The fire blight resistance QTL of Malus fusca (Mfu10) is affected but not broken down by the highly virulent Canadian Erwinia amylovora strain E2002A

Recently, Mfu10 - the major QTL for resistance to fire blight was reported on linkage group 10 of Malus fusca which could explain about 66 % of the phenotypic variation in a population artificially inoculated with Erwinia amylovora strain Ea222_JKI. In the meantime, it had been reported that the resistance of the fire blight QTL of Malus × robusta 5 (Mr5), which could explain 80 % of phenotypic variation is strain specific and is completely overcome by the highly virulent strain Ea3049 originating from Canada (E2002A). In contrast to Mr5, the M. fusca donor of Mfu10 is only very slightly affected by this highly virulent strain. In this short communication, we prove that this particular strain is not able to overcome the resistance of M. fusca but affects Mfu10. The same F1 progenies, derived from a cross between the resistant M. fusca and the susceptible apple cultivar, Idared, used to detect Mfu10, were used for phenotyping with Ea3049. Although the mean shoot necrosis of all progenies was 62.4 %, marker-phenotype association determined by Kruskal-Wallis analysis showed that markers on LG10 correlate significantly to resistance levels with SSR markers FR481A and FRM4 having the highest K values of 37.1 and 36.7, respectively. Interval mapping and multiple QTL mapping (MQM) performed with MAP-QTL®, showed that Mfu10 could still be detected on the same position on LG10, but only explaining 41.2 % of phenotypic variation. The implications of these results are discussed.