National macadamia breeding and evaluation program (MC19000)

Over the past six months, the project team has continued their field trials and evaluation of new progeny for the macadamia industry. Specifically, they report progress in the following areas:

• Two new progeny field trials of over 2,400 trees were planted at Rural Funds Management sites at Maryborough and Rockhampton. Over 1,100 trees were planted previously in 2020 meaning the project is on-track to exceed the target of 5,000 progeny planted during the project.  Increasing the population size is an important goal of MC19000; designed to increase selection intensity and thus improve genetic gain per generation.
  
  
• 998 seed were harvested that had been created by controlled hand-pollinations in spring 2021. The largest family was from a cross of a high breeding value, first-generation selection (BQBRS01-20-4) by an elite first-generation selection that is highly self-fertile (BHINK00-1-54).  Both parents were included in Lindsay Bryen’s DeCortes trial and are candidates for possible release in 2023.  A further 1,550 seed from open pollination were harvested in 2022 as part of a study on the relationship between self-pollination and yield.  All seed are currently being germinated and will be field planted in 2023.
  
  
• The genetic values or BLUPs (Best Linear Unbiased Predictions) for the 2015 planted progeny were calculated. This evaluation is based on measurements of tree size (width along and across the row and height), NIS yield (at 1% kernel MC) and total kernel recovery. Tree ID 201315007 ranked first for cumulative kernel yield to age 7 with a cumulative NIS yield of 21 kg and 43% total kernel recovery. It ranked second for cumulative kernel yield per unit of tree volume.  It was created by the combination of elite parents from the first generation of Hort Innovation funded breeding and its grandparents were HAES814, Yonik, NG7 and Own Choice. The genetic predictions will be used in a selection index to select elites which will be further evaluated for nut quality and agronomy traits and propagated in 2023.

Over the past six months, the project team reported progress in the following areas:

• In spring 2021, the research team hand-pollinated 1,872 racemes. This involved 88 combinations of parents.
  
  
• In February and March 2022, the research team evaluated the yield of 3,695 trees at our grower progeny trials at Childers, Pine Creek, Alloway and Emerald. Four elite selections were cinctured in June 2022 from the BQBRS14 progeny. The most promising selection produced 21kg NIS as a 7-YO tree and a cumulative yield of 50kg NIS with a TKR of 43 per cent.
  
  
• One virtual field day was conducted at Maroochy Research Facility (MRF) in May 2022 to showcase the macadamia rootstock trial and other components of AS18000. Bruce Topp was invited to provide participants with an overview of the breeding project and a virtual tour of the breeding blocks at MRF. A recording of the virtual field day can be viewed by following this link. Over 70 people registered for the field day resulting in 25 growers, consultants and stakeholders participating in the live event. The recording has received over 350 views since being published in May 2022.

Over the past six months, research to enhance selection methodologies has continued with revised economic weightings and finalisation of priority traits confirmed.

Completion of visual yield evaluation and calibration of B2.2 trials, (now 3YO and 4YO) was conducted at growers’ plots in Childers, Alloway and Pine Creek. A total of 2,517 progeny from 11 open pollinated families, and 283 clones of 56 standard cultivars were evaluated.

Harvesting and evaluations of the B2.1 trials, located at Bundaberg Research Facility, were also completed with a total of 1,576 trees evaluated for yield and growth traits (canopy width, height, nut-drop pattern, kernel recovery, kernel weight and nut weight).

A total of 1,872 racemes were hand pollinated at Nambour and Bundaberg in mid-September 2021. There were 41 genotypes used as parents and included elite selections. A planting site is being sought close to Maroochy Research Facility for ease of access for student research.

Research on husk spot resistance was conducted at Maroochy Research Facility as part of the PhD study by Ms Jasmine Nunn. Findings suggest that to increase genetic resistance to husk spot, selections should be based on mean number of necrotic lesions per fruit or severity evaluated for more than one year.

A breeding article was published in the AMS new bulletin summer 2021 edition, “Growers have their say on new selections from the breeding program.” The article focused on growers’ evaluation of new selections at Bundaberg Research Facility during a field day that was held in March 2021. Become a member or log in to view. See page 72-73.

Over the past six months, studies were conducted on the relationship between macadamia nut borer (MNB) damage and nut traits including husk hardness and husk thickness, with preliminary results suggesting it may be possible to reduce MNB damage by breeding for harder husks. This is important, as insect protection is required alongside breeding for increased kernel recovery and thus thinner shells. A final report for this analysis is expected in late 2021.

More than 2,800 polycross seeds were collected from the high breeding value (BV) block at Maroochy Research Facility in March and April 2021. This block was planted with elite selections from the first generation of breeding. It is isolated so the polycross seed combines the elite genes of these trees. A further 284 seeds were harvested from trees on which controlled hand-pollinations were made in spring 2020. A particular target of these bi-parental crosses was to combine parents that have a compact nut drop and investigate impact on orchard harvest efficiency.

Research to enhance selection methodologies was conducted, with a summary report produced. The work examined an economic selection model used to compare 20 candidate varieties from Regional Variety Trial – Series 3.

A field walk was held at Bundaberg Research Facility in March 2021 to display elite selections in the second-generation progeny trial, and a report was presented to the Macadamia Industry Variety Improvement Committee in April 2021 highlighting the outstanding performance of top-yielding selections in the first harvest of grower polycross trials at Childers, Pine Creek and Alloway.

In April 2020, the team collected seed from a polycross block of high breeding value genotypes, which were then germinated and grown in glasshouses over winter. The resultant seedlings were planted in a progeny field trial at Nambour in November 2020. The trial consisted of 1,094 progeny seedlings and 66 clones of standard and parent trees.

Harvesting and evaluation of the B2.1 trials, located at Bundaberg Research Facility, were completed in August 2020 with 2,200 trees assessed for yield. Some of the trees were also assessed for canopy width growth traits, height, nut-drop pattern, kernel recovery, kernel weight and nut weight.

The team inspected and evaluated the B2.2 trials, located on grower properties. The newest high-density plantings at Nambour have reduced first crop time to 3 years (nut-to-nut); a significant achievement in speeding up breeding.

To support the generation of new progeny and secondary test field trials, a total of 18 precocity trial elites were propagated by grafting in winter 2020. These will be planted at the NSW DPI Wollangbar site and the DAF Nambour site in 2021.

Preliminary field and lab data on phenotypic traits associated with husk spot resistance were collected and analysed, with a report generated.

Maintenance and evaluation of the wild germplasm trials at Tiaro and Alstonville was reported to Macadamia Industry Variety Improvement Committee (MIVIC). The team continued to share information with industry, with a field day as part of a MacGroup meeting planned for 2021.

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Log in or sign up to read this article about the project, Breeding new varieties for a more profitable Australian industry, in the AMS News Bulletin, Summer 2020 edition, pp45-47.

You can also learn more in this article, Demand driven breeding of horticultural tree crops: proof of concept using macadamia, in the AMS News Bulletin, Spring 2020 edition, pp75-76.