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A Question about hybrid vegatable seeds...

Posted by Gata z4 NH (My Page) on
Fri, Aug 20, 04 at 8:35

Hello all. I feel that this is very basic and that I should get it, but somehow the "click" eludes me. I understand that heirloom vegetable (let's say tomatoes or cucumbers) are "open pollinated" and will come true from seed if grown away from others of their kind, yes? Hybrid varieties, on the other hand, will not, because their seed was origianlly created HOW? Was the process like that of daylily hybrids where plant A and Plant B are crossed? But that doesn't make sense to me because any of the resulting plants from that cross will not necessarily show the same characteristics of eachother. So, how are hybrid vegetables created? How is it that all the seeds in the packet of hybrid tomatoes will all be the named hybrid?
Maybe your explanations will help me understand this. Thank you.


Follow-Up Postings:

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RE: A Question about hybrid vegatable seeds...

Well ... propagation / breeding is not my area of knowledge ... I must admit when I passed genetics in college I ran like a thief LOL !!!

In theory a hybrid has a gene pair where one allele is different then the other and a dominant allele will "mask" the phenotype or undesirable character of the recessive allele ... so your gene pair may look like Aa ... so an original cross AA X aa ... would result in all Aa progeny since each parent can only contribute an "A" if it is "AA" gene or an "a" if it is "aa"... additional crosses of the first generation hybrid progeny would be Aa X Aa now each parent has a 1/2 probability of donating an "A" or "a" gene and the probability is 1/4 or 25 % of the second generation will be aa and express a character that you were able to mask in the first generation of hybrid seeds ... that is the progeny are not constant like the hybrid generation.

Perhaps and I'm only ** guessing ** here but maybe heirloom vegetables have gene combinations like "aa" or "AA" which when crossed with themselves AA X AA or aa X aa would only give "AA" or "aa" combinations in future generations.

Thats about all I can add ... I'm starting to get "genetic nightmares again " !!!! Hopefully someone that really knows plant breeding will step in and help us out ....

Good Day ....


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RE: A Question about hybrid vegatable seeds...

Gata,

Yes, what The Mohave Kid said. For a specific example, if you were to hand pollinate two heirloom tomatoes, those seeds would produce an F1 hybrid tomato that would be uniform and maybe better than either parent variety, so you might like your F1 hybrid a lot.

But if you were to save seed from your new F1 tomato, those seeds would be F2 seeds (second generation seeds) and all sorts of recombinations of characteristics would occur and very few, if any, would be like your F1 hybrid. Some might be very weird and possibly, if you grew a lot of them, you might find one very similar to your original F1 hybrid. You could even conceivably find a recombination that was even somewhat better then your F1 hybrid.

If you want to grow more of your F1 hybrid tomato, without recombining vast numbers of different combinations of the two parent's different characteristics, you need only to repeat the cross using the original "pure" heirloom strains. Or, as an alternative, you could simply grow cuttings from your original F1 hybrid cross.

If you had a lot of space to grow thousands of tomatoes, you could stabilize a new open pollinated version of your F1 hybrid by growing enough F2s to find a single plant much like the F1, saving as many seed as possible from that plant (you could even multiply it by cuttings to increase that seed yield) and then grow a lot of F3s from that specific selection. Then look through all of your F3 tomatoes for one or two plants very similar to what you are trying to stabilize.

The F3s will still be showing a lot of new variations, but they will be more noticeably related to the self pollinated F2 individual that you selected. You will be filling compost piles with tomato plant rejects. You may find only one acceptable plant in a thousand or ten thousand. But each new generation, from F3 to F4 to F5 and so on, will show more convergence toward your desired new tomato, provided you ruthlessly select only the best for the seed of your next generation. By repeating this for several generations you will have stabilized an open pollinated version of your original F1 hybrid tomato.

If you were growing lots of plants in each generation and keeping only the very best it is conceivable that your stabilized variety could be even better than your original F1 hybrid variety. (And you will have created a mountain of rejected tomato vine compost as a by-product.) So now you would have a stable superior tomato that you could cross with some other open pollinated variety to create a wholly new F1 hybrid tomato, and the madness could begin again.

As you see, it is really much easier simply to repeat making the original cross to produce more F1 hybrid seed than it is to save and grow very many seeds from them in a multi-year effort to stabilize the new tomato as an open-pollinated version.

Some F1 hybrid seeds are expensive because hand pollination may be required. Some F1 hybrid seeds cost less because they have found a way to make the cross without hand labor or with much less hand labor (or with cheaper hand labor overseas.) For example, economical F1 hybrid corn is produced by lopping off the tassels of the plants of the "female" variety to prevent self pollination. These female plants are grown in rows alternating with the "male" variety which gets to retain its tassels. The wind just carries the pollen from the tassels of the male variety to the silks of the female variety and F1 hybrid seed between those two varieties is produced on the cobs of the female variety very inexpensively.

I hope that explains how F1 hybrid vegetable seed produce uniform plants. They are uniform because each has the same set of pure-strain parents.

Incidentally, if you have the space to grow quite a few plants, plant breeding can be an interesting hobby.

MM


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RE: A Question about hybrid vegatable seeds...

I think Gata's problem is confusing the 2 main types of hybrid vegetables and crops.

Most traditional hybrids were generally developed by breeders as TRUE BREEDING LINES, which requires selection of the parent stock over a number of generations to reduce heterozygosity almost to zero, before placing on the market a variety that will come true from seed for as many generations as the grower cares to save the seed. Think of tomato or bean varieties. Sorry but I've forgotten the genetic mechanisms involved, it's 40 years since I learnt them, but I think they are much as The Mohave Kid attempts to explain. Open pollination between plants of the one true-breeding variety will not introduce variation in the next generation because parents are homozygous. But if, for example, you grew 2 different tomato varieties in the one bed, open pollination might produce some seedlings inheriting genes of both varieties, or so you might think.

The other main type is the F1 HYBRIDS, best known in crops like maize. These are one-off hybrids between 2 genetically different parent varieties, maintained by the seed company purely for producing this hybrid seed. The F1 generation is highly heterozygous and thus gains hybrid vigor, while being at the same time constant in its characteristics. However, if the seed of these F1 plants is saved and sown the genes are remixed in a much more random manner (I seem to recall that chromosome crossovers are the cause of this) and the F2 and subsequent generations are not only highly variable but show reduced hybrid vigor. The upshot is that if you want to grow these high-yielding varieties you have to buy them each time from the seed company. Depending on the species, producing F1 seed can be labor-intensive, as the seed grower may have to remove all the male parts of the mother plants to prevent self-crossing. Maize is possibly one of the easier to manage, as male and female inflorescences are large and well separated.


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RE: A Question about hybrid vegatable seeds...

I know it's been four years, but this is a very interesting read.... LOL

~Angela


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RE: A Question about hybrid vegatable seeds...

yeah it is! I'm coping this and printing it out. I have a spiral notebook that I glue this sort of thing into.

if you guys are still around thankyou for posting this.


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RE: A Question about hybrid vegatable seeds...

Now 10 years old and still worthy of reading.

NECM


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