title: Putative resistance gene markers associated with quantitative trait loci for fire blight resistance in Malus 'Robusta 5' accessions.
abstract: BACKGROUND
  Breeding of fire blight resistant scions and rootstocks is a goal of several international apple breeding programs, as options are limited for management of this destructive disease caused by the bacterial pathogen Erwinia amylovora. A broad, large-effect quantitative trait locus (QTL) for fire blight resistance has been reported on linkage group 3 of Malus 'Robusta 5'. In this study we identified markers derived from putative fire blight resistance genes associated with the QTL by integrating further genetic mapping studies with bioinformatics analysis of transcript profiling data and genome sequence databases.
  
  
  RESULTS
  When several defined E.amylovora strains were used to inoculate three progenies from international breeding programs, all with 'Robusta 5' as a common parent, two distinct QTLs were detected on linkage group 3, where only one had previously been mapped. In the New Zealand 'Malling 9' X 'Robusta 5' population inoculated with E. amylovora ICMP11176, the proximal QTL co-located with SNP markers derived from a leucine-rich repeat, receptor-like protein (MxdRLP1) and a closely linked class 3 peroxidase gene. While the QTL detected in the German 'Idared' X 'Robusta 5' population inoculated with E. amylovora strains Ea222_JKI or ICMP11176 was approximately 6 cM distal to this, directly below a SNP marker derived from a heat shock 90 family protein gene (HSP90). In the US 'Otawa3' X 'Robusta5' population inoculated with E. amylovora strains Ea273 or E2002a, the position of the LOD score peak on linkage group 3 was dependent upon the pathogen strains used for inoculation. One of the five MxdRLP1 alleles identified in fire blight resistant and susceptible cultivars was genetically associated with resistance and used to develop a high resolution melting PCR marker. A resistance QTL detected on linkage group 7 of the US population co-located with another HSP90 gene-family member and a WRKY transcription factor previously associated with fire blight resistance. However, this QTL was not observed in the New Zealand or German populations.
  
  
  CONCLUSIONS
  The results suggest that the upper region of 'Robusta 5' linkage group 3 contains multiple genes contributing to fire blight resistance and that their contributions to resistance can vary depending upon pathogen virulence and other factors. Mapping markers derived from putative fire blight resistance genes has proved a useful aid in defining these QTLs and developing markers for marker-assisted breeding of fire blight resistance.
authors.affiliation: The New Zealand Institute for Plant & Food Research Limited (PFR) Palmerston North, Private Bag 11600, Manawatu Mail Centre, 4442 Palmerston North, New Zealand. sue.gardiner@plantandfood.co.nz
authors.forename: Susan E
authors.initials: SE
authors.lastname: Gardiner
authors.forename: John L
authors.initials: JL
authors.lastname: Norelli
authors.forename: Nihal
authors.initials: N
authors.lastname: de Silva
authors.forename: Gennaro
authors.initials: G
authors.lastname: Fazio
authors.forename: Andreas
authors.initials: A
authors.lastname: Peil
authors.forename: Mickael
authors.initials: M
authors.lastname: Malnoy
authors.forename: Mary
authors.initials: M
authors.lastname: Horner
authors.forename: Deepa
authors.initials: D
authors.lastname: Bowatte
authors.forename: Charmaine
authors.initials: C
authors.lastname: Carlisle
authors.forename: Claudia
authors.initials: C
authors.lastname: Wiedow
authors.forename: Yizhen
authors.initials: Y
authors.lastname: Wan
authors.forename: Carole L
authors.initials: CL
authors.lastname: Bassett
authors.forename: Angela M
authors.initials: AM
authors.lastname: Baldo
authors.forename: Jean-Marc
authors.initials: JM
authors.lastname: Celton
authors.forename: Klaus
authors.initials: K
authors.lastname: Richter
authors.forename: Herb S
authors.initials: HS
authors.lastname: Aldwinckle
authors.forename: Vincent G M
authors.initials: VG
authors.lastname: Bus
mesh_terms: D002874:Chromosome Mapping; D060467:Disease Resistance / Q000235:genetics*; D044084:Erwinia amylovora; D008040:Genetic Linkage; D005819:Genetic Markers; D027845:Malus / Q000235:genetics* / Q000276:immunology; D010935:Plant Diseases / Q000235:genetics* / Q000276:immunology; D040641:Quantitative Trait Loci
chemical_list: D005819:Genetic Markers