one is fertile with another.
> Correct?
> 
> A question about the tetraploid state. Was this caused by chemical means, of
> which I recall some talk of here, or was this a natural happenstance when
> crossing between varieties or species?
> 

Hi Steve,

I can answer part of your questions.  Tetraploids have four sets of 
chromosomes instead of two as in diploids.  Your second paragrah is correct.  In 
bearded irises, some species are normally diploid and some species are normally 
tetraploid.  Usually, when a diploid is crossed with a tetraploid you end up with 
a sterile triploid.  However, Mother Nature in her wisdom sometimes allows a 
tetraploid to result.  Modern tall bearded irises have evolved from crosses of 
tetraploid species with each other and crosses of diploids with tetraploids 
that resulted in tetraploids.  Someone else can give you the scientific 
explanation of this.

What you have been hearing about tetraploids being induced chemically 
primarily involves Siberian and Japanese irises.  Check lists for these types of 
irises specify whether each variety is diploid (the natural state) or tetraploid 
(now mostly advanced generations from the chemical change).  Modern tall 
bearded irises are assumed to be tetraploid unless otherwise stated, however, many 
historic irises are diploids.

I am not experienced enough in the arilbred area to answer any questions 
about them.

Hope this helps a little.

Dorothy Willott in Northern Ohio

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