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 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