Australian researchers have helped to uncover the origins of the world’s deadliest strain of a wheat disease which threatens global food security.

Rusts are a common fungal disease of plants that destroy over $1 billion worth of crops globally each year.

CSIRO scientists, alongside partners in the US and South Africa have published their findings into the devastating Ug99 strain of the wheat stem rust fungus today in Nature Communications.

Their research shows that the disease, named for its discovery in Uganda in 1999, was created when different rust strains fused to create a new and deadly hybrid strain.

This process, known as somatic hybridization, enables the fungi to merge their cells together and exchange genetic material without going through the complex sexual reproduction cycle.

The discovery raises concerns that other crop-destroying rust strains could hybridise in other parts of the world, as well as Ug99 hybridising with other pathogens to create new strains.

Group Leader at CSIRO Dr Melania Figueroa said Ug99 is considered one of the most threatening of all rusts as it has managed to overcome many of the stem rust resistance genes used in wheat varieties – such as those used in Australia – and has evolved many variants.

“While outbreaks of Ug99 have so far been restricted to Africa and the Middle East, it has been estimated that a nationwide outbreak here could cost Australia up to $500 million in lost production and fungicide use in the first year,” Dr Figueroa said.

“There is some good news, however, as the more you know your enemy, the more equipped you are to fight against it.

“Knowing how these pathogens come about means we can better predict how they are likely to change in the future and better determine which resistance genes can be bred into wheat varieties to give long-lasting protection.”

Earlier this year, CSIRO worked with the University of Minnesota and the 2Blades Foundation to achieve good results in wheat resistance by stacking five resistance genes into the one wheat plant to combat wheat stem rust.

“This discovery will make it possible to develop better methods to screen for varieties with strong resistance to disease,” Dr Figueroa said.

“There was an element of serendipity at play in this work. We never expected that Ug99 and an Australian isolate might be related but only through a multi-continental collaboration was it possible to make the connections needed to achieve this discovery.”