Micro dwarf x Indeterminate cross ideas.

[KaguyaCloud]

It seems that there isn't much information that I can find with regards to breeding micro dwarf tomato varieties with more flavorful indeterminate plants, but I'll try to list what I've found so far.

There are 2 described recessive and 1 unidentified recessive genes responsible for the stature of micro dwarfs specifically:
- The self pruning(SP) gene located in chromosome 6, which causes the determinant growth habit.
- The dwarf gene(d) located at chromosome 2, which causes a compact growth habit and dark, rugose leaves.
- An unidentified miniature recessive gene(mnt) responsible for shortened internode leaf length.

One study(second source) did a cross of Micro-tom with a determinant tall parent and found that 6/176 plants exhibit the Micro-Tom phenotype. Ratio of about 1:32 would indicate that there are 2 non-linked recessive genes responsible for compact growth habits.

So here's the classical idea for breeding two strains:
- Cross micro with an indeterminate tomato to create an F1. Make sure the mother plant(one growing the fruits) is the dwarf so - that it is easier to determine if the cross is successful.
- Collect seeds from the F1 to grow the F2.
- Grow all the F2's.

However, because we need to select for 3 recessive genes, the chances of an F2 generation exhibiting all 3 recessive genes(SP, d, mnt) is 1 in 64 or 1.56%. That's not great of a chance.

Here's an alternate proposal instead:
- Cross micro with an indeterminate tomato to create an F1. Make sure the mother plant(one growing the fruits) is the dwarf so that it is easier to determine if the cross is successful.
- Cross the F1 with the parent micro dwarf plant to get a back crossed generation(BC1).
- Grow BC1. Now the chances of getting a micro dwarf phenotype is 1 in 8 or 12.5% chance.

This is a less time consuming version, but this also means that BC1 is inheriting only 25% of the DNA of the non-dwarf parent.
Continually crossing of micro dwarf BC1 back with F1 would increase the percent of DNA of the non-dwarf parent while also maintaining a 1 in 8 chance of obtaining the micro dwarf phenotype.

Let me know if I got anything wrong.

Sources:
https://academic.oup.com/jxb/article/57/9/2037/622929
https://sci-hub.ru/https://doi.org/10.1 ... 12061465.x

[Frosti]

@KaguyaCloud, Interesting proposal, some thoughts:

2) This is not a way to save on time. It's a way of saving on space. With this technique additional backcrossing generations are added on top.

3) Yes, repeating the pattern of:

i) backcross with the immediate micro dwarf predecessor
ii) select for micro dwarfism (1/8) + backcross with indeterminate target
-> repeat

is an interesting way of guided breeding. If my calculations are correct the genes left from the original micro dwarf parent and indeterminate parent respectively should look like this for the first 7 generations:

genes.png

Backcrossing with the immediate micro dwarf predecessor happens at odd xs and backcrossing with the indeterminate target plant happens at even xs.
This is a worst case calculation, in reality most of the genes are presumably already identical anyway ...

Edit: Just noticed this thread exists twice...