breeding IRL Backcrossing vs Selfing

[P.E.RSPEP]

Hello, I'm wondering how much does homozygosity increase with each backcross to an established variety compared to each selfing of the filial progeny from an initial cross.

In your experience, how many generations of backcrossing would be required to end up with a stable strain?

I'm testing with an online inbreeding calculator.
On paper, with backcrossing with the same plant, the inbreeding coefficient increases the same each generation as with selfing.
And assuming the recurrent parent strain is a pure inbred one, the COI is the same in the first backcross as in the F2's.

But here is the thing, inbreeding coefficient and homozygosity are different things. COI estimates the average chance an allele would be identical by descent, but from what I understand, the possible range of homozygosity goes from 0 to double that of COI.

In my mind, the craziness of recombination makes selfing more unpredictable than using a recurrent inbred parent although on paper It doesn't seem to be that way. So I wanted to know your IRL experiences.

My projects involve what I believe is a recessive trait, which complicates things more. I'd be faster if it were a dominant one.

When the trait of interest is recessive, and you need to produce F2's of each backcross, the process slows quite a bit. (Inbreeding increases slower). I'm assuming that using the same overwintered plant each generation will help. But still...
Maybe I could come up with a test breeding method to speed things up...

 

[PollenNut]

Hello, I'm wondering how much does homozygosity increase with each backcross to an established variety compared to each selfing of the filial progeny from an initial cross.

In your experience, how many generations of backcrossing would be required to end up with a stable strain?

I'm testing with an online inbreeding calculator.
On paper, with backcrossing with the same plant, the inbreeding coefficient increases the same each generation as with selfing.
And assuming the recurrent parent strain is a pure inbred one, the COI is the same in the first backcross as in the F2's.

But here is the thing, inbreeding coefficient and homozygosity are different things. COI estimates the average chance an allele would be identical by descent, but from what I understand, the possible range of homozygosity goes from 0 to double that of COI.

In my mind, the craziness of recombination makes selfing more unpredictable than using a recurrent inbred parent although on paper It doesn't seem to be that way. So I wanted to know your IRL experiences.

My projects involve what I believe is a recessive trait, which complicates things more. I'd be faster if it were a dominant one.

When the trait of interest is recessive, and you need to produce F2's of each backcross, the process slows quite a bit. (Inbreeding increases slower). I'm assuming that using the same overwintered plant each generation will help. But still...
Maybe I could come up with a test breeding method to speed things up..

There are DNA tests that can actually give you a true co-efficient of inbreeding rather than a paper/pencil test. Having paid for a few of the DNA co-efficient of inbreeding tests I can tell you that your actual results can and will vary from the calculations you might do.
What is more important than any calculation or DNA test is the actual results you get and the actual selections you make. Grow out 1 plant each generation and you are not going to be making selections other than those that are made by chance and random assortment in that one seedling you have sown.

Sow out more to get more results and to have something to compare your results with. You can't pick the best very easily if you are not giving yourself several chances... i.e. sowing out larger numbers.

On the subject of actual backcrosses, I have made many some with both animal and plant species. In fact, I just sent out a few envelopes with many different backcross attempts as well as outcross attempts to Jalapeno and Poblano for free. What matters more than calculations are actual results and having fun. The moment it ceases to be fun I'm out of there.

Random independent assortment happens each and every time with a cross. Chromosome crossover... there is so much at play that, for me at least, I just suck it all in and try to gift and grow out enough to find a fraction of the possibilities that are hidden in many of the crosses I have made.

 

[P.E.RSPEP]

I know! more fun would come from growing lots of F2 and F3's and so on...
If I only had more space LoL

I don't want to go into details of this exact project cus I'm still waiting for germination of the F1's. And it might all fail.
Although two seeds have already sprouted in paper towel.
Plus I did some more reading, and I'm waiting to get another variety to use as the recurrent parent. To develop a second line.

I also want to experiment with grafting induced heritable variation. As it seems (from old research) the rootstock could influence the same polygenic trait of interest in the scion as the one I want from the recurrent parent. Which is pungency (somewhat quantifiable).

The funny thing is that the trait I hope to introduce is high capsinoid content, which results in a loss of pungency due to a dysfunctional pAMT gene (hopefully).
So subjective evaluations for heat levels would only be possible in each backcross. As the F1s would technically be the same. And I wouldn't have a way to know other than with a test cross if the most pungent F2's carry the desired dysfunctional gene, so given the choice, I'd rather spend another generation backcrossing than testing.

What I might end up doing is to backcross once, select the most pungent maybe do this twice, but then proceed to self-pollinate. Way faster, to stabilise the cross, but I still got to decide. I might keep Backcrossing until the recurrent plant dies!

 

[Prof.Urabay]

I know! more fun would come from growing lots of F2 and F3's and so on...
If I only had more space LoL

I don't want to go into details of this exact project cus I'm still waiting for germination of the F1's. And it might all fail.
Although two seeds have already sprouted in paper towel.
Plus I did some more reading, and I'm waiting to get another variety to use as the recurrent parent. To develop a second line.

I also want to experiment with grafting induced heritable variation. As it seems (from old research) the rootstock could influence the same polygenic trait of interest in the scion as the one I want from the recurrent parent. Which is pungency (somewhat quantifiable).

The funny thing is that the trait I hope to introduce is high capsinoid content, which results in a loss of pungency due to a dysfunctional pAMT gene (hopefully).
So subjective evaluations for heat levels would only be possible in each backcross. As the F1s would technically be the same. And I wouldn't have a way to know other than with a test cross if the most pungent F2's carry the desired dysfunctional gene, so given the choice, I'd rather spend another generation backcrossing than testing.

What I might end up doing is to backcross once, select the most pungent maybe do this twice, but then proceed to self-pollinate. Way faster, to stabilise the cross, but I still got to decide. I might keep Backcrossing until the recurrent plant dies!

This is a really interesting project. I hope your F1s germinated successfully. Have you made a decision on how you will proceed?

 

[P.E.RSPEP]

This is a really interesting project. I hope your F1s germinated successfully. Have you made a decision on how you will proceed?

Unfortunately only two seeds germinated and none survived.