Scion–Rootstock Combination Determines Pruning Responses in Young Almond Trees

Abstract

Almond growers are seeking ways to reduce costs but maintain yield. Intensive planting systems with greater planting densities using trees on growth-controlling rootstocks, combined with mechanical pruning and shake-and-catch harvesting are becoming popular. In this study we examined the responses of six almond cultivars with distinctive architecture grafted onto five rootstocks with varying degrees of vigor control. Trees were planted in 2018 in a nursery row and left to grow without pruning until Winter 2021. Pruning involved a rudimentary hedging treatment akin to mechanical pruning. Branching and tree structure were recorded in 2020, before pruning, and again at the end of 2021, after one season’s growth following pruning. A rating system was developed to record qualitative data on central leader dominance and the number, length, basal diameter, and, in some cases, branching angle of axillary shoots and including scaffold branches. Relatively few changes were recorded in the basic growth habit of these trees in response to pruning. Before pruning, the most common rootstock effect was on axillary shoot production. After pruning, the most common rootstock effects were on scaffold branching and the length of subterminal axillary shoots. Further studies are required to determine how these differences produced by the interaction between pruning and rootstock may affect the productivity of fruit-bearing trees. Although in this study with young trees we were not able to record crop yield, the results highlight that it is mainly the scion–rootstock combination, with or without pruning, that determines the potential productivity of fruiting canopies. Scion–rootstock combinations that produce narrow upright canopies naturally with strong central leader dominance and highly branched canopies are preferred for superintensive growing systems with or without use of mechanical hedging.