Newbie Crossing Question

[NYTomatoNewbie]

If I take pollen from a regular leaf plant, and pollinate a flower of a potato leaf plant, when I collect the fruit off of the potato leaf plant, if the offspring is RL the cross worked, but if it is still potato leaf the cross failed? Is that correct? I know the actual pollination time and procedure is not that simple, but I was thinking that is the easiest way to tell in this scenario if cross was successful without having to grow to fruiting.

[Hornad]

Yes

[bower]

The PL mother trick means you can tell if your cross was successful, before you have invested months of growing time and space.

[NYTomatoNewbie]

Thank you for confirming.

[wykvlvr]

You can do the same with chartreuse foliage or carrot leaf in place of the potato leaf. This little trick means when I do the crosses I have planned I can use the big plant with funky foliage as the "mother" parent and the micro dwarf as the pollen donor. These types of crosses are very helpful as they allow you to know in the seedling stage if your cross was successful

[NYTomatoNewbie]

Thank you for the tip!

[NYTomatoNewbie]

Taking the scenario above where I pollinate a PL with RL and collect seeds from the PL, if it worked I get RL….

If I then grow out two of the RL and cross them, do I have a 25 percent chance that each time I will get a tomato with PL seeds, 75 % chance RL? So if I wanted to get a potato leaf for F3 I would have to do numerous crosses to increase PL likelihood And them germinate and see if any PL pop up. Does that sound right?

[wykvlvr]

You can do it that way but don't have to.
Lets assume you made your cross between the pl and rl those seeds are F1 and will have one gene for pl. When you plant those seeds the F1 plants will be fairly similar looking rl plants. Let your F1 self fertilize and save seeds from those and plant them. That is your F2 generation. Plant out the F2 seeds and start picking out features you want. There is a 25% chance of pl showing up in those plants and if potato leaf is your main requirement you can actually start culling any regular leaf that show up in the seedlings. On the other hand if there are more criteria then leaf type you can wait and cull when they fruit and you can see which you like the taste of. The more F2 seeds you plant the better the odds of finding something special or that you want to carry forward.
You can of course keep back crossing as you mentioned instead or do both if you have room.

[NYTomatoNewbie]

@wykvlvr Thank you for the explanation, very helpful!

[bower]

Yes, the RL F1 generation should be all identical and genetically identical, assuming that both parents are stable OP's.
You will only get F1 genetic variation if one parent is unstable genetically (an F1, or an F2, or any generation short of F7 or 8).
As such it isn't necessary to cross two of them, as the selfing result is the same. and the ratio as wykvlvr pointed out 1:3 or a quarter potato leaf.
If you wanted to increase the chance of pl in the next generation, you could backcross the F1 (RL/pl) to the potato leaf parent or to any other potato leaf parent that you want in the mix (pl/pl). The F1 of that cross will be fifty fifty RL and PL.
I've done this before for recessive traits that are hard to select early on - determinate for example takes couple months of grow before you can see whether it has the trait or not. So it makes my job a lot easier and reduces the space constraint to use a backcross or side cross to double up on the desired trait.
With potato leaf, it's a trait that is easy to see early on in the life of a seedling. So as long as you have the steely nerve to firmly trash all the little RL's, it's not too difficult to grow four times the number of seedlings you have space for, and only keep the PL plants.