Thread: Backcrossing
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Old May 6, 2015   #15
Darren Abbey
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Join Date: Jun 2012
Location: Minnesota
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Quote:
Originally Posted by maf View Post
Dissecting the Genetic Pathway to Extreme Fruit Size in Tomato Using a Cross Between the Small-Fruited Wild Species Lycopersicon pimpinellifolium and L. esculentum var. Giant Heirloom

Minnesota Mato, I don't know if you have seen the above study, but it uses a cross between a pimpinellifolium and a giant fruited domestic tomato to identify the QTL's that contribute to fruit size. Six loci were identified that made a significant contribution to fruit weight, two of the most significant mapping to the classical genes fasciated (f) and locule number (lc). Not all six of these may be in the large fruited variety in your cross but it is likely there are at least three or four including f and lc so it is going to take some serious selection to recover the size you desire.

If it was me, I would select for size first and color second. For example, if I found a type that was huge fruited but red, I would grow that out in preference to one that was medium sized and black, in the hope that it segregated for gf in the next generation. Actually, a very good backcross would be the largest fruited red (or black) F2 and the green parent, I think that would give you a very big push in the right direction.
I knew that the f and lc traits were important in fruit size, as well as an unnamed gene that results in larger cells (and therefor larger seeds and fruit), but I didn't realize there were likely to be three others as well.

The more genes contribute to the large size you're looking for, the more plants (or years) you'll have to work on it... no matter if you can use backcrossing to reduce the numbers you'll need.

I'll set about checking the numbers for six traits, assuming all are recessive(?), and we shall see what sort of task you're engaging in.
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