Breeding improved apple rootstocks has been a priority research area in New York State since Dr. Jim Cummins and Dr. Herb Aldwinkle initiated crosses in 1970. In 1998, the rootstock program became a joint Cornell/U.S. Department of Agriculture program and in 2011 is headed by Dr. Gennaro Fazio. The program has focused on creating rootstocks that are resistant to the major apple diseases, fire blight (Erwinia amylovora) and crown rot (Phytophthora cactorum), and tolerant to a wide range of soils and that provide a wide range of vigor classes for all orchard situations. New rootstocks need to be precocious, productive, and easy to propagate yet free of burr knots.
Crosses were made from candidate plant material that was known to be pest-resistant and dwarfing. More than 100 genotypes have been used as parents. The most common successful parents include the hardy and disease-resistant Malus robusta (Robusta No.5), Malus floribunda, 'Beauty' crab apple, Malling 9, M.26, M.27, and Ottawa 3 (Robusta 5 x Antonovka) from the Ontario rootstock breeding program.
After successful crosses were made, progeny were subjected to a harsh selection process that weeded out those that did not show disease resistance. Then, surviving candidate rootstocks were grafted to a number of varieties for field testing, first at experiment stations across the United States. Then, the best candidates were evaluated in replicated trials on grower-cooperator farms. 'Northern Spy', 'Red Delicious', 'Golden Delicious', 'McIntosh', 'Empire', 'Liberty', 'Jonagold', and 'Crispin' were all used for these evaluations.
By 2006, seven rootstocks had been released to cooperating nurseries and now are available for planting as a result of successful field testing. It has taken 30 years and more than 300,000 hybrid seedlings to get these rootstocks ready for commercial production.
The next stage of testing is up to the grower with on-farm commercial-scale plantings. It will take more time to determine fully all the benefits and disadvantages. However, we are confident that fire blight, crown rot, and replant disease resistance, as well as improved productivity and fruit size, are advantages enough to warrant investment in these stocks.
Robinson, Terence, Gennaro Fazio, Herb Aldwinckle, Stephen Hoying, Kevin Iungerman, Michael Fargione. Where Do the Geneva® Apple Rootstocks Fit in New York State? New York Fruit Quarterly. Volume 12 No. 4. 2004.
Dr. Emily Hoover, University of Minnesota