Two quantitative trait loci, Dw1 and Dw2, are primarily responsible for rootstock-induced dwarfing in apple.
The apple dwarfing rootstock 'Malling9' ('M9') has been used worldwide both to reduce scion vigour and as a genetic source for breeding new rootstocks. Progeny of 'M9' segregate for rootstock-induced dwarfing of the scion, indicating that this trait is controlled by one or more genetic factors. A quantitative trait locus (QTL) analysis of a rootstock population derived from the cross between 'M9' × 'Robusta5' (non-dwarfing) and grafted with 'Braeburn' scions identified a major QTL (Dw1) on linkage group (LG) 5, which exhibits a significant influence on dwarfing of the scion. A smaller-effect QTL affecting dwarfing (Dw2) was identified on LG11, and four minor-effect QTLs were found on LG6, LG9, LG10 and LG12. Phenotypic analysis indicates that the combination of Dw1 and Dw2 has the strongest influence on rootstock-induced dwarfing, and that Dw1 has a stronger effect than Dw2. Genetic markers linked to Dw1 and Dw2 were screened over 41 rootstock accessions that confer a range of effects on scion growth. The majority of the dwarfing and semi-dwarfing rootstock accessions screened carried marker alleles linked to Dw1 and Dw2. This suggests that most apple dwarfing rootstocks have been derived from the same genetic source.
The New Zealand Institute for Plant & Food Research Ltd , Palmerston North Private Bag 11600, Palmerston North 4474, New Zealand.
Toshi M
TM
Foster
INRA UMR 1345 Institut de Recherche en Horticulture et Semences , 49071 Beaucouzé, France.
Jean-Marc
JM
Celton
The New Zealand Institute for Plant & Food Research Ltd , Palmerston North Private Bag 11600, Palmerston North 4474, New Zealand.
David
D
Chagné
The New Zealand Institute for Plant & Food Research Ltd , Havelock North Private Bag 1401, Havelock North 4175, New Zealand.
D Stuart
DS
Tustin
The New Zealand Institute for Plant & Food Research Ltd , Palmerston North Private Bag 11600, Palmerston North 4474, New Zealand.
Susan E
SE
Gardiner