How do hybrids work?

[jamiethemime]

So I'm VERY new to the tomatoverse, I'm currently learning about how tomato crosses work. My understanding is, the basic process for making a new, stable Open Pollinated tomato line is crossing two different tomatoes, then pollinating subsequent plants with themselves, selecting for desired traits, until you get a plant whose subsequent self-pollinations create the same variety every time and it's stable. This is the impression I've gotten from various online articles. Also, if anyone can recommend articles that explain this process in more depth would be greatly appreciated as it's very interesting to me!! I've watched a few lectures from Craig LeHoullier on youtube about dwarf tomatoes. It's hard to find, like, a straight up "first you do x, if you get y, you can do z" or something explaining it instead of a lot of more general articles written for the public about how crossing tomatoes works.

Which brings me to! The MAIN question of the post. How do hybrids work? If you cross two tomatoes, you're not sure what you're going to end up with. So how do you cross two tomatoes and get a Hybrid that you KNOW will have all the traits (disease resistance or drought tolerance or what have you) that you want? How do you know that the seeds in the packet will produce hybrids that express these traits?

Like, I understand why, when you then pollinate them with themselves, they don't produce the same plant. But how do we know that the original seeds are going to have the traits on the tin?

[Mark_Thompson]

I’m new to it too. Someone shared this link a few months back. Lot of good stuff if you keep exploring the page.

http://kdcomm.net/%7Etomato/gene/genes.html

[Frosti]

Regarding your question of how to know in advance what traits the F1 generation will express:
It comes down to the extent of your knowledge of the parents. When we're talking about crossing two open pollinated varieties, then you know for a fact that - by definition - these plants are homozygous, which results in almost perfectly identical gametes. So you know the eventual genetic makeup of the F1 plant beforehand. If your understanding of the interaction between different alleles is good enough, then you can confidently predict the phenotype of the F1 plant. It's with the subsequent generations, where the numbers game starts, if you don't happen to have access to a lab for genetic testing .

[jamiethemime]

Regarding your question of how to know in advance what traits the F1 generation will express:
It comes down to the extent of your knowledge of the parents. When we're talking about crossing two open pollinated varieties, then you know for a fact that - by definition - these plants are homozygous, which results in almost perfectly identical gametes. So you know the eventual genetic makeup of the F1 plant beforehand. If your understanding of the interaction between different alleles is good enough, then you can confidently predict the phenotype of the F1 plant. It's with the subsequent generations, where the numbers game starts, if you don't happen to have access to a lab for genetic testing .

That makes sense! Thank you!

[Cole_Robbie]

Almost all gene research at an academic level is either corn or fruit flies. With corn, the parents of a hybrid are inbred against each other for several generations, and then the inbred line is used to make the cross. Doing so maximizes hybrid vigor.

[Doffer]

Im wondering if tomatoes will give really hybrid vigor and production?
Corn is mainly cross pollinating and because of this weak recessive genes can be hidden. By crossing: these genes are again hidden and u get hybrid vigor. For tomatoes that are self pollinating these weak recessive genes are removed.
For corn we know the production will increase when all plants flower at the same time because the corn will set more fruit when there is enough pollen. Also to spread the pollen its important all the corn plants have the same height. So there are a lot of advantages why hybrid corn is increasing production. There advantages do not acor for tomatoes.
So what hybrid advantages do tomatoes have?

[MissS]

What advantages do hybrid tomatoes have? It depends on what they were bred and selected for. Some are for disease resistance, ship ability, production, uniform shape and the list goes on. Usually this is done by or for commercial growers to make the tomatoes more marketable and easier to ship. It sure would be nice if someone was breeding for flavor.

[Pippin]

I think tomato hybrids often give higher yields earlier and in total. In addition to what they were specially bread and selected for. At least this is what the marketing materials often claims.

@jamiethemime Maybe taking a closer look at the parent lines of the hybrid helps understand what makes the hybrid so special.

There is nothing Open about Open Pollinated stables lines, in fact they are just the opposite, Closed Pollinated lines. Think of siblings making babies for 8-10 generations in a row, how inbread and similar all individuals at the end would be. Your mother and father would be siblings, their parents would be siblings and so on back to multiple generations. Recessive genes, sicknesses and madness enrich and becomes visible. These are our open pollinated tomatoes.

Then take two such isolated and inbread lines, and cross them. No wonder the baby is nothing like the parents. If the two parent lines are not closely related, then the hybrid gains a lot of different gene variants from both parents. All recessive genes (which are often defects or loss-of-function genes) are masked when at least one of the parent has a (often healthy) dominant variant. There is also the hybrid vigor which means that the hybrid is often somewhat ”better” than the sum of the genes would suggest. Like giving earlier and more to harvest.

[jamiethemime]

I think tomato hybrids often give higher yields earlier and in total. In addition to what they were specially bread and selected for. At least this is what the marketing materials often claims.

@jamiethemime Maybe taking a closer look at the parent lines of the hybrid helps understand what makes the hybrid so special.

There is nothing Open about Open Pollinated stables lines, in fact they are just the opposite, Closed Pollinated lines. Think of siblings making babies for 8-10 generations in a row, how inbread and similar all individuals at the end would be. Your mother and father would be siblings, their parents would be siblings and so on back to multiple generations. Recessive genes, sicknesses and madness enrich and becomes visible. These are our open pollinated tomatoes.

Then take two such isolated and inbread lines, and cross them. No wonder the baby is nothing like the parents. If the two parent lines are not closely related, then the hybrid gains a lot of different gene variants from both parents. All recessive genes (which are often defects or loss-of-function genes) are masked when at least one of the parent has a (often healthy) dominant variant. There is also the hybrid vigor which means that the hybrid is often somewhat ”better” than the sum of the genes would suggest. Like giving earlier and more to harvest.

Okay but I'm asking how retailers provide seeds of hybrids that they can guarantee will grow a certain variety, is there not some element of chance involved in crossing genes?

[jamiethemime]

I'm not asking about specific traits at all, but theoretical genetics

[Pippin]

When the gemates (i.e. pollens or eggs) are produced in meiosis, the chromosome pairs rotates and then split. Normally this creates new gene combinations (and genetically different pollen grains or eggs), however, because the Open Pollinated stable lines are inbread without any variation, the pollen grains and the eggs are all identical - no matter how much the chromosomes rotated. This means that all (hybrid) children are identical because they have exactly the same genes.

But when the rotation is happening in the hybrid (=next generation) during meiosis, gene fragments from the mother and the father changes their places so that the pollen and eggs are different from each other.

[DriftlessRoots]

The parents are homozygous for all relevant genes so one is:

ABCDEF
ABCDEF

THE OTHER IS:

JKLMNO
JKLMNO

When they undergo meiosis each has only one of those strands and they combine every time in the F1 seed as:

ABCDEF
JKLMNO

[jamiethemime]

I get genes recombining. So, when you buy hybrid seeds from a vendor, how does the vendor know the hybrid seeds will produce what the packaging says?

[bower]

The companies that produce hybrids for sale, generally have also bred the two parent lines involved in the hybrid. Those are proprietary OP's, not generally released or circulating in the OP's available to us.
These companies produce lots of different parent lines, and they test the hybrids produced by different parent combinations until they find one that has a desirable combination of market values like high production, earliness, disease resistance, or even taste. (think Sungold).

In the case of disease resistance, they are able to test their parent lines and they know which resistance genes are present in each parent. It is possible to produce higher resistance in heterozygous plants with different resistance alleles at the same locus. So the parents are especially chosen to combine the desired alleles, and a legitimate reason for F1 hybrids marketed with known disease resistances.

WRT production, it is safe to say that they'll grow out a good number of the F1s and maybe in different seasons, to assess what the average performance is over multiple years or across multiple different sites/environments.

Hybrid vigor or "heterosis" is not guaranteed for every F1 tomato hybrid. I can say that with reasonable certainty, because I've made lots of F1's and by and large the majority are similar enough to their parents in vigor and production.
There have been scientific reports of yield heterosis involving the gene "sft", in which one allele produces plants with very few, very large fruits, but the combination of this allele with wild type from another parent produces high yielding F1's. I'm not sure if the sft mutant is represented in heirloom germplasm or not - but it might be. Or perhaps one could access the mutant by dehybridizing a commercial F1 that used this mutation to produce a higher yielding hybrid. Again I am not sure if or in what tomatoes that we know and grow, this mutant would be found.
Couple of publications on sft heterosis:
https://pubmed.ncbi.nlm.nih.gov/20348958/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3873276/

[Harry Cabluck]

Bower, Thanks for the thought-provoking information and links to to publications. Have you a favorite tomato variety that you consider the best-tasting?

[Harry Cabluck]

Bower, Wow! That's a lot of reading material on those links. Was hoping to learn the lesson in small words. Gives better understanding of why one should seriously consider "suckering" tomato plants. Have bookmarked those links and hope to study them more. Wishing you a successful 2023 growing and harvesting season.

[bower]

Bower, Thanks for the thought-provoking information and links to to publications. Have you a favorite tomato variety that you consider the best-tasting?

Harry, my space has been so taken up with crosses in the past years, that I've not had a recent taste of the favorite OPs. My current personal favorite is one of my own, a determinate small pink-black called Skipper Pink. Currently at F9 and maybe stable for all traits this year, I hope! The taste is outstanding and has been consistent for generations past, fortunately for me.
Also wishing you a wonderful tomato year in 2023! Lets hope this winter blast is over soon.

[Harry Cabluck]

Of the two crosses in this garden in Austin, Texas, one that seems to endure the heat is "Charley's June Bug." Recall that Charley Ball in Copperas Cove, Texas, crossed "Jaune Flamee" with "Black Cherry." Seeds that he shared in 2019 did not germinate this year, but seeds harvested off last year's Austin crop have germinated. "Flamee" is heirloom, of course, and "Black Cherry" is hybrid. Just hoping for no recessive genes.

[bower]

@Harry Cabluck you really can't beat a tomato that has been selected right in the same environment where you're growing. What color is Charley's June Bug? I recall his thread at T'ville about it, but don't remember if he stabilized one color. Either way it's awesome that you're giving it a go in Austin for the heat tolerance.

[Harry Cabluck]

Bower, Thanks. "Charley's June Bug" is dark mahogany, size of golf ball, tomato leafed, not as tasty as "Blackstone's Cherokee."