The Importance of Grafting and

Rootstock Selection for Fruit trees

Joel Reich M.S.Colorado State University ExtensionIntegrated Land and Garden WorkshopMarch 6, 2012

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

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”)

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

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…

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

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!

Photos courtesy of U. of Minn. Extension

A little background…• Nowadays, we can reap the benefits of

hundreds of years of development work on clonal varieties of scions and rootstocks

The Take-Home Message

• If you are only paying attention to the scion, you are missing half of the story

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

Dwarfing Terminology

• Standard – Full-size tree• Vigorous – approx. 80% of standard• Semi-Vigorous – approx. 60-70% of standard• Semi-Dwarf – approx. 40-50% of standard• Dwarf – approx. 25% of standard

• Apple is the only crop that has rootstocks in all size classes

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

Photo courtesy of U. of Minn. Extension

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.)

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

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

Peach Rootstocks

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

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 – 90-100%, cold-hardy, FB resistant• OHxF 333 – 50-60%, cold hardy, FB resistant• OHxF 51 – 25-30%, cold hardy, FB resistant