Very good flavor but splitting issues

[jmsieglaff]

Hi all,

I'm hoping those of you with more extensive tomato breeding experience can chime in here.

I have a dwarf project cross I'm working with, in 2020, I had a GWR cherry tomato with very nice flavor and excellent production--the problem was the tomatoes split like mad, as in half of them were useless. These tomatoes were grown in the same size containers as all the rest, grown in the same mix, fertilized the same, watered the same etc. etc. I'd like to capture the positives of that GWR lead but obviously lose the tendency to split so easily. I only have room for 2 or 3 plants--would I be better off growing seed saved from the splitter or go back one generation of seed and try there? I am guessing going back one generation is probably best as the genetic combination to lend to splitting may very well be tough to avoid in seed from the splitter.

Thanks in advance!

[Tormato]

I'm wondering if the shorter thicker main stems of dwarf indeterminates draw up more water, faster, than a typical indeterminate, and would lead to more splitting than normal. Good luck on the project, as it sounds like a tough challenge.

[Pippin]

Difficult problem indeed.

I have seen splitting prone F2 becoming more split resistant in F3, so at least I assume it can happen. IDK if dwarfs in general are more prone to splitting.

You could do some kind of stress test for your current GWR line, e.g. dumping some 20 or more plants into a (friend’s) backyard corner, overwatering them on purpose and selecting the best performer. Try to figure out how to grow more than 2-3 plants without wasting your valuable but limited container resource.

[bower]

I've been working with lines that were non-splitting from F2 stage which later threw a thinner skinned, softer fruited individual in the F4. I didn't grow that one out so IDK if that trend would reverse, but its appearance reinforced my impression that non-splitting traits like firmness and strong skin are dominant, and the splitting traits fruit softness and thin/weak skin are recessive.
However, those are complex traits and very likely QTLs are involved rather than or in addition to simple dominant/recessive genes.
There might also be some recessive gene in there that is epistatic to the firmness traits.
I'm speculating about the complex genetics involved, because one individual from the number of plants grown is not many. Unlikely explained by a single recessive gene.
Also, besides firmness and skin traits, fruit shape is a very complex characteristic, and plays a major role in whether fruit splits or not.
I was playing with a line involving many different shape traits, and got some super splitting fruit which seemed to be based on shape alone, as other fruit traits were not distinguishable from the sibs.
Quite possibly Pippin's F2 was splitting on shape genetics which afterwards continued to segregate and improved the condition.
I didn't grow on the lines of mine that turned toward splitting so I have no personal experience that they would not reverse the trend. These are just impressions based on the small frequency of splitters that showed up.

Bottom line, if you only have 3 spaces you don't have enough plants to determine if the condition is recessive or whether it will segregate out in the future generation, which you might find if you could grow many plants as Pippin does. You're basically depending on luck at this point.
As a small space grower, I would suggest that you mix it up. You still have a chance of another splitting fruit from the back generation, so I would probably try two from the back to seek out non splitting and one forward for the taste. Or vice versa, depending on whether great taste or non-splitting was most common in the previous.
If you find the great taste and the splitting in the forward generation, but not in the back, backcross to the non splitting fruit and grow that out. It will take a few extra generations to stabilize.
You could also grow three of one generation or the other per year and see what comes. The advantage of mixing it up is that you have the option of backcrossing to get the traits you wanted.

[Tormato]

I've been working with lines that were non-splitting from F2 stage which later threw a thinner skinned, softer fruited individual in the F4. I didn't grow that one out so IDK if that trend would reverse, but its appearance reinforced my impression that non-splitting traits like firmness and strong skin are dominant, and the splitting traits fruit softness and thin/weak skin are recessive.
However, those are complex traits and very likely QTLs are involved rather than or in addition to simple dominant/recessive genes.
There might also be some recessive gene in there that is epistatic to the firmness traits.
I'm speculating about the complex genetics involved, because one individual from the number of plants grown is not many. Unlikely explained by a single recessive gene.
Also, besides firmness and skin traits, fruit shape is a very complex characteristic, and plays a major role in whether fruit splits or not.
I was playing with a line involving many different shape traits, and got some super splitting fruit which seemed to be based on shape alone, as other fruit traits were not distinguishable from the sibs.
Quite possibly Pippin's F2 was splitting on shape genetics which afterwards continued to segregate and improved the condition.
I didn't grow on the lines of mine that turned toward splitting so I have no personal experience that they would not reverse the trend. These are just impressions based on the small frequency of splitters that showed up.

Bottom line, if you only have 3 spaces you don't have enough plants to determine if the condition is recessive or whether it will segregate out in the future generation, which you might find if you could grow many plants as Pippin does. You're basically depending on luck at this point.
As a small space grower, I would suggest that you mix it up. You still have a chance of another splitting fruit from the back generation, so I would probably try two from the back to seek out non splitting and one forward for the taste. Or vice versa, depending on whether great taste or non-splitting was most common in the previous.
If you find the great taste and the splitting in the forward generation, but not in the back, backcross to the non splitting fruit and grow that out. It will take a few extra generations to stabilize.
You could also grow three of one generation or the other per year and see what comes. The advantage of mixing it up is that you have the option of backcrossing to get the traits you wanted.

Any heavy splitting non-grow outs that were extra early, tasty, non-green gel types? Asking for a friend.

[bower]

@Tormato I will put up a post with some pics of ye olde non-green-gel curiosities, I promise! February time? It's coming...

[jmsieglaff]

Appreciate the thoughtful replies. Growing a large number of plants isn't an option for me, but yes in a perfect world that would be an option. @Bower you're onto to something with doing 2 plants from one generation back and 1 from the splitter. Still a lot of time to ponder whether I want to chase this GWR lead this year or follow another color lead.....I'm sure I'll change my mind 10 times between now and seed sowing in late March.

[Pippin]

Found this interesting summary of tomato fruit cracking theories, just sharing a link and a quote here. Many new aspects here that I have not considered before. I am not sure if cracking and splitting are exactly the same thing, but there at least are different variants and types of tomato fruit crackings, they are not all the same. Also, I haven’t thought before that e.g. low fertility (few fruits in the plant) or sweet taste might increase the risk for cracking.

According to the above theories, the greatest probability of cracking occurs when a large- fruited cultivar sets relatively few fruit. These fruit have a high soluble-solids content and are exposed to direct sun. The skin of this cultivar has little ability to stretch or resist puncture from the turning stage to the pink stage of ripening. Culturally, the cultivar is grown under conditions that result in rapid fruit growth, such as wide spacing, low conductivity of the fertilizer solution, and the removal of sideshoots and some fruit. Fruit are harvested well after the mature-green stage. Growing conditions are such that the leaves provide ample carbohydrates. Night- time temperatures are low with high daytime temperature and humidity. Soil moisture is either too high, or is low and then suddenly increases when fruit are in the pink stage. Water is present on the fruit surface for long periods of time.

https://journals.ashs.org/downloadpdf/ ... e-p216.pdf

[bower]

Very interesting about the sugars/TSS. Skin elasticity makes sense as a trait, but what genes are then involved, I can only imagine (have not read the link yet, I'm just musing about it...). I always thought thickness of the skin made a difference, where thinner skinned varieties are more prone to crack. And that is not an elasticity issue, quite the opposite really, because the thicker skins are quite tough lets say, they resist cracking by being strong, not by being elastic - at least, not that I could perceive. But maybe I'm forgetting some others that were more thin skinned but still also resisted cracking... hmmm. Yes it does make sense. A thin but more elastic skin would be better than a thick skin that is strong but inflexible.
The cultural conditions that promote splitting are well known, especially the water issues. Humidity definitely plays a role, I have seen fruit responding to a thunderstorm with cracking, even though they were in the greenhouse not exposed to any actual rain.
One day I expected to stay cool and cloudy, I made a trip to town leaving the greenhouse closed. But it got sunny unexpectedly! When I returned, I found fruit had practically exploded. Even some that were not especially crack prone (remembering Indian Stripe that time).