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Minnesota

Any experienced tomato pollinaters here. I was told that if I did cross two different genetic lines it takes up to 3-6 years to do so to fix to the desired traits, select over several generations to get the true cross? what does that mean? if I grow plant A x Plant B and got plant C, would I plant plant C the following year pollinate with the father plant, mother, any help would be appreciated. To get all the desired traits it should have.

1/4/2012 2:58:30 PM

Mount Vision, NY

Hey Richard, what you're asking could easily be the subject of a book and most likely is somewhere. The answer your looking for depends on what traits your looking to add to your new variety and if those traits are recessive, dominant or even need modifiers genetically. Most likely once you make your first cross of two different lines and get your F1 generation you would cross them and select in the F2's the traits you're looking for and recross those to get your F3's and recross and reselect again for the traits your looking to breed into you new line. It generally takes several generations to do so.
Does that make sense?

1/4/2012 5:06:31 PM

Minnesota

Yes, keep re-crossing, but, with what? with mother father or the plant now with both mother and father. Would that be your decision, the grower that would make that new seed the seed you set out to make?

1/4/2012 6:03:47 PM

Mount Vision, NY

Let's just say that you like some of the traits of Tomato Line A and some of the traits from Tomato Line B and you'd like to combine those traits into a new line called 'Richard's Wonder'. You'd start by crossing Line A with Line B and getting your F1's. These could be all over the place trait wise. What I would do is select those with the most traits you are looking to meld together in 'Richard's Wonder' and cross them together. From these you get your F2's and then you do the same thing. You could cross back into either parent line, BUT then you'd be linebreeding on that line and basically be heading back to where you began and not really combining the traits of both lines that way. Your best bet is to selectively breed down through your hybrid generations, F1, F2, F3 and so on, always selecting those traits your looking to put together in 'Richard's Wonder' and crossing them together.

1/4/2012 7:36:38 PM

Minnesota

Thank You, learning tons about tomato's.

1/4/2012 7:58:04 PM

Owensboro, Ky.

shouck65, sweet, simple to understand explanation...thanks!!! Peace, Wayne

1/7/2012 2:36:54 AM

That State Up North

Richard

I have a MS in tomato breeding, here is the timeline: We wanted 6-8 generations after the initial hybrid. The F1 may be quite consistent, but when you plant the selfed F2 it will show the variation. Variation is what you want when begging so you have something to pick from. Plant a lot of plants in F2-F4 generations (100+).
To save on years you can get 2-3 generations in a year by growing extra early plants (mine are already started), pull seeds out in May, plant them again in May, then as soon as the fruit show what you need to make a selection pull some seeds in August-September. Making the third generation will require extra heat/light for Sept-Jan growing period. You can easily grow 2 generations per year without much extra heat/light.
This allows you to finish the project easily in 3-4 years or less. Just remember that if you are selecting for flavor characteristics those change through the season with light and soil temp

good luck


Nic Welty

1/12/2012 5:02:13 AM

Minnesota

So you must grow indoors in the winter? F2-F4 100+ that equals out to 33 a generation? is this just for more to pick from to continue generations? would it still work with just a couple plants per generation? does it mean I will just have less to choose from?

1/12/2012 8:07:24 AM

East Carbon, Utah

How many generations and how many plants per generation will depend also upon how genetically similar the two parent varieties are.

F1 hybrids should, in theory, contain all the genetic material (genes) of the two parents when you cross-pollinate two true-breeding, open-pollinated varieties.

The dominant alleles (variants of a given gene) will be expressed (phenotype - what you actually observe) in the F1, while the recessive alleles will not.

When you do an F1xF1 cross to get the F2 generation, you could potentially get every combination of the alleles. Depending upon how many genetic traits differed among the original parents, you might need 20 plants or you might need 200 to assure that you get the desired phenotypes to be expressed in the F2 generation.

Even with a cross between two very similar cultivars, it could still take 3-4 generations to get the traits fixed (i.e. in the homozygous state) in the genetic line you're developing.

Imagine a cross between two vastly different varieties, such as Banana Legs and Belmonte! I won't even bother listing all of the different genetic traits one would need to consider. Even at 3 generations per year, it could still take quite a few years to get a stable, true-breeding cross - and that's assuming you relentlessly select for traits decided upon from the outset. No room for waffling in this business!

1/12/2012 5:05:33 PM

East Carbon, Utah

The more plants you produce from a given cross, the better chance you have of seeing the phenotypes you are looking for. The fewer plants you produce, the greater your chance of losing some of the alleles which you are interested in.

Even if you are looking at only 4 traits, you could get as many as 16 phenotypes in the F2 generation. If the 4 traits you are looking for all happen to be recessive, then mathematically (based upon simple Mendelian genetic inheritance), only 1 in 256 plants in the F2 generation would produce the desired phenotype. In this rare and unlikely scenario, you would be finished with the selection process at the F2.

If the traits you are looking result from dominant alleles, you will need to do repeated back-crosses (to the original parents, if possible), until you can demonstrate mathematically that you have a true-breeding strain (i.e. homozygous dominant). This demonstration alone would require dozens of plants.

If the trait is co-dominant or blended, then you may never be able to get a stable cross, at least not for that trait.

Of course the real-world commercial breeding of hybrids gets much more complicated (epistasis, multifactorial inheritance, novel mutations, etc.) than the overviews we've given here.

But please don't get discouraged about crossing two of your favorite varieties! You'll just need a goal, good record keeping, good technique, a little land, dedication, and plenty of patience.

At a minimum, consideration of these challenges gives us a little more respect for the hard-core tomato breeders and an appreciation for why hybrid varieties are so ubiquitous.

1/12/2012 5:06:13 PM