Re: RE:HYB:Oranges

In a message dated 11/23/00 6:38:52 AM Mountain Standard Time, Chuck Chapman 
writes:

<<  the tangerine
 factor appears to be partially recessive (speculation)rather then completely
 recessive. This means that it continues to influence the colour of the 
yellow.
 I say this as I have been pulling pink out of yellow by carefully looking at
 the plant (in light of pedigree) and speculating on its genetics. This has
 proven to work for me. Thus a yellow that has 3 tangerine genes will still be
 yellow, the shade of yellow will be distinctly (sometimes subtally) different
 from a yellow with no tangerine genes.  >>

As it worked for many others before you, dating back to Orville Fay!  

I have long been fascinated by the various mechanisms proposed to explain how 
the t-factor actually works.  Unfortunately, although I've read everything I 
can get my hands on and corresponded with some knowledgeable hybridizers, I 
have not been able to grow enough of this type to develop the fabled "eye".  

In hopes that your observations hold the key:

One of the older theories was that the t-factor acted as a switch, directing 
carotene production to either beta-carotene or lycopene. Because 
beta-carotene is such an intense pigment, it must be eliminated for the pink 
to show through -- so that four doses of the t-factor are required to get 
pink and the trait appears to be recessive.  IF this is the case, seedlings 
with 3 doses of the t-factor should be YELLOW-ORANGE with just enough pink to 
set them apart from those without the t-factor.

A newer theory proposed a more complex explanation: a "switch" that directed 
the conversion of neurosporene to either the gamma/beta-carotene pathway or 
the lycopene/alpha-carotene pathway, plus an inhibitor that then blocked the 
conversion of lycopene to alpha-carotene.  IF this is the case, those with 3 
doses of the t-factor should be YELLOW with just a hint of pink that sets 
them apart from those without the t-factor.

It sounds as if your observations support the newer theory -- but I don't 
want to jump to conclusions.  PLEASE elaborate a bit on the subtle 
differences you see.

Sharon McAllister

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