title: A new three-locus model for rootstock-induced dwarfing in apple revealed by genetic mapping of root bark percentage.
abstract: Rootstock-induced dwarfing of apple scions revolutionized global apple production during the twentieth century, leading to the development of modern intensive orchards. A high root bark percentage (the percentage of the whole root area constituted by root cortex) has previously been associated with rootstock-induced dwarfing in apple. In this study, the root bark percentage was measured in a full-sib family of ungrafted apple rootstocks and found to be under the control of three loci. Two quantitative trait loci (QTLs) for root bark percentage were found to co-localize to the same genomic regions on chromosome 5 and chromosome 11 previously identified as controlling dwarfing, Dw1 and Dw2, respectively. A third QTL was identified on chromosome 13 in a region that has not been previously associated with dwarfing. The development of closely linked sequence-tagged site markers improved the resolution of allelic classes, thereby allowing the detection of dominance and epistatic interactions between loci, with high root bark percentage only occurring in specific allelic combinations. In addition, we report a significant negative correlation between root bark percentage and stem diameter (an indicator of tree vigour), measured on a clonally propagated grafted subset of the mapping population. The demonstrated link between root bark percentage and rootstock-induced dwarfing of the scion leads us to propose a three-locus model that is able to explain levels of dwarfing from the dwarf 'M.27' to the semi-invigorating rootstock 'M.116'. Moreover, we suggest that the QTL on chromosome 13 (Rb3) might be analogous to a third dwarfing QTL, Dw3, which has not previously been identified.
authors.affiliation: East Malling Research, New Road, East Malling, Kent ME19 6BJ, UK Centre for Food Security, School of Agriculture, Policy and Development, University of Reading, Whiteknights, PO Box 237, Reading RG6 6AR, UK nicola.harrison@emr.ac.uk.
authors.forename: Nicola
authors.initials: N
authors.lastname: Harrison
authors.affiliation: East Malling Research, New Road, East Malling, Kent ME19 6BJ, UK Centre for Food Security, School of Agriculture, Policy and Development, University of Reading, Whiteknights, PO Box 237, Reading RG6 6AR, UK.
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Harrison
authors.affiliation: East Malling Research, New Road, East Malling, Kent ME19 6BJ, UK.
authors.forename: Nuria
authors.initials: N
authors.lastname: Barber-Perez
authors.affiliation: East Malling Research, New Road, East Malling, Kent ME19 6BJ, UK Centre for Food Security, School of Agriculture, Policy and Development, University of Reading, Whiteknights, PO Box 237, Reading RG6 6AR, UK.
authors.forename: Emma
authors.initials: E
authors.lastname: Cascant-Lopez
authors.affiliation: East Malling Research, New Road, East Malling, Kent ME19 6BJ, UK.
authors.forename: Magdalena
authors.initials: M
authors.lastname: Cobo-Medina
authors.affiliation: East Malling Research, New Road, East Malling, Kent ME19 6BJ, UK.
authors.forename: Marzena
authors.initials: M
authors.lastname: Lipska
authors.affiliation: East Malling Research, New Road, East Malling, Kent ME19 6BJ, UK.
authors.forename: Rebeca
authors.initials: R
authors.lastname: Conde-Ruíz
authors.affiliation: East Malling Research, New Road, East Malling, Kent ME19 6BJ, UK.
authors.forename: Philip
authors.initials: P
authors.lastname: Brain
authors.affiliation: East Malling Research, New Road, East Malling, Kent ME19 6BJ, UK Centre for Food Security, School of Agriculture, Policy and Development, University of Reading, Whiteknights, PO Box 237, Reading RG6 6AR, UK.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Gregory
authors.affiliation: East Malling Research, New Road, East Malling, Kent ME19 6BJ, UK.
authors.forename: Felicidad
authors.initials: F
authors.lastname: Fernández-Fernández
mesh_terms: D002874:Chromosome Mapping; D008040:Genetic Linkage; D056426:Genetic Loci; D005819:Genetic Markers; D005838:Genotype; D027845:Malus / Q000235:genetics* / Q000254:growth & development*; D008957:Models, Genetic; D010641:Phenotype; D024301:Plant Bark / Q000235:genetics*; D018517:Plant Roots / Q000235:genetics* / Q000254:growth & development*; D018547:Plant Stems / Q000033:anatomy & histology; D020641:Polymorphism, Single Nucleotide / Q000235:genetics; D040641:Quantitative Trait Loci / Q000235:genetics; D012621:Seasons
chemical_list: D005819:Genetic Markers
keywords: Apple; Malus × domestica; grafting; root anatomy; root bark percentage; root cortex; rootstock; rootstock-induced dwarfing; scion.
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