I’m reading a very interesting article about pecan genetics and very specifically about introgression of traits from other Carya species. They found that modern pecans share between 1 and 3 percent DNA with C. Aquatica aka water hickory. The shared genes are chopped up and spread across several different chromosomes indicating a cross between the species perhaps up to a few million years ago.
They also found a large introgression from C. Cordiformis aka bitternut hickory present in Major and several descendants. This represents something unique because the introgression appears to all be on chromosome 8 and shows evidence that it is highly conserved, meaning that it conveys very useful survival characteristics to pecans. It is telling that other sections of bitternut DNA do NOT show up which means they are selected against by some combination of processes. Note that this selection precedes human directed pecan breeding efforts. We have discussed this in other threads on Growingfruit so it is not really new to say that Major is a hican. Grauke documented this at least 7 years ago. I noticed it within a few hours of looking at Major nuts in the shell and at Hickory Major nuts which have thick husks very similar to other hickory species.
There was a chunk of DNA from C. Myristiciformis aka Nutmeg Hickory on chromosome 5. This is interesting because it indicates that pecan has picked up adaptive genetics from at least 3 close relatives. Nutmeg hickory is a 16 chromosome species that happens to share multiple traits with Pecan. In some ways, we could describe Nutmeg hickory as intermediate between the Carya (true hickory) and Apocarya (pecan hickory) sub groups. It would be interesting to compare a group of Nutmeg hickory trees with the pecan genome to see if the gene sharing was two way, i.e. that Nutmeg hickory picked up some pecan genes along the way.
Among the results, one of the most interesting is that pecans often contain unique DNA meaning there are genes in one variety that do not show up in another. This is consistent with a species that grows in a wide range of edaphic and climatic environments. There is a LOT of diversity in the pecan genome that is unique and likely not represented in the roughly 30 cultivars that represent most pecan production.
Good find. Lot of technical jargon, but good read.
Question that has bugged me. Since we’ve come a long way with DNA, you would think they would have enough pecans in the data base to identify both or at least one parent of all cultivars. You look up a lot of older cultivars like Schley, Success, or Stuart and all you find is seedling that someone planted or discovered.
Parentage has been verified for several more cultivars. There is a paper in the works. I asked about 5 months ago to have access to parentage records but was asked to wait until they can publish.
I was reading an article on the origin of Seneca pecan and found DNA parentage of Campbell NC-4. It is Colby X Peruque. I need to look into Seneca a bit more to see if it is viable for zone 4 growers.
Interesting.
‘Peruque’ is a lovely little pecan with extremely thin shell, high kernel % and excellent kernel quality… but it scabs here, crows/jays take the bulk of the crop in good years, and weevils love it! It’s one of the earliest ripening pecans I grow, often dropping nuts by 15 Sept. Seedlings were vigorous and made good rootstocks.
I have ‘NC-6’, another of Doug Campbell’s selections, and its nuts looks a lot like those of ‘Peruque’… I wonder if it is a parent of NC-6 as well as NC-4.
I have not found anyone who has Seneca growing. I will email Warren Chatwin and ask if it has been grafted commercially. If not, maybe request scionwood. I don’t want it here, but it might be a very good variety in zone 4/5.
I’m pretty sure Vaughn Pecan in Southern IN has the three new usda cultivars growing.
Side note does anyone know more about Dr. Clinton Graves work on hicans working towards a scab resistant pecan. From what I read he did a lot of interesting crosses but I’m not sure if theyve been dna tested to confirm.
You can find about a dozen of Graves pecans on the USDA website. From a personal communication from L.J. Grauke, none of them show as actual hickory crosses when DNA tests were done. I looked hard at a few of them as they were supposed crosses with water hickory. EW 7-22 is a pecan water hickory hybrid. Fairbanks is an interesting cross too. Neither is attributed to Graves. Short version, Graves was not doing very well isolating female blooms.
Hard to believe, based on the photo, that that CG3-22 is anything other than a pecan. There is nothing about the appearance of that nut that hints of any shellbark or nutmeg hickory parentage.
In interesting trivia, ARSGRIN shows these additional accessions which are not in the pecan database. I’m curious about them. Could one of them be the putative walnut/pecan hybrid Graves reported?
I got a response back re Seneca availability. Womack Nursery and Pecan Grove Farms are the only licensed propagators.
I called Womack and the woman I spoke with had never heard of Seneca and barely knew about Pueblo. I should get a call back from the owner to see if trees can be sourced.
If this is real, it’s mind blowing and will rewrite the evolutionary history of pecan in North America.
What I don’t understand is how even if Clinton Graves was bad at making controlled crosses, the maternal tree being “Stephens” shellbark surely wouldn’t result in a nut that looked like that? Unless he just totally mixed the whole thing up with a pecan from a totally separate tree, in which case that is very shoddy work indeed.
Bitternut introgression is also common in shagbark, especially the further north you go. I’m curious whether Carya carolinae-septentrionalis has as much/any introgression as compared to northern shagbarks with clear bitternut introgression.
When shagbark and bitternut hybridize, no f1 i have ever encountered carries on the bitter trait, so that must be recessive. Later generations and further along generally work their way back into the shagbark population if given the chance, and even most f2s will be very hard to distinguish from regular shagbark.
Carya,
The grafted bitcan at the local community college… I think you’ve seen it on a visit… is unidentified, so idk if its a F1, F2, or what, nut it still has slight astringency… If you can find a non-weevil-infested nut.
My experience with F1 bitcans is that they are 100% astringent. It is not as intense as pur bitternut, but is very obvious. Only in F2 or later when backcrossed with another non-bitter species do a few show up without bitterness.
I sampled a bitternut in North Carolina about 40 years ago which was not astringent. Mentioning this because it suggests variation in the species with some - probably very few - pure bitternut with no astringency.
Perhaps more interesting, I had a huge crop from a large old pecan tree in the edge of my yard. Several bitternuts and shagbarks are nearby. When I crack the pecans, a few are notably bitter which suggests a bitternut pollinated the pecan and affected nut flavor.
What leads you to conclude it’s a pure bitternut? I’ve found bitshags with nuts that very much look like bitternuts yet have no bitterness. However, the other characterisitics of the tree give it away as hybrid.
Yeah this is really interesting. Would you call that xenity? Fred Blankenship has made similar claims, especially regarding Juglans, though I’ve had my doubts.
I remember the tree! I’m not surprised bitcans can be bitter. Pleas is bitter for example too, but its mild enough and when cured largely goes away. Bitternut and pecan are both Apocarya which is a section with largely/mostly bitter species (except for pecan) so I’m just going to assume the gene for bitterness is fairly fixed except in pecan. The Carya section however seems to not carry the bitter gene at all in any species.
Obviously the bitterness is related to tannic acid, and how it is metabolized somehow I guess?
Xenia is when the pollen affects structures such as embryo and endosperm. The endosperm is also composed of paternal DNA. It is entirely expected that pollen traits would show up in the endosperm. Using corn (maize) for an example, if a white seeded plant is crossed with pollen from a yellow seeded plant, the endosperm produced will be yellow. Same principle applies with pecans where pollen directly affects endosperm characteristics.
Endosperm in most plants is triploid. Pollen is composed of 2 joined haploid cells which split as they travel through the pistil with one cell fertilizing the embryo and the other joining with 2 maternal haploid cells to form the endosperm. Hence, endosperm is directly affected by pollen source.
Someday we need a good thread on xenia, metaxenia, and carpoxenia.
I’ve heard Fred claim that some BWs pollen will affect the pollenated nut - he’s specifically implicated ‘Stoker’ as one that will ruin an otherwise good BW… changes the appearance of the husk and morphology of the nut itself.
I’m almost at the point of believing him… I have a ‘Thomas Myers’ in the barnyard, growing 30 ft from a ‘Stoker’. The ‘Thomas Myers’ was grafted with a scion I took from a TM tree I bought from John Brittain. The husk on the first TM tree looks very different from that of its clone growing next to the Stoker tree, and nuts from the original TM tree crack out better than those from its clone next to Stoker.
