Development of dense genetic maps for the pear (Pyrus communis L.) cultivars ‘Conference’ and ‘Harrow Sweet’ facilitates the identification of novel QTL for fire blight resistance

Abstract European pear ( Pyrus communis L.) is an important fruit species in the temperate climate zone. The cultivation of this crop faces challenges from climate change, the availability and planned reduction of the usage of plant protection products under the EU Green Deal, along with various abiotic and biotic stress factors. A significant threat to pears is fire blight, caused by the bacterium Erwinia amylovora , which is difficult to control. Breeding new cultivars resistant to this disease is the most appropriate way to ensure pear production. To make the breeding process more effective and efficient in terms of time and resources needed to develop a new cultivar, understanding the inheritance of fire blight resistance and using molecular markers closely linked to resistance are essential for early progeny selection. For this purpose, we established a segregating F 1 population derived from a ‘Conference’ × ‘Harrow Sweet’ cross and developed dense genetic maps for both parents. Subsequent QTL-mapping, following artificial shoot inoculation of both parents and the population with the E. amylovora strain Ea222, led to the confirmation of the Harrow Sweet resistance locus on linkage group 2 and two new QTL affecting disease incidence on linkage groups 5 and 11 and a minor QTL on LG17 in ‘Conference’. In addition, we report the development of tightly-linked SSR markers suitable for marker-assisted selection.