A question has come up at various times over the years in my household and I wanted to get everyone’s take.
Can the pollen parent influence the traits of the fruit or seed itself, or are new traits only expressed when the seed is eventually germinated?
I’ve heard people contend that their sweet peppers were made hot due to the fact that they were planted near hot peppers. I find this idea absurd. Cross pollination should be apparent in the next generation, not in the fruit or seeds that are the result of that pollination.
Though compelling on its face, this idea doesn’t hold water. If true, it’d be nearly impossible to harvest true to type fruits.
So why, then, are there recommendations for isolating corn types from one another? A number of seemingly reputable sources seem to reiterate this requirement. The claim is that popcorn or flint corn will negatively affect the flavor and texture of the sweet corn. Can anyone explain the rationale here?
We are planting a big 3,patch of corn here and again has discussion about isolation distance due to pollination impacting quality of kernels and ears. To me, it seems like one of those bits of gardening lore that gets bandied about and seldom looked at critically. There definitely are legitimate sources claiming this is a known issue. If that’s the case, perhaps it not worth over intellectualizing. If it is an issue, though, I’d want to know the mechanism.
Breeding is a complicated matter and I am sure my high school biology only touched on a little bit of what goes on. If I a blonde man has a sex and has a baby with another blonde girl we have more likely chances of having a blonde child. If I have sex and have a baby with a brunette as a blond man the genetics are farther broke down with the hair gene. There is a chart on which type is more likely to succeed based on dominant and recessive traits. Challenge is those traits may make a side track and even though say neither of us have red hair since one of our great great grandma had red hair our kid has a slight chance of having red hair. The genetics are made when the sperm entered the egg however. A pepper may range in heat from x to y based on water usage but it still ranges that amount. This is a good video on it Pedigree Analysis - Part 1: Autosomal Inheritance Patterns - YouTube
My understanding is that the recombinated genetic coding itself, the part that is a blend of mommy and daddy, is inside of the seed in the embryo, and not expressed on the seed nor fruit itself. The embryo carries the instructions, the rest is built from the mother plant genetic instructions on how to put together a seed (and fruit).
It is sorta like when a human female is pregnant. There are lots of things in there other than the embryo and subsequent baby and it is all part of just mom.
But sweet corn, due to its unstable hybrid nature has the following problem:
Genes affecting sweetness are recessive. If varieties having these “sweet” genes are pollinated by varieties having the dominant forms of these genes, sweetness will be lost.
I only read about this behavior in sweet corn. Although, a local gardener reported that he saw different textures in Cherimoya fruits based on the pollen he used to hand-pollinate them. I didn’t follow up with him on whether the fruits also tasted differently based on the pollen parent.
The embryo is produced by fertilisation of the egg cell by a sperm cell in the pollen. The endosperm (storage tissue of the seeds) is also produced by fertilisation, which makes it genetically different from the mother plant, which could mean that if the father is different enough, for example a sweetcorn mother, flour corn father, this should be discernable in the endosperm. But there are also seeds that have no or almost no endosperm. Concerning the peppers: does anybody know where exactly in the seeds the capsaicin is produced?
I have no idea, which is why this is so interesting!
I asked about seeds here, because if Sweet peppers can be contaminated by being pollinated by Hot Peppers, the hypothetically produced capsaicin has to be produced somewhere in the seeds, because the fruit is only maternal tissue, no?
Look up Xenia and Metaxenia to find most of the answers needed. Here - to the extent I can reduce it to simple terms - is the explanation re corn. We consume the seed of corn which is reproductive tissue, we don’t consume the ovary. Apple, pear, watermelon, etc. are examples where we consume the ovary. With corn, the ovary is the corn cob. The corn seed is produced from the combination of haploid pollen cells with haploid (diploid for endosperm!) maternal cells. The kernel of corn therefore is composed of both maternal DNA and paternal DNA and will express traits from both parents.
To further break this down, the corn seed has the germ which is diploid, the endosperm which is triploid, and the caryopsis (pericarp/skin) which is maternal tissue and typically diploid. When we eat the corn, we can taste effects on the germ (such as increased oil content) on the endosperm (such as increased sugar content), and on the caryopsis (which may be thicker or thinner depending on maternal genetics). The best overall description I have found is from an out-of-print book by Juggenheimer from iirc 1948.
Endosperm - the starchy storage tissues in the seed - for most vegetable/fruit crops grown is triploid. Sweet corn is produced when one or more genes block conversion of sugar in the kernel into starch. If the pollen grain fertilizing a kernel of sweet corn happens to be from field corn, the resulting kernel has 2 genes (maternal) to block starch production and one gene (paternal) that produces starch. The gene is dominant meaning one copy present in the endosperm triggers conversion of sugar into starch.
I could write a ton more but this is enough to give search terms to find the details.
Pepper is a different story entirely. Capsaicin is produced in the placental tissue near the seed. The seed are often coated in capsaicin - which is a thin oil. I am not aware of any proof that pollinating a sweet pepper with pollen from a hot pepper causes production of capsaicin in the sweet pepper. However, in the next generation, the seed has DNA to produce capsaicin and the fruits grown would therefore be hot as it is a dominant trait. As above, see Xenia and Metaxenia.
Maize fertilization is a form of double fertilization as the referenced link you provided indicates. The triploid endosperm which contains tissue of paternal origin is the part we eat so the paternal origin can manifest itself in seed phenotype. This complicated fertilization mechanism has actually become a tool for for modern breeders when developing inbred lines (via doubling haploids) when targeted plants are pollinated by certain pollen source lines known to initiate incomplete pollination thus producing a relatively high percentage of haploid progeny. These haploids are then treated with colchicine or some other microtubule inhibitor to generate completely inbred diploids.
In avocados, pollen parent can impact seed shape and seed size, which in turn can impact fruit shape and flesh ratio. Not usually huge differences, but measurable.
Thanks all. They say if you’re the smartest person in the room, you’re in the wrong room. @Fusion_power , that was an excellent synopsis. Heady stuff for sure. I’ve read some about the mechanics of pollination before but hadn’t picked up on double pollination forming the triploid endosperm. It had occurred to me that corn kernels being the seed rather than the fruit was probably part of the explanation, but I wasn’t aware of the dominant gene for starchy kernels. Makes sense though.
@parkwaydrive thats an interesting tidbit too. I’m not sure I understand what is meant by incomplete pollination. It must be a rare case, since ordinarily this would not lead to production of an embryo. I’ve heard it asserted that tetraploid persimmons can satisfy the pollination needs of hexaploid persimmons, though this is one a range of things asserted about persimmon pollination, which is idiosyncratic. But maybe a difference in ploidy might be such an example. What other factors could account for fertilization resulting in haploid progeny?
@swincher - avocados are a good reference point too. I suppose how things are pollinated and who by are worth considering. It seems that traits of seed affected by pollen parent might potentially cascade over into other fruit characteristics too. I’m thinking ripening time as I understand that dehiscence is signaled by the seed in some sense. It’d be good to know more details on the effects of xenia in cherimoya @californicus
As for the sweet pepper/hot pepper quandary, I think it’s just a case of garden gossip @Oepfeli I have a good friend who grows about an acre of peppers each year. He wholesales his sweet bells and makes hot sauce out his hots. He definitely doesn’t have an issue.
I’m going to add a tidbit that is very detailed but useful to know. When corn begins to form seed, a cell divides, divides again, and again, and again winding up with 16 cells in the reproductive supercluster. The final division flips from diploid cells to haploid (1 set of chromosomes). Eight of the reproductive cells then form the un-pollinated ovary cluster and eight of them gradually disappear. Two of the ovary cluster cells fuse to become the proto-endosperm. One cell prepares for fertilization and will become the embryo. The other 5 cells perform support functions. A pollen grain lands on the silk and begins to form a pollen tube to the embryo. That pollen grain divides into 2 haploid pollen cells that are normally duplicates, i.e. genetically identical. When they reach the ovary, one pollen cell fuses with the maternal embryo, one pollen cell fuses with the 2 maternal endosperm nuclei (making the endosperm triploid) and the five extra haploid cells gradually disappear, their job is done. The endosperm then undergoes division to form the starch portion of the corn kernel. The embryo undergoes division to form the long sliver-like embryo, and the caryopsis (maternal tissue) expands to become the “skin” of the corn kernel.
As noted above, when you consume the seed, the genetics of the pollen are very important, doubly so when one of the selected traits is from deactivation of a gene to produce starch. Deactivated genes are easily patched around if the pollen grain happens to have a normal gene at that location. This is exactly what happens when a normal “sugary (su)” gene is present in sweet corn but the pollen is from field corn that has a functional SU gene. The same basic statements apply to se+, sh2, du, and 2 or 3 other genes that are used to produce sweet corn. You won’t find much detail, but augmented and synergistic corn is currently all the rage. Look at crookham.com to see a sweet corn breeding business and the various lines they produce.
You’re referring to the so called “sugar enhanced” corn, I gather. I didn’t know many of the gory details.
Funny to read your play by play description of pollination unfolding. It’s something so glossed over in our awareness for the most part, you’d think it was the functional equivalent of pushing a button. Instead, what we see looking closer is untold drama at every turn. Incredible that it works at all!
Believe it or not, I still “glossed over” and only hit the high points. It would take a fairly long chapter in a book to get into all the details. For example, sometimes two pollen grains arrive at the ovary cluster at the same time and one pollen grain contributes a cell to the embryo and the other pollen grain gets to the endosperm. This particular accident has been used in plant breeding to produce hybrids of widely separated species where the endosperm requires specific pollen but the embryo is less selective. It is called using “nurse pollen” where for example pollen from maize and from tripsacum is combined and used on corn. A very small percent of seed are produced that have endosperm with normal maize genes and the embryo is a cross of maize x tripsacum.
“Sugar enhanced” is usually reserved for corn with the normal su (sugary) gene and the se gene, respectively on chromosome 4 (su) and chromosome 2 (se). Synergistic is a combination of su + sh2 + one other gene that I don’t recall. Synergy between the genes results in exceptionally high sugar content. If pollinated by any other sweet corn, the default sweetness won’t go below the normal sweetness of su corn.