F2 Tomato Question
 

Can someone please help me understand something about tomato breeding and genetics.

To my understanding once you successfully crossed 2 tomatoes, and get F1 seeds (say from a single fruit), all the F1 plants and fruits should be the same. The dominate genes from each plant coming through on the F1 cross.

My question is about the fruit from the F1 plant, producing F2 seeds. I know F2 is where it starts to get interesting and we can pick up the recessive traits again.

Can someone tell me if the variations come per seed, per fruit, or per F1 plant?

ie. if you take "one" fruit from "one" F1 plant and get say 100 seeds, will those seeds theoretically have all the genetic combinations for all the different possible breed out targets? or do you need multiple fruits from the same plant? or multiple fruits from multiple plants?

I do understand the more seed you have and the more you grow the more possible combinations you have, but is 1000 seeds from 1 tomato on 1 plant the same as say 1000 seeds from 100 tomatoes from 10 plants?

Hope this question make sense?

Thanks

Mark

If the parents were both stable (i.e. homozygous) lines, then all seeds, from all fruits, from all F1 progeny plants will have the same genotype. In the F2 generation all plants will have a different genotype, with independent segregation for each gene that differed between the original parents. The F3 seed produced on those F2 plants will again segregate. To maximize the chance of getting the "perfect" combination of the best genes from each parent, you need to plant as many F2 progeny plants as possible. Once you harvest seed from the best F2 plants, it's about finding F3 progeny that continue to express the favorable gene combinations - and again large population size helps. If you are confident there is no cross pollination, fruit number is irrelevant, it's seed (i.e. progeny) number that counts.

So let's use an example from the Dwarf Project.

Patrina crossed Golden Dwarf champion (female, small to medium yellow fruited dwarf) with Green Giant (male, large green potato leaf). she emasculated a flower on GDC and added pollen from Green Giant - the tomato developed, and all seed from that developing fruit are F1 seed, which should be identical (unless a bit of stray pollen from another variety snuck in). And that is what we found - all of us who grew this variety - which she named Sneezy - got indeterminate, regular leaf plants with medium sized yellow fruit. (Expression of the dominant traits).

So you pick one of those Sneezy fruit and save the seed - and you get all sorts of things (those are F2 seeds - so the variety of plants you get is the F2 generation being grown out). We got RL and PL indeterminates, PL and RL dwarfs, and in the dwarf growouts, we got small to large yellow and small to large green fruit on the various foliage types (we didn't grow out any of the indeterminates, but would have seen the same).

What we then found - say, we selected a nice RL yellow dwarf, F2 fruit but the seeds are F3. Growout of the F3 continued quite a lot of variation (I think having recessives for color and foliage in the cross contributed to the great variation and instability in this line) - and from that we got PL and RL dwarf, yellow and green fruit.

Interestingly, when we select an F2 that expressed both recessive traits (PL and green), stabilization happens in fewer generations.

Anyway - this is what is so fascinating about all of it! And yes, the best way to see the possibilities is to grow out as many F2, F3 etc plants as possible.

[quote]but is 1000 seeds from 1 tomato on 1 plant the same as say 1000 seeds from 100 tomatoes from 10 plants?[/quote]Yes, the exception is when one or more of the parents has even slight variation.

Got it. This is all super helpful.

So my key question has been answered.

In theory when breeding for a new tomato strain, at the F1 plant stage producing F1 fruit with F2 seeds in them, you really only need 1 plant and 1 good fruit to get seeds from.

It's at F2, F3, F4 etc plantings that the more plants you have the better you are able to hone in on the characteristics that you want.

This mean the average Joe (or Jane), if they want to breed out some tomatoes they can do a heap of different F1 generation in a small green house (or under grow lights) over winter, since you really only need 1 plant per cross and one fruit per cross. They can then plant out the larger number of F2 plants come summer.

Thanks for the information!

Mark

That's exactly what I did with my Galina's Yellow / Snow White cross - made the cross in summer and grew a single F1 plant over winter. It's an easy way to leap ahead a year.

So how come when some crosses take as long as F5-6 in stabilization but the likes of the Dizzy F2 that i'm growing at the moment are showing very little variation.:?!?:

The F2 generation will segregate at all loci for which there were different alleles in the F1 parents. The more similar the parents for the F1, the less variation in the F2. Often times dissimilar parents are used maximize genetic variation in the F2, and it takes several cycles of selection/selfing (e.g. F5-F6) to stabilize a line combining the desired combination of parental traits.