Markers linked to fire blight (Erwinia amylovora) resistance in apple; application to rootstock breeding

Fire blight (FB) is the most destructive bacterial disease in apple orchards thus FB resistance is a key objective for rootstock and scion breeding. Several sources of genetic resistance have been identified in Malus and plant response can be evaluated through inoculation in controlled environments as well as outdoors in areas of high natural disease pressure. The rootstock breeding program at NIAB EMR characterizes material prior to commercial release through glasshouse inoculation as disease pressure in the UK is usually low or very low. The program has also started to use molecular markers linked to well characterized resistance sources to test germplasm, selections under trial and breeding lines as we move toward marker-assisted breeding (MAB). Here we summarize the allelic composition of a range of apple genotypes for markers linked to FB resistance alongside the results from glasshouse inoculation and reported field responses and discuss the implications for their use in MAB.