understanding corn genetics

[DarJones]

If I am properly understanding this, what you have is a segregating population for C1, R1, and PR1. From the looks of the results, you have at least 2 variants of C1 and at least 2 variants of R1. This will skew the results a bit from what you are expecting.

You can dig out some articles on the net about the dominance of red pericarp/aleurone.

DarJones

[Joseph Lofthouse]

Here is my favorite site for looking up corn genes:

www.maizegdb.org/locus.php

PR1 -- Chromosome 5

Changes purple aleurone to red; encodes flavonoid 3'-hydroxylase

Other Comments:

Red aleurone color vs. purple. Classification is fair to good in presence of appropriate complementary factors for color; difficult in some backgrounds or in presence of in1 (intensifies to deep red, to almost black). With bz1 or bz2, expression is faint pink rather than bronze. Plant tissues with B1 Pl1 somewhat maroon, anthers with appropriate R1 allele and Pl1 maroon to oxblood.

C1 -- Chromosome 9

C1 colored; C1-I dominant colorless; c1 colorless, includes c1-p (pigment inducible by light at germination), c1-n (not inducible)

R1 -- Chromosome 10

regulates anthocyanin pathway; dominant R1 (S element) confers function in aleurone; dominants represented by R1-r or r1-r (P element) confer function in anthers, leaf tip, brace roots, etc.

Other Comments:

cold causes an 8-fold increase in r-family trancripts (using an lc1 probe)

Dominant R1 controls kernel and plant coloration by regulating genes coding for enzymes of anthocyanin biosynthesis. Extensively polymorphic

So it sound to me like the in1 gene would be important to anyone breeding corn for more pigments. Also, for those wanting colored popcorn, this gene is for you.

in1 -- Intensifier 1 -- Chromosome 7

intensifies aleurone anthocyanin pigments; In1-D dominant dilute; sequence similar to r1/b1

Other Comments:

Dosage effect; red (pr1) kernels are deep maroon color, near black, purple (Pr1) kernels are deep purple with metallic sheen in pericarp (expressing metaxenia), colorless (a1 or a2) kernels have brown pigment in the aleurone and pericarp. In some backgrounds, under conditions of very high pigment development, patches of aleurone tissue break down (appearing to have expanded and burst cells), resulting in a deckled patch. Apparent release of pigment from these areas results in pigment invading the starchy endosperm beneath.

[Joseph Lofthouse]

I ate a few hundred kernels of corn today from a segregating patch of sugary enhanced, sweet, flour, dent, flint, and pop corn.... (Sorry Holly no posoles.)

I am going to call this one polygenetic... I think that the dent/flour/flint distinction is artificial, and not something that can be attributed to simple Mendelian inheritance of one gene. The kernels I ate existed on a continuum: very-dent --> dent --> sorta-dent --> sorta-flour --> flour --> sorta-floury-flinty --> flint --> sorta-popcorn --> popcorn. There wasn't any clearly definable distinction between them: They all just sorta merged together.

I think I'd be willing to say that I consider dent corn and flour corn to be essentially the same thing as far as milling properties go.

[DarJones]

Just on principle and because I am a contrary cuss, I am going to disagree with you Joseph. Just because I'm a pain the the butt from time to time, I'm going to refer you to maizegdb where this description is found for the FL1 gene.

Exhibits a dosage effect in that the female contribution determines endosperm character, fl1/fl1/Fl1 gives floury endosperm whole Fl1/Fl1/fl1 is normal. Classification is difficult in many stocks.

I've got clear evidence that flour vs dent is controlled by a dosage sensitive gene. The endosperm can have 1, 2, or 3 copies of the gene for floury. From the above quote, you can see why I can say this. The segregating stock that shows the effect is the Whipple White sweet corn where I have distinctive seed with no floury endosperm, a small amount of floury endosperm, a medium amount of floury endosperm, and a large chunk of floury endosperm. There is a very clear and obvious segregation pattern in the variety.

DarJones

[Joseph Lofthouse]

Nov 2, 2011 20:03:49 GMT -5 DarJones said:

I've got clear evidence that flour vs dent is controlled by a dosage sensitive gene. The endosperm can have 1, 2, or 3 copies of the gene for floury. From the above quote, you can see why I can say this. The segregating stock that shows the effect is the Whipple White sweet corn where I have distinctive seed with no floury endosperm, a small amount of floury endosperm, a medium amount of floury endosperm, and a large chunk of floury endosperm. There is a very clear and obvious segregation pattern in the variety.
DarJones

I work with landraces rather than with single inbred varieties, so it's harder for me to observe the influences of single genes.

As far as I can tell, dents and flours both have floury endosperm.

You are using the words: no floury endosperm --> small amount --> medium amount --> large chunk. I'm calling it a poly-gene influenced bell chart. Are you thinking that they can be classified into distinct bins without overlap?

I think we are saying the same thing but using different vocabulary words. I'm going to stick with the conclusion of your quote "Classification is difficult in many stocks." And perhaps add: Classification is particularly difficult in landrace varieties.

[DarJones]

My thought is that in some backgrounds it is dosage sensitive. What I am seeing is that a floury line that is pollinated by a mix of floury and non-floury pollen shows the 4 separate levels of floury endosperm. I'm not saying that I know for sure that this stock has the floury gene. Just that what I see in this su variety is that there are 4 different levels of floury endosperm ranging from none to nearly filling the kernel. I would have to do some serious breeding work to say for sure what is happening.

DarJones

[Joseph Lofthouse]

I love triploid genetics!!!!

[blueadzuki]

It say I am in agreement with Joseph's "bell curve" argument. If there is a gene that controls flouryness, it probably does have a saturation effect. If it didn't, if it was a "have it don't have it" then I doubt that there would be so many native corn strains classified as "flour/flint" (throwing both) as segregating the two would be both easy and desireable (as flour and flint corns can require differnet type of grinding, and yield differnt types of meal/flour I tend to think that if seperating the two and making two discrete lines, one pure flour one pure flint, was really easy, it would have been done each time, even if the native people wanted both to give then easier grinding and better control over ratios of meal to flour.
To me the corns fall in a sort of spectrum. One one end you have the really hard flints (the kind I call "crystal" flints) which have very little soft starch (In theory the far end should be corn that has no soft starch at all, but I'm not sure I've ever seen that, even the hardest flints have a little "wick" of soft starch at thier center. As you increase the amount of soft, you then proceed through nornmal flint, "cap" flint (flint's where there is enough soft starch the kernels start to look opaque from the top, with a thin veneer of hard starch on top), "pillar" flour (where the hard starch is confined to small strips on either side of the kernel) and finally to pure soft, though again, I'm not sure that exists, even the Andean cancha's and chulpe's I play around with (which are so full of soft starch they feel like packing foam) usually have a little hard in at least some kernels). Dent sort of fits between cap and pillar; it's simply when the soft starch extends all the way on the top to the pericarp (no thin hard shrach shell) where because it is softer tissue it gets pushed down by the pressure of the neighboring kernels, making the dent (which is why many dent corns do not dent on the butt kernels, or if a kernel (due to pollination problems) has no kernels next to them.) I only leave it out of the spectrum because it is possible for a corn to bypass it depending on how the starch lies; a pillared kernel can have more soft starch than a dent and still not be dimpled.

[DarJones]

Blue, re the question of stippled kernels that you asked earlier, it looks like one form of stippled is caused by the PR1 gene in a single dose. I am not sure if there is a xenia effect or not. In triploid genetics, it would be something like pr1/pr1/PR1.

DarJones

[blueadzuki]

Thank you foer that, especially for telling me what the official term for the pattern is. With that under my belt, findiong info is a lot easier. I also learend what the "navajo" pattern is (apparantly its that one where the kernel has a dab of color on the top). I also explains why sometimes I can find kernels that seem to have two "layers" of spots or a color cap on top of spots (since there are three different versions, a kernel can I guess have one, two, or all three.)

This showed up early in my seach it seems to expain quite a lot

www.ncbi.nlm.nih.gov/pmc/articles/PMC1210000/pdf/19.pdf

[Deleted]

I have a question about hybrid vigor. I read an old 1952 Pioneer Hybrid article discussing Cornbelt dent's origins and the racial heterosis behind its high productivity, and it got me wondering if breeding in composite populations from the Andean and Mexican centers of diversity could create another distinct race and further improve CB dent's productivity and vigor (within reason, of course). I know corn races don't always combine well (if at all), but with careful breeding could the effect be intensified further since the genetic difference between, say, an Andean cancha and a CB dent is as great as what was between the latter's northern flint and southern dent parents? Here's the article, by the way:
www.bulbnrose.org/Heredity/Anderson/AndersonCornBelt/AndersonCornBelt.html

[DarJones]

The problem you get into is that hybrid corn is already reaching close to 50% of theoretical production capacity. That means the upside from more breeding is not likely to be a huge improvement. What is exciting is that discrete beneficial traits can still be moved over from other races and have a positive impact on production. This is possible because the limits on corn production are associated with environmental effects. For example, if you could bring in drought tolerance, any corn grown in a drought prone area could benefit. This is the type focus of recent breeding work. Another example would be breeding in wire worm tolerance. The amount of money spent each year to control wire worms is in the hundreds of millions. So the answer to your question is yes, there is a benefit, but it is probably not from increasing production.

DarJones

[Deleted]

I've heard about hyrbrids starting to max out, which certainly makes sense given that a corn plant can only yield so much. I'm interested in increasing an OP variety's productivity though. What I meant by the earlier post (and it was really late when I wrote it, so sorry if it wasn't clear ) is: if one bred together equal amounts of germplasm from each major racial group and stabilized a new OP breed, would it outproduce its parent races if the genes combined properly? As I understand it, that's what happened with the CB dent race in general when compared to either flints or gourdseeds. For example, if I cross a northern flint composite with a southern dent composite, stabilize it, then in turn cross it with a Mexican comp. x Andean comp. mixed breed, could the resulting race have better productivity and vigor than any of the original four parent breeds? If so, then could one synthesize a race with enough genetic diversity that it could come fairly close to an F1 hybrid's productivity by maintaining racial heterosis instead of a short, generational burst of it? I've been considering trying the aforementioned experiment, but I need to know if there is any basis for my hypothesis before I waste years attempting it.

[Deleted]

But, of course, it doesn't mean anything if the new race is totally incompatible with its environment. That's the most important thing.

[Joseph Lofthouse]

I suspect that it's a myth that commercial inbred F1 hybrids are more productive than open pollinated varieties.

In my garden, open pollinated corn is astoundingly more productive than commercial hybrids... What I really mean to say is that Astronomy Domine sweet corn out-germinates and out-grows any sugary enhanced corn that I can grow. If the goal is simply productivity, then I am already there in my garden. What point is there is growing a variety that has 5% germination year after year?

I am working on incorporating Mexican Highlands and Andean corn into my sweet corn. It's a slow and tedious process since my environment is so different than where they are from. The first year I was able to grow out some of the Oaxacan corn, due only to the lucky chance that where it was planted escaped the early fall frosts. I am pretty sure that this year's attempts at crossing with sweet corn failed, but at least I have a model in place for next year about how to go about it. (Use the Oaxacan corn as the pollen donor, and use a short season sweet corn as the mother.) I think someone in a more southern location with a longer growing season would be better able to make the initial crosses than I am.

The Hopi races are working better for me: They are more closely related to the Mexican Highland races than to the Northern Flints, so it's a shortcut for me.