Grafting Compatibility with Kevin Folta

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Hi everyone. Fruit tree grafting is like everyday magic.
When we graft fruit trees, we're actually fusing two separate trees together to create a single tree. And if you do this thoughtfully, the resulting tree can have fantastic qualities from each of the component trees. So for instance, let's say you want to grow an apple tree, but you have really heavy clay soil.
you can choose a rootstock, that's the lower part of the tree, that can thrive in those conditions. And then you take a clipping from an apple tree and you graft it onto the rootstock. That clipping is called a scion. So if this little combination works, you have now customized yourself an apple tree that is Perfect for your unique needs.
Now the magic, that happens at the graft union and that's the area on the trunk where these two distinct parts will meet. And on the show today, I'm going to chat with Dr. Kevin Folta. Professor of Horticultural Sciences at the University of Florida. And we're going to discuss exactly what happens at that graft union and why some fruit trees are compatible while others are not.
I'm Susan Poizner and I'm from the fruit tree care education website orchardpeople. com. I'm also the author of a brand new book on Amazon called Fruit Tree Grafting for Everyone, and I believe grafting is a skill that any grower can learn. But before we jump in, I want to celebrate with you guys a little milestone.
Did you know that this is our 100th episode? 100 episodes, and I'm celebrating by actually renaming the show. So, this show used to be called the Urban Forestry Radio Show and Podcast, and that's for eight years we called it that. But the thing is that over time the show has evolved, and we focus mostly on fruit trees and food forests, and my listeners are both in urban and rural environments.
So, What's the new show called? You guys ready? Drumroll, please. Okay, there's no drumroll. Oh, is there a drumroll? Yeah, a little bit of a drumroll. Okay, the show is now called Orchard People. That's what it's called. Okay, sorry, it's not that exciting, but that's the name of the show. So, the show is called Orchard People, and if you're ever looking for it on, Apple Podcasts, or on your local podcatcher, you'll find it under Orchard People, and that is where it's going to be.
Anyways, you can still access all of the older episodes. They will all be under the Orchard People name. Now, what do you think? If you're listening to the show live, I'd love to hear from you. This show is going out right now on RealityRadio101. com, so just email us right now, instudio101 at gmail dot com.
You can also send in a question on today's topic of grafting. You can send in a comment or I'd love it if you even just email to say hi. That's instudio101 at gmail. com and of course we look forward to hearing from you. Okay, finally, let's dig into the topic today. That's fruit tree grafting and compatibility.
Kevin Folta, welcome to the show today. Yeah. Hi, Susan. Nice to be back. This is great. It's so fun to have you and talking about one of my favorite topics, which is grafting. So can we start off with a basic quick explanation of what is fruit tree grafting? Can you describe what it is and how it works? you really nailed it down in your introduction.
This is, when we're breeding plants, we're combining plants sexually. You're taking pollen from one and combining that with the genetics of another. And here's an example where we're taking two. genetic isolates that don't necessarily belong together, infusing them together by combining their, vascular, and, their, lignification.
So, so fixing, combining them together using, connections in plumbing and, glue in the wood, putting those things together. It's almost like we're creating a franken tree, you're like taking pieces that shouldn't be together and you're finding a way to stick them together so it works.
But is this something that humans have invented, or does fruit tree grafting actually occur in nature? Yeah, it does. We actually thought we invented it 8000 years ago, but there you actually do find examples of fruit tree grafting occurring in nature where either trees grow together aerially, but you see it frequently in roots, especially with some ficus species and other species that fusions occur underground, allowing different compounds to transmit from one tree to another.
It's a form of direct line communication in forests or places where these trees stand. So I'm trying to figure out what the benefit is that for nature. So you've got these roots underground, fig tree number one and fig tree number two, and the roots intersect and they say, Hey, let's combine, what's the benefit?
Where, are they getting any benefit out of that? plants have evolved a lot of interesting ways to communicate with each other. So the emission of volatile compounds, other ways to, communicate back and forth that are super cool. We're learning more about it all the time, but that idea of direct transmission.
of compounds that may have to do with signaling or defense hormones or small RNA molecules, which we can talk about later. These are all signals that allow trees to talk to one another and maybe doing that through the root system. Pretty cool. Wow, mind blowing in a way to think of that, and even just the idea of, if for instance a tree breaks a limb breaks in the wind, is it possible that it would graft itself back onto itself, maybe?
I don't know. No, that's, really what the basis of grafting is, really this exploitation of a naturally occurring wound healing that occurs. So when a branch breaks, maybe just cracks a little bit, you can imagine between a limb of a tree and the rest of the trunk of the tree, just a little crack there that would occur.
That thing has some natural, desire to go back into place and the healing will occur because The piece that broke off, it's vascular tissues and is meristematic tissues. So the tissues that give rise to other tissues, the kind of the generic cells that give rise to the other differentiated cells in a plant, those things align.
And when they align perfectly, they shake hands across that union and build, what's called callus and other tissues that will heal that junction. And, very, cool. So it does happen naturally and we exploit that process for human benefit. Amazing. So we're actually copying what nature showed us is possible.
okay, we got a couple of emails already. One is from Steve. Hello, Susan. Wow. Welcome back and Happy New Year. Congratulations on your 100th. Wow. I never thought anybody would congratulate me on my 100th. there you go. Oh, am I really that old? That's interesting. there's an, also an email from Walt.
Congratulations to Susan Poizner and Orchard People. Wow. 100 episodes, a milestone. Good luck with the new format. Great guests today. Thank you so much, Walt. That's wonderful. okay. So now let's think about. What trees go together? Now, for instance, let's say we have an apple tree, like in my example earlier.
Why is it that you can take a clipping from one apple tree, whether it's Honeycrisp or Macintosh and one of the popular rootstocks, and we can talk a little bit about that later too, and sometimes it works easily, and sometimes it doesn't. Are some cultivars pickier than others? more finicky?
That's a really good question. I don't know of particular, like interspecies tend to be pretty good. So grafting apple onto apple, different cultivars tend to do well with different root stocks. I'm not really aware of any particular trends within apple, but there are some other. Other examples which are reasonably close.
So, the big thing that delineates whether or not a graft is compatible tends to do with taxonomic difference, a distance and Margaret Frank up at Cornell has done some nice work with grafting, things like eggplants on tomatoes. you could do that. Or maybe, eggplants on the tobacco that kind of study where she wants to look at where it is the how far can you go before it doesn't work.
And what are the elements of incompatibility that you see at that junction, and you study it in tomatoes and, and eggplants because those are easier than oak trees. it takes a little time, so, it seems like things like apples to apples, peaches to peaches all pretty good. But as you start to get a little more out of that taxonomy, it becomes more challenging.
Some things aren't such a, aren't so difficult when you start getting into, I'm trying to think of a good example, but I think like peaches and almonds. Yeah. are, challenging, to, or it may be even impossible to graft together. And it's still very taxonomically close. Interesting.
Okay. So that's, the taxonomy piece. let's talk about the general factors, what's happening inside that graft union, the general factors that determine the success or failure of our combinations. Okay. Give me, I know you told me in our little pre interview that there are four general factors.
Let's, tell me what they are, all four of them. Yeah, we might even have a fifth. So there's quite a few factors that play a role in this. Most of it is the structural alignment. That's a big part of it. And the cambium cells that are the meristematic cells aligning properly. So physical alignment. But also the presence of hormones, what's happening in terms of the gradients of hormones that are present inside that developing tissue.
there's questions of secondary metabolites. So, things that are formed naturally by the plant as part of metabolism, that these can actually be very strong in inhibiting a successful graft union. And then things like, small molecules like RNAs and proteins, these, molecules which are, Moving throughout the from the root stock to the scion and vice versa that arrive at that graft union and may play a role in how well that graft union heals.
That's a big part of it. And the genes that are expressed, you know what's happening at the molecular biology level at that graft union in response to the stress.
Okay. Over, that's good overview. And now let's take it apart and understand it. So let's start with the word morphology, Okay, what is morphology? And how will that affect whether or not your graft is going to work? Yeah, morphology really just refers to the physical nature of the plant and the position of stuff. And so when we're talking about the morphological features of a graft union, we're looking at how tightly that graft union is made to put Cells adjacent to other cells, which will form the successful callus bridge.
So they, what is a, cell type that kind of bridges that graft as it's cellular rises as, it begins to heal within that union and then expand to develop new vascular tissue. So getting those tissues into proximity, just to dive in. Oh, sorry. Just to dive in. We're talking about the jigsaw puzzle. Have we are the two pieces touching?
Is that what you're saying? That's all I'm saying. Yeah. Are the pieces in proximity to where the cells can shake hands across that junction. So, in other words, if I'm a terrible grafter, which, I am, I'm pretty new. And if I don't make my cuts. properly. The reason my graft doesn't work is going to be morphology.
It would likely be at that first level of morphology, just a bad architecture of the graft union. And I tell people when I teach grafting, if it doesn't look perfect, start again or throw it away because it's, not worth the investment of your time. make it perfect. And the morph, morphology is the big reason, the architecture of that graft union.
Okay, so we make our cuts. Now, does that, does the cambium have a role to play here in, in the way the cuts are made? Yeah, so the vascular cambium, so this is a, in a dicot stem, so in a typical fruit tree stem, this is a ring around the outside edge, and you can see it as a green ring in cross section, and that green ring is going to generate phloem to one side, xylem to the inside, phloem to the outside.
But that middle layer of cells is called vascular cambium, and this is what we refer to as pluripotent in the stem cell world, and stem cell, not like the cells in a stem, the, a cell that can have many, outcomes, many fates, and that pluripotent cell layer that can differentiate into vascular tissue or, or, meaning either xylem or phloem, or just, general cells In general, just like a generic cell type called callus, that cell line has to align, and if it does, it will use small molecules, maybe even direct contact, to communicate with the cells on the other side of that graft union and say, hey, we're both here, we gotta heal this thing, and that's where your healing will begin.
Okay, so that so makes sense. So I can make two beautiful cuts, one in the rootstock and one in the scion, and if I don't quite line them up properly, then that's another problem that relates to morphology, I would think. we've got another email. This one's from Janice. Hi, Susan P. Welcome back to the airwaves.
Congrats on your 100th good topic today. Three of us are listening from Toronto, Ontario. Yay, Canadians. Wonderful. Okay. Yay for my Canadians. All right.
So now let's go on to point number two, which you enlightened me about in an earlier conversation. And point number two here is called cellular physiology.
Wow. That's a mouthful. and so that talks about what's happening at the cellular level during grafting in that graft union. Tell me about that. Yeah, so what is happening to the cell on cell contact, that the cells come together across that union, and cells eventually do form a pipeline. Between one cell to the other one cell file to the next, where different molecules can flow from one set of cells to the other.
And so what's happening at that level is really important. How do these cells contact each other? What's flowing through them to communicate from one side to the other? What's going on with transmission of hormones or small molecules? All of these things are happening in that region and controlling how the cells are behaving.
So how are cells on both sides of that union now responding to each other and helping to cellularize that graft union so that eventually vascularization can occur. Okay, so let's imagine there, let's say the rootstock has like a community of cells, a little community, little village of cells near the graft union and the scion has a village of cells.
And so are there certain cells that it's okay, boys and girls, this is our responsibility. We're going to do X. And the other cells will say, yeah, let's do the while they do that, we'll do something else. is there that kind of interaction going on with those cells? I think that's happening just in those cambium cells, just in the cells, which are the pluripotent cells, which now will give rise to the, or the vascular cambium, which will give rise to some of the other cell types in that region.
And that will help to cellularize that joint. Okay. And so are the, like we talk, sometimes people say, that the cambium layer is made up of cells. they turn into glue. It glues the tree together. and yet at the same time, there's other things happening because some of them are going to be xylem and phloem.
So I read somewhere that some of the cells decide to be glue while others decide to be plumbing, right? So some of the cells will say, okay, I'm a cell. I'm a neutral no name cell. And I think I'm going to be part of the glue community. So I'm going to stick these two things together and other cells will say, since, Bob, Harry and Sally are becoming glue, why don't we be plumbers?
And I'm going to connect this top tree to the bottom tree so that water and nutrients can go up. No, that's exactly right. there's, no utility in a graft union that doesn't have both. You have to have. Good physical structural elements that tie want the top to the bottom. And so during that cellularization phase where you have cells forming in that union, you also have lignification.
So the process of the deposition of specific molecules, which will help fuse that connection and strengthen that connection between the bottom and the top. And then at the same time, you need to be able to, as you say, put in the plumbing, and that's a differentiation of xylem and phloem to connect both sides of the, of the pipe, for lack of a better, for an excellent term.
That's a perfect term for me, yeah. I wouldn't say lack of, yeah, not lack of, a better term, to underscore an excellent analogy. you have, The connection that can be made there by differentiating in that gap and then allowing that xylem to connect to xylem and flow them to flow them. So it's really remarkable when you think about it because here just these generic cell types are able to identify where they need to go and what they need to turn into to fuse that connection.
I think that's amazing. that just makes, that's just amazing to think about that. So, all right. So, so far we've talked about morphology and that's how good or bad my cut is. Then we talked about cellular physiology. We talked about the little communities of cells on both sides and whether they work together to maybe become glue, to maybe become plumbing, to lignify or harden the, All those things that they do.
We've got a couple more points, but first, we've got an email from Dave. Hello, Dave. Hi, Susan. Any contests today? Good luck with your new show ideas. Happy 100th. Does Kevin have a website? Thank you, Dave. let's start at the end. Kevin, do you have a website? That's a good point. I just have a pro, I have my university website, which is at University of Florida.
I also have the Talking Biotech podcast where we, where that website is, available. also, if you go to kevinfolta. com That's a lot of the work I do in strategic communication as well as, science, but, not a lot on there on grafting. there are some grafting things out there that I've written, here and there, and you can find those just by searching my name with the term grafting.
And on your podcast, I know you've got a few interviews on grafting because I've got lined up. I'm going to be listening to those very soon. So, yes, Talking Biotech, is your podcast? That's right. And I did an interview with Dr. Charles Melnick a few years ago, and he's an expert on grafting and what happens at the level of the cell on either side of that union.
And we had a really nice conversation. I look forward to listening to that one. That's going to be good. Your other question, any contest today? I'm sorry, today we do not have a contest. Sorry about that. But your prize is that we get to talk to Kevin. Yay. So that's my prize. Okay. So thank you, Dave. Oh, we got a whole bunch of little questions here.
Let's see what else we've got. Gloria. Hi, garden show. Is this discussion just for fruit trees or flowering plants as well? That's a good question. I love it. should I answer that? Yes, please. There's been more and more interest in grafting, non woody species, especially in the area of horticultural crop plants.
So, I don't know about flowers. I'm sure that can be done. But, there have been tremendous benefits of things like watermelons, other curbits, tomatoes, because rootstocks can impart really strong, traits such as disease resistance to a shoot or to the scion. And in China, they graft by hand. and by machine on millions of tomatoes and watermelon plants in here.
I've done it. I graft tomatoes and you get some very nice traits from the roots which help with disease resistance and stature control. I have a friend, John, who may be listening to the show and he is. Famous for his grafted tomatoes that he grows. They grow huge, very big. Okay, got a message here from a Sammy.
Sammy writes, Hello, I have been doing grafting in my backyard for a number of years now. Every once in a while, I will read an article stating that a royalty should be paid for using some scion cuttings. Can you please clarify whether this is true? Love this topic of grafting. Thanks to you and the guest.
Wow. good question. No, absolutely. There are some materials which are still protected under plant variety protection and vegetatively propagated plants that are developed through private or public breeding programs. Do have patent protection, so you can't necessarily do your, you're not supposed to do it for one at all, and if you do decide to do it, a royalty should be paid to the patent holder, and that all has to be arranged before I've.
been interested in trying to propagate some rootstocks, things like that, which are under patent. And if I do that, I have to first let the patent owner know and then pay them the royalty for doing it. And you know what? I think it's great investment to, to do that. I'm glad you brought up this question because plant variety improvement is an extremely expensive process.
and we need to keep our breeders in mind if we propagate what their invention is. so that's a great question, because let's say my neighbor has a Macintosh apple tree. Am I being naughty if I snip off some branches and graft it onto something else? no. Macintosh is long expired in terms of its, in terms of its patent protection, if there ever was.
And so what you just have to do is be cognizant of what the new varieties are when the patents expire. And, no one's going to get too upset if you do one for your neighbor in your own home. it still is breaking the law, but it's one of these things that's mostly made to deter widespread commercial propagation of something that has been protected that took a long time to develop.
If there's any listeners as well who have fruit tree nurseries, we'd love to hear from you about your perspective on this because you guys are growing all this scion wood, snipping it and making plants for us. And so maybe there's some feedback there. We've got an email here from steve. Is this susan poisoner?
Really? We missed you in your show. Oh my gosh Sorry the imposter Actually, we when the months that we weren't able to be on reality radio 101 we actually went out live on youtube It was pretty hairy for me because I was doing the technical stuff. So yeah. Anyways, thank you. I'm glad you noticed I was missing so glad to have you back.
Does kevin have a book or videos to help us out on this? Thank you. it's, I don't, and I wish I did, and I need to develop the videos. I'm, working on this. book wise, I've got so many irons in the fire. It's crazy. I'm an active researcher. I'm an act, I farm with my wife. we are busy, but I would love to do it someday.
So keep an eye out. Maybe one day I'll be able to do that. And if it is a specific grafting book that you are looking for, I just publish grow fruit tree grafting for everyone. I'm super excited. So check that out. You might be interested.
Okay, Jolene writes, I love your show. Can you graft a zone five apple varieties onto a zone for rootstock?
Ooh, how cool. Yes, you can. as long as they're species compatible. That's what matters. And this is what makes grafting so important. The traits of that rootstock can be transmitted to the scion and vice versa. So there are people who are committed just to develop new rootstocks that have enhanced disease and even percocity, built into them.
And dwarfing, dwarfing qualities. there's one that we're trialing for apple, which gives us earliness. potentially, which means that here in Florida, we may be able to grow more of the northern varieties and still have good bud break and lots of them, even with less chilling, that would be pretty exciting.
So basically it can like it's, I guess it's not just the zone that's important. So it could be like a zone five cherry tree onto a zone for, I don't know, pear tree, right? Yeah, that would be a little bit. You know what I mean? That might be tricky. That's a taxonomical, bridge you may not be able to cross.
But in terms of if you know that the varieties are compatible, then the zone, there's some flexibility there. Yes. Good question. then we have this lovely email from Don. Hi, guys. Susan, great topic today. Congratulations on the new podcast name and your 100th episode. And that's from Dawn.
Thank you, Dawn. Okay. It let's do this. We've got two more big topics to talk about in terms of what makes a graft union successful and what doesn't, but let's take a little break and listen to some words from our sponsors. And then we'll come back after that and dive right back into the topic. Are you okay hanging on the line for a couple minutes, Kevin?
Of course.
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You are listening to Orchard People, a radio show and podcast about fruit trees, food, forests, and permaculture. This is reality radio one Oh one. And I'm your host, Susan Poizner from the fruit tree care training website, Now in the show today, we've been talking to Dr. Kevin Folta, professor of horticultural sciences at the university of Florida. And our topic is fruit tree grafting compatibility. And what happens at the graft union when you are merging two trees into one? So, we are going to talk further about that in just a moment, in just a minute.
But first, I want to hear from you. Do you graft fruit trees? When do you find that your grafts are most effective and successful? What questions do you have about the science of grafting? If you're listening to the show live today, send us an email right now to instudio101 at gmail. com with a question. a comment or just to say hello, and be sure to include your first name and where you are writing from.
I look forward to hearing from you.
So now back to Kevin. Kevin, we talked about morphology and how things fit together when you're grafting. We talked about the cells and what they're doing inside that graft union. I wanted to talk about hormones. How do plant hormones get involved in this whole activity of merging two trees into one?
plant hormones are so pivotal in every aspect of plant growth and development. And plants, hormones, they really establish where a cell is. a cell knows where it is by its hormonal environment and knows its proximity to adjacent cells as well as to the top of the plant, to the bottom of the plant.
It knows where it is in space. Typically because of environmental signals, but the internal signal of plant hormones. And when you have a break, a wound in a plant, such as those that may be incurred by your grafting knife, that those cells immediately say we've been wounded and hormones begin to accumulate that now will facilitate the cell division and the cell adhesion necessary to reestablish that graft union.
And one of the big players is auxin. People have heard about auxin. It's the one that controls, bending towards light and, suppression of apical, lateral axial buds, and apical dominance, all that good stuff. Auxin seems to be a big player in the differentiation. Of or the, proliferation of cells and callous.
So the generic cell type that we call callous that are just cells in that meristematic cambium that are like just generic cells. They're looking for something to become, but they go to this generic cell type first. And it seems that in most cases the graft is established as with what's called a callous bridge that auxin gets these cells to divide and divide and form that bridge between the two sides of that union.
So I'm fascinated because from what I understand, those auxin hormones, they spend all their time at the tips of branches. They usually, help the branches become longer and longer. So let's say. There is a break in the branch that we caused with our grafting knife. We cut the branch. How does, how did the auxins get there to tell the cells, hey guys, let's get active, can we heal this please?
Yeah, that's a great question. So auxins are produced apically. They're done at the apex of the plant in the apical meristem and then migrate, as we say in plant physiology, bascipitally. They move down the plant body. And so they move down the plant body. Now, if you move down the plant body and all of a sudden you run into A cut where your vasculature doesn't go on anymore.
Now you start to accumulate auxin in that spot. And that accumulation of auxin signals other things to happen inside those cells. other genes associated with auxin, transport. Maybe lateral transport of auxin. Or, turnover of auxin. But also that, accumulating auxin causes that development of callus.
And, that's really what we're exploiting here. So logically speaking, inside my head, I'm thinking, okay, I'm grafting onto an existing tree in my backyard. I've cut off a branch so that I could graft onto it. I'm throwing away the auxin at the tip of the branch, so I've cut it off and I'm taking a piece from another tree and putting it there.
How are the auxin gonna get to where they need to go? No, that's a good question because yeah, you, if you don't use the tip, where do the auxin come from? There's auxin that are present inside the inside that. branch already and cells will make their own auxins. things like plant hormones are really carefully controlled in terms of their levels.
And if we think about it, they have mechanisms that turn on the production and also turn over the production. And so it's plant cells are stepping on the gas and the brakes at the same time. And so when, you have that break, maybe you have a, An injury, I should say. Now all of a sudden you lift your foot off the brakes a little to accumulate more of the hormones that are going to be necessary for establishing that connection and healing that union.
I love that image. That's an interesting idea. okay, we've got an email here from Carrie. Hi, Susan. Fruit tree grafting is very interesting. My mother in law told me that it was very easy to do. My question, does it matter what type of fruit tree is grafted to the main tree? And please add me into the drawing if you are having one.
Oops, no contest to me. Sorry, Carrie. And Carrie is from Oregon.
okay, so the question is, does it matter What type of fruit tree is grafted to the main tree? Yeah. Yeah. So this goes back to that idea of, what they call heterografts and, how far can we move taxonomically away from each other before there's incompatibility.
And there's no really good rules on this. I mentioned earlier, it's, maybe apricot and almond can't. can't graft, but peach and plum can. And so those are interspecific, meaning two different species can graft together, but you can even do intergeneric grants, grafts. So, in citrus, we do it all the time.
there's something called Poncirus. It's a very durable trifoliate orange that's used as a rootstock that we graft on. regular citrus. And so here you're going not just different species, but different genera, and even some inter family familial grafts have been done. but it's all really dependent upon, other factors as to whether that graft will be compatible.
So, what I would say to the listener is, you gotta give it a try. You got to give it a try. And report your results. Exactly. I always say that, how many experiments can I do in my own backyard? I love hearing from other people. And also I've got, and at the end of the show, I'll mention there's a few other episodes that we talked about, for instance, multi fruit, grafting, with, Javier Rivera was talking about that.
We've got about four different podcasts on So you may find your answer in those other ones.
Okay, so we talked about morphology, pieces of the puzzle fitting together. We talked about cellular by physiology, the little communities of cells who are going to get and kick into action and become either glue or plumbing or whatever the union needs.
We talked about hormones. The last thing that I have on my list here is molecular biology. Oh, boy. What role does this play in grafting? Ah, yes. Yeah, tell me about, what is it anyways? molecular biology, that's what I do for a living. Molecular biology is really what's happening at the level of DNA and RNA, the nucleic acids.
That are the genes that are being expressed and what you find in grafting is very interesting that there's a whole series of, small RNAs. So going back to our central dogma of molecular biology, you have DNA in your cells as a master blueprint that makes this transient copy of certain genes, which is reflected in what's called RNA.
And RNA goes into the cell where it gets translated in the protein. So the information makes the proteins that are the enzymes in the structural elements of the cell. RNA is actually translocated through a graft union in many cases, and even as some believe, some have shown evidence, that small RNAs, little pieces of RNA, have a role in the healing of the graft union.
So it's a messenger, a little signal, that like a hormone is changing the way genes are expressed that will help heal that graft union. Molecular biology also plays a role in the genes that are associated with auxin and cytokinin synthesis. So plant hormones like auxin, cytokinin, maybe gibberellins to some extent, ethylene.
These are all playing a role in the cellular fate and differentiation of the cells in that graft union. Not only their proliferation to make generic cells, but also playing an important role in their final differentiation into either plumbing or glue. So this is all happening at the level of the gene.
That's what's controlling this ultimately. Okay. So here's where I'm totally confused because what I understand about grafting is the, genetic identity of your root stock is. Stays the same and the top of the trees genetic identity stays the same. So if I have a Macintosh apple tree on the top and it's grafted on to let's say a golden delicious rootstock That wouldn't really happen, but just to give it a name, right?
So each of them stay what they are they keep their own sort of DNA identity So what you're saying is well, there is a little bit of stuff bleeding from one into the other in terms of Yes, yeah, but that shouldn't surprise us because we buy root stocks based on the traits they conferred of the scion, right?
So something has to be either moving through it or some sort of signal that gives the scion enhanced ability or it could just be that there's a little bit of incompatibility there that's making the Plant stress out. And when that little bit of stress is present, you don't have a problem as less susceptible to disease because stress related genes may already be elevated in the scion.
now that you got, it's if you, go outside and your shoes are too tight, it tends to affect many things you do throughout the day. and so it's, it's how that, that, that scion may be reacting to a slightly incompatible, incompatible rootstock.
Okay. So now we have a bit of a broader understanding of what's happening in the graft union, whether these combinations will work, whether it's apple to apple, whether it's plum to apricot, there's, there are also, for instance, cherry.
Cherry trees and that's a stone fruit and I understand that a lot of stone fruits are similar in character But cherries don't seem to graft very well onto plums or apricots. That just doesn't happen. So why would that be a problem? Yeah, it's prunus to prunus crime, isn't it? Yeah, so it's probably because of There's enough genetic distance, even though they're similar at the level of the gene that metabolically there's some differences.
And this is a big one that I mentioned in the beginning that there are a number of secondary metabolites. So these are just chemicals that the plants make that Tend to coalesce at these wounds and that those wounds can play a role in, or those compounds, presence of those compounds can play a role in that incompatibility.
And that's been studied in a lot of, graft unions, both newly established as well as, maybe, longer term. graft unions that fail. they can fail after 15 years. so what was present that caused it to stop working? And it turns out it's usually the presence of these secondary metabolites.
Okay, here's another question. Some people have reported That stone fruits do not take as well when you do them in spring grafting versus summer budding. They work better with budding. Yes. So if you're doing peaches, most times fruit tree nurseries will bud them in the summer rather than graft them in the spring.
Why would that be? Whereas apple trees, for instance, are great if you do them both in the spring and in the summer. Yeah, I'm, so the main reason that at least down in my neck of the woods where we do bud grafting, shield grafts, those kinds of things is because of disease transmission. And down here where Xylella is endemic, where you have lots of other diseases that are present, they're not as likely to transmit when you transmit them with buds because they haven't developed a full vasculature for the bud for disease to move within the vascular tissue.
So the young developing bud when that's grafted is less likely to cause problems going forward. Interesting. So when you, obviously in the spring, we're using a piece of a branch, it's a little, it's older than a bud, it's, stuff has happened, it may have sucked in some of the disease that's in the tree, so in the summer when we're budding with a teeny tiny little bud from our, the plant that we want to propagate, it's so young that hopefully it hasn't taken in those diseases.
So that's the reason people prefer to do stone fruits budding in the summer rather than the spring. Okay, that makes sense. now I got a question, and I'm sorry I don't remember the name of this, this listener.
Would warmer climate chestnut cultivars that are resistant to blight be successfully grown in cold areas if they were grafted onto a tree with more resilience in colder areas like oak and beech.
So I guess here the question is, could you, in terms of nut trees, or native trees, or whatever, can you graft chestnut Onto oak or beach. Now, that would not be a compatible, not likely be compatible. I've never tried it, so I can't say, not likely be compatible. It is interesting that you could use some of the, potentially resistant, chestnut types if the American chestnut is still there, in many of the forests, although not growing well because of blight.
And, if those roots stock, or if the roots are still present, and you do see shoots of them coming up here and there, from what I understand, that could certainly be grafted onto, but I think the idea of, repatriating Appalachia, by grafting, it might be a far flung idea. Okay. So, yeah. I love it.
Yeah. It would be great if it worked for sure. If you had that flexibility. I've got,
there was also a discussion on Facebook here. And so I got some interesting questions. One was from Paul in Michigan. I'm curious about grafting pear onto quince. Yeah. Yeah. Only some pear cultivars are compatible. So what's going on there?
Yeah. Yeah, that's another example where quince can provide a very strong dwarfing effect on two different pair cultivars. And, but again, it's cultivar specific and it has to do more again with taxonomic distance. I think if you were to look at the genetic sequences of the ones that worked and the ones that didn't or metabolic profiles, you'd find that they grouped up very nicely, that there is, just, and this is why grafting is so cool.
It's only recently been. available to our modern molecular tools. everybody's been studying other stuff and now looking at what's happening on either side of that union is becoming possible because we can say what's happening in a single cell. we can look at that now. Wasn't possible before.
So, yeah, that's a great question. Quince is a, allegedly a very good rootstock for certain kinds of pears. And, again, it makes you, like, when we think of pear cultivars, we think, they're all pears. And what you're saying is, whether it's a Bosque pear or another variety, it could be on a genetic level or a DNA level, maybe very different.
Am I right? Is it the d dn DNA level that would be different, that might not be compatible with the quince? My, my guess is that it would be that the DNA sequences are very similar. If you look across the rosaceous crops, such quince and per are both rosaceous crops and relatively close together taxonomically, they're very similar at the DNA level, but something is not allowing those cells to shake hand or is allowing in some, not allowing in others.
And it mo very likely is. That my guess is, that it has the ability to form that union because of its similarity, but doesn't form it because of some secondary metabolite or some secondary difference that doesn't allow that to occur. So something that's present in either the pair or the quince that, that disallows that formation to occur.
And so I think scientists like you over, in the next two, three years, you guys may have answers for us on this. You may have specific answers because now you're able to check and research it. Yeah, there's some great people on this. Charles Melnick, who I mentioned before, Dr. Melnick's doing great work in Sweden.
Margaret Frank at Cornell. There's some Dr. Margaret Frank. there's so many people doing beautiful work around the cells of that union, and we're learning all the time and I'm, interested in it, but I'm not doing the research because smarter people are doing it and I can, I'll just read what they write.
Sounds good. Okay, we've got something here from Adam from Michigan, writes, I grafted the superfin European pear variety onto a rootstock called OHXF87. Not a very fancy name, but anyways, and it began to throw root suckers. So it started to grow root suckers. So he says it wasn't really successful. But when I took a cutting from that superfin European pear and then grafted it onto a different rootstock, O H X F333, it grew just fine.
Later he told me actually that, the original one, the one that suckered, did survive at least for a while. But he felt that the fact that it suckered so much meant it wasn't a successful graft. So what do you think? What did the, fact that your rootstock starts to send up a lot of alternative shoots instead of putting its energy into the graft, what does that mean to you?
Yeah, that's a good question. I'm not that familiar with the OHXF suckering habits of all the individual ones, because there's many different ones. And some rootstocks are just more prone to suckering, irrespective of the grant that, the graft that's applied. So, I would hate to give you bad guidance there.
I don't know that it means your graft failed. M111 is a popular apple rootstock that makes suckers all day, and you got to keep cutting those suckers off. we see it with Ponsiris and Citrus, they always are making more, from the base. it's more important to manage those suckers because they're taking away potential of the scion.
And, even in some cases, like with persimmons, I've seen people who had persimmons trees. And some peach trees where the rootstock actually outgrew the scion and, ended up, providing some false hope that their tree was doing extremely well. Oh, interesting. Okay. Yeah. So, so the suckering itself doesn't mean that it was necessarily a problem.
It's good to know. Okay. I think we've got time for one more comment here.
This is from Javier in Florida. And Javier is talking about his favorite combinations. My favorite combinations to graft are apples to G890 rootstock. Okay, so, Javier's in Florida. I like grafting ornamental cherries and stone fruit scions onto Mariana 2624.
Through interstems and we talk about this in Javier's program a lot about interstems But we can mention it now. What hasn't worked well for me in the past is any peach or nectarine grafted onto citation rootstock as they don't seem to survive past one year in my area Even though I give them good soil and good drainage So what, what could be the problem here?
And I think this is a perfect example of what we talked about in the beginning of the show. Grafting is, in a way, it seems complicated. It's a simple art. It really is learning to make some basic cuts, learning the science behind it, but some combinations just don't want to cooperate or shake hands. So any comments on, that?
it's a little bit tough. I know Javier. yeah, citation, that's the problem in citation is a California rootstock for stone fruits. Florida is extremely fickle with respect to rootstock compatibility with the soil. So it doesn't matter what you stick on top. the peach rootstocks don't do well here at all.
Nemagard was developed in Florida for Florida. That one's kind of waning. Florigard does very well with the nematodes and other disease pressures and the sandy rotten soil. really it's so important in the grafting process to make sure that the, the roots that you choose are going to be compatible with the soil it's going to be in.
And so I don't know, Cytation, Javier has played with that one a bunch, but, I'm not too sure about that, how that one performs here. Interesting. So, so you're bringing in one at the end of the show, but that's one extra piece of the puzzle is it matters where you live. You can have the best combination of, whether it's citation rootstock and, a peach and nectarine and it works perfectly in California.
Guess what? Doesn't work in Florida. The climate's different. The conditions are different. So. Like I said, it's a beautiful science, grafting. It's actually a simple science when, you start to play with it. and yet you can go into a very deep rabbit hole and, encounter some issues, but that's the fun, isn't it?
do you enjoy grafting, Kevin? Is it, something that you like doing? Yeah, I do thousands of them a year. I can count to nine.
I love grafting. It's so much fun. It's fun seeing the different combinations you can do. I can grow all kinds of fun mulberries on my property because I have a native rootstock that I can graft to. There's so many fun things you can do once you start understanding what works in your place and what you can graft onto it.
Wow. Native roots. So what's the native rootstock? So you have a native. Mulberry that's growing naturally on your property and then you're taking scions from really yummy varieties and popping them on something that's already in the ground in your backyard. That's right. And it gives them good vigor and it makes them grow so much faster than if they're on, if they're on their native roots, because things like nematodes just feast on mulberries, but they don't touch the native ones.
So it gives me the opportunity to grow something nobody else has. How fun. That is so fun. Okay. That is so great. Now we're going to wrap up the show in a minute. First I want to remind everybody, if you are interested in this topic, there are other episodes that you will love, and you'll find all these other episodes at.
podcast. orchardpeople. com. So, episode 65 is about the tree of 40 fruits, and my guest was Sam Van Aken, the artist that makes these incredible trees. Episode 77 is about fruit tree grafting for beginners with Steph Roth of Silver Creek Nursery. Episode 91 is about multi fruit trees, and we talk there about interstem grafting.
And Javier Rivera was my interviewee there. And then finally, episode 88 is about apple rootstocks. It's explaining more about apple rootstocks. That was fascinating with John Strang. So you guys can find those episodes at podcast. orchardpeople. com. And if you're interested in my new book, You can go to Amazon and look for fruit tree grafting for everyone and I will teach you how to graft your own fruit trees with help from an expert.
So anyways, I hope you guys love the book. So thank you so much Kevin for coming on the show today. It is always so fun to have you on and we really appreciate you spending the time to explain things to us. Oh, anytime. I love the topic. So thank you for doing what you do. So that was fun.
Thank you to Kevin for coming on the show and for the rest of the listeners.
Why don't you head over to the Orchard People YouTube channel later? You're going to be able to see the video of this podcast or you can go to Apple Podcasts or your local podcatcher and subscribe to the Orchard People podcast. Finally, if you want to get emails from me about upcoming shows, go to OrchardPeople.
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Thank you so much for tuning in. I hope you're going to join me again next month when we're going to dig into another great topic. See you then. Bye for now.

Creators and Guests

Susan Poizner
Susan Poizner
Author, fruit tree educator, and Creator of the award-winning fruit tree care education website
Grafting Compatibility with Kevin Folta
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