Australian onion growers affected by crop losses linked to fungal pathogens will soon have access to a DNA-based diagnostic test designed to improve disease identification and management.
The test has been developed by Queensland-based biotechnology company Metagen as part of a project funded by Hort Innovation and supported by AUSVEG, titled "Rapid test and fungicide resistant screening for Stemphylium leaf blight in onion". The project was initiated following concerns raised through the VegNET network, delivered in South East Queensland by Lockyer Valley Growers Inc, over rising disease pressure in onion production.
© Metagen Aus
The research focused on improving detection and diagnostic accuracy for onion canopy diseases, particularly Stemphylium leaf blight. The work was led by Dr Ben Evert, in collaboration with plant pathology researcher Dr Noel Knight, microbiologist Dr Neil Wilson, and agronomist and Metagen co-founder Shane Fitzgerald. A quantitative PCR primer was developed and calibrated at Metagen's Gatton laboratory and is expected to be made available for the upcoming onion season. The method will also be published for broader use, as onion canopy diseases are increasingly reported in multiple growing regions.
Field surveys were conducted across 17 onion crops in the Lockyer Valley, combining disease assessments, lesion sampling, and soil chemistry analysis. The results identified Stemphylium species as the dominant fungal pathogens present, with downy mildew detected at lower levels. Purple blotch was found only in limited cases.
Dr Evert said the work confirmed that Stemphylium vesicarium can persist on alternative host plants, including weeds in border areas, after harvest. He noted that infection levels can increase as temperatures rise, while downy mildew activity declines once temperatures exceed 29 degrees Celsius. Increased thrips populations were also found to be associated with higher levels of Stemphylium infection.
© Metagen Aus
The research also examined fungicide sensitivity. Laboratory assays and genomic analysis identified fungicide groups where reduced efficacy was observed, as well as others where efficacy remains. These findings are intended to support future disease management strategies within the onion sector.
According to the project team, the qPCR test allows for earlier detection of Stemphylium leaf blight in the crop canopy, including at stages before visible sporulation. When combined with climate data and soil analysis, this information can support more targeted disease management decisions.
Findings from the project will be shared with growers at an industry event in Gatton in February, focused on crop resilience and disease management practices.
© Metagen AusFor more information:
Metagen Aus
Tel: +61 1800 229 994
Email: [email protected]
www.metagen.com.au
