Re: MDBs continued (and an MTB question to boot.)

John Montgomery wrote:

>  Would you please elaborate on 'parallel lines'?

By this I mean lines that have their own, separate purposes, but interact=

within an overall plan.  This will be easier to explain by example.

I started with foundation stock of diploid arils, tetraploid arils, diplo=
id
TBs and tetraploid TBs.  Each of these is a separate fertile family. =

Members of each group can be crossed among themselves to produce fertile
cultivars, some of which are worthy of introduction.  They can be treated=

as completely independent groups, which fit the intuitive definition of
parallel lines.

My original goal was to make enough crosses and grow enough seedlings to
understand how C.G. White had obtained his fertile arilbreds.  At the tim=
e,
it was widely believed that even White himself didn't know how he'd done
it.  After reading the bits & pieces published about his work, I conclude=
d
that he had worked with a quite detailed master plan.  The only thing he
didn't know was EXACTLY which cross had produced the breakthrough in
fertility because of the type of record-keeping he'd had to resort to in
order to work on such a massive scale. =


So I reconstructed his master plan to the best of my ability from various=

published references and proceeded to test my theories.  My primary
measure-of-success was to be the production of cultivars subjectively
indistinguishable in appearance from advanced-generation C.G.White-type
halfbreds, and genetically compatible with them.  At the same time, I hop=
ed
to produce a more gardenable line.

I made my first crosses in this program in 1977.   If I had worked strict=
ly
from that foundation stock, progressing one generation at a time, I would=

not yet have attained that goal -- but I've made enough progress that I
believe I could do it in another twenty years using foundation stock alon=
e.
 I've already obtained answers to almost all of my questions, though, by
adopting two time-saving strategies.  =


The first was to supplement foundation stock with cultivars from other
hybridizers.  I gave up hybridizing TBs many years ago -- it's just too
difficult in this climate.  So the TBs I use are not my own line, but a
collection from other hybridizers chosen for the traits I want.  My clima=
te
is also too hot for many tetraploid arils, so I import additional breedin=
g
stock for this line. =


The second was to add parallel lines in advanced generations.  For exampl=
e,
 a 1/3-type triploid is the product of a first-generation cross.  I've
raised some of these, but this is a very difficult cross to make in my
climate and few seedlings survive to bloom size.  So I've used some of Ge=
ne
Hunt's for my experiments. Similarly, a quarter-bred is the product of a
second-generation cross, so if I had worked strictly from foundation stoc=
k
I couldn't have made a quarter-bred X tetraploid aril cross until the thi=
rd
generation.   But I have been able to test my theories by using existing
quarterbreds to make such crosses "in parallel" with those in my basic
line.  BTW, I learned that the majority of the resultant seedlings were
indeed indistinguishable from conventional halfbreds in appearance and
fully compatible with them.  =


This is what I meant in my earlier message by the time-saving use of
parallel lines.  It can be extended to any type of complex, long-term
program because it's really nothing more than making use of existing plan=
t
material for crosses that test your theories' predictions.  =


Sharon McAllister
73372.1745@compuserve.com
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