Final Report QLD Citrus Improvement Scheme: Finding Better Rootstocks for Australia Project leader: Malcolm Smith Delivery partner: The Department of Agriculture and Fisheries, QLD Project code: CT13004 Hort Innovation – Final Report Project: QLD Citrus Improvement Scheme: Finding Better Rootstocks for Australia – CT13004 Disclaimer: Horticulture Innovation Australia Limited (Hort Innovation) makes no representations and expressly disclaims all warranties (to the extent permitted by law) about the accuracy, completeness, or currency of information in this Final Report. Users of this Final Report should take independent action to confirm any information in this Final Report before relying on that information in any way. Reliance on any information provided by Hort Innovation is entirely at your own risk. Hort Innovation is not responsible for, and will not be liable for, any loss, damage, claim, expense, cost (including legal costs) or other liability arising in any way (including from Hort Innovation or any other person’s negligence or otherwise) from your use or non‐use of the Final Report or from reliance on information contained in the Final Report or that Hort Innovation provides to you by any other means. Funding statement: This project has been funded by Hort Innovation, using the citrus research and development levy, co‐investment from Queensland Department of Agriculture and Fisheries, Queensland Citrus Improvement Scheme and contributions from the Australian Government. Hort Innovation is the grower‐owned, not‐for‐profit research and development corporation for Australian horticulture. Publishing details: ISBN 978 0 7341 4484 3 Published and distributed by: Hort Innovation Level 8 1 Chifley Square Sydney NSW 2000 Telephone: (02) 8295 2300 www.horticulture.com.au © Copyright 2018 Horticulture Innovation Australia Limited Hort Innovation – Final Report: Qld Citrus Improvement Scheme: finding better rootstocks for Australia Content Qld Citrus Improvement Scheme: finding better rootstocks for Australia ......... 1 Content ........................................................................................................................... 3 Summary ........................................................................................................................ 4 Keywords ........................................................................................................................ 4 Introduction .................................................................................................................... 5 Methodology .................................................................................................................. 7 Experiment One: Gayndah ‘Imperial’ Rootstock Experiment ................................................... 8 Experiment Two: CTV Replication and Movement in Advanced Rootstocks ........................... 18 Experiment Three: Emerald ‘Imperial’ Rootstock Experiment ............................................... 29 Experiment Four: Breeding new P.trifoliata hybrids with CTV resistance ............................... 34 Experiment Five: The Commercial Value of “Extreme hybrids” as Rootstocks ........................ 36 Additional project related activity: A. High-throughput phytophthora screening .................... 42 Additional project related activity: B. Salt screening ............................................................ 48 Additional project related activity: C. Molecular marker verification ...................................... 54 Additional project related activity: D. K15 pomelo rootstock trial .......................................... 74 Additional project related activity: E. Rootstocks for new scion varieties ............................... 76 Outputs ......................................................................................................................... 77 Experiment One ............................................................................................................... 77 Experiment Two ............................................................................................................... 78 Experiment Three ............................................................................................................. 78 Experiment Four ............................................................................................................... 79 Experiment Five ................................................................................................................ 80 Outcomes ..................................................................................................................... 82 Monitoring and evaluation............................................................................................ 83 Industry Adoption ............................................................................................................. 83 Communication and publicity ............................................................................................. 83 Recommendations ........................................................................................................ 93 Refereed scientific publications .................................................................................... 94 References .................................................................................................................... 96 Intellectual property, commercialisation and confidentiality ........................................ 97 Acknowledgements ....................................................................................................... 98 3 Hort Innovation – Final Report: Qld Citrus Improvement Scheme: finding better rootstocks for Australia Summary The aim of this project was to breed and develop superior rootstocks that would help support the future commercial viability of Queensland and Australian citrus growing. One new rootstock was released and is now entering commercial production. It represents germplasm distinctly different from currently available rootstocks thus expanding the genetic diversity of the Australian citrus industry. This new rootstock was named ‘Barkley’ in recognition of Mrs Patricia Barkley (Broadbent), one of Australia’s most distinguished citrus researchers. A second new rootstock is poised for commercial development as final testing has been expanded. The influence of rootstocks on fruit quality is no more strongly felt than is the case with citrus – and the choice growers make at the time of planting influences economic viability for the life of the orchard. Through a series of integrated breeding and evaluation experiments, this project has delivered new information and unique germplasm to give growers better choices for modern orchards, and deliver improved fruit quality to consumers. The project was built around five key experiments that captured research and development activities across the full spectrum of “risk verses return”. Indeed, some of the activities that seemed “left-field” at the start of the project and with a high risk of failure now show promise of a high return on investment as new germplasm with commercial application. For example, some native Australian citrus species have been used in the breeding program and after multiple generations of crossing are now showing promise in trials on commercial citrus orchards. In their primitive state, these species are highly susceptible to viral infection and they die within a few years of planting. Conventional breeding has solved this problem and created unique germplasm that is now beginning to reveal useful traits such as resistance to phytophthora diseases. This represents an important step forward for international breeding efforts. Large replicated trials have been established on commercial orchards with almost 500 different genotypes currently being field tested at five diverse locations. Many thousands more hybrids were screened for a range of important traits before choosing these genotypes for field trials. Techniques to efficiently screen for Citrus tristeza virus resistance, phytophthora tolerance, salt tolerance and apomixis have been developed and refined during the project. Large families of hybrids can now be quickly screened for most of the traits that are needed by the Australian citrus industry. Close industry collaboration, monitoring and input have ensured this complex project stayed on track, achieved all of the promised outputs and delivered outcomes that are useful to commercial citrus businesses. Keywords citrus, breeding, rootstocks, disease resistance, salt tolerance, graft compatibility, fruit quality, citrus relatives, germplasm, citrus tristeza virus, phytophthora, apomixis 4 Hort Innovation – Final Report: Qld Citrus Improvement Scheme: finding better rootstocks for Australia Introduction Better rootstocks are a zero-cost solution to many problems affecting commercial citrus production. Of particular interest is the opportunity to improve fruit quality. For example, Australia’s most important mandarin variety ‘Imperial’ is plagued by granulation problems which threaten to undermine consumer confidence in the category as a whole. This makes ‘Imperial’ the obvious scion of choice for rootstock research, and success in previous research demonstrates how quickly growers will adopt new rootstocks that show promising results. It is conservatively estimated that around 100,000 new trees are planted commercially in Queensland each year, and nationally the figure