Charcoal rot is a significant disease of sorghum as well as most other major summer crops, including mungbeans, maize and soybeans. It is challenging to manage, due to the lack of effective cultural, agronomic and chemical management options But Dr Barsha Poudel might have discovered new knowledge to better inform its management.

Originally from Nepal, where she attained a bachelor’s in biotechnology from Kathmandu University, she has added a master’s in bioinformatics from Wageningen University in the Netherlands to a PhD from the University of Southern Queensland. She brings a special set of skills to this industry issue.

“My PhD project investigated the genetic and pathogenic characterisation of Pyrenophora teres and their hybrids – the causal agent of net blotch – on barley,” Dr Poudel says.

Her current position at the University of Southern Queensland (USQ) as a GRDC-supported postdoctoral researcher is supervised by Dr Niloofar Vaghefi.

The project here focuses on characterising the genetic variability and structure of what is thought to be the major cause of charcoal rot, the fungus Macrophomina phaseolina.

“The project was started by Dr Neeraj Purushotham at USQ, then carried out by myself since early 2020,” Dr Poudel says.

“I collected samples from sorghum paddocks in Queensland and NSW, and have been analysing their diversity using genotyping-by-sequencing approaches. The work aligns very well with my PhD work (on net blotch).”

An associated rot

Dr Poudel’s current work is focused on understanding two aspects of charcoal rot disease on sorghum. The first is to characterise the genetic diversity and population structure of charcoal rot pathogens in sorghum paddocks in the northern grains region to increase this knowledge base.

“This is important because to develop effective strategies for charcoal rot management, we need to first develop a good understanding of its biology and epidemiology,” she says.

Charcoal rot symptoms caused by Macrophomina observed in sorghum stalk. Photo: Niloofar Vaghefi, USQ

The second aspect is to understand the impact of moisture stress and different levels of Macrophomina inoculum in soil on charcoal rot severity in sorghum plants. The commonly used symptom-based disease assessment method takes into consideration lesion length, which may not be adequate to reflect charcoal rot severity in sorghum as it is not a true reflection of the extent of tissue colonisation by the pathogen.

“This has given me the opportunity to use a DNA-based pathogen quantification tool (PREDICTA® B, provided by the South Australian Research and Development Institute) to quantify pathogen biomass within sorghum plants.”

It was through Dr Poudel’s investigative approach that a discovery was made.

“A novel fungal species was detected in sorghum paddocks in the northern grains region. Previously, only Macrophomina phaseolina was considered as the cause of charcoal rot in sorghum in Australia, but our research revealed a new Macrophomina species, named as Macrophomina tecta.

“Our study detected long-distance dispersal of this pathogen among Queensland and NSW sorghum paddocks. This suggests that seed-borne inoculum may have a more important role in pathogen dissemination than previously assumed.

“The moisture stress work confirmed that moisture stress has a significant impact on charcoal rot development on sorghum. Under moisture stress, infections in sorghum were observed even at low pathogen inoculum levels in soil.”

Implications

Dr Poudel has found the DNA test (PREDICTA® B) has the potential to provide an accurate and reliable method to estimate charcoal rot severity in sorghum and that it could be a useful tool to assess inoculum levels before sowing sorghum.

Additional management practice changes could also assist in the management of charcoal rot.

“Any practices that minimise moisture stress will help in managing the disease. While it is not possible to predict seasonal conditions, sorghum should be sown into paddocks with good soil moisture, with row spacing and plant densities optimised to reduce moisture stress post flowering,” Dr Poudel says.

Clearly, Dr Poudel enjoys her role as a pathogen detective and providing management solutions for the Australian grains industry.

“I am looking forward to continuing to expand my skills and experience, finding novel solutions to support sustainable agriculture and effective disease management.”

More information: Barsha Poudel, 0402 051 342, barsha.poudel@usq.edu.au