Disease research at a fever pitch

If barley crops could talk, they would have some stern words for pathogens: “You make me sick!”. Development of disease is a key constraint for barley production in Canada, with the most significant yield losses coming from foliar (leaf) diseases, where the risk has steadily increased over the last 20 to 30 years. Fortunately, science is fighting back with projects such as “Barley pathogen variations and implications for managing disease via host resistance". In the course of the study, researchers will generate virulence information for barley leaf pathogens as part of identifying sources of resistance to key Canadian barley diseases. In addition, they will strive to develop molecular tools that could be useful for breeders and pathologists for further research to improve integrated management of these barley leaf spot diseases.

“In Western Canada, we have three major barley leaf spot diseases,” said Dr. Xiben Wang, research scientist – Plant Pathology and Molecular Biology with Agriculture and Agri-Food Canada (AAFC) at the Morden Research and Development Centre in Morden, Manitoba.

These diseases include scald, which causes significant yield losses in cooler, wet seasons; net blotch, which damages the leaves and, in severe cases, seeds of the plants, causing spread of the disease and possible reduction of yields; and spot blotch, found everywhere that barley is grown and leading to significant yield losses in warm, humid conditions.

“Each disease is caused by a different pathogen and has its own lifecycle,” said Wang. “It is crucial that we determine which diseases are predominant in farmers’ fields so we can recommend the best management practices to combat them.”

Shock and awe

Since no single strategy will control everything, growers must take an integrated approach that includes multiple weapons such as genetic resistance, crop rotation and fungicide treatments.

“Host genetic resistance is a crucial part of managing barley foliar diseases. The problem is that some resistant varieties can become susceptible to pathogens over time. We need to know when this is happening and advise producers to stop using that line in their region, while providing alternatives that will offer that much-needed resistance going forward.”

In many cases, this breakdown in resistance is caused by genetic variations or mutations in pathogens that allow them to penetrate the plant’s defences. Identifying these variations has always been a lengthy procedure, so part of this project aims to expedite that process using molecular markers.

“Traditionally, we would need to visit the field, isolate the pathogen and test it on different resistance genes. We want to develop molecular markers that will quickly identify these changes and allow us to address them in a timely manner for growers.”

Does it still pay to spray?

Another aspect of the study is exploring fungicide sensitivities.

“The use of fungicides is a critical component of our current disease management systems. Because there is only a limited choice of chemicals to control pathogens, and producers have been employing them for many years, we are hearing reports of fungicide-resistant strains developing in western Canada and parts of the United States. This prompts some important questions: What are the current trends in fungicide use and resistant strains? Can we keep using these chemicals or are they being rendered irrelevant in some cases? Which ones are still effective and which should be dropped from your disease management program?”

This is cutting-edge research that harnesses the power of new technology, something that Wang embraces.

“I am really into adapting next-generation sequencing techniques for traditional plant pathology work to enhance the effectiveness of what we do. Generating solid molecular markers is a huge step in detecting fungicide sensitivities and isolating emerging pathogens with more speed and precision.”

Researchers are currently in year one of the four-year study, but are already working feverishly to gather data. Scientists in Alberta, Saskatchewan and Manitoba are combing farmers’ fields to collect infected leaf samples, which will then be returned to the lab for isolation of the pathogens involved.

“We plan to test the virulence profile of each pathogen and try to sequence them to home in on genetic variability among the pathogens.”

It is a multi-pronged project, which seems fitting when dealing with a complex problem like disease resistance.

Resistance is not futile

“Without ongoing foundational screening activities for key barley diseases, the development and release of new disease-resistant varieties would be slow, resulting in an increasing number of varieties with poor disease resistance packages. As a consequence, farmers and the barley industry would need to rely more heavily on other strategies, especially fungicide application.”

While fungicides are a vital tool for managing barley diseases, their long-term effectiveness and availability are at risk thanks to several factors: adaptation of pathogens to fungicide active ingredients; public perceptions and desire for sustainable farming practices that address climate and sector resiliency concerns; ongoing Canadian and global regulatory re-evaluation of pesticide actives; and slow development of new fungicides by the pesticide industry today as compared to three or four decades ago.

“This research will ensure that producers have advanced barley varieties with superior agronomic characteristics and improved resistance to key diseases, which will lead to enhanced production and quality while improving net returns.”

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