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Old January 19, 2018   #29
crmauch
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Join Date: May 2013
Location: Honey Brook, PA Zone 6b
Posts: 399
Default Linkage Blues (Back to the drawing board)

Wanted to post about what I've realized about the Hi-Beta breeding I've been attempting.

The tomato I'm trying to achieve is a high beta-carotene, indeterminate paste tomato.

At this time, I'm going to ignore the "paste" part and concentrate on achieving a high-beta indeterminate tomato.

However the gene for high-beta (B) is located on the same chromosome as the gene for indeterminate/determinate (which is noted as sp (self-pruning) so indeterminate is (sp+). The linkage is close enough that I've now realized that it is unlikely to break for the numbers of plants I can deal with (20+ with up to 45 or so if I grow no other tomatoes). So I have realized for breeding purposes I have to effectively treat the beta gene and it originating growth type as a unit.

There is a third gene I want for this tomato - designated as mog. This is a modifer gene that increases the beta carotene from 50-60% to near 90% only in the presence of the high beta gene. the one I want is the recessive form (I'm going to use just (m) as the designator for this gene in the further parts of this post.

So the tomato I want to ultimately acheive is sp+sp+BBmm

Again the genes are
sp+ - indeterminate
B - high-beta carotene (50-60% when alone)
m - in the presence of B increases beta-carotene to ~90%.

The main 4 tomatoes I've worked with thus far:

97L97 - A high beta-carotene breeding tomato genetics (spspBBmm) (it's determinate)
Jaune Flammee - high-beta french tomato without the modifier gene: (sp+sp+BBMM)
Opalka and Shannon - for this purpose they have similar genetics: (sp+sp+bbMM)

All these tomatoes have the R (red) gene which I'm going to ignore for the moment, but I wanted to note that B does not 'work' in the presence of the other form of yellow/orange tomatoes that are caused by the recessive (r) gene.

The one advantage I have is the coloring of the tomatoes shows me the beta/modfier genetics:

bb-- (modifier gene doesn't matter the fruit will be red )Red.png
B-M- (high Beta without modifier gene with be orange-red (orange, then developing an red blush (although the blush can be slow to appear) OrangeRed.png
B-mm (High Beta with modifier gene will be orange and never develop a red blush)Orange.png

So a cross between 97L97 and Opalka yields an F1 Hybrid of sp+spBbMm OrangeRed.png

and a cross with Jaune Flammee and Shannon yielded an F1 Hybrid of sp+sp+BbMM which is also OrangeRed.png

I thought of crossing the two hybrids but the results were disappointing. Also in looking at the Punnet square that instead of the 8X8 square you'd think of with 3 separate genes it is much smaller because you're handling the sp gene and the beta gene as a locked unit:

Hybridcross.png

So I considered taking either of my original F1s and BC to the other Beta

(97L97 X Opalka) X Jaune Flamme

HybridOp97BCJF.png

The F2 generation look like this (depending on whether the seed you got is MM or Mm

BC97xOpBCJFF1Breedout.png

I actually like the BC of the 97L97 back to the Jaune Flammee X Shannon slightly better:

HybridJFShBC97.png

And the resulting F2s:

BCJFXShBC97F1Breedout.png

So I'm going to do that and I'm also going to cross Jaune Flammee and 97L97:

The F1:

JFx97F1.png

And the resulting F2:

JFx97F2.png

And all this is long before I get to breeding toward a paste!!!!
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