Influences of Propagation Method, Rootstock, Number of Axes, and Cultivation Site on ‘Fuji’ Scions Grown as Single or Multi-Leader Trees in the Nursery

Paolo Lezzer,Stefano Musacchi,Brendon Anthony,Stuart Tustin,Alberto Dorigoni,Sara Serra,Luca Corelli-Grappadelli

doi:10.3390/agronomy12010224

Abstract

The adoption of high-density plantings (HDP) in apple orchards started with the introduction of dwarfing rootstocks from East Malling’s (UK) breeding program. A range of spindle-derived training systems have been developed to improve light interception/distribution with a variation in leader numbers. Many of these training systems cannot guarantee early, consistent, and uniform illumination of the entire canopy. For this reason, planar 2-D canopies have been developed with varying numbers of primary axes with numerous second-order shoots. In this trial, carried out at the nursery level, three sites were selected: one in New Zealand (Hawke’s Bay Research Centre) and two in Italy (Bologna and Trento). Trees were produced with a single-, bi-, and tri-axis system utilizing three rootstocks (‘M27’, ‘M9’, ‘MM106’), characterized by an increasing level of vigor. The cultivation site played an important role in modulating early tree performance. Multi-leader trees reduced average shoot length in the Italian sites in the first year after grafting. The number of shoots and total growth developed on multi-leader trees was higher than single-axis trees. This may benefit growers that seek to use canopy architecture manipulation to fill space and control vigor when establishing HDP orchards.

Highlights

The concept of high-density plantings (HDP) in apple orchards began with the launching of the dwarfing rootstocks from the East Malling Research Station’s (UK) rootstock development program
More than 70% of the bench-grafted trees trained with a single leader reached a commercially acceptable tree size expected for a spindle nursery tree, irrespective of rootstock (Figure 1B)
The wide range of training systems proposed for apple cultivation in the last few decades share some common features: the rapid achievement of high light interception and early cropping, the preservation of optimal light distribution within the canopy over the season and orchard lifespan, and more efficient harvesting due to canopy size control and planar architectures

Summary

Introduction

The concept of high-density plantings (HDP) in apple orchards began with the launching of the dwarfing rootstocks from the East Malling Research Station’s (UK) rootstock development program. The most popular rootstock from the East Malling M-series was the dwarfing, ‘M9’ [1]. A joint breeding program between the East Malling Research Station and the John Innes Institute in Merton, England, focused on producing woolly apple aphidresistant rootstocks. The most evident effect of dwarfing rootstocks is the reduction in tree height. The ‘M27’ rootstock is one of the most dwarfing apple rootstocks, and it can reduce the height of a tree by up to 80% compared to a seedling rootstock. ‘MM111’ only reduces tree size by approximately 20% compared with a seedling rootstock [3]. Rootstocks provide other agronomical advantages, including variation in different aspects such as precocity [4,5], floral induction [4,6,7,8], fruit set [3], photosynthetic activity [9,10], disease susceptibility [11], cold tolerance, and resistance to unfavorable soil conditions [12]

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