A common fungal disease of plants, rusts destroy more than $1 billion worth of crops each year. In Australia, for the past 60 years rust-resistant crop varieties have been grown.
The researchers found that the deadly Ug99 strain of the wheat stem rust fungus - named for its discovery and naming in Uganda in 1999 - was created when different rust strains simply fused to create a hybrid, through a process known as somatic hybridisation.
It enables the fungi to merge their cells and exchange genetic material without going through the complex sexual reproduction cycle.
CSIRO group leader Dr Melania Figueroa. Supplied
The findings indicate that Ug99 could again exchange genetic material with different pathogen strains to create a whole new enemy.
That rust strains could hybridise was known from laboratory studies in the 1960s, but the new research provides the first clear molecular evidence that the process generates new strains in nature.
CSIRO group leader Dr Melania Figueroa said Ug99 was considered one of the most threatening of all rusts.
“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,” she 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.”