Breeding Apples for Scab Resistance: 1945-1990

Abstract

The breeding of apples resistant to scab incited by Venturia inaequalis(Cke.) Wint. is a genetically-based strategy for the control of this major fungal fruit pathogen. A concerted breeding effort began with three cooperating Agricultural Experiment Stations in the late 1940s and early 1950s. Soon afterwards collaboration was extended to research workers in Canada and Europe, and later to other continents. The effort that continues today in at least 17 breeding programs throughout the world was based on a modified backcross program to combine genes for resistance to apple scab from Malus floribunda821, and other species with commercially-accepted traits. Since 1970, 48 scab-resistant cultivars have been released worldwide of which 37 purportedly carry the V _f gene from M. floribunda821, one of which (‘Freedom’) carries additional polygenic resistance from ‘Antonovka,’ one (‘Imrus’) with V _f from M. atrosanguinea804: five with other genes [one (‘Rouville’) with the V _m gene from M. atrosanguinea804; one (‘Nova Easygro’) with the V _r gene from a Russian apple seedling from the Caucasas Mountains (R#12740-7A); one (‘Murry’) with V _m and/or V _f from M. micromalus;and three (‘Romus 2,’ ‘Gavin’ and ‘Generos’) with polygenic resistance only. There now exists a wide range of genotypes containing the V _f gene ranging in maturity from 75 days to 180 days or longer after flowering, with large fruits, crisp flesh, good storage benavior, and a wide range in flavor and skin color. A number of selections have been identified that contain varying degrees of resistance to other diseases and pests.