Riverside and Apache are used as rootstocks in the southwest. Curtis and Elliott are used in the southeast though in my opinion, both have shortcomings as rootstocks. Stuart is used as a general purpose rootstock capable of good performance through northern KY and similar climates. I’ve read a few negative comments re using Kanza as a rootstock. Most were along the lines of highly variable seedling growth. Kanza almost never self-pollinates which is highly in favor of using it as a rootstock. Major has been widely used for northern regions and Lucas has been recommended for ultra-northern plantings.
L.J. Grauke wrote this re rootstocks: http://sepga.com/Presentation/WEB2010pres/LJ_Grauke.pdf
The single biggest issue facing pecan rootstocks is nematodes. So far there is very little evidence of nematode resistance in the pecan genome. I found a single reference to a nematode resistant rootstock from Womack. Close investigation suggests it has very limited resistance. L.J. Grauke published some material about nematode trials that is worth digging up if you want more info. Check the pollination spreadsheet to find varieties that rarely self pollinate. Amling and Kanza are two that look like possibilities.
Long term, I think there is a lot of potential for pecan crosses with C. Myristiciformis and/or C. Aquatica to find nematode resistance and gain a boost of hybrid vigor. I have about 25 hican nuts that are stratified and will be planted in a few days. If they turn out to be what I think they are, they have decent potential as rootstock on a wet area of my land.
One thing Grauke stated is that a pecan grower should cull the weaker and slower growing seedlings. “Cull poor quality seed to improve stand uniformity. Since self pollinated seed has lower fill, culling seed further reduces selfed seed, increasing the vigor of the stand. Rogue out the smaller seedlings from nursery rows. Since self pollinated seedlings have lower vigor, culling smaller seedlings is the final step to ensure maximum heterosis and vigor due to outcrossed seed.”
On a different tangent, we had a frost a couple of days ago. Temperature dropped to about 29 degrees. A few pecan trees had budded far enough to expose leaf tips and some catkins. The trees that had budded furthest show significant damage that will take time to recover from. I have not been out on my land in a few days so have not checked the varieties there. Here at the house, Adams #5 and Amling show excellent performance. Buds on both are slightly expanded but not opened and have little or no damage. Buds on several seedling trees were opened and have damage from slight to severe. Zinner was partially expanded and has dead leaf tips though the buds are not hurt. A couple of mockernut hickory trees in my yard had growing tips up to 6 inches long. About 10% of the growing tips are dead and most of the catkins are brown and crumbly.
I just compiled a list of pecan varieties that are unlikely to self-pollinate. This suggests some of these may be useful as rootstocks. “Amling, Byrd, Cunard, Hark, Headquarters, Huffman, Ideal, Kanza, Kiowa, Lakota, Maramec, Moneymaker, Norton, Pawnee, Posey, Sioux, Tanner, Tom, Carter, Grabohls, Oklahoma, and Teche” From that list, Amling, Huffman, Kanza, Lakota, and Posey have pretty good scab resistance. I think Adams #5 will also fit in this category though I do not have pollination data on it yet.