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Ongoing project

Innovative rootstocks for the Australian macadamia industry (MC16000)

Key research provider: The Queensland Department of Agriculture and Fisheries

What’s it all about?

This investment is analysing and identifying rootstock genotypes that offer the best prospects for productivity improvements in the Australian macadamia industry. Over 2000 mature trees utilising some 200 rootstocks are bring assessed under commercial orchard management conditions, with productivity and quality assessments compared to those of current industry rootstocks Beaumont and H2.

The project team has made recommendations to nursery and orchard operators regarding varieties that warrant semi-commercial evaluation as rootstocks. These recommendations emerge from the long-term field performance assessment of 204 rootstock treatments (141 varieties, 8 pollination environments) of a trial with nearly 2,000 trees planted in 2007.

The most promising treatments from this trial have also been incorporated into a new field trial funded by the Queensland Department of Agriculture and Fisheries where the reduced need to screen diverse germplasm enables greater replications as well as assessment of pollination environments.

The project team reports good progress on the following activities:

  • The first nut yield harvest was undertaken in February-2019 and was repeated at approximately three-week intervals, with the fifth and final assessment in May-2019. Nut drop was assessed immediately prior to the five rounds of commercial nut harvesting. Yield data from this harvest period as well as from past seasons were collated and submitted for professional statistical analysis to examine rootstock performance.
  • The project team quickly responded to data generated in the 2019 season and collated all available information to collect a new round of promising seed (before it was removed by commercial harvest). This seed was used to generate nursery trees which are now growing in the nursery at Bundaberg Research Station along with the Hancock germplasm nursery trees which presented promising results from a previous assessment period.
  • Observations were made of Abnormal Vertical Growth across the trial site. There is no evidence that AVG has increased beyond the initial slight levels seen in 2018 in the south-eastern section of the orchard.
  • Canopy density was assessed on all plots. Significant leaf drop occurred after the first harvest in 2020, and according to the orchard managers was associated with heavy rainfall at the end of the drought.  This may necessitate an additional assessment of canopy density.
  • Tree size (trunk circumference) was assessed in relation to the rootstock used, however the project team found little variance in tree size regardless of the high range of genetic diversity.
  • Overall yields from this orchard were found to be high.

The research team reports that they have completed the 2018 measurements including nut yield, tree size, canopy density and any symptoms of abnormal vertical growth.

Nut yield was measured during five nut-drop periods, the first of which occurred far earlier than expected. Production from the orchard was excellent, reflecting the high level of management expertise that is being brought to this commercial orchard. 

As a small number of interesting rootstocks start to emerge, the research team made checks of kernel quality, but found all were of excellent quality. Yield is therefore a central focus for the project from here on.

Now that the trees have reached maturity, with hedging and skirting for the last three seasons, it is anticipated that the 2019 season will provide sufficient data to be able to make suggestions about which rootstocks warrant commercial testing and which should be avoided. 

Assessments were made throughout the 2017 season, and will ultimately be used with other seasons of data to provide a full picture of rootstock influence on macadamia performance. Information is being collected from more than 660 plots includes nut yield, tree size, canopy density and any symptoms of abnormal vertical growth (AVG) – though it will only be through the collation and analysis of data from multiple seasons that project results will be known.

For 2017, the researchers report that nut yield estimates made prior to each commercial harvest strongly correlated with actual nut production, and that tree health has remained strong – though early signs of AVG have been observed in some trees, in a specific section of the orchard, and is being monitored.  The researchers note that this is an important research finding, and creates an opportunity to monitor development of the disorder as part of the project. AVG is normally associated with a dramatic decline in nut production, so the early detection of potential AVG trees creates an opportunity to study any changes in nut yield using the data already being generated in this project.

The team also report that been demonstrated for the assessment of commercially important traits in a large mature rootstock experiment managed under commercial conditions.  This will now be applied to examine any rootstock influence on tree performance in the critical period after canopy closure, and as canopy management inputs become more frequent and severe in order to maintain machinery access.  Early signs of the disorder Abnormal Vertical Growth have been detected creating a unique opportunity to study impact on productivity from an early stage.

Related levy funds

This project is a strategic levy investment in the Hort Innovation Macadamia Fund