Author Topic: Inadvertent Selection  (Read 1692 times)

Joseph Lofthouse

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Inadvertent Selection
« on: 2018-12-19, 11:45:21 AM »
I do a lot of selection in my plant breeding for traits that I don't even know that I am selecting for. Here's a couple of examples:

Last summer, a collaborator gave me some maxima squash that she had grown. Thinking that they might get added to my landrace. Two of the three varieties were so hard that I couldn't even cut them open! One had a woody skin. The other was just hard fleshed in general. I hadn't realized that over the years I have been selecting for soft fruits that are easy to handle in the kitchen.

Today, the germination test for Solanum habrochaites finished. It germinated at 100%, and was the quickest to germinate of any of my tomato varieties... That was startling to me, because I have a note in my seed catalog that germination on S habrochaites is erratic, and that germination can be expected in flushes every few weeks. Ha! I suppose that during the 4 generations that it has grown on my farm, that I inadvertently selected for quick germination.

What sorts of inadvertent selection have you noticed with your seed saving?

Walt

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Re: Inadvertent Selection
« Reply #1 on: 2018-12-19, 01:44:35 PM »
Back in the early 1980s, I was working with Maximilian sunflower, Helianthus Maximilianii, at the Land Institute.
H. max, as we called it, in the wild, has strong seed dormancy.  One our interns did germination tests on different lots of the cultivar 'Prairie Gold.  She found that seed of Prairie Gold we received from the Kansas state seed multiplication farm had 15% germination.  Seed saved from the first generation we grew had 20% germination.  The next generation had 25% germination.  The intern thought she saw a pattern.
So the intern called the people who had selected and multiplied the seed before us.  The seed they collected in the wild had 5% germination.  The next generation had 10%.  Their next generation had 15%.  We started with the 15%, the next generation had 20%, the next had 25%.
Actually, I have rounded off a little.  But the actual numbers were within 1% up or down from these numbers.
Makes sense of course.  Those that didn't germinate contributed nothing to the next generation.  We never bothered to select for better germination as we had planned to do.

reed

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Re: Inadvertent Selection
« Reply #2 on: 2018-12-19, 03:29:29 PM »
The spring after finding my first sweet potato seeds I didn't know what to do with them. Literature I found about sprouting them talked about all kinds of what I consider ridiculous things like soaking in sulfuric acid. I don't do stuff like that, I don't even do tight control of light or temperature. I worried over it awhile since they were so few and so rare but finally decided to heck with it. If they don't like me and my technique they can just not grow and most didn't.

I think I inadvertently selected for less picky ones. Folks I'v sent seeds to report much higher germ rates using more controlled technique, even higher than any literature I found spoke of absent the sulfuric acid and such, so I think my seeds are pretty good.

It's purposeful now rather than inadvertent but I'm keeping up my sloppy technique cause although germination is still quite low, it goes up each year and now that I can afford to throw more seeds at it, I might even get more sloppy.

Walt

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Re: Inadvertent Selection
« Reply #3 on: 2018-12-20, 12:41:08 PM »
Years ago, I used to have 4 0'clocks blooming in my mostly vegetable garden.  They started as a mix of red, white, and yellow.  Starting in their second year, I noticed a reduction in the number of reds.  One night I was in my garden later than usual.  I noticed that at dusk, the white and yellow 4 0'clocks were clearly seen, and were attracting moths which pollinated them.  I could hardly make out the reds, which the moths didn't interact with.  I think the moths weren't seeing them either.  Bummer.  I  liked the reds best.

bill

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Re: Inadvertent Selection
« Reply #4 on: 2018-12-21, 05:12:12 PM »
I often find that my selections germinate better and have a longer seed life than what I started with.  For example, my parsnips and root parsley stay above 80% germination after four years.  I think a lot of that is just due to increased heterozygosity though.  I also seem to be getting a lot more resistance to standing in wet soil in crops that I harvest last.  I used to lose a lot more potatoes to rot.

Carol Deppe

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Re: Inadvertent Selection
« Reply #5 on: 2018-12-21, 06:03:13 PM »
I do a lot of selection in my plant breeding for traits that I don't even know that I am selecting for. Here's a couple of examples:

Last summer, a collaborator gave me some maxima squash that she had grown. Thinking that they might get added to my landrace. Two of the three varieties were so hard that I couldn't even cut them open! One had a woody skin. The other was just hard fleshed in general. I hadn't realized that over the years I have been selecting for soft fruits that are easy to handle in the kitchen.

Today, the germination test for Solanum habrochaites finished. It germinated at 100%, and was the quickest to germinate of any of my tomato varieties... That was startling to me, because I have a note in my seed catalog that germination on S habrochaites is erratic, and that germination can be expected in flushes every few weeks. Ha! I suppose that during the 4 generations that it has grown on my farm, that I inadvertently selected for quick germination.

What sorts of inadvertent selection have you noticed with your seed saving?

There are a couple of major genes in cucurbits associated with the woody skin. These can literally have a very hard wood layer that actually blunts your knife if you try to pound it into the squash. They are best opened by dropping them on the driveway from the right heights so that they break cleanly in two. Most of the varieties we grow don't have the woody skin, because grocery store shoppers don't know how to open them. Those hard shelled varieties can be very nice to have if you have a problem with rodents eating your squash as they finish maturing in the field.

Automatic selection in squash seems to be for bigger seed cavities, thinner flesh, and smaller seeds but more of them. I select every fruit to counter these in every generation. I think this is the reason why so many commercial varieties start out good and then deteriorate year by year after released.

If you save seed from volunteers you can select for seed dormancy mechanisms. At least, where the seed represents seed you planted in some earlier year that did not come up that year.

Usually, where we save seed only from the patch we planted that year, we automatically select against seed dormancy mechanisms.

Usually, wild species are outcrossers and often have incompatibility mechanisms. But the domesticated derivatives have often lost incompatibility mechanisms. So we seem to often automatically select for inbreeding tendency when we domesticate plants. My guess is that what happens is that inbreeders are more likely to present us with new phenotypes based upon homozygous recessive mutations, and we tend to save and preserve and play with anything different. Such new recessive mutations have a much harder time presenting us with the new homozygous phenotype when in obligate outbreeding material.

I think people often times accidentally select for slow germination and wimpy growth by letting transplants overgrow so much that those that grew fastest become severely pot bound and are so badly damaged in in transplanting that the plants are rogued in the field.

I think you can also select for slow germination and wimpy growth by planting frost-tender plants too early. Then you get a hard frost, and all those that came up first are killed. And your entire plot is derived from plants that had not yet emerged when the frost hit.

I routinely get automatic selection against bush and semi-bush squash. I sow about 3X to 10X as much seed as needed so as to select for the fastest growing plants. This pretty effectively eliminates all homozygous and heterozygoust bush plants, since they don't develop root systems as big as full vine plants, and the plants just don't grow as fast. If I actually want any bush plants from segregating material, I have to take special precautions not to eliminate them automatically.
« Last Edit: 2018-12-21, 06:32:25 PM by Carol Deppe »