Re: Hybridization...

Chick:

>Over time, all streaked plants will revert to single color or
>variegated plants, and when a streaked plant no longer produces 
>streaked leaves and instead, produces leaves that are all uniformly 
>colored, they are considered stable.  At that point, they no longer 
>produce streaked or variegated seedlings.

Your comments here are interesting as this is a question I asked Jim 
Hawes in some private email in regard to the formation of variegated 
hostas.  I'm interested in understanding the nature of variegated 
hostas and how they are created.  The fact that you mention that 
streaked hostas have to be constantly divided to maintain the streaked 
form suggest that these streaked forms are mericlinal chimeras.  A 
hosta seedling that germinated variegated and was stable would be a 
periclinal chimera.  However, there is a problem in figuring out how 
variegated hostas are created, and I would like anyone to comment on 
the following.

Regardless of whether or not the pod parent was a stable periclinal 
chimera or a unstable streaked mericlinal chimera, all hosta seedlings 
start out as a single cell.  A egg cell fertilizes with a sperm cell 
to produce a single cell zygote.  A single cell zygote can not be a 
chimera.  Thus all chimeras are lost when they go through a sexual 
process.  The single cell zygote divides into two cells, then 4, and 
onward until it forms a dormant embryo. A single cell zygote doesn't 
have  L1, L2 or L3 layers.  Somewhere between the single cell zygote 
and the dormant embryo the developing embryo develops the three 
histogenic layers.  

Now, here's where the problem arises.  All three layes have to have 
the same cytoplasm because they all came from the same single cell 
zygote.  There is no way that a hosta seedling can develop a 
cytoplasmic periclinal chimera, much less a mericlinal chimera.  Thus, 
there shouldn't be any variegated hosta seedlings if the variegation 
is based on some cytoplasmic factors.  Also, some stable periclinal 
chimeras that form from streaked hostas should also produce variegated 
seedlings.  A streaked hosta will likely produce ovules that are 
derived from both the L1 and L2 layers since these hostas are most 
likely mericlinal chimeras.  However, the important point is that each 
ovule can only come from either a L1 cell or a L2 cell, but not both. 
In a stable periclinal chimera most of the ovules will develop from L2 
tissue.  A stable periclinal variegated hosta formed from a streaked 
hosta is going to be producing ovules derived from the same L1 or L2 
tissue of the streaked parent, so why shouldn't they also produce 
variegated seedlings?  

Joe Halinar

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