What was it all about?

From 2016 to 2022, this investment analysed some 200 rootstocks under commercial orchard management conditions to provide the Australian macadamia industry with greater understanding of rootstock performance.

The approach was to screen as much diverse genetic material as could be found, and to do so under commercial production conditions for a long period of time; recognising that results from young trees in short-term trials can produce misleading information.  More than 200 rootstock treatments were included in the experiment, representing 141 named varieties collected from eight different pollination environments.  ‘HAES741’ was used as the standard scion across the whole trial.  These trees were propagated by the project team and planted (3.5 m x 7 m spacing) within a new commercial planting at Bundaberg in December 2007. Evidence for the high standard of orchard management is reflected in the strong commercial production harvested from the trial site, with yields averaging more than four t/ha (nut-in-shell at 10 per cent moisture) in the five-year period of this project.  This provides confidence that the rootstocks have been assessed under optimum production conditions.  New and more efficient methods of yield assessment were developed so that this large field trial (~2,000 trees) could be measured prior to every commercial harvest in the first ten years of production. 

The project identified a handful of new rootstocks that should be tested in large scale commercial plantings.  These include ‘A268’, ‘Own Venture’ and ‘A4’.  These newly discovered rootstocks may provide growers with an opportunity to improve productivity without any change to management activities or input costs. The current commercial rootstocks ‘H2’ and ‘Beaumont’ were mid-range in their performance amongst the 141 named varieties in the trial, and still represent a good choice until the superior performance of our new rootstock options is confirmed in large block plantings.  Results also demonstrated poor performance of many treatments in the experiment, with the implication that growers must insist on known rootstock germplasm when establishing new plantings.  While there was good evidence that rootstocks influenced yield, obvious impacts on tree size and vigour were lacking beyond a few rootstocks that produced small and unhealthy trees.  There were no clear opportunities to reduce tree size using rootstocks, despite the large amount of genetic material screened in the experiment. 

Focusing on the big-picture of rootstock genetic diversity has opened up new opportunities for rootstock development using these few best-bets with greater replication and investigating the role of the pollen parent.