Validation of LSB-PCR diagnostic for ratoon stunting disease and characterisation of non-Lxx strains of Leifsonia associated with sugarcane: final report 2014/086
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Ratoon stunting disease (RSD), caused by Leifsonia xyli subsp. xyli (Lxx), is a major disease of sugarcane worldwide. Diagnosis is problematic because RSD lacks specific external symptoms. This project adapted the LSB-PCR technique (Young et al. 2014) into a quantitative protocol (LSB-qPCR) delivering the most efficient and sensitive test available for RSD (Young et al. 2016). These techniques are significantly more sensitive than the EB-EIA technique. LSB-qPCR has now been trialled in almost all production areas in Australia, where it has successfully identified RSD in a range of varieties, ages and crop classes, sampled throughout all months of the year. This includes finding RSD in areas where it was believed not to occur. LSB-qPCR represents a quantum leap in RSD diagnosis and has revealed that the EB-EIA/PCM diagnostic framework has significantly underestimated the incidence of RSD in plant sources. In conjunction with these studies, a range of novel bacterial strains related to but distinct from the RSD pathogen have been found to be present in all Australian sugarcane regions (Young and Nock 2017). The epidemiological significance of these strains is unknown, but they have been identified in approximately 17% of all seedbeds screened, including 'clean seed' from approved seed plots. One of the strains was isolated from expressed xylem sap, but it is not known to be pathologenic. A novel qPCR protocol has been designed to diagnose these strains. This project has delivered significant advances in the diagnosis of RSD and the identification of new strains and species of Leifsonia of unknown pathology.