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RE: Tetraploids

  • Subject: RE: Tetraploids
  • From: halinar@open.org
  • Date: Fri, 29 Jun 2001 22:54:01 -0700 (PDT)

Jim:

>First, Ben states that you can have tetraploid x tetraploid 
>sterility, but has anyone ever seen this in Hosta?  I assumed that 
>tetraploids crossed easily.

Think of tet hostas as if they were diploids with 120 chromosomes 
instead of 60, because that is the way fertile tets will behave.  A 
tet hosta that is fertile is fertile because it has diploid like 
bivalent pairing.  If you look at these hostas under a microscope you 
will see 60 pairs of chromosomes lined up at meiosis and it would look 
just like a diploid.  As a matter of fact hostas are probably already 
ancient amphidiploids.  All the fertility problems that are present 
with diploids will also be present with tetraploids.  

>Ben has determined that Sum and Substance is a triploid (topic of 
>discussion at the National Convention), However it would be a rather 
>fertile tetraploid.  I would be curious what you opinion is.  

I have not used Sum and Substance.  I don't know if hostas have 
triploid block or not.  If hostas do have triploid block then we would 
expect to see few triploids.  Triploid block is not 100% effective.  
Some triploids can be reasonable fertile.  Triploid lilies are quite 
common and many of them will produce some seeds with tetraploid 
pollen, but rarely with diploid pollen.  If Sum and Substance is a 
triploid, then I suspect that tet pollen would be more likely to set 
pods on Sum and Substance then diploid pollen.

>But in any rate, these are the criteria that we use to determine a 
>'presumed tetraploid.'  <snip>  1)  The thickness of the leaf 
>increases and the leaf becomes more shiny.  This means that the
>plant also has more substance.  2)  The plant grows more slowly and 
>often to a smaller size.  3) The plant is harder to TC especially 
>when it come to making roots.

If you have a sport of a hosta and can compare them, then leaf 
thickness and substance may be a clue to suggest polyploidy.  However, 
I suspect that flower size may be a better clue.  Also stomata size 
and pollen grain size should also be larger, and both are relatively 
easy to measure.  Unfortunately, I don't have any good examples of a 
tet sport that I can compare to its diploid parent.

Mary:

>If it works, will I get fertile tets that are easier to work with?

I can't answer the specific question you refered to, but as a general 
rule tets become more fertile the longer you work with them.  
Tetraploid daylilies got their start in the 60's and fertilty was a 
major problem, along with some other serious problems, but today the 
tets are generally very fertile.  

Ben:

>I dont understand how a discussion about tets at the convention 
>could be meaningfull without the only person who has actually 
>investigated the subject present.

Could you please tell us who this person is?  And why can't there be a 
meaningful discussion of tets without this person being present?  And 
why do you think this person is the only one who has ever investigated 
tets in hostas?  I haven't seen or read anything about this person or 
the research this person has or is doing.  Who ever this person is, it 
sure would be nice if this person would present his or her data and 
results so we could all learn from this great individual.

Joe Halinar
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