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Stripe rust fungus, caused by Puccinia striiformis f. sp tritici, is one of the top five threats from disease and pests to wheat and barley production in Canada. Fungi have the potential to rapidly and dramatically acquire genetic changes by transferring DNA between individuals (somatic hybridization), allowing them to become more pathogenic. This causes a threat to growers as new fungi strains may be able to overcome the genetic resistance or fungicide that protects their plants, having the potential to decimate the entire crop.  

Drs. Gurcharn Brar from UBC and Guus Bakkeren from Agriculture and Agri Food Canada studied the four stripe rust lineages present in Canada to understand their origin, how they have evolved and how they are related to one another. Untangling these relationships provides important information on the formation of more virulent pathogens which can cause disease on plants that were previously resistant to them. ? 

The team developed and improved methods to sequence DNA from individual fungus cells and use this to create a detailed map of the fungal genome (high-quality fungal genome assemblies). This result strengthens our ability to study fungal genomes at a very precise level. The team looked closely at the DNA of two common strains of the stripe rust fungus, PstS1 and PstS1-related. By studying the genomic sequences they’d generated they found that these two lineages shared exactly 50% of their DNA. This confirmed that the PstS1-related lineage originated from a somatic hybridization event – a complete merging of DNA from genetically distinct strains of the fungus – PstS1 and an unknown lineage. From this merging event one whole nucleus was transferred from the two types of stripe rust fungus to create the PstS1-related lineage, causing immediate and rapid genetic diversity.? 

Confirming this mode of DNA reassortment has implications for the agricultural sector as it means that fungi pathogens can rapidly become more virulent and harder to control, which may leave growers unprepared in the face of emerging strains. This discovery also helps researchers better understand how and where new, possibly more virulent lineages may appear and their impact on cereal production, leading to improved monitoring and better management strategies for growers. ? 

Developing these protocols and generating high-quality genomic data greatly benefits the research sector and lays the foundation for the use of rapid, single-cell genomics for ongoing pathogen surveys of cereal rusts, enhancing the capacity of growers do deal with future threats.?