Relationship between branch composition and reproduction during development of young macadamia trees

Abstract

Macadamia trees develop large canopies composed of complex branches, which in turn influence their reproduction. A better understanding of the establishment of the relationships between branch composition and reproduction can ultimately lead to optimised orchard management and productivity. One of these relationships is yield e iciency, defined as the ratio between yield and canopy volume per tree. This study aims to evaluate how the number and type of shoots on individual branches are related to flowering and yield e iciency during development of young macadamia trees grown in a subtropical climate. Shoot and raceme production was monitored in 20 branches from two macadamia cultivars during the first three productive years, that is, from the fourth to the sixth year after planting. Characteristics of each shoot were recorded: position (apical, lateral), number of nodes and length. Tree canopy volume and yield were determined each year. The number of racemes produced per branch was highly related to its number of nodes. The number of nodes, but not the number of racemes, was related to each branch’s proportion of lateral shoots. Moreover, during the second and third productive years, mean internode length of flowering shoots and yield e iciency were both negatively related to the proportion of lateral shoots. Our results suggest that flowering was driven and limited by characteristics like the number of nodes, and therefore buds, available in the branches. Branch composition, e.g., proportion of lateral shoots, changed over time and became related to the internode length of flowering shoots. The architectural changes at branch level over the course of development were linked to di erences in yield e iciency across both cultivars. This work highlights the relevance of assessing the relationships between macadamia architecture and reproduction, which opens perspectives for selecting suitable cultivars and canopy management practices to improve orchard productivity.