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Bacterial wilt of lucerne A market access issue for lucerne seed growers By Dr. Kathy Ophel Keller
November 2005
RIRDC Publication No 05/101 RIRDC Project No SAR 48A
Overseas markets require phytosanitary declarations for bacterial wilt in lucerne. Argentina and Chile will accept a phytosanitary declaration based on a seed pathology test while the European Union, Tunisia and Uruguay will only accept phytosanitary declarations based on field inspections. In addition Western Australia has a legislative requirement for freedom from bacterial wilt of lucerne seed.
Field surveys in the 1960’s and 1970’s detected bacterial wilt in many of the lucerne growing areas adjacent to the river systems in NSW, Victoria and SA but not in the major seed production areas.
Surveys to support declarations of area freedom in the seed producing areas were last conducted in 1978.
In 2002, a field disease survey of lucerne stands was initiated to update area freedom from bacterial wilt of lucerne in seed production areas in South Australia and Victoria. The survey was based primarily on testing of seed lots as well as a limited number of paddock inspections. Bacterial wilt was detected by field inspection in one seed crop paddock in the South East of SA.
After the detection of bacterial wilt, the lucerne seed industry recognised the need for phytosanitary inspections to maintain market access via area freedom on a place of production basis. A field inspection and sample testing protocol was developed, which has been adopted in SA and Victoria.
These requirements meet International Plant Protection Convention and AQIS requirements. This was done for the first time in spring 2003 and the phytosanitary service incorporated inspection and testing for bacterial wilt, stem nematode, Orobanche spp. (branched broomrape and native broomrape species) and Cirsium arvense (perennial thistle).
Phytosanitary inspections for bacterial wilt occurred in spring 2003 in lucerne seed production areas in SA and western Victoria. Plant samples were collected by accredited inspectors, as part of the phytosanitary paddock inspection in October/November. A further 9 infected paddocks and 15 unconfirmed infected paddocks were detected in SA. The infected paddocks were growing the bacterial wilt susceptible lucerne cultivars Hunter River, Hunterfield and Sirosal. Stand life of infected paddocks was greater than 4 years old with the majority being greater than 15 years old.
At the same time, international acceptance of a seed test developed in a previous RIRDC project (SAR 15-A) is being pursued via the International Seed Testing Association (ISTA) process. Ideally, seed test standardisation should be based on inter-laboratory comparisons on naturally infected seed.
Efforts to find naturally infected seed have not been successful, even from seed of infected lucerne plants grown in the glasshouse. Infected plants from paddocks where bacterial wilt was detected produce infected tillers but have not produced infected seed, indicating that transmission to seed is extremely low. This is likely influenced by environmental conditions. As a result, international seed test standardisation is proceeding with artificially infected seed. Ultimately, an internationally accepted seed test will provide lucerne seed growers with less restrictive export options now bacterial wilt is known to be present. An internationally accepted seed test is still a desirable aim but work is progressing slowly. As well as technical difficulties, the test must be accepted by EU authorities.
The measures to maintain
export market access have been communicated directly to lucerne seed exporters
with ASF taking a lead role. The approach being taken satisfies International
Plant Protection Convention and AQIS requirements.
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