The mysteries of plant rust are being unraveled at the genetic level.
Researchers are using genomics to understand this costly fungal disease that has plagued farmers around the world for centuries.
“Rust is an old disease but it is a constantly evolving pathogen and that’s why we are interested in getting a better understanding of how this evolution takes place and why rusts are so adaptable,” said researcher Richard Hamelin of the University of British Columbia’s forest sciences department and Natural Resources Canada.
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About 7,800 species of rust are known. It attacks many plants and valuable agriculture crops such as wheat, coffee and soybeans. Symptoms vary from dusty orange powder on leaves to cankers on trees.
“Every year you get a new rust,” said Hamelin, who is working with Agriculture Canada scientists.
“You get recombinations, you get mutants, so you can’t be asleep at switch. It is an arms race against the rust.”
The researchers will sequence the rust genomes affecting wheat and poplar trees and then analyze them and compare them to one another and other fungi to see what is unique in rust. They already know fungi have a fairly small genome compared to humans or trees, which may explain why it is so adaptable.
Understanding the genetics of rust and how it evolves can help scientists better identify fast and slow evolving genes. They can then target breeding programs to identify the resistant genes that are active against the slower evolving gene and speed up the development of new resistant crops.
The technology, which was not available five years ago, will be able to sequence an entire fungal genome in a few days for less money compared to past projects.
The sequencing will be done in Vancouver but Agriculture Canada collaborators also work in Quebec, B.C.’s Okanagan Valley and Manitoba.
“It makes this kind of project really feasible and it opens the doors to the same approach for any kind of plant disease or microorganism attacking plants or animals,” Hamelin said.
Researchers already know that different species may have hybridized and created new progeny that could attack new hosts.
However, most of the hybrids are biological dead ends.
“They cannot reproduce or cannot survive but even if a few thrive, they can be trouble makers,” he said.
“They could infect a crop that are resistant to other types. We hope by conducting this work, we will have better tools where we can monitor this.”
Understanding how rust works at the genetic level could help researchers identify other pathogens and lead them to the correct treatment.
“In the coming years, when you have a new epidemic of a pathogen, you can go ahead and sequence the genome of a population so you can identify the races,” he said.
“We think in the future this will be the first thing you do.”
Rust has heavily influenced the history of prairie plant breeding, wrote Brent McCallum and Ronald DePauw of Agriculture Canada in their paper,A Review of Wheat Cultivars Grown in the Canadian Prairies.
“One of the major achievements of wheat breeding in Western Canada has been the improvement of disease resistance, particularly rust resistance.”
Their review found that stem rust epidemics were responsible for varying levels of crop loss from 1891, with widespread losses starting in 1902.
Plant breeders had to include rust resistance in their programs.
For example, Red Fife wheat was introduced to Western Canada in 1870 and spurred on wheat production in Manitoba. However, it was a late maturing crop and susceptible to lodging and stem rust.
The hunt was on for a productive and disease resistant crop and led to the development of Marquis.
It was widely grown across the West, but became highly susceptible to stem rust and suffered substantial yield losses during epidemics starting in 1921.
A stem rust resistant replacement was needed and Thatcher was introduced in 1939. It became the parent crop for many modern varieties, but it was susceptible to leaf rust. Still it was the favoured variety until the 1960s because of its other superior qualities.
Breeding efforts to develop stem and leaf rust resistance led to the release of Selkirk and then Neepawa, which was rapidly adopted in all parts of Western Canada.
It remained the leading western wheat until it was replaced by Katepwa in 1986, with its good bread making qualities and better stem and leaf rust resistance.
AC Barrie and Laura also had good leaf rust resistance.
AC Barrie was the predominant wheat variety from 1998 to 2005, but it too became susceptible to leaf rust. It was widely seeded because it had an intermediate level of resistance to fusarium head blight and good lodging resistance.
