The Geneva Apple Rootstock Breeding Program

摘要

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. This isthe case for certain clonal apple rootstocks, which were recognized for their ability to dwarf apple trees and increase the fruit/wood ratio produced by the same trees. Increased understanding of how dwarfing rootstocks can be used in orchard productionsystems 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. Therefore, it was realized that breeding of new productive, disease-resistant, dwarfing apple rootstocks using modernselection techniques could have positive impact on apple production by increasing orchard productivity, which in turn translates into increased profit margins for growers. Cornell University's Geneva~R Apple Rootstock Breeding program initiated in 1968 is one of a handful still in activity out of a dozen initiated in the same period. What made this breeding program unique in the world was the focus on disease resistance to biotic stresses common in northeast America such as fire blight (Erwinia amylovora) and soil-borne diseases common to all apple growing regions such as crown and root rot (Phytophthora spp.), which was fueled by the vast genetic resources available in Geneva, NY. In 1998, the apple rootstock breeding program was converted to a jointbreeding program with the U.S. Department of Agriculture (USDA) with a USDA breeder as the lead scientist. Breeding apple rootstocks is a lengthy and resource-intensive endeavor (research occurs in greenhouse, laboratory, nursery, and orchards) that features a multistage 20-30-year breeding process that 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 forimportant orchard traits, and multiple evaluations in replicated orchard experiments of annual data for yield, yield efficiency, tree vigor, suckering, nutrient uptake efficiency, and response to any other unique stress events.