A new three-locus model for rootstock-induced dwarfing in apple revealed by genetic mapping of root bark percentage

Nicola Harrison*, Richard J. Harrison, Nuria Barber-Perez, Emma Cascant-Lopez, Magdalena Cobo-Medina, Marzena Lipska, Rebeca Conde-Ruíz, Philip Brain, Peter J. Gregory, Felicidad Fernández-Fernández

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

45 Citations (Scopus)


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.

Original languageEnglish
Pages (from-to)1871-1881
Number of pages11
JournalJournal of Experimental Botany
Issue number6
Publication statusPublished - Mar 2016
Externally publishedYes


  • Apple
  • grafting
  • Malus - domestica
  • root anatomy
  • root bark percentage
  • root cortex
  • rootstock
  • rootstock-induced dwarfing
  • scion


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