Hybrid vigour and genetic bottlenecks

[Raymondo]

With the number of projects, large and small, going on, I began wondering about genetic vigour. I know that tomatoes are self-fertile, and certainly appear to be happy inbreeders.
This would suggest that there's little to be gained from hybrids. But I've noticed with my own crosses, and grow outs of other people's crosses, that these hybrids seem to exhibit what could be described as hybrid vigour. The plants are often vigorous and less disease prone than the OPs around them.
I wonder too about the effectiveness of home seed saving. Many homegardeners, me included, often save from just a single fruit from a single plant. I can't help feeling that by doing so we are creating genetic bottlenecks.
What do others think?

[goodwin]

My personal observation, which is probably in the minority, is that there is only a slight boost in vigor because there is too little genetic variation in the standard varieties of tomato. One estimate I've seen put the genome at about 80% of the native stock, which would indicate a high degree of line breeding. Crosses to more widely separated strains and other species show much greater
F1 vigor I believe. Traditionally, seed was saved from the best of a number of plants, which rewarded adaptation to a particular environment. Crosses can be part of that process, but you have to grow them out in order to select for desirable traits.
So I would say continue to save seed, but selectively.

[Wi-sunflower]

Acording to Carol Deppe's book on growing/creating hybrids, tomatoes don't show "hybrid vigor". Personally i think what we may think is hybrid vigor may just be the differences we could see because of a different growing season -- more or less heat & water and at specific times.


Many homegardeners, me included, often save from just a single fruit from a single plant.


That sentance tho does bother me.

I made trades last winter for many new-to-me varieties. Several of them were very "mixed". For 1 variety, only 1 out of a dozen plants looked like the variety should.

My feelings are that if you are only growing 1 plant of a variety and have a whole lot of plants close together, they will most likely grow into a jungle and inter-mingle the stems and then can do an accidental cross. Saving seeds under conditions like that are bound to lead to problems. Personally I wouldn't trade under those conditions unless I bagged blossoms.

Personally I try to have at least a dozen + plants in the ground so I can see if there is some varietion or not. We plant in rows wide enough to us the tractor mounted rototiller, at least 7 feet wide. We try to plant each plant 3-4 feet apart in the row. We often won't pick the fruit from the first and last plants if they are growing too close to/mingled with their neighbor.

Just my opinions. Take them for what you will,
Carol

[mjc]

If I don't bag or have a fairly reasonable assurance (like the first fruits of the first plant to bloom, or a mix of fruit from a single variety patch) that there isn't the likelihood of a cross, I won't trade the seed. I may save it and grow it out for myself...but nope, not trade it. I even warn that the not bagged seed is not bagged and if it wasn't, why not.

I prefer saving seed from more than one fruit, because I like having a fair amount of it. I prefer having at least 30 seeds of any variety and of course I like having some on hand to trade...

[travis]

I have observed hybrid vigor in the tomato crosses I have made. The F1s have been measurably more vigorous than either parent in most cases. I'm a believer.

With regard to potential genetic bottlenecking, I'm not concerned hugely about saving seeds from limited numbers of sibling plants because through selection of the better examples among the siblings, I have observed improved performance in the following generations. I'm thinking since tomatoes are 95% self-pollinating naturally, some degree of "bottlenecking" would occur with or without human interference.

[TZ-OH6]

An open pollinated, self pollinated, variety is a genetic bottle neck. What you are doing is saving a facsimile clone of the parent plant in seed form. The reason to save from multiple plants is not to preserve genetic diversity [a la wildlife management] but to dilute genetic diversity in case there was either cross pollination or genetic mutation in one fruit, or if that one plant was an accidental F1.


You may see hybrid vigor in F1 plants, but that does not ensure flavor, size color and shape will be better than either parent. I grew out a bunch of F1 and F2 this year and for the most part they tasted worse than the parents, got all of the same diseases, and showed quite a bit of variability in vigor. I had some tremendously productive plants that tasted terrible.

These crosses were from very different parents, so if you crossed two similar varieties [say pink/red beefsteaks] you might have better luck/consistency.

[carolyn137]

I would expect to see hybrid vigor in the F1 of a new cross, but there are few who do such crosses that are doing it just to get F1 seed. Almost all save F2 seed, plant out, make selections, continue doing, to see what they get and then determine what they want to work with to get out to the OP state.

As for saving seed I have NEVER saved seed from just one fruit unless I had no alternative. Always many fruits from one plant or better still many fruits from several plants. And fruits of all sizes as was discussed here in another thread.

MY reasoning for doing so is since I don't bag blossoms I want to dilute out any naturally X pollinated fruits to lessen any F1 seeds in any given fruit.

I used to save 500-1000 seeds of all my varieties for SSE listings and I'm telling you, folks could go thru maybe 500-700 of those seeds and then an offtype would pop up. To some that's a problem while for others it's an opportunity.

Mark Korney is still working on an offtype from KB seeds from 2004 I sent him and is getting red and pink hearts. For him it's an opportunity while others will just complain.

There already is a genetic bottleneck with our garden types of tomatoes and if I think of the name, I can find it, you can Google her work. She's been working mostly on what genes are involved in tomato shape and size. And there's another person who has been involved in doing DNA analyses of species as opposed to non-species and coming up with some interesting information.

[travis]

Interesting stuff, TZ and Carolyn. I agree generally. But my observations were more in direct response to the questions asked initially about hybrid vigor and potential bottlenecking if not saving seed from several plants. I guess I saw those as the two questions.

Again, I see hybrid vigor clearly exhibited in many custom tomato crosses I have made. I'm talking about vigor in growth, vine health and production. Not necessarily flavor or fruit qualities like Brix which I have never measured, meatiness, seediness, wall thickness, those kinds of things. Just growth vigor, plant health and fruit production. I see it so I believe it. I'm guessing professional breeders can answer to whether there actually is hybrid vigor exhibited with regard to other characteristics.

I agree that saving seed from several fruit from the same plant waters down stray cross pollinations. I agree that saving seeds from several plants of the same variety lessens the effect of possibly saved F2 seed.

But shouldn't the discovery of an F1 plant in a block of open pollinated vines been made prior to saving seed? I mean by a keenly observant seed saver?

And I'd have to ask, in general, how many plants of the same variety do you think the average amateur tomato hobbyist grows to save and trade seeds from? Two? Four? So how much bottlenecking are we dealing with. Or is bottlenecking even a concern in self-pollinating species really?

I prefer to save seeds from several tomatoes off the same vine and even if growing multiple vines of the same variety, I prefer to save seeds from only the best single vine or couple of vines in each variety.

If the questions were asked about an active outcrosser like corn, I'd have a whole different outlook on hybrid vigor and bottlenecking. But the questions were about tomatoes.

[goodwin]

Like Travis, I often have the parents of crosses growing side by side with their offspring, but I usually don't see much or any F1 boost or the significant dropoff you would expect in the next generation.
The exceptions are interspecies crosses like the l. esculentum (common tomato) to it's relative l. hirsutum below. It's just a monster compared to the plants in the background.

[SteveS]

Whoa! That is a monster. Where'd you get that? And was the fruit any good?

Steve

[goodwin]

Yeah, Steve, it was a really decent red, high solubles from the wild parent and produced bushels. I gave them a fancy name and took them to market.
The next generation should be interesting as the lines segregate.
Lee

[travis]

Are those F1 or F2 or subsequent fruit? How large are they? How large was the esculentum parent fruit?

[goodwin]

They are F1, about 2 inches in diameter, so salad size. The parent I don't know. I've done my own crosses now, but this was seed from a supplier.

[travis]

Oh, I was thinking the tomatoes in the picture were the esculentum x hirsutum crosses you did. Were the ones in the picture from a commercial supplier or private breeder?

Do you have any problems getting such a cross species pollination to take?

[goodwin]

Well. Travis, it's probably a combination of this cross being difficult and me being fairly inept, but I had no luck last year. So I ended up getting crossed seed from a supplier for planting this spring so I could see how it segregated the following year. Then I started the pure hirsutum (f. flavin) I'd saved and out of a dozen attempts this summer only three fruited and set seed.
Lee