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Post by Joseph Lofthouse on Aug 7, 2010 22:31:18 GMT -5
Since the pericarp is maternal tissue, I wonder how much influence the genetics of the embryo have over pericarp thickness? There is likely to be some modification, but will it be enough to tell the difference between homo-su1 and homo-su1-se?
Regards, Joseph
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Post by DarJones on Aug 8, 2010 8:46:50 GMT -5
When I tried with seed germinated this past spring, I got 100% thick skin seed from Merit (su), 100% thin skin seed from Silver King (se+), and a range of thickness in seed from a known su/se cross that should segregate 1:4 homozygous se.
As I said, it looks very promising.
DarJones
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Post by Joseph Lofthouse on Aug 8, 2010 12:09:02 GMT -5
As I said, it looks very promising. DarJones I agree. Thanks for sharing an excellent idea. I soaked some corn seed overnight in water and tested the pericarp thickness today using an se+ sweet corn and a normal sweet corn. The sugary enhanced pericarp was around 0.002 inches thick. The normal sweet corn pericarp was around 0.005 inches thick. A very noticeable difference. It was hard to separate the pericarp from the endosperm without destroying the kernel but I think it would be easier in a few days after shoots emerge. I used a normal machinist's caliper to measure the thickness. Even without an instrument the difference in thickness is evident. I noticed another thing that could prove valuable... The sugary enhanced kernels had swelled up and were plump with water: As smooth as if they were fresh off the cob. The normal sweet corn kernels were still very wrinkled. I'm speculating that the combination of higher sugar and thinner pericarp causes the kernels to absorb water quicker... (Just the opposite of the commonly mentioned effect that homozygous kernels dry down slower: They also plump up quicker.) So I envision taking the segregating seed, and tossing it in a pail of water the night before planting and then only planting the plump kernels. That technique might allow a home gardener seed saver to maintain the seed in a sugary enhanced state even if the population was not 100% homozygous. If you at least know that the mother plant was se+ then you will not get any non-enhanced duds. The soaking technique would be much quicker and easier to implement than my current strategy of measuring the sugar content of individual kernels at milk stage, and then doing a statistical analysis to identify the mother's genome. Soaking would also have the advantage that I can use it to identify the genome of the mother cob during the winter when things are slow and not during the summer with it's heavy workload. Besides that the statistical analysis is simpler and more reliable if you can easily test 30 seeds at the same time. Regards, Joseph
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Post by Joseph Lofthouse on Aug 8, 2010 13:23:10 GMT -5
If you at least know that the mother plant was se+ then you will not get any non-enhanced duds. Whoops.... The endosperm is grown from a fertilized cell. So if a kernel absorbs water quickly that tells us about the genome of both parents, not only about the mother. Now I am really excited!!! If I can identify the phenotype of the embryo before planting then that eliminates all sorts of nuisance, and work, and gene dilution caused by back-crossing. Regards, Joseph p.s. I love collaborative research.
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Post by grunt on Aug 8, 2010 16:43:28 GMT -5
Thank you both for sharing these insights with us. Joseph, truly seeing what you are looking at "I noticed another thing that could prove valuable" is what we have to do to garden/farm as well as our forbears did. Unfortunately most of us don't, a good portion of the time. Kudo's to both of you.
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Post by DarJones on Aug 9, 2010 0:17:55 GMT -5
Joseph, When I soaked seed of an su/se segregating cross, over half of the seed plumped up quickly. I take this to mean that pure se/se (homozygous se) and at least some of the Se/se (heterozygous se) seed absorbed water quickly. Your idea may still have a lot of merit because it would allow you to quickly cull plants that are Se/Se (homozygous normal sugary). Given that you want to maintain a line that is trending toward pure se+, you could select based on kernel plumpness and within 5 years have a nearly pure se+ seed line.
I still intend to use the pericarp thickness as a test but may give a try with soaking seed too.
On second thought, it might be even better to pre-soak the seed and then start seed trays with only the seed that plump the fastest, and then when it sprouts, measure the pericarp and grow only the plants with the thinnest measurements.
Don't you mean Genotype? DarJones
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Post by Joseph Lofthouse on Aug 9, 2010 5:58:27 GMT -5
"If I can identify the phenotype of the embryo." Don't you mean Genotype? DarJones Good to know about the plumping. The phenotype of a plant is something that I can observe in my garden. I am not able to determine with my limited equipment and knowledge what the genotype is of anything that I grow. I can assume that the phenotype I observe is due to a genotype that I can't observe, but I can't really be sure if the physical traits which I am observing are due to any particular allele. For example if I did a mass cross and then started selecting the 5% of cobs each year with the highest sugar I wouldn't know for sure if the high sugar was due to expression of the su1/se alleles or if it was due to some other combination of alleles. Regards, Joseph
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Post by mnjrutherford on Aug 9, 2010 10:34:27 GMT -5
The phenotype of a plant is something that I can observe in my garden. I am not able to determine with my limited equipment and knowledge what the genotype is of anything that I grow. I can assume that the phenotype I observe is due to a genotype that I can't observe, but I can't really be sure if the physical traits which I am observing are due to any particular allele. For example if I did a mass cross and then started selecting the 5% of cobs each year with the highest sugar I wouldn't know for sure if the high sugar was due to expression of the su1/se alleles or if it was due to some other combination of alleles. So, "PHENOTYPE" would be the physical characteristics defining a plant? And "GENOTYPE" would be the molecular characteristics defining a plant?
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Post by Joseph Lofthouse on Aug 9, 2010 11:08:30 GMT -5
So, "PHENOTYPE" would be the physical characteristics defining a plant? And "GENOTYPE" would be the molecular characteristics defining a plant? Yes. Nice definition.
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Post by Joseph Lofthouse on Aug 9, 2010 12:02:48 GMT -5
I don't have any segregating F2 seed to work with, but I did some experiments with what I do have.
I soaked Astronomy Domini (normal sweet corn) seeds and some se+ seeds in water.
After 10 hours the sugary enhanced seeds were mostly filled with water. After 22 hours they were totally filled with water and were soft and squishy.
After 22 hours the Astronomy Domini seeds were hard and wrinkly.
I expect to have BC1 seed (F1 Back-Crossed to se+) in a month or two. I hope to report on more experiments at that time.
Regards, Joseph
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Post by DarJones on Aug 9, 2010 16:28:19 GMT -5
Just a quick point Joseph, If you have a test - any test - that positively identifies the genetics, then you are looking at the molecular characteristics. So if you can soak seed overnight and only the pure se/se seed are fully plumped at that time, then you have a test that positively identifies the genotype of the seed. Not saying that this works, just that the genotype is what you are defining. Phenotype is what you see when it grows. By definition, phenotype can be influenced by environment. So by Occam's Razor, the correct term above should have been Genotype.
DarJones
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Post by Joseph Lofthouse on Aug 9, 2010 17:23:26 GMT -5
Just a quick point Joseph, If you have a test - any test - that positively identifies the genetics, then you are looking at the molecular characteristics. So if you can soak seed overnight and only the pure se/se seed are fully plumped at that time, then you have a test that positively identifies the genotype of the seed. Not saying that this works, just that the genotype is what you are defining. Phenotype is what you see when it grows. By definition, phenotype can be influenced by environment. So by Occam's Razor, the correct term above should have been Genotype. DarJones I vigorously disagree. (Mostly because I can't imagine any gross physical measurement that "positively identifies" the DNA). I cannot in any way measure or observe the genotype of my seeds. I can only measure and observe the phenotype of my plants and seeds. If I was a gambling man I could use my observations to make inferences about the genetics of my plants, but the suppositions might not match the genetics. The only test that could positively identify the genetics of a plant that I am working with is a DNA analysis. I do not have the equipment or training to do a DNA analysis, so I cannot know for certain what the genetics of my plants are. I cannot know when I observe seeds plumping up quickly after being soaked in water if that is due to them being homozygous for su1 and for se, or if it is due to some other combination of genetic traits. For example, the seed that I tested supposedly carries the se allele, but what if the seed company messed up and gave me sh2 seed instead? I can't observe or measure the DNA of a plant. I can only measure physical traits that are larger than about 0.001 inches. Or in other words: Phenotype describes those things that I can see and measure. Genotype describes only the DNA. (Including that of the organelles such as the mitochondria, chloroplasts, etc.) I might sometimes get sloppy and use phenotype and genotype as synonyms, but I believe that they describe vastly different ideas. Regards, Joseph p.s. Does anyone know of a mtDNA/chloroplast pedigree in corn that is particularly desirable? I have been doing my crosses so as to preserve the Indian Corn mtDNA. Might I get better results going the other way and preserving the sweet corn mtDNA?
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Post by DarJones on Aug 9, 2010 18:26:44 GMT -5
Joseph,
Classic genetics.
Genotype + environmental modifications + random elements = phenotype.
Phenotype is the observable set of traits while genotype is the set of instructions driving the cellular machinery. Genotype is inherently a part of the phenotype. If I have a yellow kernel of corn, then the phenotype is "yellow". The genotype might be one gene for dominant yellow and one for recessive white.
Where things get hazy is when you consider a specific trait. For example, I grow tomatoes that are determinate in habit. I can grow a plant and if it meets all the criteria of having short plants less than 4 ft tall, 2 internodes between flower rachis, then I must have a determinate plant and therefore it carries the determinate gene. But this is NOT genotype. this is just a measure of phenotype. That same putative determinate plant might have 1 determinate gene and 1 dwarf gene in which case, offspring would segregate (but not 1:4 because there are two separate genes for these traits)
But my statement was "if you have a test, any test, that positively identifies..." Then the test inherently is looking at the genotype, not the phenotype.
I could make arguments on both sides of this but since I don't see much to argue over, lets just grow some corn instead and see if we can get a stable se+ line.
DarJones
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Post by Joseph Lofthouse on Aug 9, 2010 18:43:11 GMT -5
Genotype + environmental modifications + random elements = phenotype. [...] lets just grow some corn instead and see if we can get a stable se+ line. DarJones Right on! I don't care what the genotype is... I'm looking for those phenotypes that thrive on my farm, and are highly sought after by my customers. If 20 years from now someone does a genetic analysis and determines that there is no se gene in 'The tremendously sweet and amazingly thin pericarped sweet corn', I would not be disappointed that I failed in my original goal to develop a multi-colored sugary enhanced sweet corn. And I won't care if I had accidentally selected for the su7 allele instead of the su1 allele. Giggles, Joseph
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Post by mjc on Aug 9, 2010 19:22:09 GMT -5
And I won't care if I had accidentally selected for the su7 allele instead of the su1 allele. And who really cares if it tastes good and grows well in a specific location?
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