The Importance of Rootstock Selection

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
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
– 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
• G.16 – 25-30% dwarfing (8’), strong FB resistance*
• M.26 – 40-50% dwarfing (10’) very common, disease
• G.11 – 40-50% dwarfing (10’) strong FB resistance*
• G.30 – 50-60% dwarfing (12’) very cold hardy, FB
• 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
• 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
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

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