First report on the presence of fire blight resistance in linkage group 11 of Pyrus ussuriensis Maxim.

Fire blight, caused by the gram-negative bacterium Erwinia amylovora (Burrill) Winslow et al., is a dangerous disease of pome fruits, including pear. A pear breeding program for fire blight resistance was initiated in 2003 at the Department of Pomology, Warsaw University of Life Sciences, Poland. Since several Asian species are considered to be potential sources of resistance to fire blight, the susceptible Pyrus communis 'Doyenne du Comice' was crossed with the resistant P. ussuriensis. The F1 full-sib progeny composed of 155 seedlings was tested for susceptibility to fire blight by artificial shoot inoculation. A framework linkage map of both parents was constructed based on 48 AFLP and 32 SSR markers and covered a length of 595 cM and 680 cM in 'Doyenne du Comice' and P. ussuriensis, respectively. For the first time a putative QTL for fire blight resistance in P. ussuriensis linkage group 11 was identified. Another putative QTL in linkage group 4 of 'Doyenne du Comice' seems to indicate that sources of fire blight resistance can be identified also in the susceptible cultivars.