AVOCADOS - Biosecurity New Zealand

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93 HORTICULTUREPROTECTINGOUR AVOCADOSMAF Biosecurity New Zealand recently declared New Zealand free ofAvocado Sunblotch Viroid – a disease that threatens our avocadoproduction and export markets. This successful outcome was achievedthrough extensive collaboration between the Avocado Industry Counciland MAF Biosecurity New Zealand (MAFBNZ).Avocado Sunblotch Viroid(ASBVd) was believed to bepresent in New Zealand as aresult of testing undertaken by theMinistry of Agriculture and Forestry(MAF) during a subtropical cropsurvey in 1999.However, the disease has never beendetected since, despite extensiveindependent surveys and testingcarried out by the Avocado IndustryCouncil (AIC). This raised uncertaintyabout the previous detection and led tothe formation of a joint MAFBNZ–industry working group in 2005 thatwas tasked with designing surveillanceand testing protocols based oninternationally recognised standardsand best practice.The overarching objective of thisproject was to determine the status ofASBVd within New Zealand and toprovide MAFBNZ with the assuranceand confidence for any reassessment ofcountry status. The aim was to developa programme for preserving access tooverseas markets. This is of greatimportance to the avocado industry,which exports a high percentage of itscrop to Australia valued at between$20–35 million a year.The working group comprisedtechnical advisers and scientists fromwithin MAFBNZ and industry,drawing together the necessary skillsand expertise from both parties. Thegroup developed a new MAFBNZsurveillance standard for the detectionof ASBVd and was responsible for theco-ordination of MAFBNZ-approvedservice providers. MAFBNZ was alsoresponsible for auditing the serviceproviders for compliance to thestandard and for the validation of testresults.In February 2009, the AIC contractedthese service providers to carry out asurvey of avocado sites to meet thesampling and testing protocolswithin the MAFBNZ standard. InJune 2009, the survey wascompleted. The field samplingand mapping component wasdelivered by AsureQualityLimited, which utilisedsample bar coding/scanningand GPS readings to individually16 MAF BIOSECURITY NEW ZEALAND
HORTICULTURE93“The collaborative approachprovided an opportunity forachieving the best outcomefor everyone concerned.”identify sample trees and enable ease oftraceability. Samples were tested byLinnaeus laboratory using state-of-theart,real-time polymerase chainreaction (PCR) technology. ASBVd wasnot detected, and, as a result,MAFBNZ has since declared NewZealand free of ASBVd.AIC Chief Executive Alan Thorn saysthat, from the AIC’s perspective, thejoint working group has beeninstrumental in contributing to thesuccess of this project.“There was a wide representation fromwithin MAF Biosecurity New Zealand,including surveillance, borderstandards, Plant Health andEnvironment Laboratory (PHEL) andcompliance and enforcementpersonnel. This gave our industry agood understanding of the concernsand requirements from the collectiveMAF Biosecurity New Zealandviewpoint.”Katherine Clift, Surveillance Manager,Post Border, MAFBNZ said thecollaborative approach provided anopportunity for achieving the bestoutcome for everyone concerned.“It enabled us to work through theproblems together, ensuring the needsof both parties were met, withoutcompromising the overall integrity ofthe result.”Another major factor contributing tothe success of the project was theexpertise of the late Dr Rod Bonfiglioli,technical director of RiversunNurseries Limited and its subsidiaryLinnaeus. His knowledge of ASBVddetection methodologies was a crucialfactor in providing the level ofassurance that MAFBNZ was seeking.The project has been a bigcommitment for both parties.MAFBNZ provided a large amount ofexpertise and staff resources, and therehas been heavy investment by the AIC.Both parties are pleased with thecollaborative approach and theoutcome, and would encourage otherindustries to consider collaborativeapproaches to their own biosecurityprojects.AvocadoSunblotchViroidASBVd is a viroid that is readily transmitted viagraft transmission during propagation or frominfected seedlings.Avocado trees affected with ASBVd may beeither symptomatic (express physical symptomsof the disease), or asymptomatic and exhibit nosymptoms of the viroid but still be capable ofinfecting other trees.Symptoms can be seen on trees, twigs, fruit andleaves, and include:• infected trees that are stunted and have asprawling growth habit;• twigs that have a light-yellow, sunken streakthat follows the length of the twig;• fruit that has localised yellow and reddepressed lesions generally extending fromthe stem to the base of the fruit;• leaves that display areas of “bleached”symptoms and are sometimes distorted.Affected trees suffer from reduced yields ofbetween 15–30 percent, and losses are furtheraggravated by down-grading of disfigured fruit.Once trees are infected there is no controlfor the disease and infected trees should beremoved to avoid any further contamination ofother trees.■Karen Pugh, Senior Adviser Plant Response, MAFBNZ,karen.pugh@maf.govt.nz; Vivien Thomson, AdviserSurveillance, MAFBNZ, vivien.thomson@maf.govt.nzMAF BIOSECURITY NEW ZEALAND 17
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