I ordered a bud 9 this spring with plans on using it in the future for interstem material. When it arrived I snipped a piece off the top and grafted it on a seedling apple . It is looking nice , I think I may put pristine on this one.
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Interstems are fascinating and not well understood. At face value we get fruit like normal but in the case of my pears the interstem and rootstock has much more influence than most people would care to hear about. They influence growth, color, vitamins and minerals, storage etc…
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I never thought much beyond tree size, early fruiting, and drought tolerance using interstems. Not an exact correlation but my one standard pear tree has progressively produced better tasting fruit each year. I suspect it will take longer for my dwarf interstem pear trees to achieve a similar quality. Many unknowns about growing fruit.
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@Auburn
Bill ,
one of the many reasons I grow full sized trees is the fruit has tasted like its better quality to me. If we think about it reasonably in Kansas the top 3-4’ of dirt were farmed very hard raising grains , cattle etc. .the big trees are pulling nutrients from 30 feet down. Which would you rather eat a pear raised in the top 8 feet of soil or the one raised with roots 30-40 feet down? The big standards produce more pears in the same space, are more deer tolerant, pull nutrients from deeper, are more drought tolerant because as the water table falls the roots are deeper etc… the interstem can have as much influence as the rootstock on growth. If we could afford it and did a laser burn test to find out the nutrients in the fruit I’d bet we’d be shocked at the differences rootstock and interstem made on the minerals detected in the burn test.
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I was pointed to this thread with a pear question- but this snippet from Cummins has me thinking. Do you think this G11 interstem would work on another root- say G890? Those are what I would have to work with now, could order something else to try. P18 or B118 or Antonovka are also deep rooted, but too large for my space. I’d love to try, I want a more drought-resistant freestanding orchard.
Alright folks - I am going there. I know this thread has focused on apples and pears, but what about other “non-traditional” fruit? I am particularly interested in if anyone has tried an interstem for pawpaws?
Obviously disease resistance/dwarfing characteristics aren’t as important as with apples and pears. I am particularly interested in passing traits such as high vigor onto less vigorous cultivars. I was thinking mainly about using ‘Mango’ to possibly reduce the years to bearing fruit for other cultivars as KSU Chapell is patented and I’m not sure on vigor compared to ‘Mango’ for others like Kentucky Champion and Regulus (two others that might fit the bill). So has anyone tried it, and any good results? @Barkslip @TrilobaTracker @Blake @RNeal @mamuang @PharmerDrewee or anyone else?
Are there any other specific traits that I’m not considering that I should be? Am I over-thinking this?
Interesting information.
i am verry intrested in interstems to.
Where with normal grafting you can mix and match faforable traits from 2 varieties. With interstems your adding a 3e to the mix 
I have searched a bit. But interstems don’t seem to be that reasearched. And the mechanisems not (completly) understood.
the most plausible thing i can think of/came accros (could not find the source right now. If i see it again ill try and post it here)
Im oversimplifying a bit. So just a heads up.
Hormonal balance and effect on rootstock interstem and top of tree.
Cytokines
In tree’s the Roots produce a group of hormones called Cytokines. They get produced mainly in the activly growing root tips. These Cytokines move against gravity only. So they tend to build up on the highest part of the tree/branches.
Cytokines increase shoot growth. But determining if a bud will form a shoot and how fast that shoot will try to grow.
Auxines
On the oposite side of the tree, the growing shoots produce hormones from the auxines group (well known for it’s rooting effect in cuttings)
These auxines only move with gravity, downwars in the tree. These auxines inhibit the growth of shoots. And when they reach the roots. They increase the rootgrowth.
These 2 groups of hormones thus have roughly oposite effects. And keep the tree automatically balanced (rootsystem vs top growth)
balance disbalance and dwarfing
It is theorised that, a lot of the dwarfing rootstocks offset this hormonal balance. Either by producing less cytokines. Or breaking down the cytokines in the growing stem. Or by other unknown factors. Or maybe a lesser sensitivity to auxines in the roots. (lower auxine sensitivity leads to less roots gives less cytokines gives dwarfing top growth)
Resourche bottleneck
Next to these hormones, You also have the tree itself. Some varieties might have more efficient leaves. Or more efficient flow of sap etc. This means more resourches, which makes more vigerous growth possible. So even if you have enough hormones for vigerous growth. The lack of resourches (sugar starch minerals) might form a bottleneck. (which also could infer a darfing effect)
cloncusions + assumptions
This would explain why some dwarfing rootstocks give no dwarfing effect as interstem. (low hormone brakedown/botteleck in stem.) Those rootstocks probably have another mechanisem of dwarfing. (like lower production of hormones in roots. Or different sensitivity to hormones or resourche bottleneck)
And some other rootstocks do have a dwarfing interstem effect.
As far as i could find, the rootstocks that dwarfd as interstem. Also dwarfed when budded high (leave a long stem below graft union)
This seems to at least partialy exclude the theory of a “poor graft union between rootstock and interstem” being the bottleneck that causes the dwarfing effect.
I also assume the hormonal balance/sensitivity to be the main driver of dwarfing effects in comercial rootstocks. Since poor resource efficiance would probably lead to poor yields/sickly plants. Even in dense plantings. Although it will probably still play some part in most rootstocks. (i just assume it’s not the main driver of dwarfing effect. not that it plays no effect at all)
In the end. for your use case (increasing vigor with interstem)
The easier fix would probably be to try and find/layer/root a own root vigerous pawpaw. Try and get it to sucker. And use those suckers as rootstocks to graft high on. (roots of vigerous variety + interstem of same variety)
That way if the vigor source comes from a “better stem hormone or resourche transport” or from “more sensitive roots to auxines. Or more cytokine producing roots” Your good either way.
You could also graft an interstem. But if it does not increase vigor. It is likely that that variety is more vigerous because it is more resourche efficient (“better” leaves branches etc) or more sensitive to hormones (cytokines).
I would be amazed if you got significant more vigor from a pawpaw interstem. Id think you’d get more vigor for less effort by looking for more vigerous rootstock. (either seeds from vigerous varieties, or suckers from vigerous varieties)
I have almost no experiance with pawpaws. (saw them once irl and have seeds in fridge)
But has anyone seen a commercial planting of the same variety? Was there a difference in vigor between the tree’s? Could this be due to rootstocks? (where the seedling rootstocks tree’s from a controlled source? or random from multiple varieties?)
Another way to increase vigor might be how you treat your seedlings for rootstocks. As i understand it, pawpaws make a single taproot. When growing the seedlings for grafting. You can grow them in situ (on the spot of the eventual tree) beneath shade cloth. Or grow them in long tubes as pots (cut up rain-pipe or drain pipe?)
This consevers the tap-root and might lead to more long term vigour.
This was based more on my personal opinion/theory than hard proven “facts”. So take it for what it is
If anyone knows any good science thats done on interstem mechanisems. Please enlighten me 
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Sadly I haven’t tried it. Mango and Chappell as you’ve noted are purportedly more vigorous.
Honestly I’ve never delved into the world of interstem and don’t actually know anything about it LOL
One thing I had planned to try was a sort of in-arching or multiple rootstock graft with pawpaws but I chickened out - seemed like if I failed it could spell the demise of all the stock involved.
Yea I know what you mean. I feel like it’s a catch 22 for pawpaws. Going the interstem route as a bench graft is a challenge to the way I plan to graft (hot callus pipe) because you then need 2 successful takes before putting the tree in the ground. The taproot vigor is the other side of it, as I’d rather plant directly in ground at graft time rather than risk damage going from a pot with a deep root. @oscar might be onto something with the Mango on it’s own roots strategy. Once I (hopefully) have extra wood to play around with, I might do some trial and error if I can get Mango to sucker/clone.
dig up root. force it to sucker
since pawpaws sucker over a large distance. You could also dig up a root. And pot it up and see if it grows a new plant.
Most plants that sucker further away from the main stem. Don’t sucker from a latent bud on the main stem. but from a root itself. This means the root has the ability to form a bud. Not all plant roots have this ability. But im guessing pawpaw has.
Root graft
Or cut up a root and root graft it. (graft the root to a scion of pawpaw)
W&T or bark grafts or clefts i would try for root grafting.
You can heal root grafts in damp coco-peat inside. Don’t coompletly cover the root graft in parafilm or plastic. Just a grafting rubber is fine. You don’t want to lock moisture in. opposed to above ground grafting. you want to keep the graft airy/open with root grafting. Still peressure on the graft union is needed fopr good contact.
"Book smart" limited pawpaw experiance
noting again. im purly theoryizing here. I have some experiance with root grafting and suckering plants. But almost 0 experiance with pawpaws specificaly. keep that in mind before trusting me blindly
Only thing i’ll add is that to my knowledge no one has ever successfully propagated pawpaw from root cuttings or wood cuttings.
Some labs are trying tissue culture with very limited progress last i heard (5 years ago).
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hhm intresting knowladge!
So it seems hard to get a root cutting to form a bud and grow a plant.
I wonder what mechanisems is at play. If seen pictures of 100’s of root suckers from a pawpaw “thicket”. Those suckers clearly came from roots, and not the main stem. That would suggest root cuttings could work. But i belive you when you say the root cuttings don’t “work” (if they would work, id assume more people to use them. Or people to not run expensive tissue cultures)
still root grafting might be worth a go.
@oscar the issue being that the roots you are starting with are always going to be the rootstock, not the desired cultivar. I don’t think anyone has had success with getting a bud of the desired cultivar to root, as @TrilobaTracker alluded to. I may experiment with grafting buds below soil surface, scarring the bud, and applying root hormone. It’s hard to put bottom heat on a bud with a 14"+ taproot though. You would almost have to try putting the tree horizontal and seeing if you could force it to sucker while sideways. Lots more effort for an unknown result vs an interstem, hence my original post.
Edit: you also run into the unusual circumstance that pawpaws only grow their roots while they have already broken dormancy. If there was some way that you could trick the roots to want to grow before vegetation broke dormancy, that would be a potential way to make rooting occur. I am no expert though.
Second edit - for a cultivar like Jerry’s big girl where the tree likely still exist, that would be an obvious way to get a sucker on its own roots with the same genetics. Unfortunately many pawpaws are short-lived.
As Ryan says… root growth only during the active growth season is a most important thing to keep in mind, with regard to pawpaw… Asimina is the sole surviving temperate-climate member(at the genus level) of the tropical Annonnaceae. It is quite different - in many ways - from most of the temperate-climate deciduous trees most of us are acquainted with. It is NOT an apple/pear/peach/oak/pecan, etc.; it is a VERY different critter.
Unlike most temperate deciduous trees, it has a fleshy root system that does not grow appreciably following the top going into dormancy in fall or before budbreak in spring. Best time to attempt digging and replanting suckers would be in late summer/early autumn, while still in leaf, but as the growing season is winding down. I’ve done it, but not with great success rates.
There’s far too much ‘magic’ ascribed to taproots, and certainly that goes for pawpaws. Cutting them is not a death sentence… I’ve grown mass-planted pawpaw seedlings in 3-5 gallon pots and just lopped off huge masses of circling taproot in the bottom of the pot the next spring before repotting to individual 3/4 to 1-gal. pots(not deep-pots), with no adverse effects.
I kept some pawpaw seedlings ‘imprisoned’ in 20 oz styrofoam cups for several years… yes, they rooted out through the drain hole I’d punched in the bottom, but I just severed that, and whacked off the mass of circling roots in the bottom of the cup - or, maybe I sort of ‘straightened them out’ somewhat - when I transplanted them to a permanent location… but 15+ yrs later, they’re all alive and fruiting well.
Many of the first trees we planted here were M9/M111 combos, but the only personal experience I have with actually grafting interstems is a number of pears that I grafted onto callery seedlings, with an 8-10 inch piece of OHxF513 as an interstem. 513 is compatible with both Euro & Asian pears, without issues of Asian Pear Decline; dwarfing is only supposed to be 65% or so of ‘standard’. I did W/T grafts of scion variety onto the interstem, then stuck that combo unit onto the callery seedlings. They all took off and grew like a house afire. No dwarfing that I can ascertain, as they’re all taller than the older pears on 513 alone.
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Interesting information.
Thanks for sharing Lucky! Glad to hear someone with experience both on interstems and pawpaws weigh in. I wonder if keeping a couple grafted seedlings intentionally constrained to a smaller pot than necessary would encourage them to root if an experiment as I suggested above for putting the desired cultivar sideways to get it to sucker was performed… I am thinking of a Rubbermaid under bed storage container type of setup, with a grow light above and root hormone towards the end of the growing season, possibly trimming the taproot right before? My main concern would be the tree rotting before rooting. The more we discuss this, the more inevitable it is that I’ll be subjecting a couple poor trees to my experiment 
Having a method to produce own rood cultivars would be a big step in pawpaw production though, in my opinion. Even if it is to create interstems as we are discussing, that would be pretty cool.
As you discussed with pears Lucky, I remember reading in another thread that an interstem can “bridge the gap” between certain cultivar species that would otherwise be incompatible for various fruits. I bet stone fruits could open some interesting options with this (I’m sure many have already figured out what works).
@disc4tw
if your gonna do an pawpaw rooting experiment.
Please post about it on the forum 
Id recomend a soil-less media for rooting.
I use mixed coco-peat and perlite for most softwoord cuttings (passion fruits etc)
And pure coco-peat for things i root in a box (figs grapes hardwood dormant cuttings of berries/fruits)
you add just enough water to a “brick” of compressed coco-peat so make it just damp enough that if you squeeze real hard with your hand it releases 1-2 drops of water. It feels to 'dry" but it works perfect. Airy and damp enough to promote rootgrowth but since the pure cocos fibre almost does not rot/decompose (virtually sterile compared to potting soil) you have less fungus and rotting problems.
graft + cutting in 1 of grapes. That i treated this way
i just put the lid on. aired it for a few seconds every other day. And never gave it any more water.I use clear boxes in a dark closet. When i see enough roots. I take the box with me. And “unpack” them just before planting in the garden.
You can try rooting dormant cuttings in that style (without the grow light)
Although others noted, that pawpaws don’t root from cuttings.
If your using seedlings. You could also try laying them near horizontal. But with the roots slightly higher than the stem/leaves.
Since the cytokines (hormone group that mainly makes shoots grow) can only move up. it might save up in the roots. And force suckers.
i think rooting hormones from the auxine family will surpres suckers.
The auxines get produced by the top growth. (ie. if the tree is larger above ground then below ground. you get a higher concentration of auxines in the roots, witch leads to more root growth)
The cytokines get produced by the roots (tips). And when the rootsystem is larger than the topgrowth you get more cytokines than auxines, and the cytokine concentration rised, witch leads to shoot formation.
If you think about it. A lot of times when you get suckers. you have a larger rootsystem than aboveground tree. (if you prune heavily above ground you can get suckers. If you use a interstem to make the tree aboveground smaller. You have the vigerous roots belowground. like with MM111/B9 interstem. if you don’t plant the B9 below ground in that interstem, it’s also reported to sucker.)
There is also a cytokine paste. Some-one posted about it i think in a cherry topic. was used to get orchids to make a new plantlet (force a bud to grow a new plant)
i think it was called keki paste or something. Was in the last few weeks on this forum. But can’t seem to find it 
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My experience grafting stonefruits is limited to grafting ‘Guthrie’ Chickasaw plum onto native P.angustifolia understock, and a small ‘experiment’ grafting Japanese hybrid plums and an old heirloom white-fleshed peach onto Nanking cherry.
Nanking is actually more closely related to plums than to true cherries, and accepted Japanese hybrid plums - and grew them with vigor, but was extremely dwarfing to the peach… I don’t think it ever exceeded 4 ft in height in a 10 year timeframe. I never tried it as an interstem, but suppose it might work, at least in some scenarios.
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just noticed i misread your post.
You’r not planning to get the roots to sucker. But you want the part after the graft union to root.
Basicaly (air) layering.
For this auxine rooting hormone can help.
Another thing you could try.
Make it grow shoots from below-ground
Burry the graft union (and a few buds above the graft uninion.) and prune all above ground wood away. This way you force it to grow a new shoot from belowground.
Shoots that grow below ground in a moist/dark enviroment tend to form “wood” that roots more easy.
If your going the scarring bud/auxine route. It migt still be valuable to keep the roots higher than the bud. Otherwise the auxine might get transported away from the bud.
grow your own rootstock variety
It’s more long term. But you could polinate 1 vigerous variety with another one. Plant the seeds. See which ones are most vigerous. And try to get them to sucker.
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