Early Micro Detection

[mwamsley]

I'm looking for tips on early micro detection in seedlings.

How early can you determine a 8" micro from a 18" small dwarf? Can you detect in cotyledon stage? In dwarf project seedlings, I found it apparent.

In reading the posts, it seems that even in F4+, larger plants can still show up.

Mark

[dfollett]

I'm not a genetics expert. I understand barely enough to be dangerous. You are correct. In the Dwarf Project it was obvious at the seedling stage which ones were dwarfs and which ones weren't. The dwarf gene makes them short and stocky with rugose leaves. They were easy to identify. Once it manifests, it is fixed for future generations - no muss, no fuss.

I've not seen anything as definitive where the micros are concerned. I have my own theories that I've developed from 5 years of working with them and making crosses between them and lots of different indeterminate, dwarf and micro varieties. This is all based on my experience. I’ll explain my theories at the end.

"How early can you determine a 8" micro from a 18" small dwarf?" --- You can’t for sure until you grow them out. Some keep growing and others don’t. Picking the plant at the seedling with the shortest distance between the leaf nodes seems to be the method that gives the best results, but it is not foolproof.

"Can you detect in cotyledon stage?" NO. You can find the ones that are either dwarf or micro, but you can't tell them apart at that stage. They gradually distinguish themselves as they mature (and some you think are micros just keep growing and end up dwarfs).

"In reading the posts, it seems that even in F4+, larger plants can still show up?" That is correct, unfortunately.

My theory:

As stated above – the dwarf is controlled by a single recessive gene. I’ve read numerous posts in different forums theorizing that there is a second gene that works with the dwarf gene to create the micro. I wish that were the case, but I disagree with that notion.

I think there are several different genes that work together with the dwarf gene to make the micro. I have not seen anything in seedlings that manifests like the dwarf gene does – nothing that gives any assurance that any specific ‘smallness’ gene is present.

I am sure the dwarf gene is present in all the different crosses I’ve made, but I’m not sure the dwarf gene is required to make a micro. I believe a micro is possible with enough of the other ‘smallness’ genes even if the dwarf gene itself is not present.

With all of the crosses I’ve made Micro X indeterminate, the F1 has been indeterminate. With all of the crosses I’ve made Micro X Dwarf, the F1 has been dwarf. In most of the crosses I’ve made Micro X Micro, the F1 has been micro, with some being more dwarf like. However, with one cross of a micro X Pinocchio Orange (a small micro), the F1 reached 4’ in height from a 6” pot indoors. I started topping it at 4 feet.

I also think the determinate gene can play a big role in making a micro.

I'll explain more as we go along, but that is the basics - and why finding a micro is not as simple as finding a dwarf.

[HL2601]

And that's what makes this micro project so special...so much is not yet determined or completely understood. As we all grow them and compare our results, hopefully we will make some new discoveries as to what really makes a great micro. The prize is worthwhile- a great tasting tomato we can all grow on our porches as the sun fades for us with minimal effort at that time. I am willing to put time in now with many that became too big to find those special few that make growing an easy pursuit for tomato growers in the future who may not have access to big gardens.

[mwamsley]

I'm at the point where I have projects seedlings at the 2nd+ set of true leaves. I'm growing them in the same trays that contain rows of Jochalos and Orange Hat to compare their growth.

One thing I've noticed is the spacing of leaves. Jochalos, Orange Hat and 13x all have very minimal space between the cotyledons and first true set of leaves. Jochalos and Orange Hat also have 1/2 - 3/4 length cotyledons. 13x seedlings are very squat compared to 135x, 35x, Jochalos and Orange Hat.

I found a paper that discusses the genetics of Micro Tom. It seems that with Micro Tom, and presumably others, we are dealing with two dwarfing genes: dwarf (d) and miniature (mnt). I wonder if some of these project micros have lost their mnt gene and have varying degree of the dwarf and determinate genes? Maybe plant size in (d) plants is regulated by container size?

This is a pretty interesting read. They determine height as the length of the first five internodes.

Free download:

Genetic and physiological characterization of tomato cv. Micro-Tom

Mark

[wykvlvr]

it can't entirely be container size though that does play a part in it. For instance when I was learning about the variety Bonsai it was described on one site as "8 inches tall in a 3/4 to 1 gallon pot" HOWEVER another person says it can reach 12 inches in a 5 gallon bucket. So something is keeping it small and not just the pot size...

[SeanInVa]

It's not "just" container size. Genetics is the primary deciding factor, and then from there you have a range.

For example, and perhaps a case-in-point, this year I transitioned from "backyard gardener" to "wannabe-plant-sales-gardener". COVID-19 threw a damper on that, but, I had scaled up. With probably over a hundred tomato plants, across several dozen varieties - including dwarf and micros.

I started all seeds in seed flats, and then transplanted into 3.5 or 4" african violet style pots. For the indeterminates, despite lack of water and nutrients, I still had these neglected indeterminates, in 3" of soil growing 2+ feet tall, flowering, AND setting fruit.

Had they been more comfortable, they might have been 4' tall.

If there is one thing I've learned, and heard repeated over and over in gardening - "genetics, genetics, genetics".

You can take a store-bought tomato, save the seeds, and grow them out in the most perfect conditions ever and get a massive harvest. And it's still going to taste like a store-bought tomato. You can take an heirloom tomato, and abuse the heck out of it, and only get a couple of tomatoes, that are ugly and withered - and they are still likely to taste better than that store bought, saved-seed, grown under perfect conditions.

All that to say - genetics determine max height, possible taste profile, coloring, etc, environment determines range - and this aligns with what wykvlvr was stating in the post above mine. 1 gallon -> 5 gallon and only gained ~4" in height (small sample, not scientific, yadda yadda). On the inverse of that, had they grown that same plant in a 4" african violet pot, even with perfect watering/feeding, it may have only grown to 5" and produced three fruits.

We definitely seem to be dealing with AT LEAST two genes which control height/growth profile, and yes, there is variability in there even under perfect growing conditions. So far we've seen, in the same cross line, plants that range from 6" to plants that go past 24" and everything in between.

[dfollett]

I found a paper that discusses the genetics of Micro Tom. It seems that with Micro Tom, and presumably others, we are dealing with two dwarfing genes: dwarf (d) and miniature (mnt). I wonder if some of these project micros have lost their mnt gene and have varying degree of the dwarf and determinate genes? Maybe plant size in (d) plants is regulated by container size?

Mark

Micro Tom is not in the ancestry of any of the crosses I have. The micro that they all go back to genetically is Red Robin. I've always felt there were more than just two genes that made micros, like I said earlier in this string. I don't know if Red Robin has the mnt gene or not. My guess would be that it does.

As to size being regulated by container size.... I am sure it has an influence on final plant size, but I think it takes a significant back seat to genetics. That's an interesting idea we need to explore more thoroughly.

[mwamsley]

Yes, the development of all living things is based on genetics and the response to their environment.

I'm growing an indeterminate variety in the ground and one in small container. In the small container, all vegetative growth is much smaller. Flowers and fruit are regular size.

Maybe mistakenly, I was under the impression that Micro Tom was one of the first commercial micro tomatoes. I imagined everything after being a derivative of Micro Tom. Does anyone have historical info about micros?

[Diane Whitehead]

I decided to look in some of my oldest vegetable books:

1976 English Tiny Tim 37 cm (15 in) high, tiny fruits It was probably being grown well before the book was published

Garden Seed Inventory Micro-Tom World's smallest tomato PVP 1992 FL AES (I don't know what all that means)

[SeanInVa]

From https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2691670/

The miniature and dwarf S. lycopersicum cultivar Micro-Tom (TGRC accession # LA3911) was bred for home gardening purposes by crossing cv. Florida Basket and Ohio 4013-3 [46]. From the late 1990s, the Micro-Tom has received attention as a model cultivar for molecular research on tomato.

and

The miniature growth phenotype of Micro-Tom is attributed to at least two major recessive mutations, dwarf (d) and miniature (mnt) derived from its ancestors [22]. The D gene encodes cytochrome P450 protein, which is a brassinosteroid biosynthetic enzyme [47]. Reduced brassinosteroid content in Micro-Tom results in its rugose deep-green leaves and shortened internode phenotype [48]. Although the mnt mutation has not been well characterized, it is suggested to be associated with gibberellin (GA) signaling without affecting GA metabolism [48]. A mutation in the SELF PRUNING (SP) gene is responsible for the determinate phenotype of Micro-Tom [48]. SP is an ortholog of the Arabidopsis TFL1 (TERMINAL FLOWER 1) gene, which is involved in continuous growth of the shoot apical meristem [49].

Reference 46 is to
https://www.worldcat.org/title/micro.../oclc/21500682

I have so far been unable to find this article online.

Florida Basket: https://davesgarden.com/guides/pf/go/31105/
Ohio 4013 is an indeterminate, but can't find much else on it

Another paper, highly cited, claims micro-tom was bred for ornamental purposes (so a variation of "home gardener" I suppose).

https://pubmed.ncbi.nlm.nih.gov/16687436/

Now, Red Robin is, as Dan has stated, is where the "micro" traits have originated in his crosses. I have seen Red Robin listed differently at different places. Some list it as an OP, and some as a hybrid. I've saved seed from the "OP" version and it grew again as a micro. I also have the hybrid version, supposedly, from Park Seed.

A poster at Dave's Garden posted on the entry for this variety:

Red Robin was developed by the Sakata Seed company. It is a hybrid that was designed for basket use and seed cannot be saved (the company told me this when I inquired about that possibility) as the F2 generation would vary and not be the same as the parent plant. Still trying to grow this variety as seed purchased online did not produce the expected Red Robin "type", plant grew to be 2 feet tall, fell over (so not the sturdy tree type described) and produced orange tomatoes rather than red. Am trying again from a different seed source. I have seen this planted listed an an open pollinated heirloom which is inaccurate as hybrid status is confirmed.

https://www.sakataornamentals.eu/pot...icum/red-robin

I can find no information, so far, on the origin of the OP version, and can find no information so far, as to when the F1 was introduced by Sakata

Edit: Sakata lists an OP version here:
https://sakatavegetables.com/homegro...rdy-red-robin/

edit 2: Park Seed now lists Red Robin as OP. The packets I received last year for 2019, which I no longer have, clearly stated "Hybrid"

edit 3: clarified that Dan claimed Red Robin is the origin of micros in HIS crosses, not that Red Robin is the origin of the micro growth habit in all tomatoes.

[dfollett]

Now, Red Robin is, as Dan has stated, is where the "micro" traits have originated in his crosses. I have seen Red Robin listed differently at different places. Some list it as an OP, and some as a hybrid. I've saved seed from the "OP" version and it grew again as a micro. I also have the hybrid version, supposedly, from Park Seed..

Correct. And to clarify further, I did not make the cross with Red Robin. I grew out a cross Red Robin X Rose Quartz multiflora from F3 to F9 for Chris Kafer. He made the original RR cross. He gave me permission to make crosses with it. That is the MMF in the nomenclature on my pedigrees.