Interstems reveal scion cultivar potential to transport nutrients

An experiment aimed at understanding the genotypic potential of certain widely planted scion cultivars to transport nutrients in their vascular systems (stems) was set up by raising apple trees that featured interstems of different scion cultivars. We produced four interstem tree replicates for each cultivar using the vigorous rootstock 'B.118' as both root system and scion with a 15 cm long interstem made with cultivars 'Empire', 'Golden Delicious', 'Honeycrisp', 'Ida Red', 'Jonagold', 'Liberty', 'Mutsu' and 'Red Delicious' for a total of 32 trees. We collected 10 fully expanded leaves from the top 1/3 of each nursery tree and processed for nutrient analysis which yielded concentration values of N, P, K, Ca, Mg, S, and other micronutrients. Finished trees were planted in an orchard in Geneva, NY, in June 2018. In November 2019, an XRF instrument was used to monitor the relative concentration of P, K, Ca, S, and some micronutrients like Fe, Mn, and Cu in one and two-year-old stems. We noticed some general trends for each of the nutrients when comparing genotypic means to the overall mean for each nutrient. From the leaf analysis data, we found that leaf calcium concentration means ranged from 0.8 to 1.1%, with values for 'Red Delicious', 'Liberty', 'Honeycrisp' and 'Empire' interstems were below the overall mean (0.99%) while the values for the rest of the cultivars were above the mean. Honeycrisp displayed the highest values (1.8%) for leaf potassium whereas 'Empire' and 'Liberty' had the lowest values (1.3%). Leaf sulfur and leaf nitrogen were highly correlated variables, and among cultivars, 'Honeycrisp' had the highest means (1.88% N and 0.13% S), and 'Liberty' had the lowest means (1.61% N and 0.11% S). Vascular transport of nutrients may be an intrinsic genetic property of scion cultivars. This work has implications for the practice of top-working older orchards or using interstems.