Evaluating Seven Macadamia Seedling and Cutting Rootstocks for Their Effect on Scion Growth

Plant vigour is one of the key obstacles of efficient orchard system in macadamia (Macadamia integrifolia, M. tetraphylla, and hybrids). Vigorous trees restrict low-density planting in commercial orchards. In absence of low vigour scion and dwarfing rootstocks this problem is addressed by pruning and hedging in mature macadamias, which appear to be the major expenses for nut production. However, the ability of rootstocks to reduce tree vigour has been explained as an important advantage for many fruit-crop growers. To identify vigour managing rootstocks, this study investigates 21 diverse genotypes of macadamia including 12 elite selections from the national breeding program, an accession of the wild species Macadamia jansenii, and eight cultivars. Scions of HAES 741 were whip-grafted onto 245 seedlings and 188 cuttings. Both rootstocks and scions were phenotyped for growth parameters (tree height, rootstock and scion height and trunk circumference, canopy width and depth) from 2017 to 2021. The variability in plant vigour traits due to the effect of rootstock genotypes and propagation types (grafted and ungrafted / seedlings and cuttings) are being evaluated. The growth parameters of the rootstocks in nursery and in the field will be compared. Results from this study will provide a basis of selecting superior rootstocks for high performance in future high density orchard systems.