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Re: hosta-open DIGEST V1 #985


>I have been working with some crosses this year trying to mix 
>Tretraploidi hosta with the standard Diploidi type.

Some plant genera have what is called triploid block.  When you cross 
a tetarploid with a diploid you would expect a triploid, but with 
triploid block the triploid embryos abort.  Supposely, Ben Z. has done 
some ploidy level studies with hostas, but hasn't presented any of the 
data on this robin.  I believe his studies revealed at least some 
triploids, but the presence of triploids in a genera that has triploid 
block doesn't invalidate triploid block.  Potatoes have a strong 
odd-ploidy block - triploids and pentaploids.  Potates are either 
diploid, tetraploid or hexaploid.  There is actually a genetic 
mechanism for this breakdown in triploid block, but it's difficult to 
understand.  If you cross diploids with tetraploids and consistently 
do not get any seed set, then you can expect triploid block.  
Daylilies have triploid block, but true lilies, genus Lilium, does not 
have triploid block.  If you do have triploid block and cross a 
diploid with a tetraploid and get seeds, then the diploid is producing 
unreduced gametes and acting like it is a tetraploid, and thus will 
produce tetraploid progenies.  If you do have a triploid it is better 
to use it as a pod parent then as a pollen parent.  Many triploids 
will produce a few viable egg cells.  I'm not sure about hostas, but 
in lilies triploids used as a pod parent usually do the best when 
pollinated with tetraploid pollen.

Joe Halinar

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