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

[bower]

Welcome to the forum KaguyaCloud.
Sounds to me like you got it right. Backcrossing is a great way to reduce the numbers, if you don't have much space.
There's also the possibility of early selection cues - at least, if you have the rugose leaf, it would be a tell for at least the dwarf character, so you could cull all the non dwarfs at the seedling stage.
If it was (is?) possible to identify the microdwarfs early on, what a great space saver that would be.

[KaguyaCloud]

Thanks.
Apparently according to the breeding results from the first source between Micro Tom and a tall determinate plant, there's a strange 1 in 32 chance that an F2 with non-rugose leaves(no dwarf gene) to also exhibit a micro dwarf growing habit. But those with rugose leaves(dwarf gene) exhibit a 1 in 8 chance to exhibit micro dwarf growing habits.

Overall having the dwarf gene lowers average height for F2, but that's not really important if we are selecting the smallest progeny for breeding. About 42% of the plants exhibiting micro dwarf behavior in F2 had smooth leaves instead of rugose.

So there may be a very small possibility to isolate the mnt gene and have micro dwarf tomatoes with regular smooth leaves. And if that is the case, then it might make the process of micro dwarf breeding easier if we only need to select towards one trait only.

[Whwoz]

@KaguyaCloud welcome to the Junction. Good luck with your project, lots of folks here like micros.

You may also find the information about the micro tomato diversity project on Tomato-Talk.com of interest also.

[bower]

Yes, Dan Follett and SeaninVA and others have done a ton of work on microdwarves! And you're right they have all kinds of leaves. Tomato Talk is the place to read about their work or talk to someone who has been watching the results come in over some years.
And KarenO also has an active microdwarf breeding thing going, not sure if any are released yet but she posts mainly at Tville and also her Facebook blog - Northern Gardener.
Dan used to post at Tville as well, and I remember his pics of indoor growouts in the winter - the kind of thing that would get your variety stable pretty quick.

But the step of getting from indeterminate to micro in the F2, that's the tough one for numbers.
I even find it a challenge to get all the aspects of indeterminate growth out of the determinates I've been breeding. Long internodes, QTL's for that sort of thing, responses to environment, there's a lot feeding into growth habit - at least without the mnt and other micro things.

[Doffer]

Dwarf tomatoes can already be recognized in the seedling stage. The cotyledons or germ leaves do not close at night.

Can you recognize the mnt gene without d or sp genes?
Then you can also breed 3 lines, always backcrossing to the tasty tomato and growing a test generation in the winter to see which plants contain the recessive genes. You can grow fewer test plants by pollinating the test seeds with the recessive parent.

If u want a tasty tomato as parrent try Ivas Red Berry or Sungreen 4029 F1 or Limotello F1 of Nebula F1. These varieties have very high brix.

Maybe u can also ad the brachytic br gene for short internodes in youre new variety!

[wykvlvr]

As others have said check out TomatoTalk. It is pretty inactive but there is some good information in there like this thread https://www.tomato-talk.com/forum/the-m ... -detection

[KaguyaCloud]

@Frosti
I just realized that my math is wrong on a conceptual level in the first article's research data due to taking their conclusions in face value.

Population was 287 F2 plants(micro x determinate). If there were only 2 recessive alleles(dwarf and mnt), then 1 in 16 plants(6.25%) would exhibit the micro dwarf phenotype(very short stature when measured at 5 internodes). This would mean that there should be about 18 plants of the 287 that exhibit the micro dwarf phenotype with rugose leaves. However, only 6 did. That means there's only a 2.1% chance instead of a 6.25% chance. This would be closer to 1 in 64 chance or 3 recessive alleles.

And not only that, there were plants with non-rugose phenotypes that exhibit dwarfing. When adding all the micro dwarf phenotypes and dividing by the total number of plants, this does come closer to a 1 in 16 exhibiting the micro phenotype, but it's independent of the dwarf gene(otherwise none of the non-rugose leaf plants would shrink).

Let's call this third recessive gene mnt2.

The ratio between the number of smooth leaved micro plants(8) and rugose leaved micro plants(6) is also very interesting. This is a 4:3 ratio, which doesn't really make much sense initially. If there are two other genes other than d that are independent of the dwarf gene, then there should be 3 times the number of smooth leaved micro-dwarfs(assuming that you need either mnt or mnt2). Yet there isn't. What could be the reason? I have a theory. What if the micro phenotype can be achieved by a combination of only 2 of the 3 genes?

Let's say you only need 1 recessive allele, mnt, mnt2, or d. What would the distribution look like in the population of 287 plants?:
210 Smooth leaved(no d gene): 69 micro
70 Rugose leaves(d gene): 18 micro
This combination doesn't really match up.

Let us say that you only need 2 recessive alleles mnt and mnt2. Not d. What would the distribution look like in the population of 287 plants?:
210 Smooth leaved(no d gene): 10 micro
70 Rugose leaves(d gene): 4 micro
That's a near 3:1 ratio.

Let us say that you only need 2 recessive alleles mnt, mnt2, or d. What would the distribution look like in the population of 287 plants?
210 Smooth leaved(no d gene): 10 micro
70 Rugose leaves(d gene): 8 micro
This is a 5:4 ratio, which is closer to the 4:3 ratio exhibited.

And guess what is the likelihood of having a micro dwarf phenotype using this hypothesis?
1 in 16. Almost the same as just having 2 recessive genes, but again only 2 recessive genes doesn't make sense in this context. It is 1 in 16 with and without rugose leaves, which leans on supporting the results of the study.

[KaguyaCloud]

@wykvlvr @dfollett
This may also be why we are seeing breeders getting non-micro plants from their F3+ lines. If they do not know the genotypes of their micros, and that micros only need 2 of the 3 genes to exhibit micro behavior, cross pollination between micros with different genotypes may result in dominance in 2 of the 3 genes, causing non-micro growth.

[KaguyaCloud]

This makes back crossing the F1(micro x indeterminate) with the original micro both more and less complicated.

We now cannot assume that all micros except for maybe very small micro varieties('Original Micro Tom' and 'Baby') contain the same genotype of 3 recessive genes. And if that is the case, we now have a definitive way to know if a micro dwarf variety is genetically recessive in all 3 recessive genes.

If the micro is genetically pure, we can breed out mnt and mnt2, as 25% non-rugose leaved plants would be micros. This would make it harder to select seedlings due to not having rugose leaves, but at least there is only two known variables to determine dominance. In addition, if the micro is genetically pure, 3 in 4 rugose leaved plants would exhibit the micro phenotype. Those with rugose leaves and are phenotypically micro can be heterozygous in 1 of the 3 recessive genes, which leads to making any pure line basically a gambling game of statistics. You might also be able to select genetically pure recessive micros by only choosing the absolute shortest micros in your rugose arrangement(25% rugose progeny would be pure in all 3 recessive genes).


If the micro variety is not genetically pure, then all non-rugose leaves seedlings in BC1 will be tall. There would be no sign of any micro phenotype in non-rugose BC1 instead of a 25% chance if it was pure recessive. However, this guarantees that there are only 2 genes that we need to select for. Culling the taller rugose leaved plants leads to a gene arrangement similar to the original micro parent.

Best case scenario:
We have an impure recessive line that has rugose leaves(d) that is also homozygous dominant in either mnt1 or mnt2. 2 recessive micro genes would only need to be selected for. With the need to also select for the self pruning determinate gene, there's still a 1 in 8 chance that we get a micro dwarf that is genetically homozygous.

Worst case scenario:
We have a pure recessive line. Meaning the genotype of all following generations of rugose leaf micros could be heterozygous or homozygous dominant in 1 of the 3 genes d, mnt, or mnt2. To maintain a pure line with rugose leaves, we would have to isolate and self the individuals of further generations without knowing whether you have a recessive mnt or mnt2. You could however, select the micro with no dwarf(d) genes, as that should be genetically homozygous for mnt and mn2.

[wykvlvr]

@wykvlvr @dfollett
This may also be why we are seeing breeders getting non-micro plants from their F3+ lines. If they do not know the genotypes of their micros, and that micros only need 2 of the 3 genes to exhibit micro behavior, cross pollination between micros with different genotypes may result in dominance in 2 of the 3 genes, causing non-micro growth.

I thought you might find his experiences interesting. In my head I divide my micros into tree, flat, and sprawling as far as growth habits. Tree would be like Rosy Finch, flat is like Baby, sprawling is like those that grow very little height but have longer branches and tend to sprawl near the ground. Not all sprawling plants are micro dwarfs but many would meet the definition if it relies only on height. And this leads to the question again of what exactly is a micro dwarf?

At Tomato Talk they have talked about the difficulty of reestablishing that small size when crossed to larger plants. In fact I believe they have mostly abandoned the idea of making new lines and are working now with a limited number of lines from Dan. Honestly I think the original premise of the Micro Tomato Diversity Project has been proven false in many ways. The recent introductions of other micro dwarfs from Europe and by Bunnyhop have shown that there are folks hard at work with the little ones trying to bring diversity to them even if they are not standing up and shouting about it or the crosses used to produce their new lines. Karen Oliver has been showing some of her micro dwarfs on her page and wow those are going to be on my must buy list when they come out. Which means the micro dwarfs are a lot more diverse then the folks at the MTDP project thought.

I was not sure reading your posts if you are thinking that Micro Tom was the first micro dwarf or not but Tiny Tim is older having been introduced in 1944/1945 as a plant to be grown for Christmas decoration in a 5 inch pot which leads me to believe that there were other older plants that would now be called micro dwarfs. AND Micro Gemma and Micro Tina came from the same lines as Micro Tom but it was Micro Tom that got all the glory in 1989 when they were introduced.

I have grown Micro Tom with seeds from a commercial source. Those seeds actually gave me true flat forms like Baby AND taller less flat forms. I also got round tomatoes from some and true tiny little heart shaped tomatoes from other plants (not ox heart shaped but rather like a drawing of a heart shape) So I do find them very interesting even if not very tasty. I may very well order some more seeds for them just for a house plant which is actually what they were developed for...

[KaguyaCloud]

And this leads to the question again of what exactly is a micro dwarf?

Those are very interesting classifications of phenotypes based off your observations, I wonder if multiple pairs of segregate dwarf genes are responsible for each growth habit. Assuming that no one has isolated mnt or a hypothetical mnt2 from the dwarf(d) gene, those classifications would possess 3 of the 4 potential phenotypes that micro dwarfs may exhibit from those combination of 2-3 genes. We do however know that the dwarf gene reduces height by 33% for F2 crosses counting up to the 5th internode.

The tree phenotype(based on images I see of rosy finch) seems like there's no major shortening of the main stem internodes.
The sprawling phenotype seems like there are no major shortening of the branch leaves, leading to the outward growing habit.
And flat might just be a combination of both short main stem and branches. How very interesting.

Personally, I believe that like in nature, there isn't really a point where one stops being dwarf and one starts being micro. This chart here in the first study shows how much height varies in the F2 generation of a micro x determinate F1. Chart A shows the distribution of the plants without the dwarf gene and Chart B shows the distribution of plants with the dwarf gene:


That being said however, you can see in the chart that there is a very steep drop in number of plants with a height of less than 4cm. You could maybe define micro dwarfs as "tomato plants that exhibit a height of less than 4cm between 5 internodes", but that may be too exclusive. Another interpretation of what constitutes a "micro dwarf" could be what we can rule out. For example, plants that exhibit only the dwarf gene(d) are not micro dwarfs. Therefore, maybe we can consider any plant with at least 2 genes responsible for smaller growth habits to be considered micro dwarf. Having all 3 genes is the ideal(I think people are starting to call that phenotype "nano") but likely not required.

We would first need definitively prove that we can segregate plants with different micro growing behavior like you have. From there, it's possible that we might be able to cross those segregated lines to see what happens. If the results match our hypothesis, we can make up a generalized theory and find other means on proving if the hypothesis is wrong.

Oh that's an interesting fact about Tiny Tim's I didn't know that. I am merely using Micro Tom due to the fact that it now a model tomato plant for scientific research.

I live in a very tiny space with only 3 hours of tree-shaded sunlight going through a window. And unfortunately I like gardening. It might take me a while, but I really want to grow some tasty micro dwarf tomatoes that are bred for purely flavor and indoor gardening. It's just more convenient that way. And in my context, dwarfs that exhibit sprawling or flat behavior are fine by me. The shorter the better. I also want to see if other people can cross better tasting tomatoes using different methods as well.

[wykvlvr]

The newer releases were selected for flavor so I would check them out if you haven't already. Bunnyhop (Heritage Seed Market has some good ones and Karen Oliver has some selected for flavor among other traits that will probably be out in a few years. One reason for the lack of flavor in many of the current micro dwarfs is they were selected for size not flavor.
Micro Tom is good for the researchers not just for the small size but for the early maturity. My plants were already setting fruits within 60 days of me planting the seeds!!! I had to double check my planting dates with those and they spent their whole life inside under lights.

[KaguyaCloud]

Oh I am definitely a step ahead. I already bought Jochalos and Vilma from bunny hop seeds just for flavor and sweetness. I also got a Rosella Cherry to cross with either of the two varieties. I really wish there were many more to grow with intense flavor profiles. This is going to be a small project due to my space constraints.

I actually kept track of my 1 year old Orange Hat tomatoes for the first 11 weeks, and I think I will use that as my baseline reference for micro dwarf growth behavior:

[bower]

I've always thought I would start with tasty determinates as parent if I decided to work on micro crosses. Rather than indeterminates. Even better, a dwarf determinate parent already has two of the relevant genes. So much has come from the dwarf project, there must be lots of tasty candidates available for that.
It is interesting that Dan and friends found similar issues getting from leggy long parent vine back to the perfectly tiny state. Even the choice of a compact indeterminate vs a very sprawling one can make a difference, IMO, in the outcome.

[wykvlvr]

I have not grown Jochalos or Vilma yet but have heard/read great things about them.

IF/WHEN I start playing with the littles again I want to use Rosy Finch as one of my parent plants. The reasons are I tend to favor the upright growth habit of the Rosy Finch plants I have grown and they have larger grape shaped tomatoes. Sadly I found their flavor bland even after letting them sit for a while to make sure they had ripened but I like strong flavors... I found it much easier to find their tomatoes then in something like the flattened growth habit of Baby where I was constantly finding tomatoes and flowers I had not seen due to the thick leaf growth. Oh and as far as colors grin Rosy Finch can contribute the genes for clear skin. Most others out there have yellow skin.

Another variety I would use is Pygmy. Also an upright growth habit Their round tomatoes were smaller then Rosy Finch but had better flavor with a few very close in flavor to my big heirlooms. BUT WOW the amount of tomatoes I got from each plant was I felt incredible. One of my heaviest bearing plants totally filled a paper plate about an inch high with tomatoes and that doesn't include the ones I had eaten already and the ones still growing on that plant. IF I can find them I saved seeds from that single plant and I think some may have been sent out the first year I did the swap. They really must be one of the most prolific micro dwarf out there
FYI Baby also made some that had flavor that rivaled my heirlooms. Of course in both cases those wow tomatoes could have been dead ripe or even over ripe so that is something to keep in mind.
The photo is my harvest the first year I grew micro dwarfs. I had to bring in everything in due to a snow storm. So this is only some of my total harvest as I did save some plants and set them back outside when it warmed up. The center row of plates are all from my Pygmy plants. The really full plate at the back near the planter are all from 1 plant.
micro 2020 harvest by spindledreams, on Flickr

[KaguyaCloud]

Woah those tomato yields look fantastic!

I found a very interesting research article:
https://researchrepository.wvu.edu/cgi/ ... blications

This part is the most important:


Diagram A shows a regular Micro-tom(left) and one without the dwarf gene(right). The size of the plant without D, is drastically larger but still small compared to other determinates. This may indicate that breeding out the dwarf gene might not be a good idea since it contributes quite a deal in the small stature.

Diagram B shows a regular Micro-tom(left) and one with the indeterminate gene(right). The internodes between the stems seem longer than normal and the plant seems to be growing in a weird tree like fashion. Is this similar to the "tree" phenotype that you were talking about? The indeterminate plant still seems to be only double the size of the original strain.

I have also found a diagram from this research article showing the architecture of the micro tom with different indeterminate/semi-determinate genes backcrossed into the strain:
https://sci-hub.ru/https://doi.org/10.1 ... 015.01.003


I find it quite strange that both these research articles have differential counts on how many leaves Micro-tom produces before flowering. But considering personal observations from my orange hat tomatoes, it seems that flowers coming out at around 5 leaf nodes may be an indicator of dwarf/micro-dwarf growing behavior regardless of determinate genes.

[wykvlvr]

Ugh you got me interested in doing crosses again. So I decided to go back to a friend's request for a good tasting white micro dwarf. Using information you posted I decided to avoid the indeterminates and look for dwarfs that produce white/ivory tomatoes. Found out there are at least 9 of them, 5 potato leaf 4 regular leaf.

I picked out two:

Dwarf Desert Star Cherry an early potato leaf small cherry variety that was selected from the “”Plucky”” family
Dwarf Mandurang Moon an early/mid potato leaf cherry which was selected from the "Snowy" family. This one is also described as very short with large potato leaves.
Now to pick the micro dwarf or micro dwarfs to use as parents. Normal method is to cross a white to a yellow but leaves you with the need to visually be able to tell your clear skinned pale yellow (whites) from the yellow skinned pale yellows.
However I like the logic in this thread viewtopic.php?t=2025 about using red as a parent when looking for an ry or r- color. This way could need LOTS more seedlings grown to fruiting but would make identifying those recessive genes when they make an appearance.

Honestly I am leaning towards using Rosy Finch. Lots going for it but they are described as bland to tasteless so flavor would have to high on my list of requirements. Things I do like about Rosy Finch size, growth habit, size and shape of the tomatoes, and since it is regular leaf and I am crossing to potato leaf dwarfs I can actually do my crosses both ways and still be able to tell in the F1 which seedlings are from a successful cross.

[KaguyaCloud]

Honestly I am leaning towards using Rosy Finch. Lots going for it but they are described as bland to tasteless so flavor would have to high on my list of requirements. Things I do like about Rosy Finch size, growth habit, size and shape of the tomatoes, and since it is regular leaf and I am crossing to potato leaf dwarfs I can actually do my crosses both ways and still be able to tell in the F1 which seedlings are from a successful cross.

There have been several experiments done on selecting micro tomatoes for color. I think you might find this article interesting. So it is indeed possible with some backcrossing:
https://sci-hub.ru/10.17660/ActaHortic.2009.836.30

It is indeed going to be a lot of seedlings if you go straight to F2 without backcrossing the micro parent.
Although there's this weird thing that I've found out when you mentioned potato leaves. It seems that the potato leaf gene and the determinate(sp) growth pattern are located in the same chromosome:
Potato leaf: https://solgenomics.net/locus/1201/view
Self-pruning: https://solgenomics.net/locus/1322/view

This means that all micro dwarfs that have potato leaves can be an indicator of determinate growth patterns if the micro dwarf exhibits both potato leaf and determinate growth. There might be chromosomes that have potato leaves with indeterminate growth, but I am unsure.

What I have noticed from looking at the tomato-talk discussions that were linked here is that quite a lot of their "micro" varieties that they have bred still have the indeterminate gene growth pattern and regular rugose leaves. And it is very easily visible due to the fact that the tomatoes continue to grow their stems after creating a flower truss. Determinate tomatoes terminate stem growth after they've flowered in the main stem. Another case that I have seen is the tomato variety inkspot. It's a sprawling plant that is indeterminate in growth habit and regular leaves(https://digitalcommons.usu.edu/cgi/view ... dwarfcrops). I wonder if Rosy finch doesn't actually have the determinate(sp) gene due to its regular leaves.

It may be easier to select for 2 of the genes of a micro(potato leaf) x indeterminate cross(regular leaf) if you select seedlings that exhibit potato(determinate) and rugose leaf growth(dwarf). If there were 4 genes to select(sp, d, mnt, mnt2), then backcrossing the F1 with the parent micro allows me to be able to weed out 12 out of the 16 undesirable phenotypes.

The determinate sp gene, as far as I am aware of, is important to define for a micro dwarf. However if you prefer a more upright growth habit, it might be better to prioritize just the dwarf gene and the mnt gene.

[wykvlvr]

That was some very interesting reading, thank you for the links.
Yes many plants called micro dwarfs grow larger in larger pots but are micro dwarf size in the small one gallon size pots and that seems to be the definition many are using. Rosy Finch and a few others look like dwarfs but are under 14 inches tall with some shorter. And yes Rosy Finch seemed to have a determinate growth habit when I raised it.
It was nice to read that Rosy Finch had good germination rates in the experiment and that does mirror my experience with it, As does the fact it is later flowering then others in their experiment.
Factors that make Rosy Finch desirable in my mind for this "experiment" are the color (pinks have clear skins just like whites), it makes larger grape sized tomatoes and it has the size and growth habit I want in my finial plants. Back crossing for size won't set me back as far as if I went with a red and it does look like that is one of the best approaches to bring size down. Of course I can always run one line that I back cross and one that I don't and see how they compare in a few generations.