Genetic Control of Mineral Uptake Correlated to Fruit Quality in Apples

A principal function of root systems is to forage for mineral nutrients in the soil and move them into different parts of the plants including the canopy where they are used to aid in plethora of biological functions including fruit production. Grafted root systems allow the discernment of root (rootstock) dependent traits from scion dependent traits by joining genetically different plant parts in a composite tree system where variation that may be cause by intrinsic canopy traits may be eliminated by using the same genetic stock as the canopy (scion) and genetically different root systems as the rootstocks. We utilized field planted ‘Brookfield Gala’ trees grafted onto a replicated full sibling population of apple rootstocks from parents ‘Ottawa 3’ and ‘Robusta 5’ and measured mineral nutrient concentration for potassium (K), sodium (Na), phosphorous (P), calcium (Ca), copper (Cu), sulfur (S), zinc (Zn), magnesium (Mg), nickel (Ni), and molybdenum (Mo) in fruit and leaves during two consecutive growing seasons. Significant genotypic mean correlations were detected between years in pairs of same mineral concentration values (e.g., Pearson correlations between leaf K in 2013 and leaf K in 2014 was 0.65 and p<0.0001) and between fruit and leaf values for same mineral per year data. Quantitative trait loci analysis (QTL) revealed several loci positions were the same between years, including K on linkage group (LG) 5 and 11, leaf P on LG 5, 11, and 16. Additional QTLs were discovered in single year data for Ca, Cu, Mg, Na, S, Zn, and N. Fruit quality parameters (soluble solid content, flesh firmness, and red peel color) were measured in 2013. Significant correlations were detected between soluble solids and fruit Ca (-0.35 p=0.0001), soluble solids and fruit Cu (0.4226, p<0.0001), red peel color and fruit Mg (-0.29, p=0.0017), firmness (-0.26, p=0.0051). Multivariate two-way clustering grouped fruit Zn and Ca with peel color and fruit N and S with soluble solids and flesh firmness. Our initial analyses on the genetic effects rootstocks have on scion fruit quality reveals complex relationships among nutrients and fruit quality characteristics. We hope that additional analysis of this and other datasets will provide a genetic roadmap for identifying existing and breeding for new rootstocks that increase fruit quality.