Air root pruning containers alter root architecture and increase canopy and root growth of apple trees compared to field grown liners

Tree expenses account for the majority of costs when establishing high-density plantings. The vast proportion of nursery trees are produced in the field and shipped bare-root. These trees are prone to transplant-shock and may require additional time to fill orchard space. The objectives of this project were to compare two nursery production systems (air root-pruning containers and field-produced liners (i.e., bare-root trees)) on the growth and development of above-ground and below-ground organs of apple trees, during the formative 'nursery' year prior to planting in the field. We hypothesized that container-produced trees would develop higher-quality root systems, mitigate transplant-shock, and promote rapid canopy infill. In 2017, 'Gala' and 'Honeycrisp' scions were bench-grafted to M9 (Nic29) rootstock and divided into two production systems: Ellepot-containers and field-liners. Entire plants of each production system were carefully harvested during rapid growth in mid-summer and at the end of the growing season. Above ground plant growth was quantified and whole root systems were cleaned and scanned to determine root growth characteristics and architecture. Compared to the field production system, vegetative growth (shoot growth and leaf area) of Ellepot-produced 'Honeycrisp' trees was significantly greater and more uniform by the end of the season. Ellepot-produced 'Gala' trees had a significant growth advantage by mid-summer but higher late-season growth rates of field-produced liners resulted in nearly equivalent canopy size by the end of the season. Ellepot-produced trees had markedly higher fine root production and greater total root length compared to field liners, irrespective of cultivar, indicating a potential advantage for Ellepot trees when established in an orchard.