Oral Presentation Science Protecting Plant Health 2017

Monitoring of airborne Sclerotinia sclerotiorum ascospores in southern New South Wales canola growing regions using quantitative PCR (4452)

Audrey Leo 1 , Gerard O'connor 1 , Kurt Lindbeck 1
  1. Department of Primary Industries, Wagga Wagga, NSW, Australia

Sclerotinia stem rot caused by Sclerotinia sclerotiorum, is a yield limiting disease of canola in Australia. Senescent petals infested with airborne ascospores of S. sclerotiorum are the primary source of inoculum leading to the development of stem infection. The incidence of stem rot is common in some districts of southern New South Wales (NSW) where the intensity of canola production is high and characterised by a long flowering period and reliable spring rainfall. The severity of the stem rot varies between years and paddocks, which makes it difficult to manage disease outbreaks. As disease management relies heavily on foliar fungicide applications at 20-50% bloom stage, understanding of the release patterns of airborne inoculum and its quantity during the flowering period will aid growers in making informed decisions on the optimal spraying time and reduce unnecessary fungicide applications. To achieve this, six Burkard (Hirst-type) spore traps were deployed in 2014-2016 growing seasons across different canola growing districts located in the medium-high rainfall cropping region of southern NSW. The daily spore tape samples were analysed by nested quantitative PCR (qPCR) using Sclerotinia sclerotiorum species-specific primers. The study showed that the developed qPCR assay was specific and sensitive enough to detect as low as one ascospore. On most occasions a low amount of ascospores was observed daily, indicating the continual production of ascospores throughout the growing season (July – October). The peak levels of ascospore release varied across different districts and were mostly observed in late winter and early spring when weather conditions were wet and cool. High levels of ascospores during this period when plants are flowering and senescent petals are in abundance is critical as it may lead to stem infection. Thus, foliar fungicide application may be necessary during this period to reduce potential infection levels and yield loss