Hybrid vigor in tomatoes

[Fred Hempel]

I used to be skeptical that it was common, and I was completely uninterested. Not so much anymore.

There are probably a number of mechanisms by which it can occur, including this one:

http://www.plosgenetics.org/article/...l.pgen.1004043

Now my questions with regard to hybrid vigor are more like: "Is there typically a flavor penalty with yield hybrid vigor?"

Up until now I have been largely ignoring the F1 generation and viewing it as mostly a source of F2 seed which can be selected (to create true-breeding/open-pollinated lines). This is the first year I will be looking more closely at potential cross combinations that might have hybrid vigor.

Anyone want to chime in about their experiences?

[Fusion_power]

Crossing between most of the domesticated tomato varieties gives relatively low levels of heterosis. Wild species crosses can give incredibly high levels. I've got a few crosses in my garden this year that demonstrate just how much of a difference an F1 can make in production, disease tolerance, and pest tolerance.

[Fred Hempel]

How much of a flavor cost is there, when crossing with wild species. Are there any wild relatives that are associated with good F1 flavor?

Also, are there seed viability issues when making these crosses?

Originally Posted by Fusion_power

Crossing between most of the domesticated tomato varieties gives relatively low levels of heterosis. Wild species crosses can give incredibly high levels. I've got a few crosses in my garden this year that demonstrate just how much of a difference an F1 can make in production, disease tolerance, and pest tolerance.

[carolyn137]

Fred, your initial question was about heterozygosity as related to tomato taste. And I'll get back to you and give some examples and pose some other questions.

I have two main passions, one is tomatoes, the other is tennis and right now it's the fourth round at the French Open in Paris and my TV is calling to me about the current match between Tsonga and Djokovic.

Carolyn

[frogsleap farm]

As you know Fred, I've been interested in this for a couple of years and am now convinced, and the literature supports, that there can be heterosis for both yield and flavor. I think there may be a yield /flavor tradeoff at very high levels of fruit yield - but less so with indeterminate plants. Certainly there is room for improvement for both flavor and fruit yield and I think F1 hybrids offer some advantages in this regard. http://frogsleapfarm.blogspot.com/20...varieties.html

[Fusion_power]

Fred, I have plants of the cross Piennolo del Vesuvio X LA0417 in my garden and within a couple of weeks to ripe fruit. LA0417 is an exceptionally good flavored regular leaf S. Pimpinellifolium with a complex background. The original notes indicate seed were sampled from multiple plants in a population that was segregating from a cross of S. Pimpinellifolium with S. Lycopersicum.

http://tgrc.ucdavis.edu/Data/Acc/Acc...contains=false

I grew out a large number of plants from TGRC seed in 2012 and 2013. One single plant in 2013 showed good tolerance to septoria. I sampled the fruit and was surprised to find that they were sweet as sugar and had a rich complex tomato flavor. I used pollen to make a cross with Piennolo which is potato leaf and allowed me to easily pick out the crossed seedlings this spring.


From my experience with other in-species hybrids, flavor is usually compromised to some extent, usually as a result of decreased sugar but also from reduced flavonols. Crossing to wild species generally demolishes flavor with the single exception of crosses to S. Pimpinellifolium which can in some cases actually improve flavor. Crosses to any of the greenfruited wild species is particularly damaging to flavor in the F1, but can be selected for recessives in further generations to significantly improve flavor.

I wrote this and put it in the tomato wiki. It will help to understand the complex relationships between the wild tomato species and the domestic type.

Including Solanum lycopersicum, there are currently 13 species recognized in Solanum section Lycopersicon. Three of these species—S. Cheesmaniae, S. Galapagense, and S. Pimpinellifolium—are fully cross compatible with domestic tomato. Four more species—S. chmielewskii, S. habrochaites, S. neorickii, and S. pennelli—can be readily crossed with domestic tomato, with some limitations. Five species—S. arcanum, S. chilense, S. corneliomulleri, S. huaylasense, and S. peruvianum—can be crossed with domestic tomato with difficulty and usually require embryo rescue to produce viable plants. The Lycopersicon section has not been fully sampled within wild species in the South American range, so new species may be added in the future.
Solanum section Lycopersicoides and section Juglandifolium are represented by two species each that are considered bridge species genetically intermediate between tomato and non-tuber bearing potato species. S. Lycopersicoides can be crossed with domestic tomato and introgression lines [68] have been developed. This species was significant in moving the domestic tomato from separate genus status into the Solanum group because it directly links the tomato into the potato family.

I don't expect to find anything exceptional in terms of fruit flavor in most of the wild species, but there is some potential in S. Habrochaites, S. Pennelli, and particularly in S. Pimpinellifolium. The flavor of Sungold for example is derived from S. Habrochaites.

[carolyn137]

Originally Posted by carolyn137

Fred, your initial question was about heterozygosity as related to tomato taste. And I'll get back to you and give some examples and pose some other questions.

I have two main passions, one is tomatoes, the other is tennis and right now it's the fourth round at the French Open in Paris and my TV is calling to me about the current match between Tsonga and Djokovic.

Carolyn

Tsonga lost.

Fred, I started to read your link but it was very long and I'm not enough of a geneticist to understand all that was being discussed. So I skipped to the footnotes to see if I knew any of the authors of any of the papers referred to and I sure did.

This is a bit offtopic but it was Zach Lippman, whom I once knew well. He graduated from Cornell and while there worked with Tanksley who is the head of the Cornell tomato gene project. I can't remember how we first met but he was doing a post doc in Israel with Dani, forgot how to spell his last name, who has a world wide reputation as a tomato geneticist. Zach wanted me to send him 1000 different varieties for the work he was doing. I had to ask Glenn Drowns and Craig LeHoullier to help and we corresponded with each other so we didn't do duplicates. I never read any of his papers.

There was fighting in Isreal at the time and he and his family had major problems, and I remember him saying he couldn't wait to get back to the US for safety and where the pizza was good.

Anyway,now he's at Cold Spring harbor, and here's a GOogle link and perhaps some of you can understand better than I can what he's working on now.

https://www.google.com/#q=zachary%20Lippman

Sorry for the diversion and now some questions.

What degreeof heterozygosity is known to qualify a variety as being an F1 hybrid. Right now i don't think that can be done by any current tests, but I'm curious, and here's why.

Andrew Chu in Fl introduced the variety Santa F1, bred by the Known-You seed company in taiwan.I got to know him well.it was the first grape variety that the public became aware of although there were others before it that were grape shaped;

He was raising many thousands of plants each season for commercial purposes, salesof fruits,and toldme that 99% of saved F2 seed came true, I spread that around with his OK and some folks are now on the F8 or F9 and it's perfectly stable.

The off type has round fruits,not grape shaped, and the Brix level is much lower.

Again,what percentage of genes have to be in the heterozygous state in order for a variety to be called an F1 hybrid.

Another example.

I dehybridized Ramapo F1 since it was said it was going out of production. I knew someone at Rutgers and he provided me with some F1 seeds. A friend in NJ, a retired lawyer had sand bagged F1 seed and sent me 6 F1 plants to use as a comparison when making initial selections.

At the F3 it looked OP and very stable, so I sent it to Barkeater, who posts here and was a large scale market gardener in NJ at one time and had grown Ramapo F1 many times. He could not tell the different between the F1 and my OP and that relates to taste as well.

The two parents of Ramapo F1 are known.

So at least for Santa F1 and its OP and Ramapo F1 and its OP,no differences could be detected by those who tasted both.

Which is the question you asked. Whether it would be different with more modern hybrids with many more parental inputs, I don't know.

Carolyn, too tired to go back and edit out any word bloopers.

[Tom Wagner]

The literature is full of examples of 'hybrid vigor' however most of it simplistic or overly complex...you be the judge.

I have made thousands of my own hybrids and though some are outstanding, most are not and I use the term 'hybrid vigor' loosely. I am rather fond of the term 'combining ability' since it implies that the right combination is needed to achieve success to claim a viable hybrid vigor or hybrid advantage.

Combining ability in potatoes is a valuable mechanism for improving potato varieties. Most potatoes are crossed among hybrids in the first place and the chance combination that works is easily seen when you see the near perfect potato clone. This so-called "hybrid vigor' in potatoes is obvious but not so in tomatoes because crossing indiscriminate varieties may not result in good combinations.

Test hybrids must be done to check out the advantages from the cross. Is it really better yielding? Does it have a more vigorous root system? Is is earlier?
Is it better tasting? Some of the best hybrids on the market are those that have very similar parents save a difference in as few as one trait. I could list many of the hybrids where the only real difference is in the nematode resistance, or nipple gene, or verticillium or fusarium resistance genes, ripening inhibitor (rin), potato leaf, determinate/indeterminate, and so on.

I have lots of inbred lines of tomatoes that I feel are weak by themselves but devilishly glorious in a hybrid. Woolly lines are classic in my opinion.

Sometimes hybrids are best tested out as scions on grafted rootstocks. The rootstocks are usually hybrids between domestic lines and wild species and the 'hybrid vigor' of the root growth doubles as an influence on the potential yield and quality advantage of a grafted variety. I have my DANCING WITH SMURFS out there on grafted roots being sold all over the western states. I even have the hybrid DANCING WITH SMURFETTS on rootstocks and it will be fun to see the comparison of that sales effort.

What could constitute 'hybrid vigor' with a few examples? Well, many classic varieties are somewhat late but making a hybrid between them makes the cross much earlier and in a cold climate as here in the PNW...that makes a big difference. The many hybrids I have made with late blight tolerance is going to prove to a few locals that the darn things will outyield the others simply for the longer harvest season.

Flavor combinations are a must in determining which hybrids actually have an enhance flavor package. I am doing this with hybrids with frost resistance/chilling resistance genes that allow the tomato fruits to taste better late in the season when it gets too cold and rainy for most tomatoes.

I am making hybrids with the indeterminate short internode traits. This will allow more fruit to set on trusses along the main stem.

I was showing one of my sponsors that a cross between the Indigo Rose and Green Zebra makes for a very productive plant and the same for Black Pineapple x Green Zebra. The latter has a super flavor whereas the former is good but not that good, probably some genetic drag from the Indigo Rose. My Brady Bunch blue is my best flavored inbred among my breeding lines. I am testing out the many hybrids this year to see if the F-1's have the combining ability I want for flavor.

I have a habit of crossing my F-1's with other F-1's. The resulting combining ability within these progenies is all over the place. A quick selfing out of these outstanding clones give me great potential clones to use as tester hybrids as F-2's, F-3's, and down the line until I find the best candidates for making hybrids as they become stable around the F-6 level.


I am constantly re-selecting my breeding lines and making crosses to see if the traits combine in a hybrid the way I desire. The hybrid I call Muddy Hawaiian below is but one example of combining blue, black and Pineapple variety backgrounds.

http://i.imgur.com/UurTXUy.jpg

I don't profess to know a whole lot about hybrids as I am still learning after these 61 years of making hybrids. You can bet that I will be making a lot of related line hybrids....that way I can predict the amplification of the good traits such as flavor to be paramount along with the 'piggy backing' of the classic genetic combinations. A serendipitously intoxicating mix of recessives and heterozygosity will be evident. I have just got to see that some of these hybrid seeds are pinpointed to be available on one gallon grafted plants only. OK...OK..maybe a few hundred thousand to the high row tunnel growers.

[heirloomtomaguy]

Wow Tom that tomato is black as it gets. Beautiful.

[doublehelix]

I have been told that heterosis in tomatoes does not exist or is limited at best. However, that does not support what I have been seeing in my own breeding efforts. Sometimes I can see the difference in a tray of seedlings and I almost always see it in fruit production.

I would ask any breeder here to reflect on their experiences with “chasing” an F3 for the same production of fruit you saw in your F2 selection. At least anecdotally this would appear to be evidence of hybrid vigor. I have lost count of how many selections I have made in the F2 because the chosen plant had the flavor, look, and production that was appealing to me, only to have trouble recovering all 3 of those qualities in subsequent generations. It can also be challenging to find a selection in the F2 that was as productive as the F1.

I don't think flavor is compromised by hybrid vigor. I do a lot of breeding with modern hybrids and they are likely to have the uniform ripening gene as well as being determinate. As has been noted elsewhere, the uniform ripening gene has a lot to say about flavor. I have found a few exceptions, but if you remove the uniform ripening gene you have a better chance of catching flavor in the progeny.

Nothing really scientific, just my observations.

[Fred Hempel]

Yes. I am well aware of your fruit quality/flavor results, as it relates to hybrids. And also your work with rin lines. I also should have cited your blog post on hybrid vs OP tomatoes at the top of the thread.

This photo of the sft results is particularly striking, and highlights how plant architecture may be one key component of production heterosis -- and it shows that plant size is not always correlated with total fruit production.

http://3.bp.blogspot.com/-NcIc-lRefS...-heterosis.jpg

Originally Posted by frogsleap farm

As you know Fred, I've been interested in this for a couple of years and am now convinced, and the literature supports, that there can be heterosis for both yield and flavor. I think there may be a yield /flavor tradeoff at very high levels of fruit yield - but less so with indeterminate plants. Certainly there is room for improvement for both flavor and fruit yield and I think F1 hybrids offer some advantages in this regard. http://frogsleapfarm.blogspot.com/20...varieties.html

[Fred Hempel]

Dar,

Once again you are a great source of information for the rest of us.

Thanks for elaborating on wild species hybrids with domesticated lines. I found the statement about Sungold below particularly interesting. Did you figure this out based on similarities between Sungold and your own habrochaites/domestic hybrids?

Or is there information out that indicating that one of the Sungold parents has habrochaites parentage? I always assumed that the Sungold parents were a closely guarded secret, but Sungold foliage (and vegetative aroma) is so distinct so I can see how perhaps anyone working with habrochaites would quickly put 2 and 2 together.

Originally Posted by Fusion_power

I don't expect to find anything exceptional in terms of fruit flavor in most of the wild species, but there is some potential in S. Habrochaites, S. Pennelli, and particularly in S. Pimpinellifolium. The flavor of Sungold for example is derived from S. Habrochaites.

[Stvrob]

Would it make any sense, for seed saving purposes, to purposefully cross two heirlooms of the same variety. Say two Brandywines, growing next to each other in a row, cross one with other, bag the blossoms and growing out the seeds for the next season? Is there greater genetic variance between individual plants than their is among male and female parts of the same flower? If so, would this tend to prevent your line of seeds from becoming too inbred? Kind of like marrying off your daughter to her second cousin instead of her 1st cousin? The kids will still probably have redhair and freckles?

[joseph]

Originally Posted by Stvrob

[...]purposefully cross two heirlooms of the same variety[...] Is there greater genetic variance between individual plants than there is among male and female parts of the same flower?

Always yes. But from a practical standpoint, plants that have been inbred for long enough to be considered heirlooms (50 generations?) are functionally clones even if there is some minor variation between plants.

Originally Posted by Stvrob

If so, would this tend to prevent your line of seeds from becoming too inbred?

In my world view, by the time that you have done enough generations of inbreeding to call a plant an heirloom (or merely stable) it is already too inbred.

But all heirlooms are not created equal... This spring someone sent me seeds from a "Croatian Brandywine". Already at 5 weeks old there are two different types of plants with different shaped leaves. I don't have any way of knowing whether the plants are crossed, or if the variety has retained that much genetic diversity from the beginning. A note that accompanied the seed said "The bees were all over this last summer." When I look up "Croatian Brandywine" in Tatiana's tomato database, a variety by that name is described as regular leaved with 15% to 20% potato leaved. Since this is an individual's heirloom from the old country there is no way of knowing whether the variety's archetype would describe a population that is 25% potato leaved or whether this is due to an inadvertent cross pollination. If the variety is highly attractive to pollinators then ongoing crossing between regular-leaved/potato-leaved individuals might be part of the variety's archetype.

[carolyn137]

Originally Posted by joseph

Always yes. But from a practical standpoint, plants that have been inbred for long enough to be considered heirlooms (50 generations?) are functionally clones even if there is some minor variation between plants.



In my world view, by the time that you have done enough generations of inbreeding to call a plant an heirloom (or merely stable) it is already too inbred.

But all heirlooms are not created equal... This spring someone sent me seeds from a "Croatian Brandywine". Already at 5 weeks old there are two different types of plants with different shaped leaves. I don't have any way of knowing whether the plants are crossed, or if the variety has retained that much genetic diversity from the beginning. A note that accompanied the seed said "The bees were all over this last summer." When I look up "Croatian Brandywine" in Tatiana's tomato database, a variety by that name is described as regular leaved with 15% to 20% potato leaved. Since this is an individual's heirloom from the old country there is no way of knowing whether the variety's archetype would describe a population that is 25% potato leaved or whether this is due to an inadvertent cross pollination. If the variety is highly attractive to pollinators then ongoing crossing between regular-leaved/potato-leaved individuals might be part of the variety's archetype.

Joseph, some back history about the two leaf forms of the Croatian Brandywine:

http://tomatoville.com/showthread.ph...ian+brandywine

And if you do a search here at Tville I think you'll find that apparently the Croatian Brandywine did not originate in Croatia and is not a Croatian heirloom . No doubt someone sent seeds for Brandywine to someone in Croatia and the person who offered it at that plant sale in CA named it Brandywine from Croatia, b'c that's where the seeds came from.

There are many of us who send seeds to persons in many countries and there are also many seed sites in many countries that sell tomato seeds from many countries, including the US/

Brandywine originated in the US.

Carolyn