Time analysis of rootstock mediated nutrient transport in 'Honeycrisp'

An experiment aimed at understanding the genotypic potential of certain rootstocks to influence the nutrient concentration of ‘Honeycrisp’ fruit was conducted over two years (2016 and 2017) on trees that had reached production maturity. Four or five replications of trees grafted on B.9, G.11, G.214, G.30, G.41, G.210, G.814, G.935, M.26, M.9 Pajam2 rootstocks were used as the source of tissues for this experiment. The nutrient concentration of leaves, pedicels, and fruit was monitored 8-10 times in two-week intervals from the time fruit reached 10 mm in diameter to harvest. Nutrients like boron, potassium, sulfur, phosphorous and calcium showed good correlation among rootstock/tissue combinations. Overall, nutrient concentration changed in tissues over time with some nutrients like boron and potassium displaying higher concentration early in the season then decreasing over time in a similar way for all tissues. Other nutrients like calcium displayed discordance between tissue types as all tissues started from the same concentration, with leaves increasing concentration, pedicels remaining constant and fruit decreasing in concentration with time. Nutrient ratios like K/Ca and (K+Mg)/Ca showed starkly different trends in fruit tissues (increasing with time) compared to pedicel and leaves where the ratios remained relatively constant. These ratios were slightly influenced by rootstocks genotype over time, indicating effects that could be tied to rootstock specific influence on fruit quality parameters like bitter pit. While Ca increased in leaves, it was constant over time in the pedicel and slightly decreased in fruit. K in the pedicel and the fruit decreased over time in a similar way, however leaf K displayed a different rate of decline and was more variable during the season. Rootstock genotype significantly affected the overall concentration of certain nutrients and as previously observed in a previous experiment, M.9 Pajam 2 displayed the lowest levels of boron in all tissues compared to other rootstocks. This work is part of a larger project aimed at understanding the connection between rootstocks and fruit quality being studied in the USDA NIFA Specialty Crop Project “AppleRoot2Fruit”.