Andrew Geering
- 1. Better control of avocado sunblotch disease through improved diagnostic technologies By Andrew Geering and Vish Steele Horticulture and Forestry Science, Industry Services
- 2. Queensland Primary Industries and Fisheries Avocado sunblotch viroid (ASBVd) • Smallest pathogen in the world (genome of 247 nts). • Only detected using molecular methods or by grafting bark patches onto indicator host such as cv. Hass. • Three strains: symptomless carrier (ASBVd-SC), variegation (ASBVd-V) and bleaching (ASBVd-B). • Differences between strains very minor – a single mutation can result in change from ASBVd-V to ASBVd-B. © The State of Queensland, Department of Employment, Economic Development and Innovation, 2009
- 3. Queensland Primary Industries and Fisheries Economic impact of ASBVd • Smaller and fewer fruit – estimates of yield loss range from 18-95%. • Fruit disfigurement – more than half of fruit may be downgraded on quality standards. • Symptomless carrier trees may still show significant yield decline. • Quarantine restrictions may affect export of fruit from affected orchards. © The State of Queensland, Department of Employment, Economic Development and Innovation, 2009
- 4. Queensland Primary Industries and Fisheries Transmission of ASBVd • Cannot be transmitted by insects. • Cannot survive for any length of time outside of the plant (i.e. in the soil). • Transmitted at a very high rate in seed. • Transmitted in scions used for grafting. • Probably transmitted at a low rate on the blades of pruning tools. • Transmitted by root grafting. © The State of Queensland, Department of Employment, Economic Development and Innovation, 2009
- 5. Queensland Primary Industries and Fisheries Control of ASBVd • Infected plants cannot be cured. • Infected plants should be removed to prevent further spread – all living tissue must be destroyed. • New blocks should be established with plants certified to be free of ASBVd: – i.e. from a nursery participating in the Avocado Nursery Voluntary Accreditation Scheme (ANVAS). © The State of Queensland, Department of Employment, Economic Development and Innovation, 2009
- 6. Queensland Primary Industries and Fisheries Objectives of research project • To develop quality-assured diagnostic tools. • To survey for ASBVd in south-east Queensland/northern NSW. © The State of Queensland, Department of Employment, Economic Development and Innovation, 2009
- 7. Queensland Primary Industries and Fisheries Quality-assured diagnostic tools • Two types of error in diagnosis: – Healthy plant mistakenly diagnosed as infected. – Infected plant mistakenly diagnosed as healthy. • The latter mistake is most serious. Causes of error: • Human error. • Sample degradation. • Sampling error. • Assay inhibition. © The State of Queensland, Department of Employment, Economic Development and Innovation, 2009
- 8. Queensland Primary Industries and Fisheries New PCR assay for ASBVd including internal control (plant gene) Positive ASBVd status Negative ? Plant gene ASBVd © The State of Queensland, Department of Employment, Economic Development and Innovation, 2009
- 9. Queensland Primary Industries and Fisheries How significant a problem is ASBVd in Australia? • ANVAS established in 1978. • 34% of Australian avocado trees 6 years or younger. • Less than 10 records of ASBVd from Australia and mostly from germplasm collections. • Last published report of ASBVd was in 1989. Question: Is ASBVd still present in Australia? © The State of Queensland, Department of Employment, Economic Development and Innovation, 2009
- 10. Queensland Primary Industries and Fisheries Verified records of ASBVd in Australia – cv. Mexicola, Alstonville Research Station, NSW (1962, 1989) – budwood obtained from ‘interstate’. – cv. Zutano AV35, 2 field trees, Coomealla, NSW (1981) – cv. unknown, CSIRO Division of Horticultural Research, Merbein, Victoria (1981). – cv. Carlsbad, post-entry quarantine, Canberra (1981). – cv. Fuerte, field tree, Alstonville, NSW (1981). – cv. Hass, 1 field tree, Red Cliffs, Vic (1981) – cv. Hass, 2 field trees, Qld (1981) – cv. Hass, 1 field tree, NT (1981). – cv. Bacon, 1 field tree, Paringi, NSW (1989). © The State of Queensland, Department of Employment, Economic Development and Innovation, 2009
- 11. Queensland Primary Industries and Fisheries Surveys for ASBVd in south-east Queensland and northern NSW • All trees in the multiplication blocks of Anderson Avocado Tree Nursery, Duranbah, NSW, and Birdwood Nursery, Woombye, QLD, have been tested and all were NEGATIVE. • 2100 trees from commercial properties in south-east Queensland and northern NSW have been tested and all were negative, except: – One cv. Fuerte tree of age >20 years old. This tree was symptomless. © The State of Queensland, Department of Employment, Economic Development and Innovation, 2009
- 12. Queensland Primary Industries and Fisheries Conclusions • ASBVd is very rare but not yet completely eradicated from Australia. • ANVAS is successful and ASBVd progressively being eradicated. • To ensure ASBVd-freedom, buy planting stock from accredited nurseries. • If you suspect you have ASBVd, please talk to me at conference and we will test samples for free. © The State of Queensland, Department of Employment, Economic Development and Innovation, 2009
- 13. Queensland Primary Industries and Fisheries Acknowledgements • Funding from Horticulture Australia Limited and Avocados Australia is gratefully acknowledged. • THANK YOU FOR YOUR ATTENTION © The State of Queensland, Department of Employment, Economic Development and Innovation, 2009