The apple wild species accession Malus fusca MAL0045
had been found to be resistant to fire blight in artificial
inoculation trials with Erwinia amylovora strain Ea222_
JKI. Consequently, using a population derived by crossing
MAL0045 with Idared, the corresponding fire blight resistance
locus of M. fusca (Mfu10) was mapped on chromosome
10 explaining up to 66% of phenotypic variation at
a logarithm of the odd (LOD) ratio of 31.0 with the strain
Ea222_JKI. Moreover, the very aggressive strain Ea3049
only minimally affected MAL0045 but significantly affected
the population although could not overcome the
resistance of Mfu10. To further understand the resistance
mechanism of M. fusca, we evaluated resistance of the
original mapping population, comprised of 134 individuals,
to E. amylovora strain ZYRKD3-1 which causes the
breakdown of the resistance of M.×robusta 5 (Mr5) and
the Mr5 fire blight resistance QTL on LG3. Our results
showed that the major QTL of M. fusca on LG10 could
still be detected at the same exact position with a higher
effect on fire blight resistance, indicating that ZYRKD3-1
has no effect on Mfu10, although the mean percent lesion
length of the population was almost doubled compared
with Ea222_JK