Stalk Stamp – a simple, yet effective, new diagnostic test for detection of ratoon stunting disease in sugarcane

Ratoon stunting disease (RSD) is found in all Australian sugarcane-growing regions and is responsible for yield losses of up to 60%. Identifying sugarcane infected with RSD has been difficult as there are no external disease symptoms. To test for RSD, a xylem sample is taken from the stalk and sent to a central laboratory where a quantitative real-time PCR is used for analysis. Extracting the xylem can be time consuming and difficult. An alternative sampling method that is easy to collect in the field and that produces consistent results, has been developed. I describe a new method for quick and easy sample collection; the Stalk Stamp, which is coupled with a sensitive quantitative real-time PCR (qPCR) assay for the detection of Leifsonia xyli subsp. xyli (Lxx), the causal agent of RSD. Stalks of sugarcane plants are cut off at ground level, the fresh cut end of the stalk is pressed onto chromatography paper and held for approximately 10 seconds, and the Stalk Stamp is then air dried and stored in a zip-lock plastic bag for transport to the laboratory. The advantages of the Stalk Stamp method are: Lxx can be detected in a single stalk; simple and quick collection of samples; no blowing xylem juice; no overnight soaking; no sub-sampling; no freezing; no concern over sample spoilage during transport; no complex packaging for postage; and many fields can be sampled each day. Lxx has been detected by the Stalk Stamp method in 10-week-old sugarcane, much earlier than the current sampling method allows. Key words Ratoon stunting disease, ratoon stunt, quantitative real-time PCR, Stalk Stamp