I. Mineral nutrient profiles and relationships of 'Honeycrisp' grown on a genetically diverse set of rootstocks under Western New York climatic conditions

We measured mineral nutrient concentrations in leaves, fruit flesh and fruit peel from field grown apple trees grown on a genetically diverse group of rootstocks from year 5 through year 8 of planting (2014-2017) and identified relationships between nutrients in leaves and fruit of `Honeycrisp' apple. We also evaluated the constancy of rootstock influence on scion nutrient profiles over the four years. Boron concentration in both leaf and fruit was consistent in different seasons, with rootstocks M.9 (several clones), B.9, M.26EMLA, PiAu51-11 and B.71-7-22 resulting in consistently low boron levels, while G.935, CG.2034, CG.4004, G.222 and CG.5087 provided consistently high boron levels. Unlike boron, calcium concentration in scion tissues was somewhat variable in different seasons suggesting a role for climate and perhaps management factors in the rootstock induced absorption and translocation of calcium. We identified a group of rootstocks that yielded high calcium levels in scion tissues (G.214, B.10, G.41, B.9, G.935, G.11, CG.4003) while another group yielded low calcium levels (M.26, M.9-T337, G.202, CG.4004, G.814). We also identified a group of rootstocks that induced low potassium values in scion tissues (CG.4003, G.935, G.222, and G.202), whereas B.70-20-21, B.67-5-32, B.70-20-20 yielded consistently higher values. Rootstock B.10 and CG.2034 induced consistently higher potassium values in fruit tissues. The ratio of K/Ca in leaves and fruit was the best predictor of bitter pit in `Honeycrisp' apples, suggesting that rootstock induced levels for both nutrients play a role in this disorder and that the addition of potassium fertilizers on potassium-efficient rootstocks might increase the susceptibility to bitter pit. Rootstocks CG.4003, B.10, G.41 N, and G.214 seemed to produce fruit with lower levels of bitter pit. Our data indicates that some rootstocks are more efficient at absorbing nutrients than others, which implies that fertilizer recommendations developed using one rootstock, such as M.26 or M.9, might be too high for other rootstocks which are more efficient and could thus be causing tree and fruit physiological disorders. Newer rootstocks might be already supplying the needed amounts of minerals to scion tissues.