Breeding new rootstocks for the Australian citrus industry (CT18004)
What’s it all about?
Established in 2019, this investment is developing new rootstocks for the Australian citrus industry. By building on existing knowledge, new germplasm will be created – heavily screened for disease resistance and local adaptation – and then tested under commercial conditions to determine long-term viability.
The project team is incorporating diverse germplasm to increase genetic diversity, performance and resilience of commercial rootstocks in Australia. The intention is to provide citrus growers with rootstocks that are innovative, unique and outperform existing material, as well address a number of production issues such as phytophthora, salinity and vigor control.
The project will liaise with the existing project Evaluation of new rootstocks for the Australian citrus industry 2017-2022 (CT17002) and share relevant information on variety evaluations.
Three commercial field sites were chosen, prepared and maintained in Gayndah, Emerald and Wallaville to conduct assessments of the new germplasm on fruit quality, productivity and tree growth/health.
A week was spent in March 2020 to assess the 891 trees that make up this Imperial rootstock experiment (151 rootstocks). The project team found that granulation levels were high and crop load was somewhat reduced compared to last season. Wind breaks were found to reduce granulation, however they also reduced crop size. The impact of rootstock strains was predictable on tree size and trunk structure, however not on fruit quality which varied between seasons and replicates. Key insights suggest the true value of the rootstock can only be determined by averaging across multiple seasons.
Fruit quality testing of 245 rootstocks and 490 trees was conducted in April 2020. Crop load was very light and generally the amount of granulation was high. Extensive effort was put toward finding rootstock hybrids in this trial that may be of value, however, assessment over consecutive seasons will provide more accurate averages and present sensible choices of the hybrids that show the most promise.
Trees at this field site presented granulation levels lower than expected finding only a handful of trees stripped because of excess granulation. Additionally, only a few trees needed to be stripped because they were too small to carry the crop. Assessments also found that large vigorous rootstocks (US812, Benton, Barkley, D77) were not producing fruit, whereas many of the small or intermediate size trees had lots of fruit.
Some progress has been made and new rootstocks are beginning to emerge that have only moderate granulation while also offering benefits in other important traits such as fruit size, and tree productivity. Most notable being rootstock 05C009 and its hybrids with P.trifoliata similarly have amongst the lowest granulation.
Results from field trials are guiding the choice of parents in the breeding work and this information will be used in the August to September pollinating season.
Testing has been conducted on C. wakonai x P. trifoliata hybrids, which have been field planted at Bundaberg Research Station and are being observed for seed structure as they fruit.
This project is a strategic levy investment in the Hort Innovation Citrus Fund