Origin of Modern TBs

Diana Louis asked me to expand a bit on "how modern TB's got here, especially
with this large number of species as progenitors": 


It's easier to understand if you look at what happened in three stages.

The oldest varieties came from crosses between various diploid species.  In the
pedigrees I've traced, I. pallida and I. variegata are the most prevalent -- but
one of the problems in puzzling out TB history is that many decades passed
between the time this work was done and the registration system was established.
For many early varieties, not even the parents are known, much less the
ancestral species, but it's generally accepted that the diploid TBs were
descendants of the European diploid species.

Similarly -- but many years later -- the early tetraploid varieties were
produced by crosses among the various tetraploid species.  By this time, there
was a growing interest in pedigrees so more information is available concerning
exact species background.  The tetraploid species came from around the
Mediterranean -- hence their undoubtedly well-deserved reputation for being less
cold-hardy -- but they were valued for their larger flowers, better form, and
good substance. 

Modern TBs are descended from these two groups.  When a diploid and tetraploid
are crossed the offspring are normally relatively infertile triploids but
once-in-a-while the diploid parent will contribute an unreduced gamete and the
result is a fertile, tetraploid offspring.   SNOW FLURRY is a famous example.
Superior offspring resulted from crossing breakthrough breeders like this back
to varieties derived solely from the tetraploid species, and the ones that
combined the gardenability of the diploids with the flowers of the tetraploids
came to dominate the gene pool.  Today's TBs have evolved so far from their
ancestral species that they are really a new fertile family -- what some term an
artificial species.

Hope this thumbnail sketch helps  --  I'm sure our historians on the list can
supply more details.

Sharon McAllister
73372.1745@compuserve.com
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