Backcrossing

[crmauch]

Yes, that's pretty much the 'chart' I was looking for. In this case on this page: http://kdcomm.net/~tomato/gene/genes3.html it has a way to enter the number of recessive genes and it gives you the number of plants.

However - can you not speed the selection for dominant genes by following a line of a plant? For each plant that has the set of genes you want, plant out a large number of plants (keeping each set of seeds segregated by parent). If over a very few generations that "line" is not having the recessive gene being expressed, won't you have bred out the recessive in a speedier fashion? This of course assumes other factors like taste, productivity, etc aren't being affected. If none of our lines are 'pure breeding' for the dominant gene, you have to start selecting the best out of your still segregating lines.

Originally Posted by carolyn137

I think that same information is also given at Keith Mueller's website in a very different way where he explains and gives numbers as to how many gens need to be grown out to give different percentages of purity.

http://www.kdcomm.net/~tomato/

Go to Culture, there go to tomato gene basics, read that and then click on the segregation link at bottom of that.

Carolyn

[bower]

Originally Posted by Fusion_power

Selecting in the F2, then doing the cross with the best F2 plant(s) is usually the best choice. There is a factor of how much chromosome fragmentation occurs from cross-over. Doing a backcross using an F2 allows for more effective selection as the fragments become smaller.
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These concepts are very interesting to me, but haven't been able to do an effective search to learn more about fragment size in different filial generations and how that impacts breeding.
Minn Mato, I have a really small space to work in, so it's hard to grow enough plants at once to find a stack of recessive genes in one plant - my plan is to look for one recessive at a time, and if I can find two of the desired traits in two F2 plants, I'll cross them... That may not work for a six gene trait like fruit size though, if you can't tell which traits are present.

As regards fruit size, I think the smallest fruited can be identified at the bud stage - flower buds very small at maturity. That's what I'm seeing here as I try to select before planting out. Also the 'beefsteak' type buds (example Indian Stripe, Black Early) are fat and round, a different shape from the typical pointed bud of a cherry or a heart or small fruit, in the group of seedlings I'm working with...

[Darren Abbey]

Originally Posted by bower

Minn Mato, I have a really small space to work in, so it's hard to grow enough plants at once to find a stack of recessive genes in one plant - my plan is to look for one recessive at a time, and if I can find two of the desired traits in two F2 plants, I'll cross them... That may not work for a six gene trait like fruit size though, if you can't tell which traits are present.

The problem with this strategy is that when you cross the two F2s with different homozygous recessives... you end up with a new F1 that is heterozygous for those alleles and you have to then look for the multiple-homozygous progeny again.

[Minnesota Mato]

It is very interesting to see how many different ideas and different ways there are to achieve the same goal. I realize the art isn't in the crossing but in the care and the selecting of the following generations. Anyone can make a cross but knowing what to look for and finding it in the following generation is what makes a plant breeder.

[crmauch]

I agree with you, but crossing is an art too. I remember my first year (when I was still trying to vibrate blossoms to get them to expel pollen (I found a *much* better method next year). and with breakage of styles when trying to strip the blossom for pollination. I got only one success take that year.

Last year I got many takes, and would have had even more crosses than I had if late blight hadn't devastated me mid-August.

Originally Posted by Minnesota Mato

It is very interesting to see how many different ideas and different ways there are to achieve the same goal. I realize the art isn't in the crossing but in the care and the selecting of the following generations. Anyone can make a cross but knowing what to look for and finding it in the following generation is what makes a plant breeder.

[bower]

Originally Posted by Darren Abbey

The problem with this strategy is that when you cross the two F2s with different homozygous recessives... you end up with a new F1 that is heterozygous for those alleles and you have to then look for the multiple-homozygous progeny again.

Yes, this could happen, but the odds of seedling A being heterozygous for the recessive trait found in seedling B and vice versa are better than none. If recessives are one from each parent, you go back to square one for one trait when backcross to the parent. Backcrossing to the F1 is an even better strategy that gives a 1/2 chance of finding the recessive in the subsequent generation.

Not that I think this is a best way to proceed, but humbly submit in my circumstance I can only take my chances, stir the pot and enjoy the journey for as long as it lasts.

[Darren Abbey]

Originally Posted by bower

Yes, this could happen, but the odds of seedling A being heterozygous for the recessive trait found in seedling B and vice versa are better than none. If recessives are one from each parent, you go back to square one for one trait when backcross to the parent. Backcrossing to the F1 is an even better strategy that gives a 1/2 chance of finding the recessive in the subsequent generation.

Not that I think this is a best way to proceed, but humbly submit in my circumstance I can only take my chances, stir the pot and enjoy the journey for as long as it lasts.

Agreed. Fortunately all the plants that don't reach the ideal you're going for will still produce perfectly edible fruit. ;-)

[Fusion_power]

Fortunately all the plants that don't reach the ideal you're going for will still produce perfectly edible fruit. ;-)

Does this mean we get to eat our mistakes? I saw a bumper sticker a few months ago that said "in case of _______, eat the kids first!". Substitute your favorite disaster in the blank.

I have 46 plants of a Sunlucky line growing in the garden in hopes this particular group will be the ephemeral much desired stable cross that produces super sweet bicolor fruit the size and shape of an egg. It takes a LOT of space to do significant selection for fruit traits.

[bower]

Originally Posted by Fusion_power

Does this mean we get to eat our mistakes? I saw a bumper sticker a few months ago that said "in case of _______, eat the kids first!". Substitute your favorite disaster in the blank.

I have 46 plants of a Sunlucky line growing in the garden in hopes this particular group will be the ephemeral much desired stable cross that produces super sweet bicolor fruit the size and shape of an egg. It takes a LOT of space to do significant selection for fruit traits.

I was thinking about that, that you'd need to grow out a lot to verify a stable OP for release, after the seven year selfing, and the selection of the fruit traits which also takes more space.

I hope you got it, but if not... you're going to need some help to eat all those mistakes.
I'd love to know more about the process of taste testing 46 similar or identical fruit... you should make a video.

[Keen101]

interesting discussion. I'm looking into trying my hand at growing and perhaps even attempting crosses with wild tomato species this next summer.

I just learned that Purple Smudge has some S. peruvianum heritage so since S. peruvianum is one of the harder crosses to do i'm wondering if attempting a backcross with Purple Smudge x S. peruvianum would have a higher rate of success since some wild genes may still be floating around (though perhaps very little at this point).

It seems the orange version of Purple Smudge is the only one now commercially available, so i'm not sure if that further dilutes the wild genetics even more. But regardless i think i'll give it a go if i can. I've ordered some seed for the orange fleshed Purple Smudge anyway. Worth a try in my opinion. In my experience sometimes tinkering with things will occasionally pay off. And if not, i'll have fun trying anyway.

I gather from the other species that are more easily crossed they are still essentially one-way crosses by using the more domesticated parent as the pollen receptor since there are fewer genes that will reject it. This seems to hold true with other species like teosinte -> corn crosses and others. So thinking of that it would be best to try using Purple Smudge as the receptive parent and S. peruvianum as the pollen donor.