Micro Dwarf Characterization

[William Schlegel]

Had to pay $30 to have someone scan it, but I finally got access to the original document for "Micro-Tom. A miniature dwarf tomato" overall it's brief, but interesting. I'm posting it for free because, I feel that the internet should have this:
https://files.catbox.moe/7p01cd.pdf

So it seems like Micro-Tom, while not the first small dwarf variety, is the first known variety with proportional characteristics in terms of fruit, leaf, and stature. I find it amusing that Micro-Tom is called a miniature tomato, while Red Robin is just classified as a dwarf with short internodes. It seems that the classification Micro-dwarf might've been derived from Micro-Tom, but has been loosened over time to refer to smaller tomato varieties with the dwarf gene.

That's interesting if I am reading that pedigree correctly it was about 1/12 L. minutum which is referrable to the species pair Solanum neorickii and Solanum chmielewskii. I wonder if they got anything useful from that introgression such as a trait that contributed to the microdwarf characteristics?

[KaguyaCloud]

Found something here about L.minutum:
https://vcru.wisc.edu/spoonerlab/pdf/Tomatomonograph.pdf

Using data from morphological characters, mating systems, ecological preferences,
reproductive isolation and allozyme types, Rick, Kesicki, Fobes, and Holle (1976) described two new species, L. parviflorum and L. chmielewskii, from the central Peruvian Andes. These two species were previously referred to as "L. minutum," a name never validly published (Chmielewski & Rick 1962). Lycopersicon parviflorum was shown to be strictly autogamous, with small flowers and style included in the anther tube or slightly exserted, whereas L. chmielewskii is autogamous and facultatively allogamous, with larger flowers and exserted styles and stigmas. Lycopersicon chmielewskii was considered
as the ancestral species from which L. parviflorum evolved (Rick et al. 1976). Fertile hybrids among these two sibling species were obtained experimentally by reciprocal crosses, but no natural hybrids were found in sympatric populations (Rick et al. 1976).

It possible that the small flowers and fruit set from Micro-Dwarfs may be derived from the unofficial "L. minutum" species classification. The flowers on varieties such as Micro-Tina, Orange Hat, and Jochalos exhibit very small and delicate flowers. I wonder if that co-segregates with one of the micro genes considering how conserved the flower size is with small stature.

AHA! Small and reduced leaflet count in L. parviflorum in page 4! You were onto something William!
https://link.springer.com/article/10.1007/BF00281917

Leaves broad, flat, interrupted-pinnate, 6-9 cm wide x 7-10 cm long, with 2, occasionally 3, pairs of opposite major segments and variable numbers of small foliolules, margins serrate or undulate, pseudostipules lacking, the leaves in their simplest form resembling those of L. peruv/anum var. humifusum.

It's possible that the L. minumum that they crossed with may be Solanum neorickii(renamed from L. parviflorum) due to the small flower set and reduced leaflet number.

[Roland]

So Micro Tom is the first miniature dwarf tomato variety?

[KaguyaCloud]

So Micro Tom is the first miniature dwarf tomato variety?

It seems that Micro-Tom, at the very least, is the first known documented miniature dwarf variety. It's possible that other mutants exist that are smaller. But, there's no way to know  for sure.

[KaguyaCloud]

Update 11/9/24:
It has been almost 1 year since I have started and I am in the middle of growing the 4th generation(F3) of my micro x indeterminate project(Jochalos x Rosella Cherry).

Characterizing micro parent Jochalos:
Dwarf with rugose leaves. Main shoot immediately terminates to 2 flower trusses after growing 9 leaves. Axillary shoots produce 1-3 leaves before growing a flower truss with sympodial repeats. Flowers are very small and delicate, with high pollen production. Has the multi-locule gene.
Plant architecture diagram described here:
https://imgur.com/a/PzJI8OJ#EP26Chj

I have been growing 2 plants per generation and only selecting 1.
Generation 1(11/18/23): Rosella Cherry x Jochalos. Crossed and saved seeds.
Generation 2(02/23/24): Joro F1. Grew 2 plants and saved 2000 seeds.
Generation 3(07/05/24): Joro F2. Selected and grew 2 dwarf plants. Dwarfs were selected based off of whether or not their cotyledons closed at the night cycle. Saved seeds for both and continued the Pale(white fruit) fruiting line as it had superior flavor.
Generation 4(11/22/24): Joro F3. Currently being grown. Also backcrossing the selected F2 with the cherry parent for further flavor improvement.


Based off of the F2s and the F3s, there seems to be several traits that can be isolated and characterized that can make up a micro dwarf. However, some strange traits did pop up.

• Dwarf(d) gene: Recessive. Causes internode shortening and rugose leaves. Seedlings with the genes grow half as tall as the non-dwarf genes.
• Self pruning(sp): Recessives. Leads to early termination of the main stem with sympodial repeats(leaf, flower, leaf, etc).
• Early flower termination: I do not think this one has been characterized in the literature. The main stem grows a set number of leaves and then immediately terminates with 2 flower clusters. This vastly decreases the overall size of the plant. Axillary shoots start immediately growing flower trusses after 1-3 leaves have grown. Recessive.
• Reduced leaflets: Leaflets are reduced from a 3-5-7 pattern to a 1-3-5 leaflet pattern. Internode are extremely short. Flowers are extremely delicate like the micro parents. Root mass is potentially diminutive when germinating on a paper towel. Recessive to 3-5-7.

Strange traits that popped up:

• Lower leaf to first flower: F1 and beyond all grew a flower truss after 7 leaves have grown. In the parents, the leaves grown to first flower truss is 9 leaves(Jochalos) and 8 leaves(Rosella Cherry) respectively.
• Parthenocarpy: One of the F2 plants exhibited fruit set with no mature seeds. At first I have thought it could have been sterile, but further fruit set does show seeds. I have also noticed that the pollen yield from the flowers are extremely small compared to regular tomatoes. Rosella Cherry is likely the contributor of the gene, as all the micros I have grown exhibit high pollen and seed count in their fruits.
  https://imgur.com/a/joro-f2-update-9-3-24-dGW9bdP
• Twin stemming: The F2 plants that I have grown exhibit 2 stems growing from the cotyledons. This trait is present regardless on whether the plant is determinate or indeterminate. The trait is maintained into the F3.
  https://imgur.com/a/joro-f2-week-2-O7o1vtA
  https://imgur.com/a/joro-f3-update-11-8-24-Z4Es7DC

Overall, I think it's very beneficial to cross micros exhibiting traits similar to Jochalos with non-dwarf indeterminates. Selection for size and the dwarf trait is not that difficult to do. F2 selections for the dwarf traits only require picking seedlings that are half as tall and do not close their cotyledons at night.

[Weston Adams]

Fascinating. I wonder how Orange Hat compares to Micro Tom genotypically. I've been crossing Orange Hat to other indeterminates.

So, I assume you weren't able to get good ratios from the F2 population, if you only grew out 2 plants? It would be interesting to know how many plant morphology phenotype categories would arise in the F2 population if you grew out like 1000 plants.

[Weston Adams]

Has anyone here ever grown out a large F2 population of micro dwarf x indeterminate to make firsthand observation on segregation ratios?

[KaguyaCloud]

Fascinating. I wonder how Orange Hat compares to Micro Tom genotypically. I've been crossing Orange Hat to other indeterminates.

So, I assume you weren't able to get good ratios from the F2 population, if you only grew out 2 plants?

Orange hat is very morphologically similar to Jochalos and Micro Tina in terms of growth habit based off my own observation of growing 4 micro varieties(Orange Hat, Micro Tina, Jochalos, and Vilma).

In the F2 population, I only germinated 20 of the 2,000 seeds I collected and managed to get 2 individuals with a dwarf trait. The 2 individuals were selected at the cotyledon stage, as micros do not close their cotyledons during the night cycle as young seedlings.

I hypothesize that I got extremely lucky with my F2 selection, as I estimated that I would require 256 seeds(4 recessives) to be sprouted to get 1 micro phenotype. However, that was nearly achieved with only 20 seeds. F2-1 had dwarf, leaf reduction, and an indeterminate growth habit, leading to a micro-like tomato with the endless indeterminate growth pattern. The F2-2(pale F2) grew exactly like the micro dwarf parent Jochalos, but had longer internodes and 3-5-7 leaflet pattern(it was heterozygous for the leaf reduction gene).

Isolating dwarf, sp, and early flower termination was only a 1 in 20 chance, which is very questionable. Unless the sp and early flower termination gene are in fact part of the same segregation characteristic. This would lead to a 1 in 16 chance to get a micro-like phenotype. I would like to grow out as many F2s as possible, but I do not have the space to do so and can only grow 4 plants at a time. This made selections at the seedling stage and early growing stages very important for me to focus on, which includes root growth pattern.

Based off my observation with micro-dwarf variety Vilma, the leaf reduction gene isn't entirely required to obtain a micro phenotype. However, it does significantly shrink the size of the plant itself as both leaves and germinated roots are reduced.

[KaguyaCloud]

Has anyone here ever grown out a large F2 population of micro dwarf x indeterminate to make firsthand observation on segregation ratios?

Strangely enough, yes there is. Although the segregation ratio is very weird.

1:27 chance of obtaining micro phenotype from crossing a micro with a determinate:
https://plantmethods.biomedcentral.com/articles/10.1186/1746-4811-6-23

31/861 or 1:27 selection based off of hypocotyl length
Micro-MsK: a tomato genotype with miniature size, short life cycle, and improved in vitro shoot regeneration.
Solanum peruvianum is an indeterminate tomato plant, which is very interesting since this would mean that it's possible that the ratios are the same regardless on whether or not sp is present, making me to think that there is a miniaturizing gene in the same chromosome as sp.
Lima et al
https://www.sciencedirect.com/science/article/pii/S0168945204002079?casa_token=4eHjFWMau2QAAAAA:rHf4-xZAy7rIEbHqwFNnMRwCVNySfBaBJbwzpLk_ZZhXzvCM0f6Xb3hdE0HYBFsENA1he7Vxig

6/176 or 1/29 chance Meissener et al (pg 1468)
https://sci-hub.ru/https://doi.org/10.1046/j.1365-313x.1997.12061465.x


Overall, it seems like the conclusion is that there needs to be 2 recessive and 2 dominant traits for a micro phenotype to show up. But based off my personal observations, there aren't that many dominant traits visible in the F1. They also did not specify specific morphological characteristics at all. That being said, it seems that the segregation ratios in the F2 are closer to the ratio that I have obtained compared to my estimates(1/256).

[Cathy A]

What you seem to have missed is that Micro Tom, and all micro dwarf tomatoes, also have the sun dwarf gene.  This creates extremely short internodes under high light intensities, it is most likely sd.

Does this mean that micro dwarfs grow larger under lower light intensities?

Summer light is on average less intense here in New England than in the mountains states where William and Joseph do their breeding experiments.

[Weston Adams]

Interesting. You've put a lot into this! I wish that the genetics of micros were simple...but from what I've read it's far from simple. Pardon my confusion, but if you don't mind, I'd like to clarify a few things.

You mentioned that you got 2 plants with the "dwarf" trait, but then in the next sentence it sounded like you referred to them as "micros." Were they micros or only dwarfs?

You also mentioned that one of them was an indeterminate. Is there such a thing as an indeterminate micro? In that case does it even count as a micro?

Thanks for being willing to tackle this whole genetic puzzle!! I'm sure that somebody has mapped out all of this...but perhaps it's considered proprietary.

Weston

[Weston Adams]

Another thing that might help...I wonder if anyone has grown out a large F3 population saved from seed of a micro F2 selection? If the micro phenotype came back 100% true-to-type in the F3 population, then we could assume that the phenotype was controlled by recessive genes. However, if larger off-types showed up in the F3 population, then we could assume that there were some dominant genes at play in the phenotype.

[KaguyaCloud]

Does this mean that micro dwarfs grow larger under lower light intensities?

Summer light is on average less intense here in New England than in the mountains states where William and Joseph do their breeding experiments.

I am unsure of the genetics of the sun dwarf gene being in micro dwarfs specifically. The only sources I can find are blog posts with no attached research articles in question.

[KaguyaCloud]

You mentioned that you got 2 plants with the "dwarf" trait, but then in the next sentence it sounded like you referred to them as "micros." Were they micros or only dwarfs?

You also mentioned that one of them was an indeterminate. Is there such a thing as an indeterminate micro? In that case does it even count as a micro?

I wonder if anyone has grown out a large F3 population saved from seed of a micro F2 selection? If the micro phenotype came back 100% true-to-type in the F3 population, then we could assume that the phenotype was controlled by recessive genes. However, if larger off-types showed up in the F3 population, then we could assume that there were some dominant genes at play in the phenotype.

To answer your first question, sorry I was not being specific. All micro dwarf varieties I grow do not close their cotyledons at night. However, I have heard that any plant with the dwarf trait(d) does not close their cotyledons at night. So the F2s are dwarf, but similar-looking to micro dwarfs.

Yes in fact, if you read up this article, it shows that they considered variety Inkspot as a micro dwarf tomato:
https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=1015&context=cpl_dwarfcrops

And as you can see from the vines, it has an indeterminate growth habit. One of my F2s behaved similarly. It had very compact internodes and small leaves. Basically if you imagine what a micro looks like, the stems never stopped growing. I would say that it looks like a micro with an indeterminate growth habit as the leaves are still extremely small compared to a regular tomato plant.

As far as I know about the F3s, which I have grown 2 of, the very major dwarf and early flower termination gene is true to type. The internodes are longer, but it seems like the recessive early flower termination gene is stable to the next generation.

[KaguyaCloud]

In my opinion, a classic micro dwarf requires only 3 of 4 properties to attain a very compact growth habit:

Dwarf gene(d): Required
Determinate gene(sp): Required? Unsure if early flower termination is linked here.
Early flower termination: Optional. Needs to be one of the 3 properties.
Leaf reduction: Optional. Needs to be one of the 3 properties.

Overall I think what a micro-dwarf transcends measurable height at this point, and it should be more focused on traits that severely stunts the overall size of the stems and leaves.

At the very least, I would define the growth habit of Micro-Tom and Micro-Tina as a baseline micro-dwarf growth habit. These habits include:

1) Dark, rugose leaves. Indicating the dwarf gene(d).

2) Main stem has no sympodial repeats and terminates to 2 inflorescences. Meaning that the main stem grows 6-9 leaves, then it stops. At the very tip of the stem there are 2 fruit trusses.

3) Axillary shoots(aka suckers or side shoots) grow 1-3 leaves before producing a flower truss. They proceed to do any variation of sympodial repeats before terminating.

4) Small, compact shaped leaves with usually 3-5 leaflets per leaf. This might be linked to smaller root size at germination as well.