Is there a chance that a scab-resistant apple cultivar will become scab-susceptible?

Yes, and several scab-resistant cultivars already are scab-susceptible at some locations. Most scab-resistant apples trace their origins to a collaboration between Purdue University, Rutgers University, and the University of Illinois. The PRI apple breeding program began in 1926 when crosses made from the crab apple, Malus floribunda 821, were found to show some resistance to apple scab. The PRI group then bred the resistant Vf gene from Malus floribunda 821 into commercial apple cultivars. Decades of subsequent hybridization and selection produced high-quality, scab-resistant eating apples. Since 1970, approximately 80 percent of the scab-resistant cultivars released worldwide reportedly carry the Vf resistance gene from M. floribunda 821, including ‘Williams’ Pride,’ ‘Jonafree,’ ‘Liberty’, ‘Enterprise,’ ‘Prima,’ ‘Pristine,’ and ‘GoldRush.’

Relying solely on disease-resistant apple cultivars to manage scab has resulted in the breakdown of Vf-based scab-resistance worldwide. In 1993, scab lesions were found on ‘Prima,’ a Vf– selection in an orchard in Germany. Although ‘Prima’ is now susceptible to scab, these scab isolates were not able to infect the resistant parent M. floribunda 821 or other scab resistant apple varieties. Unfortunately, scab was found infecting M. floribunda 821 in England in 1994. Scab was found on Malus floribunda 821 in North America in 2007 in Indiana, Illinois, and Ohio. In 2008, scab was found on ‘Pristine,’ ‘Pixie Crunch,’ and ‘Jonafree’ in Indiana and Illinois. And in 2009, scab was found infecting ‘Enterprise’ in Indiana.

For more information on managing scab-resistant apples, see Publication BP-76-W, Managing Scab-Resistant Apples (

Adapted from an article by Dr. Janna Beckerman, Purdue University.