Stabilizing my first cross

[Mark_Thompson]

I do want to try my hand at this whole tomato breeding thing, but it's intimidating. I've watched enough YouTube videos on the actual act with the tweezers and all that I think I can muddle through it.

So here's my theory, I have a small wild/volunteer red cherry from my friend's house right down the street. This plant has zero signs of Septoria, in spite of every other plant around getting blasted with it. Is it silly to cross it with something big, KBX for example? Should I stick to trying to cross it with another cherry? Also I read over on Tville back in the day that if you cross a RL with a PL, that you can tell whether your cross took when the seedlings are little, which seems cool to me. I don't think I'm emotionally equipped to wait months only to find the exact same wild cherry I started with.

Any and all advice for a first timer is totally welcome.

[Shule]

KBX is potato leaf. So, if your cherry is regular leaf, you'll want to pollinate KBX with your cherry's pollen, rather than the other way around. Then, if the seeds from KBX turn out to be regular leaf, you should have a cross.

[Toomanymatoes]

You can cross whatever you want. However, do not expect to see a large slicer like KBX until further generations (if ever).

The first cross, F1, will all be regular leaf. It is a dominant trait. You wont' see any with potato leaf until the next generation, which is F2. Even then, only 25% will be PL. That does not necessarily mean 1 out of 4 grown, but more like 25 in 100. So, you have to try your luck. I am not sure what a good number would be, but the more the better.

Even if you do get PL, it does not mean you will have resistance to Septoria. Again, I am not sure of the genetics behind Septoria resistance, but you have to select for it in your subsequent generations. If for some reason the resistance gene is located near the RL/PL gene you will be in luck as chromosome segments generally migrate together.

It is generally accepted that a variety is 'stable' after 8 generations. So, you have to select at F2 and continue to select for several generations after that.

Here are some examples of the variability you can see in the F2 generation:

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This site provides some good information on genetics and crossing:
http://kdcomm.net/~tomato/gene/genes.html

[Shule]

If the F1 cross isn't resistant to Septoria, then it's probably a recessive trait; so, you'll have to grow out a bunch of F2s to find the resistant ones.

[Tormato]

I do want to try my hand at this whole tomato breeding thing, but it's intimidating. I've watched enough YouTube videos on the actual act with the tweezers and all that I think I can muddle through it.

So here's my theory, I have a small wild/volunteer red cherry from my friend's house right down the street. This plant has zero signs of Septoria, in spite of every other plant around getting blasted with it. Is it silly to cross it with something big, KBX for example? Should I stick to trying to cross it with another cherry? Also I read over on Tville back in the day that if you cross a RL with a PL, that you can tell whether your cross took when the seedlings are little, which seems cool to me. I don't think I'm emotionally equipped to wait months only to find the exact same wild cherry I started with.

Any and all advice for a first timer is totally welcome.

My first thought would be to save seeds from tomatoes of that plant, which I believe you have done since you want to cross it with something. I like the idea of finding PL varieties to cross with, as it will not waste time if the cross was not made. I'd also try to have several of the wild/volunteer plants next growing season (year-round?), to see if there is any variation in tomatoes, along with Septoria resistance.

I'll let others recommend types of tomatoes to cross with.

[bower]

Plenty of good advice already! Tormato makes a really good point, do save seed from the disease resistant parent for future growouts. Depending on the season and other environmental conditions it can be tough to select for disease resistance unless you have the resistant plant to compare, just how bad is it getting. It's always helpful to have a parent plant in your growout to see how similar or different the kids are for some trait. Also, in the event your first crosses might fail, or not be as tasty as hoped, you can use this parent again with some other tomato in another year. and finally, supposing your cross turns out amazing, you might well want to breed more amazing tomatoes with this lucky parent!!

I've seen that advice about PL crosses so many times, but honestly, I've never seen a crossed fruit that turned out to have selfed. Not once in, what, a dozen years?
The real key to avoid selfing is to choose a flower at the right stage of maturity. If you can emasculate before the petals turn dark yellow, you should be good. I try to pick a new cluster at a convenient height on the plant for me to see what I'm doing. When the first flower is at the stage where it's going to fully open the next day, there is usually a second flower in the cluster not far behind. I will emasculate both of them for the cross, so I have two chances. Also noted, that plants tend to lavish their care on the first fruits in a cluster, this increases your chances of success. Some people also remove the uncrossed flowers from the cluster (I don't: fruit pig. The first fruit in the cluster still get the benefit of their station.).
The interesting thing, these flowers are not fully mature and not necessarily ready to receive pollen at the time you remove the anthers. The pistil has a knob at the end - this knob is bigger on a multi-locule fruit and smaller on a cherry but you'll see it on both, and it continues to develop after emasculation. When the flower is actually ready to receive pollen the knob becomes sticky. I always pollinate on the same day and then repeat my cross two or three times on consecutive days, looking for the pistil to make a clear line in the pollen pool (collected on a shallow lid or lens) which tells me it was sticky and receptive, and gathered a load of pollen as I dragged it gently across the pollen covered surface. There is often a difference in maturity rate for flower #1 or #2, which might need an extra day to reach the same level of maturity. With luck you will get two crossed fruit, and if you have any doubts about flower #1 being already too mature at the time of crossing, you can use the seeds from fruit #2 to be on the safe side.

So IMO there is really no need to restrict your choice of parents to a PL mother, in order to confirm in F1 that the RL father pollinated.

Another thing I've learned from experience is that some plants make willing mothers for crosses, while others do not! There's no way to know which plant is friendly to being crossed until you tried it. Those that reject crossed fruit are difficult or impossible to work with. For example, I tried for years repeatedly to get my Oaxaca Jewel PL to be mother to a cross, and failed every single time. I finally used her as a pollen donor instead. But for a person trying their first cross, this would be a disaster - you would think you were doing it wrong.
So choose your parents based on your desired qualities, not leaf type, and do a reciprocal cross if you want to maximize the chance of combining those two parents (assuming you've never worked with them and determined if they are good 'mothers' or not).

The first time I did any crosses, my success rate was 50%. As years have gone by, I still often had no better than 50%. So I have built in some redundancy with the expectation that half of the crosses may fail. That way I am not often completely disappointed. It's not a difficult process, but there are a lot of things that can go wrong, including what is up to the plant, to reject a fruit if they don't want to grow it for any reason. So build some extras into your plan, and try out different parents too, so the first experience will also boost your confidence.

[Mark_Thompson]

@Toomanymatoes
That link with the eggs is awesome

[Mark_Thompson]

Thanks everyone, lots to think about. I’m not set on KBX, just threw that out there as an example of a big slicer. Does a cherry x slicer always, sometimes, or never result in another large tomato? The cherry is red, should I cross with something with a similar color just to not be working with so many variables?

[Pippin]

Good comments all, just wanted to add that the PL rule applies to any recessive trait that expresses early, e.g. using a dwarf mother in a cross with a normal father gives normal non-dwarf F1. But have to agree with @Bower that if the cross took and the flower set a fruit, it tends to be a successful cross.

What I typically do when growing the F1 from a RL x RL crosses is to sow some 5-6 mother seeds in one pot and same amount of F1s in another at the same time. When growing them side by side in the same conditions, I have always been able to tell that the plants in these two pots are in fact different although all are RLs. The F1s may grow slightly faster, have larger leaves, have more rounded or sharp leaflets etc than the mother seedlings. You may need to wait for a couple of true leaves but definitely not until you see the F1 fruit. And if you doubt the success, you can try another cross with the same mother even befor you see the F1 fruit.

[Shule]

Thanks everyone, lots to think about. I’m not set on KBX, just threw that out there as an example of a big slicer. Does a cherry x slicer always, sometimes, or never result in another large tomato? The cherry is red, should I cross with something with a similar color just to not be working with so many variables?

Big fruits sometimes do happen with a beefsteak-cherry cross, but it seems like it's pretty rare in my observation (and don't expect it to be big again necessarily the next generation; they seem to get smaller every generation, until they're stable, usually). It seems like bigger fruits more often occur when the mother plant has bigger fruit, but that could just be coincidence (and doesn't have a basis in what I know about genetics, unless such as mtDNA or cpDNA, or etc. relates to fruit size).

@Bower
Keep in mind I don't actually cross-pollinate my stuff manually. I find natural crosses and work with those (so, the PL trick is important for me). That's good to know that it's easy to avoid it self-pollinating, though, and I'm sure Mark appreciates it!

[Mark_Thompson]

Does anyone remember the name of the member who has the Septoria resistant variety Lorelei? Maybe we could tag him and see if he might have something specific to add

[bower]

In a cherry x beef cross your F1 will be a cherry. In order to select for larger fruit you need to grow lots of F2.
Basically in shape/size genetics you have the two locule condition of a cherry, which is dominant, and you have a gene called locule number that increases the number to five.
You then have an additional shape gene that adds massively to the size, called 'fasciculated' or fas for short. This greatly multiplies the number of locules in the fruit. Afaik I believe fas is never expressed unless locule number is already present.
In order to recover beef shape and largest possible size, you need to select for fruit that have both locule number and fas in the F2 or F3.
Besides the shape genetics that contribute to size, there are several QTL type loci for fruit weight. Different combinations will give you a different size.
So overall, size and weight is complex to select.
Frogsleap wrote an interesting analysis that showed a skewed distribution towards smaller fruit.
But this just means you have to grow out more to find them, and select for size in every generation.

[Mark_Thompson]

So I decided to go with a red antho cherry as the mother. I had a hell of a time getting pollen from my friends wild type, those ittybitty flowers are tough. I tried six and looks like I got one. Going to baby this fruit like I’ve never babied a cherry before If it ends up being self pollinated there’s a high likelihood I actually cry.

I’m also growing the Septoria resistant plant myself so I can keep playing with it going forward, but it’s about 3” tall still.

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[Tormato]

If it turns out self pollinated, I want to see the youtube video of you crying, in 3D, and super slow motion, with quadraphonic audio of the teardrops hitting the ground.

[Tormato]

Fusion_power is the one who knows about Lorelei.

[Mark_Thompson]

Well my one fruit ripened. It only had five seeds in it. Is that a good sign? I feel like if it self pollinated it would have the normal amount? Anyways, fermented, dried, planted, alongside some seeds from the mother, so I guess I’ll know in the next few weeks if I’ve got a F1 or if I’m recording myself crying in slow motion quadraphonic 3D for the YouTube…

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[bower]

@Mark_Thompson I've had crossed fruit with only a half dozen seeds before, and they were true crosses.
Now that I think about it, I recall this happening specifically with the more difficult 'mother' plant. So not surprising it took six to get one fruit - and awesome that you did!

[Mark_Thompson]

Well got my first (hopefully F1) plant in the pot. I think it looks slightly different from the mother, but that may be wishful thinking.
So how do I know for sure, wait for fruits and if they look different I’m good?

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[bower]

Is that antho cherry red or orange, Mark?
Anthocyanin (Aft) has a capital A, which usually means a dominant trait. That means you will see it in the F1.
Red is dominant, so F1 fruit will be red. Except with a Beta orange, you can get Orange-red, and see the Beta/- there too.

[Mark_Thompson]

Red is the color under the antho. The pollen donor is also a red fruit.