Another Lycoris question

Jim McKenney
Sun, 16 Aug 2009 15:48:29 PDT
Adam wrote: “Jim.  The backcross in this case would be  squamigera pollen
onto either of its putative parents.  The reciprocal (reverse)  cross is not
the same…”


We'll have to let Jim Waddick weigh in on this one, but I doubt very much
that he meant what you are trying to say he meant. In fact, I think what he
was suggesting was neither a simple back cross nor a reciprocal cross. As I
understand what he wrote, he was trying to suggest ways of getting Lycoris
squamigera to set seed. 


The back cross with respect to Lycoris squamigera would be (if we accept its
parents as Lycoris longituba and L. sprengeri) a cross of the progeny of the
original cross (L. squamigera) on to its putative parents. But it makes no
sense to attempt this cross. Why? Everything which I've read about breeding
with triploids stresses that to use triploid pollen is to court failure.
One typically applies tetraploid pollen to the triploid plant, never, in
practical terms, the other way around. It's not that it's impossible; it's
just that the probabilities are stacked against success when triploid pollen
is used. That's why I believe that Jim Waddick was not suggesting a simple
back cross. 


Reciprocal crosses have nothing to do with what we are discussing. A
discussion of reciprocal crosses would be interesting in trying to reproduce
the cross which originally (or if there were multiple instances,
subsequently) produced plants answering to what we call Lycoris squamigera.
But that was not what we were discussing. 


On the other hand, if Jim Waddick was talking about things more likely to be
in the realm of the possible, then crosses of Lycoris sprengeri pollen or L.
longituba pollen onto L. squamigera might have some chance of success.
Trials using diploid pollen on triploids are in rare cases successful, but
success in those cases depends on the serendipitous failure of a pollen
gamete to undergo reductive division. This might explain the success
Caldwell reported using what he knew as Lycoris chinensis. Note that we do
not know what really happened in the situations Caldwell reported. The
viable seeds he got and germinated might have been hybrid seed or it might
have been seed produced by apomixis. In the latter case, any seedlings would
have simply been yet more Lycoris squamigera. 


And the arithmetic rules you cited, important as they might be in their
relevant contexts, have nothing to do with what we are talking about here.
Adam, if you would like to take on another assignment in which you could
strut you arithmetic stuff, then explain to the group why triploid plants
are less likely to yield successful results when used as the male parent in




Jim McKenney

Montgomery County, Maryland, USA, 39.03871º North, 77.09829º West, USDA zone

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