Services to Industry

Budwood Supply
Budwood source trees are located at Dareton NSW (near Mildura VIC, on the Murray River), with a supplementary supply of new varieties located at Monash in South Australia, under the management of the South Australian Citrus Improvement Society (SACIS). Budwood of some varieties is also cut from indexed trees maintained at the Department of Primary Industries Research Station at Griffith, NSW.

Rapid multiplication
New varieties released from post-entry quarantine undergo rapid nursery and field multiplication at Dareton. The aim of rapid nursery multiplication is to quickly increase the quantity of high quality budwood available, thus reducing the time to achieve commercial production of new varieties.

Importation of new citrus varieties
Since 1986 more than sixty public citrus varieties have been imported for the Australian citrus industry, most of these by Auscitrus. The major focus has been on importation of new mandarin and navel orange varieties.

In future, most new varieties, of both local and overseas origins, will be patented, and require acquisition fees and payment of tree and/or production royalties. Auscitrus is entering into agreements with 'commercialisers' of these patented varieties to maintain foundation trees, to provide independent horticultural evaluation and to multiply budwood and seed of high health status.

Repositories of virus-free and pre-immunised trees
The Auscitrus repositories for virus free and pre-immunised clones are located in insect-proof screenhouses at NSW Agriculture's Elizabeth Macarthur Agricultural Institute (EMAI) at Camden, and at the Auscitrus multiplication facility, at Dareton NSW..

To protect against grapefruit stem pitting strains of tristeza virus, all grapefruit varieties are pre-immunised with a mild isolate of tristeza virus, a process referred to as mild strain cross protection.

These foundation trees are the insurance policy for the Australian citrus industry and ensure that high health status material will be available in the advent of a disease outbreak.

Pathogen testing
Many viruses and viroids can exist in citrus without expressing obvious symptoms. However these pathogens can be very destructive when infected scions are grafted to sensitive rootstocks or transmitted mechanically on secateurs or budding knives, or by insect vectors, to susceptible scions.

Auscitrus budwood and rootstock seed trees are tested for graft transmissible citrus viruses and viroids using both glasshouse (biological) and laboratory techniques, referred to as indexing. All source trees are indexed on a rotational basis. Suspect trees are indexed as required. Indexing takes place at the Elizabeth Macarthur Agricultural Institute (EMAI) at Camden.

All trees providing Premium budwood are indexed once every three years on Etrog citron indicator plants for Citrus Exocortis Viroid and for milder viroids that may cause dwarfing. Trees showing suspect symptoms on Etrog citron are tested further using a laboratory technique called sequential polyacrylamide gel electrophoresis (sPAGE) to determine which viroid (CVd I-IV, CEV), if any, is present.

Trees are indexed once every ten years on sweet orange seedlings for orange stem pitting strains of Citrus Tristeza Virus and for psorosis virus.

Grapefruit trees in the budwood blocks undergo annual biological indexing to determine the severity of CTV strains present and if necessary, molecular tests are carried out to ensure there has been no ingress of severe strains.

Pathogen elimination
Shoot-tip grafting in conjunction with heat therapy, is used to remove viruses and viroids from infected parent trees. The process involves excising a 0.15mm shoot tip from the infected plant and grafting it onto a 2 week old rough lemon seedling growing in sterile media in a test tube. The resulting plant is indexed to confirm that all viruses and viroids have been eliminated.