Australian researchers have revealed the intricate relationship between two major fungal wheat diseases – septoria nodorum blotch and yellow leaf spot – and how the order of infection can dramatically influence disease severity and plant resistance.
The breakthrough study was led by scientists from the Centre for Crop Disease Management (CCDM) in collaboration with the Western Australian Department of Primary Industries and Regional Development (DPIRD) and Australian Grain Technologies (AGT).
CCDM is a national co-investment of the Grains Research and Development Corporation (GRDC) and Curtin University.
Following development of a digital Polymerase Chain Reaction (PCR) method to quantify the pathogen presence in samples, researchers have discovered that when the yellow leaf spot pathogen infects wheat first, it primes the plant for septoria nodorum blotch, breaking down host resistance.
Conversely, when the septoria nodorum blotch pathogen strikes first, it suppresses yellow leaf spot and outcompetes the pathogen.
This study builds on an earlier PhD to investigate the finer details of interactions that occur during co-infection, providing intriguing insights into the cooperation and competition between pathogens.
CCDM Research Assistant Leon Lenzo using the digital PCR machine. Photo: Lisa Smith, CCDM.
CCDM researcher Leon Lenzo said the new digital PCR method, which allows the analysis of pathogen DNA, was an essential development for this study.
“Studying disease symptoms such as lesion sizes works well to estimate the pathogen presence when you have controlled conditions and only a single disease infection,” Mr Lenzo said.
However, using digital PCR, we could reliably distinguish between these two common diseases, and get accurate quantifications on their relative presence within the crop.
Researchers collected leaf samples from WA field sites in the 2022 growing season, including a long-term AGT disease nursery in Northam and DPIRD trial plots in South Perth.
These trials tested how infection order influences disease severity using cultivars with varying resistance levels. The study found co-infection was common, with most symptomatic wheat leaf samples infected by both pathogens.
“Plants infected first by the yellow spot pathogen had a significantly higher disease load compared to single disease infections, particularly the elite cultivar Scepter,” Mr Lenzo said.
The opposite occurred when septoria nodorum blotch was introduced first, suggesting both a co-operative and competitive relationship depending on which disease gets the upper hand.
“We don’t know the exact mechanisms that drive this yet, but the reality is that the yellow leaf spot pathogen often strikes first in nature, as its spores release earlier in the season than septoria nodorum blotch, and are generally better at surviving harsh conditions.
“Now that we know this can drive co-infection with the septoria nodorum blotch pathogen, it should be a consideration for growers when looking at crop resistance to these diseases,” he said.
DPIRD plant pathologist Geoff Thomas emphasised the importance of these findings for industry, suggesting they could help improve resistance rankings for wheat varieties.
“This work explains how these pathogens interact and how infection order influences disease expression and resistance response. This impacts our thinking on how to best rate varieties for their resistance, so growers in regions where both diseases are prevalent can have a better idea on how crops will respond to this co-infection complex,” he said.
CCDM Director, Professor Mark Gibberd, praised the team’s achievement, highlighting its significance for future breeding and management strategies.
“This study is a significant first step in working towards the development of management strategies to simultaneously control multiple pathogens through genetic resistance and cultural practices,” said Prof. Gibberd.
The research showcases CCDM’s focus on addressing problems that regularly occur in field for Australian growers, and the centre’s ability to work deeply and collaboratively with other experts in the state.
“Work such as this ensures Australian agriculture remains a global leader in grain production research and innovation.”
The paper, Fair-weather friends. Sequential co-infection demonstrates priority effects in the outcome of Parastagonospora nodorum and Pyrenophora tritici-repentis polymicrobial foliar disease of wheat, was recently published in the journal Plant Disease.
For more information on this project, watch the video.
