QTLs for Fire Blight (Erwinia amylovora) Resistance in Pyrus ussuriensis

Fire blight is the most devastating bacterial disease of apples and pears. The need for highly disease-resistant cultivars is more pressing than ever. Genetic disease immunity or resistance is recognized as an important feature of integrated pest management (IPM). In this study, we used an F-1 progeny of Pyrus communis 'Doyenne du Comice' x Pyrus ussuriensis to build parental genetic maps and to identify quantitative trait loci (QTLs) related to fire blight resistance. Linkage maps were constructed using a set of microsatellites and enriched with amplified fragment length polymorphism (AFLP) markers. For the first time QTLs for fire blight resistance in P. ussuriensis were identified by the Kruskal-Wallis test in its LGs U9, U_a, U_e, Ug, and U11. QTLs identified in LGs U_e and U_g are linked to AFLP-RGA markers that additionally confirms the presence of resistance genes in these LGs. Despite the high susceptibility of P. communis 'Doyenne du Comice', four QTLs for fire blight resistance in this cultivar were localized in LG K3, K4, K11, and K_a. These data confirm the existence of the interspecific transgression phenomenon, also previously observed on the basis of infection level evaluation of seedlings belonging to the studied hybrid family.