Fire blight resistance of the wild apple species Malus fusca (accession MAL0045) has been previously reported.
This accession, crossed with the domesticated apple cultivar ‘Idared’, allowed for studies on the genetics of
the resistance of this crabapple with the resultant F1 population. A major fire blight locus (Mfu10), found on
chromosome 10, explained up to 66% of the phenotypic variance amongst the M. fusca × ‘Idared’ progenies.
Although fire blight resistance is strain specific for some Malus accessions, leading to the breakdown of resistance
in few resistance donors by highly aggressive strains of Erwinia amylovora; no strain able to breakdown the
resistance of M. fusca itself or Mfu10 has been found. This makes this wild apple an interesting model for
resistance studies with different wild-type and mutant strains of E. amylovora. A candidate gene (FB_Mfu10),
underlying the major locus, was recently proposed. FB_Mfu10 was predicted on the sequence of a bacterial
artificial chromosome (BAC) clone, spanning the fire blight locus on chromosome 10 and encodes B-lectin and
serine/threonine kinase domains. Preliminary functional analyses showed, that the open reading frame (ORF),
together with its border sequences upstream of the start codon and downstream of the stop codon (~ 6000 bp), is
present only in resistant F1 genotypes with 8bp distinguishing between susceptibility and resistance. Furthermore,
with a dense genetic map of M. fusca and studies with a mutant of an aggressive strain of E. amylovora, a minor
fire blight locus has been identifie
