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Old January 8, 2018   #1
maxjohnson
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Default Crossing tomato noob question.

How important it is to decide which should be the male and which the female plant, and does it matters at all?

Thanks.
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Old January 9, 2018   #2
Ann123
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I've been wondering about that too.
I read somewhere on a blog (forgot where) that it doesn't matter but that it is easier to take the plant with a visual recessive trait as mother. So if you cross a yellow mother with a red father you should see red fruit in the first generation. If you see yellow fruit it got self pollinated.
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Old January 9, 2018   #3
dfollett
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Quote:
Originally Posted by Ann123 View Post
I've been wondering about that too.
I read somewhere on a blog (forgot where) that it doesn't matter but that it is easier to take the plant with a visual recessive trait as mother. So if you cross a yellow mother with a red father you should see red fruit in the first generation. If you see yellow fruit it got self pollinated.
Ann is correct. Another example that would tell you if the cross was successful very early is a Potato leaf mama and a regular leaf papa. If the cross is successful, the F1 will be regular leaf. If the F1 is potato leaf, the plant is a self of the mama instead of a cross.

If you made the same cross with the RL as the mama and the PL as the papa, the F1 will always be RL and you wouldn't know if the cross were successful until you grew out the F2s. If the cross were successful, 1/4 of the F2s would be PL.

Other than that, there would be no difference in future generations.
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Old January 10, 2018   #4
Ann123
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Thank you. Maybe I read this on your blog?
I think this summer I will try for the first time to make a cross.
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Old January 10, 2018   #5
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Well.. it is not entirely true that the choice of mother doesn't matter in all cases. That's because some traits (which may or may not be important to you) are more or less strongly affected by maternal DNA - that is, mitochondrial DNA and chloroplast DNA, which come only from the mother plant. I've read for example that specific traits including earliness, cold tolerance, potassium metabolism and even sweetness of the fruit can be affected by the mtDNA and cpDNA of the mother. As I understand it, it may be more difficult to recover the trait if it is coming from the pollen donor instead of from the mother plant. Not to say impossible, but you may end up having to grow more plants perhaps? I actually noticed this effect in some of my breeding lines, and had to go back and reconsider a backcross using an early mother, where the earliness I hoped for didn't turn up in the F2. It was easy to find early plants in that cross!

So it can sometimes matter.
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Old January 10, 2018   #6
BigVanVader
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We should turn this into a noob breeders thread, cause I'm doing my first crosses this year as well and this stuff is very confusing to me. I'm so ADD I have to read everything over and over before I understand it.

For example, how do you know what traits are recessive vs dominate? Also is there a good book that would be helpful?
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Old January 10, 2018   #7
Ann123
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Thank you, Bower. Very interesting. Since earlyness and cold tolerance are important for me (living in a cool climate) I should the plant with those characteristics as a mother.
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Old January 10, 2018   #8
bower
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BVV no worries, we are all reading it over and over again.
There are some good resources online for tomato genetics. For example this list of known genes:
http://tgrc.ucdavis.edu/genes.html
As regards recessive or dominant, you'll find the dominant traits by convention start with a capital letter, recessive with a small letter, as you scroll down the list.

So for example...
Beta - for beta-carotene orange fruit, is dominant written with a B

sp - "self pruning" aka determinate, is recessive.
pl potato leaf, gf "green flesh" , these common concerns are all simple recessives

But what is more complicated, some traits that are "additive" aka "QTL"s or "quantitative trait locus" iirc, may look like recessives but they aren't really.. If it was all Mendelian with no linkages either, it would be so much easier... but you wouldn't get as many surprises, and they can be good. Surprises can be the best part.
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Old January 10, 2018   #9
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I love reading about other peoples' projects so I hope you all keep us posted on your new crosses this summer!
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Old January 11, 2018   #10
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Thanks bower. Here is another question. I'm growing a bicolor det. from Joseph Lofthouse. It is early and cold tolerant. If I crossed your cross with that, then backcrossed the F2 back to yours. Wouldn't that increase the odds of finding the det/early/black fruits/earthy flavor genes? I'm going to do several different crosses this year.
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Old January 11, 2018   #11
dfollett
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Quote:
Originally Posted by bower View Post
Well.. it is not entirely true that the choice of mother doesn't matter in all cases. That's because some traits (which may or may not be important to you) are more or less strongly affected by maternal DNA - that is, mitochondrial DNA and chloroplast DNA, which come only from the mother plant. I've read for example that specific traits including earliness, cold tolerance, potassium metabolism and even sweetness of the fruit can be affected by the mtDNA and cpDNA of the mother. As I understand it, it may be more difficult to recover the trait if it is coming from the pollen donor instead of from the mother plant. Not to say impossible, but you may end up having to grow more plants perhaps? I actually noticed this effect in some of my breeding lines, and had to go back and reconsider a backcross using an early mother, where the earliness I hoped for didn't turn up in the F2. It was easy to find early plants in that cross!

So it can sometimes matter.
Thanks for the correction and clarification, Bower. I'm a noob also.
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Old January 11, 2018   #12
Fred Hempel
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Back-crossing clearly would favor the traits of the parent you are back-crossing to.

It also delays for another generation the process of developing a true-breeding line.

But, if you have a very specific set of traits you are looking for, back-crossing is very, very helpful.

The other approach to stacking a bunch of traits into one line is to take a hybrid approach. If you have a few true-breeding parents that can contribute the traits you want, making a number of hybrids is another way to try to construct a line with all the traits that are most important to you.

The hybrid approach does require probably 4-6 prospective parent lines. But, for example, if you had 6 lines that you though might be good parents you could easily make 20 unique crosses.

But, using a hybrid approach does require that if you want to have recessive traits show up in the hybrid, you will need both parents to be recessive.

Quote:
Originally Posted by BigVanVader View Post
Thanks bower. Here is another question. I'm growing a bicolor det. from Joseph Lofthouse. It is early and cold tolerant. If I crossed your cross with that, then backcrossed the F2 back to yours. Wouldn't that increase the odds of finding the det/early/black fruits/earthy flavor genes? I'm going to do several different crosses this year.
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Old January 11, 2018   #13
BigVanVader
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My brain just melted.

To clarify for my benefit. So your saying make 6 specific crosses or 6 pollen donors then cross that with the mother plant?

Quote:
But, using a hybrid approach does require that if you want to have recessive traits show up in the hybrid, you will need both parents to be recessive.
So if I wanted a PL det I would have to use 2 PL varieties correct?
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Old January 11, 2018   #14
Fred Hempel
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Yes, if you want a potato leaf hybrid, both parents need to be potato leaf.

No. With a hybrid approach, the ultimate goal is for an exceptional hybrid that you produce over and over.

The crosses are unique crosses between parents

For example, if you have 6 parents, the crosses you can make are --

1 X 2
1 X 3
1 X 4
1 X 5
1 X 6
2 X 3
2 X 4
2 X 5
2 X 6
3 X 4
3 X 5
3 X 6
4 X 5
4 X 6
5 X 6

15 total crosses (not 20)
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Old January 11, 2018   #15
bower
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Quote:
Originally Posted by BigVanVader View Post
Thanks bower. Here is another question. I'm growing a bicolor det. from Joseph Lofthouse. It is early and cold tolerant. If I crossed your cross with that, then backcrossed the F2 back to yours. Wouldn't that increase the odds of finding the det/early/black fruits/earthy flavor genes? I'm going to do several different crosses this year.
Cool! I've been meaning to grow that one myself... You could get some really interesting fruit, and they'll all be determinates from the F1 onward.
I'm not sure at all about the genetics of bicolor - not much is written about it, and I haven't done any bicolor crosses so no observations to report.. KarenO could tell us something about the ratios that she got.
In any case, it is independent of the gf (black fruit).
So just to answer about your backcross plan, at least for the simple recessive black fruit gf,
JL bi F? (-/-) X Rodney F4 (gf/gf) - the F1 will be (gf/-) so not black.
(Since the parents aren't stable, you can expect variation in the F1, so I would advise to grow several and take F2 seeds from the best. )
JLbiR F1 gf/- X Rodney F5 gf/gf would give you 1/2 black offspring
while the growout of JLbiR F2, the odds of gf/gf are 1/4.
(You also have the same odds of (-/-) in the F2, that is, no gf allele 1/4. And 2/4 will be gf/- so although not black the allele is still there. If you backcrossed the F2 to Rodney F6 randomly in this generation, the odds of black fruit would be 3/4).
So you don't need to wait til F2 to increase the odds of black fruit and flavor genes from Rodney if you want to do that. You could also cross back to Rodney after you ID the black fruit in F2 if you want to, for 100% black fruited with variance in the other traits.

Traits like taste, cold tolerance, earliness are complex and they are additive involving multiple QTL's (many genes involved). What is really cool is that you can get unique flavors emerging from combination of parents, also earliness and cold tolerance combinations that are an improvement on either of the parents.
That is not even to mention the 'tricolor' effects from crossing black and bicolor.
So the main thing really is to play along with what nature provides you to select from. If you have the chance to do some backcrosses, do them and stash away the seeds, is my attitude. You may decide you want to use it somewhere down the line.

I will be interested to hear, whether Joseph's bicolor is earlier and more cold tolerant than Rodney. There is room for improvement, always!
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