The reliability of woody indexing for detection of grapevine virus-associated diseases in three different climatic conditions in Australia

Background and Aims In Australia, grapevine varieties are tested for viruses by woody indexing (WI) in combination with other procedures during post-entry quarantine and prior to their introduction into the nucleus collections of high health certification programs. The aim of this study was to determine the reliability and accuracy of WI for virus detection in different climatic conditions. Methods and Results Replicated experiments were conducted in a hot climate, a cool climate and a screenhouse. Indicator plants were inoculated with Grapevine virus A, Grapevine virus B, Grapevine fleck virus, Grapevine leafroll-associated virus (GLRaV) 1, GLRaV-2, GLRaV-3, GLRaV-9 and Rupestris stem pitting-associated virus. Indicators were observed during three years for characteristic symptom development and tested for viruses by reverse-transcription polymerase chain reaction. Virus transmission was not always successful. Symptoms were not always observed in each year at each trial site even if viruses could be detected by reverse-transcription polymerase chain reaction. Conclusions WI reliability was affected by the success of bud-take, transmission of the virus from the candidate bud to the indicator and different climatic conditions. It is recommended that WI be carried out for a minimum of three years in the field. Significance of the Study Understanding the effect of different climatic conditions on WI will improve the reliability of grapevine virus detection in Australia.