1. The Importance of Grafting and Rootstock Selection for Fruit trees
Joel Reich M.S.
Colorado State University Extension
Integrated Land and Garden Workshop
March 6, 2012

2. A little background…
First, you need to understand that just about every tree fruit you have ever seen or eaten was grown on a grafted tree.
A grafted tree is comprised of two components:
Scion
Rootstock
Graft Union

3. A little background…
All tree fruit varieties, such as ‘Fuji’ apple, ‘Navel’ orange, ‘Bartlett’ pear and ‘Bing’ cherry are clones.
They are the result of either:
many generations of genetic recombination (“breeding”)
a random mutation (“a sport”)

4. A little background…
Once a desirable variety (genotype) has been found, we want to stop all genetic changes so we can keep growing the fruit we like.
Examples:
Breeding  ‘Honeycrisp’ apple, ‘Santa Rosa’ plum
Sport  ‘Navel’ orange, ‘Pinot Blanc’ grape

5. A little background…
Since seeds are the product of genetic recombination (a.k.a. “sex”), we do not grow fruit trees from seed because the resulting trees would have a different “genotype” from the mother plant, resulting in different and almost always inferior fruit.
Because of this, we grow clones…

6. A little background…
Clones are made from a piece of tissue of the desired variety
This tissue (a twig or even just a bud) is referred to as the “scion”
It is difficult to get a scion to grow roots, so we graft the scion onto an existing and compatible root system

7. A little background…
Initially, any seedling rootstock was used as an adopted set of roots for our desired varieties…
Then people noticed that some seedlings made particularly good rootstocks…
Disease-resistant, cold- and/or drought-hardy, precociousness, dwarfing.
So we started cloning good rootstocks, too!

8. Photos courtesy of U. of Minn. Extension

9. A little background…
Nowadays, we can reap the benefits of hundreds of years of development work on clonal varieties of scions and rootstocks

10. The Take-Home Message
If you are only paying attention to the scion, you are missing half of the story

11. What we (hope to) get from a Rootstock
Control tree growth & size
Promote earlier fruit production (precocity)
Disease & insect resistance
Fire Blight, Phytophthora, Verticillium
Wooly apple aphid, nematodes
Adaptation to different soil conditions
Adaptation to different climates

12. Dwarfing Terminology Standard – Full-size tree
Vigorous – approx. 80% of standard
Semi-Vigorous – approx % of standard
Semi-Dwarf – approx % of standard
Dwarf – approx. 25% of standard
Apple is the only crop that has rootstocks in all size classes

13. Seedling rootstock (standard) vs. M.9 (dwarf)

14. Photo courtesy of U. of Minn. Extension

15. Apple Rootstocks
M.27 – 15-20% dwarfing (3-4’) very compact bush, poorly anchored
M.9 – 25-30% dwarfing (8’), susceptable to FB
Bud 9 – 25-30% dwarfing (8’), FB resistant, very cold hardy*
G.16 – 25-30% dwarfing (8’), strong FB resistance*
M.26 – 40-50% dwarfing (10’) very common, disease probs.
G.11 – 40-50% dwarfing (10’) strong FB resistance*
G.30 – 50-60% dwarfing (12’) very cold hardy, FB resistance
M.7 – 55-65% dwarfing (12-14’) good FB resistance, not super cold hardy)*
MM.106, 14-18’(adaptable to many soils, FB probs.)

16. Cherry Rootstocks
Gisela 5 – 50% dwarfing, sweet cherry, very precocious, good availability
Gisela 12 – 70% dwarfing, sweet cherry, precocious, limited availability
Gisela 6 – 80% dwarfing, sweet cherry, good availability
Mahaleb – 90% dwarfing, best stock for tart cherry, drought and cold hardy
Mazzard – 100%, best full-size for sweet cherry, also used for tart where soils are heavy and/or wet

17. Plum Rootstocks
Myrobalan – 100%, strong, well-anchored. Adapted to diverse soils
Pixy – 60% dwarfing (about 9-10’), small fruit
Krymsk 1 – 50% dwarfing (about 8’), very cold-hardy, precocious, big fruit
PumiSelect – 30-50% dwarfing, not compatible with all varieties, Prunus pumila

18. Peach Rootstocks Seedlings
Lovell (most common in Palisade-area orchards)
Bailey (slightly more cold-hardy than others)
Halford (better on high pH soils)

19. Pear Rootstocks
Bartlett seedling – 100%, most common pear stock worldwide
Provence Quince – 50-65% dwarfing, high yielding, adapted to calcareous soils, winter tender, FB probs.
OHxF 97 – %, cold-hardy, FB resistant
OHxF 333 – 50-60%, cold hardy, FB resistant
OHxF 51 – 25-30%, cold hardy, FB resistant