Graft Incompatibility.

When Two Trees Become One

And Then Fall Apart........ (Geez that's dark).

Many trees are actually two trees grafted together at the nursery: a rootstock and a scion. This usually works well, but over time they can become incompatible. When they fail to communicate, vascular and structural problems follow.

This ornamental plum had some bad news hiding under the soil line. After performing a root collar excavation, Tsuga Treeworks was able to get to the bottom of it.

What Is Graft Incompatibility?

Graft incompatibility occurs when the rootstock and scion produce a poor graft interface, leading to vascular disruption and structural failure. Both sides quite literally have communication issues, kinda like that aunt and uncle that only visits when food is a plenty!

The Science Behind It (Arborist Nerdery Ahead)

Differentially expressed genes (DEGs) play a large role in incompatibility over the lifetime of the tree. Here is what goes wrong at the cellular level:

• Genes responsible for lignin production become downregulated, causing xylem (wood) to form in a weaker and less stable way.

• Hormones lose their ATP subscription to their favorite cytoplasmic streaming services, which disrupts the normal flow of energy and signals through the tree.

• An overexpression of clamp genes / 9-1-1 complex signals that programmed cell death has begun. (I thought I said don't hit the big red button)!

In short: Trees can develop complex and self-destruct if they don't act right....

How to Diagnose It

External symptoms are often easy enough to identify the problem, but when more evidence is needed, the tree can be drilled and the sawdust from both sections stained with iodine. Excess starch buildup in the rootstock confirms the diagnosis! You know, the same iodine-and-starch experiment us homeschooled 90's kids did..........The potato that also became a clock for a week......... and then your friend as it rotted and sprouted under your bed until mom found it....

Guess that was just me........

Many species, including Prunus (ornamental plum, cherry, and related trees), can go over a decade before symptoms and visible disfigurement appear. This delay makes early detection through root collar excavation especially valuable.

What Can Be Done....... Not Much....

Outside of bridge grafting from the rootstock to the trunk, there are limited options to slow the decline. Technically a similar species could be planted against it and then grafted to the trunk, but now you have a Franken-Tree! Similar to modern day dating, as incompatibility progresses, the tree often weakens, enters a mortality spiral, and may even break off at the base from girdling itself.

The best plan of action:

• Keep the tree well-irrigated through hot, dry months.

• Have an ISA Certified Arborist / BCMA to assess structural stability on a regular basis.

• Invest in bridge grafting to possibly prolong the trees life, or remove when dead and unstable.

Note:

This was learned, knowed, and typed by a real human being called Cody Willard, he is the primary human of Tsuga Treeworks.