Side Project B: Isolating micro traits via growing out F2 seed.

Hypothesis:
The dwarf gene(d) causes the cotyledons in micro dwarfs to not close during the night cycle.

The gene sp in micro dwarfs might be very different from the typical sp in determinate tomatoes. I went through Pippin breeding projects that bower mentioned and it seems that there's quite a lot of variability in determinate flowering patterns.

The small root trait prevalent in Micro-Tina, Jochalos, and Orange Hat might be a sign of a micro trait. Short roots occurred in 4 out of 20 germinated seedlings, indicating that it is a recessive trait. This may not be entirely necessary, but appears in the smallest micro dwarfs. Vilma and Joro F3-1, for example, have not expressed the small root trait and have a slightly larger, more open growth habit.

Process:
Plan 1:
I could be extremely conservative in individual preservation by seeing the possibility of isolating just sp and d alone. Perhaps keeping track of root length could be part of this as well. If the micro version of sp is different, I should be able to obtain the micro-like growth habit(early flower termination, axillary shoots skipping the vegetative cycle) in only 1 out of 16 seeds germinated. It's possible that this trait may be recessive to other determinate sp tomatoes, as it seems that most people are having difficulties in isolating this trait or have not notice this pattern due to crossing with larger determinates.

Plan 2:
Germinating 16 seedlings at a time in 4 separate batches. Cull all seedlings without the small root trait. Plant the theoretical 4 seedlings in a single 4 inch pot. Of the 4, 1 statistically should have the dwarf trait. Begin germinating the second batch of 16 seeds and repeat until there are 4 pots. Statistically, I should be able to have 1 individual plant with the dwarf gene, small roots, and the sp gene. If there is another gene that controls early flower termination in micros, it is statistically unlikely

I like the Plan 2 best, if only because larger numbers will help to confirm your ratios and selection process, also giving you more experience with real vs theoretical numbers.
Chris Mauchlin at Tville did a nice piece of work that combined genetic frequency with probability to give actual number of plants you need to grow for percent certainty of finding your recessive trait(s). IDK, I've probably mentioned that before.
Okay I went looking and found that old thread at TV:
http://www.tomatoville.com/showthread.php?t=38505
In the first example given, your chance of finding a one in four recessive with four plants is 68%. I usually bump the number to 6 plants for an 80% chance, and that is enough to find it, more times than not. It doesn't seem like a huge gain in probability, but it is so disappointing to go all season with 4 plants and not find your carry forward.
Obviously you don't have the same seasonal constraints, so it may not really matter, especially since your plan is to start additional waves of seedlings for selection.

Update 1/3/25


Out of the 19 fruits from Joro F3-1, I obtained 3 viable seeds from 1 single fruit.
Out of the 14 fruits from Joro F3-2, I obtained 1 viable seed from 1 single fruit.
The pattern of having completely seedless fruits has surprised me to no end, on top of the fact that the size of the fruits are not an indication of pollination.

I have decided I will attempt a backcross on both Joro F3-1 and F3-2 on Rosella. After giving the tomatoes more time on the vine, it seems that Joro F3-1 has much better flavor, not to mention a higher potential yield despite being grown in the same size pot. However, the flavor is still diluted compared to the Pale F2 parent it came from. If isolating the 3 traits still ends up with inferior flavor, I will try my hand in packing even more genes from Rosella by using F3-1 as a more stable flavor reference.

I wonder how small the tomato plant might be if I were to just select for Dwarf and the early termination gene.

Quick Update 1/7/25

I accidentally broke off a half ripe fruit(reached past breaker) off of Joro F3-2. I obtained 30 seeds from one fruit. I suppose don't need to worry too much about saving a diverse population seeds anymore. This would indicate though, that the early flowers transferred less pollen than the later flowers. Flowers that were produced later in the flowering cycle in both F3s exhibited high amounts of pollen production and will likely produce a lot of seed as a result.

Is this a normal phenotype for cherry tomatoes? Rosella Cherry and the F1 exhibited similar exerted stigmas in the early flowers followed by non-exerted stigmas later in the truss. In the F3 generation, the entire shaft of the stigma is exposed in these early flowers.

I can only venture to guess that the distance from the lights might play a part in how well they shed pollen, although there is not a lot of height difference in those plants so maybe not. But considering that the soil is watered therefore higher RH close to the ground, vs the later flowers which are lifted highest on the plant, in the lowest RH situation closer to lights, it might be a factor.
OTOH for parthenocarpics it may be normal that earlier fruit are seedless, with seeds being produced late. That was more or less the pattern I saw with Siletz, and perhaps such patterns are more genetically determined than I thought. We assume they are doing this to cheat early spring environment factors, but maybe it's genetically selectable?
And then again, maybe most likely of all, the plants decide whether to make seeds or not based on their maturity status.

Update 1/26/25:


This will probably be the final update for the Joro F3 generation before doing another round of backcrossing. Overall the yield data is relatively good.

Joro F3-1 has tasty fruit, although more diluted than the F2. Growth habit is noticeably larger. Yield so far is 353.36g(12.45oz) after harvesting 67 fruits.

Joro F3-2 has fruit with just a slight amount of flavor, but it is still quite bland compared to the F2 parent. Growth habit seems to be very similar to it's micro parent. Yield so far is 304.05g(10.73oz) after harvesting 64 fruits.

Do u think u lost a micro gene in Joro F3-1?

Doffer wrote: ↑Sun Jan 26, 2025 1:50 pm Do u think u lost a micro gene in Joro F3-1?

Joro F3-1 had a very similar growth habit to the F2 parent, so I don't think a micro gene was lost. But, F3-2 is smaller than both the parent and F3-1, which likely hints that the F2 parent might have been heterozygous for another micro gene. This recessive gene involving smaller stature might be related to root morphology/length during germination.

I've noticed that Orange Hat, Jochalos, and Micro-Tina exhibit short root length that tend to form a spiral shape as it grows in the germination chamber. And I know that larger micro varieties such as Vilma do not have this trait(it has short roots, but does not spiral around). F3-2 seems to have expressed short root length just like the other micros and exhibited a more stunted growth habit.

I will be able to determine if this is true through growing out the F2 seeds to figure out the trait segregation.

Found another interesting article relating to seedling traits in Micro-Tom.
https://pmc.ncbi.nlm.nih.gov/articles/P ... %20%5B5%5D.

When they applied a brassinosteroid hormone to the seedlings, the root length, height, and overall mass increased significantly.
https://www.ncbi.nlm.nih.gov/core/lw/2. ... 6-g001.jpg

This might indicate that root size might be an early indicator of being deficient in a certain brassinosteroid hormone, and therefore a possible micro trait. However, smaller root size isn't entirely an indicator of having a dwarf gene, as some of the root systems of my micro project exhibit normal growth.