Apple rootstocks' dwarfing loci relationships with mineral nutrient concentration in scion leaves and fruit
Apple rootstock mediated tree dwarfing is mainly controlled by genetic factors Dw1 and Dw2 located, respectively, on Chromosome 5 and 11 of apple. While the effect of these factors have been described with regards to tree architecture and productivity, very little is known about their effect on mineral nutrient status of the scion. We utilized an apple rootstock replicated field trial with 'Gala' scion grafted onto a population of 186 rootstocks (progeny of dwarfing rootstock 'Ottawa 3'), which is segregating for both dwarfing loci, providing dwarfing class combinations Dw1+/Dw2+ (fully dwarfing), Dw1-/Dw2+ or Dw1+/Dw2- (semi-dwarfing) and Dw1-/Dw2- (Vigorous) for comparisons. Scion fruit and leaf tissues were used to monitor the concentration (dry wt. basis) of nitrogen (N), potassium (K), phosphorous (P), calcium (Ca), magnesium (Mg), sulfur (S), iron (Fe), copper (Cu) manganese (Mn) and aluminum (Al) as influenced by rootstocks. Molecular markers linked to the dwarfing loci were used to ascertain their effect on mineral nutrient concentrations by comparing means of contrasting alleles that were inherited by each rootstock in the population. Tree size was negatively correlated with fruit concentration of S, N, Cu, Mg in order of decreasing effect and significance. Tree size was positively correlated with leaf concentration of K, P and Ca in order of decreasing effect and significance. Markers associated with Dw1 showed that plants heterozygous for the dwarfing allele had significantly less leaf S than homozygous non-dwarfing plants, whereas Dw2 alleles had no significant effect. This is in contrast with fruit S which displayed significantly higher concentration in dwarfing plants where either Dw1 or Dw2 dwarfing alleles had displayed higher concentrations. Fruit N concentration was higher in fruit grown on rootstocks that possessed either of the dwarfing alleles following a similar pattern with S, the correlation between fruit S and N concentration was 0.79 (P‹0.0001). More significant effects of Dw1 and Dw2 were observed on fruit concentration of Ca, P, K, Mg and Zn, and on leaf concentration of P, K, Ca, S and B. While Dw1 and Dw2 do not seem to be related directly in mode of action to mineral nutrition, segregation of these loci shows that they can have a significant effect on the nutrient status of leaves and fruit.
Fazio, G., Grusak, M. and Robinson, T.L. (2017). Apple rootstocks' dwarfing loci relationships with mineral nutrient concentration in scion leaves and fruit. Acta Hortic. 1177, 93-102
Malus × domestica, dwarfing genes, fruit quality