New Releases from the Geneva® Apple Rootstock Breeding Program

Authors: Fazio, Gennaro; ROBINSON, TERRANCE - Cornell University

Submitted to: New York State Fruit Quarterly
Publication Type: Trade Journal
Publication Acceptance Date: 3/1/2023
Publication Date: 4/15/2023
Citation: Fazio, G., Robinson, T. 2023. New Releases from the Geneva® Apple Rootstock Breeding Program. New York State Fruit Quarterly. 31(1):29-33.

Interpretive Summary: n/a

Technical Abstract: Since its inception the Geneva apple rootstock breeding program has had the objective of breeding rootstocks with disease resistance. This emphasis has resulted in the release of several apple rootstock varieties (G.11, G.16, G.41, G.935, G.214, G.213, G.210, G.969, G.890) which are resistant to several rootstock diseases such as fire blight, apple replant disease complex, crown and root rot, and insects such as woolly apple aphids. While disease and insect resistance has been the main goal of the breeding program, whole orchard productivity, a trait influenced by dwarfing, early bearing and the propensity of the rootstock to impact partitioning of photosynthate away from excessive vegetative growth and into fruit production have been essential parameter used to select all new apple rootstocks. More recently, the program has been focusing on additional traits that modulate fruit quality, including the ability of apple rootstocks to increase the average fruit size of grafted cultivars, or modify its nutrient profile including the ratio like potassium/calcium which can lead to more or less bitter pit in apples depending on what nutrients rootstocks promote in a particular environment. Among the rootstocks we have released we have discovered two contrasting apple rootstocks in G.41 and G.214 in terms of absorption of potassium and nitrogen (high in G.41 and low in G.214) which leads to very different outcomes with regards to fruit quality of ‘Honeycrisp’. This has resulted in very different fertilization management for each rootstock in order to produce the best outcome. In the same realm of tree nutrition, G.935 is exceptional at mining boron from the soil and sending it to scion – a trait which might contribute to yield efficiencies that are 110-135% of M.9 which is known to be very poor at up taking boron. Another trait that we have witnessed in the Geneva breeding program is one of brittle graft unions with some scion/rootstock combinations, where Cripps Pink/G.41 is very brittle and Cripps Pink/G.214 is very strong. In addition, several novel scion varieties like NY-1 (SnapDragon) have weak growing habits and need stronger rootstocks to support productivity and canopy development. Some apple orchards are also leveraging increased the increase vigor of semi-dwarfing Geneva rootstocks which induce early bearing to establish multi-leader training systems with planar canopies. As we learn more about each of the Geneva® rootstocks, it is clear that each has many positive traits but also has less desirable traits. In addition, each orchard is unique in its soil and climate characteristics. This combined with different scion cultivar characteristics and vigor means that no one rootstock is the best choice in all situations. This leads us to continue to look for new rootstocks which are better in certain niche situations than all other rootstocks. All these considerations, in addition to new nursery and field performance results have led the Geneva® apple rootstock breeding program jointly conducted by U.S. Department of Agriculture – Agricultural Research Service, and Cornell University to release three new rootstocks this year: Geneva® 257 (G.257), Geneva® (G.484), and Geneva® (G.66).