Status of fire blight resistance breeding in Malus

Malus domestica (apple) is one of the most important fruit crops worldwide. Fire blight, caused by Erwinia amylovora, is one of the most destructive bacterial diseases that impacts apple production systems worldwide. Although it is possible to manage fire blight using antibiotics such as streptomycin, kasugamycin or oxytetracycline, the quest for sustainable and eco-friendly production makes breeding for fire blight resistance the most promising and desirable approach. Breeding for resistance is a long, resource-intensive process due to the high susceptibility of most commercial apple cultivars, and the fact that most resistance sources being characterized are from wild genetic backgrounds with unpalatable fruits, and apple’s long generation times. Nevertheless, establishment of pre-breeding materials is crucial. This review highlights the status of breeding for fire blight resistance in Malus, taking into account, 1) major and minor resistance sources and their interaction with E. amylovora, 2) progress and challenges associated with using wild species as resistance sources, 3) progress and challenges associated with using elite cultivars as resistance sources, 4) advances in biotechnology for use in enhancing the production of durable fire blight resistant cultivars.