The Geneva apple rootstock breeding program

Authors: Fazio, Gennaro; ROBINSON, TERENCE - Cornell University; ALDWINCKLE, HERBERT - Cornell University

Submitted to: Plant Breeding Reviews
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/30/2015
Publication Date: 10/15/2015
Citation: Fazio, G., Robinson, T., Aldwinckle, H. 2015. The Geneva apple rootstock breeding program. Plant Breeding Reviews. 39:379-424.

Interpretive Summary: Grafting is an ancient practice meant to preserve and increase a desirable plant by attaching pieces of it onto another compatible host root system. This practice became more sophisticated when it was realized that certain properties of selected root systems could be beneficial for increasing the productivity of the grafted tree. This is the case for certain apple rootstocks discovered sometime in the 16th or 17th centuries, which were recognized for their ability to dwarf apple trees and increase the productivity of grafted apple scions. Increased understanding of how dwarfing apple rootstocks can be used in orchard production systems has shaped the notion that rootstocks are the foundation of a healthy and productive apple orchard, and that as the interface between the scion and the soil, and by providing vital elements such as anchorage, water, nutrients, and disease protection they ultimately affect the sustainability of the orchard. Breeding apple rootstocks is a lengthy and resource intensive endeavor (research occurs in greenhouse, laboratory, nursery, and orchards) that features a multi stage 20-30 year breeding process which starts with a large number of seeds from planned crosses and is whittled down to a handful of ‘elite selections’ by multiple rounds of inoculation with diseases, the application of molecular markers for important orchard traits, and multiple evaluations in replicated orchard experiments where annual data for yield, yield efficiency, tree vigor, suckering, nutrient uptake efficiency and response to any other unique stress events. The breeding program applies genomic and bio-informatic tools for marker assisted breeding of apple rootstocks while leveraging discoveries in whole tree phenomics and metabolomics. For most Geneva® apple rootstocks released so far the multistage breeding process has taken on average more than 30 years. In addition to advances in whole tree physiology, apple rootstock genomics, transcriptomics and phenomics, the ongoing 40+ year effort in apple rootstock breeding described below has yielded a dozen of disease resistant and productive apple rootstock varieties which are being deployed in all apple growing regions of the world. These new rootstocks are allowing growers to plant where fire blight and replant disease pressure made it virtually impossible to plant new apple orchards.

Technical Abstract: The ancient practice of clonal propagation of perennial fruit crops by means of grafting was transformed when humans realized that certain properties of selected root systems could be beneficial for increasing productivity of that fruit crop. Certain clonal apple rootstocks were recognized for their ability to dwarf apple trees and increase the fruit/wood ratio produced by the same trees. Rootstocks are the foundation of a healthy and productive apple orchard, and as the interface between the scion and the soil, they provide vital elements such as anchorage, water, nutrients, and disease protection affecting the sustainability of the orchard. Breeding new productive, disease resistant, dwarfing apple rootstocks can have positive impact on apple production by increasing orchard productivity and profit margins for growers. Breeding apple rootstocks is a lengthy and resource intensive endeavor (research occurs in greenhouse, laboratory, nursery, and orchards) that features a multi stage 20-30 year breeding process which starts with a large number of seeds from planned crosses and is whittled down to a handful of ‘elite selections’ by multiple rounds of inoculation with diseases, the application of molecular markers for important orchard traits, and multiple evaluations in replicated orchard experiments where annual data for yield, yield efficiency, tree vigor, suckering, nutrient uptake efficiency and response to any other unique stress events. The breeding program applies genomic and bio-informatic tools for marker assisted breeding of apple rootstocks while leveraging discoveries in whole tree phenomics and metabolomics. Elite selections are increased to perform highly replicated tests including exposure to replant soils, multiple strains of fire blight, wooly apple aphids, crown rot, viruses, and graft union strength with multiple scion varieties. At the same time the elite rootstocks are also distributed to cooperating commercial nurseries to bulk up production and evaluate propagation potential in preparation for nationwide and worldwide evaluation. During this stage, a particular rootstock may be tested in 30+ different locations and for 7-12 years at each location providing about 200 combined years of replicated data. The best elite selections are then increased in production for commercial level tests (large orchards, few rootstocks), followed by release to nurseries and orchard growers. For most Geneva® apple rootstocks released so far this multistage process has taken on average more than 30 years. In addition to advances in whole tree physiology, apple rootstock genomics, transcriptomics and phenomics, the ongoing 40+ year effort in apple rootstock breeding described below has yielded a dozen of disease resistant and productive apple rootstock varieties which are being deployed in all apple growing regions of the world. These new rootstocks are allowing growers to plant where fire blight and replant disease pressure made it virtually impossible to plant new apple orchards.