Dispersal patterns of grapevine trunk disease pathogen spores in Australian vineyards

Eutypa dieback (ED) and botryosphaeria dieback (BD) are important grapevine trunk diseases causing significant yield reduction and threatening the sustainability of Australian vineyards. The spores (ascospores and conidia) of these pathogens are dispersed by rain splash and wind and infect primarily through pruning wounds resulting in cankers, dieback and eventually death of vines. Understanding the spore dispersal patterns of these pathogens will assist in determining the critical times of the year when spores are abundant in Australian vineyards and will also assist growers in making decisions on optimal timing of pruning and the application of wound protection treatments. The spore dispersal patterns of ED (Diatrypaceae) and BD (Botryosphaeriaceae) pathogens were investigated over 3 years in four wine growing regions in Australia. From 2014-2016, four Burkard spore traps were deployed in South Australia (Barossa Valley and Coonawarra) and in New South Wales (Hunter Valley and Griffith). The spore trap tapes were collected and replaced monthly at each site and analysed by qPCR using group-specific primers for Diatrypaceae and Botryosphaeriaceae spores. ED and BD pathogens spores were released all year round but numbers and species varied between regions, season and year. The ED and BD pathogen spores in South Australia were primarily detected in late winter and in early spring while a high number of spores were trapped over summer in New South Wales. Spores were generally detected during or immediately after rain but not all rain events resulted in spore detection. The spore numbers and frequency of detection varied between years with 2016 having the highest number of spores being recorded, particularly for Diatrypaceae species. Preliminary computer modelling of data showed very weak correlation between other weather fa ctors (temperature, relative humidity, dew point, wind speed), indicating that the spore release may be difficult to predict for these pathogens.