Posts Tagged ‘wheat stem rust’

Study finds large-scale expansion of stem rust resistance gene in barley and oat lineages

USA SeedQuest – Central information website for the global seed industry
December 7, 2020

Stem rust is one of the most devastating fungal diseases of wheat and historically has caused dramatic, widespread crop failures resulting in significant yield losses around the world. Stem rust epidemics in major wheat growing areas could cause a major threat to global food security. Scientists have identified a resistance gene, Sr22, as one of the few characterized genes that protects against a large array of stem rust races. 

Given its effectiveness against stem rust, Sr22 is an important gene. It was recently incorporated into a multi-Sr transgene stack and found to achieve complete field-immunity to stem rust. As a result of this success, scientists are looking for ways to deploy the gene in the field.


A new study in the MPMI journal describes the functional and evolutionary characterization of Sr22, based on a comprehensive search of the genomes and transcriptomes of 80 plant species. The study found that the gene is conserved among grasses in the Triticeae and Poeae lineages.

“We originally set out to mine Sr22 alleles and their function then expanded the work to include a large-scale comparison of the Sr22 locus across monocot species,” explained Dr. Guru Radhakrishnan who works for the John Innes Center in the United Kingdom. “This is when we discovered the surprising large-scale expansion of the Sr22 locus in the barley and oat lineages.”

This study also describes the sequence variation between different Sr22 alleles, which may be due to intra-allelic recombination. Three of the alleles were functionally characterized in transgenic wheat and two of these were found to confer resistance to the notorious Ug99 isolate of the wheat stem rust pathogen.

“To our knowledge, this is the first study to comprehensively explore the evolution of a resistance gene across a broad range of monocot lineages in addition to exploring allelic variation between accessions of monocot species,” added first author Dr. M. Asyraf Md. Hatta. “With more high-quality monocot genome and transcriptome assemblies becoming available, such studies are expected to provide valuable insights on the evolution of resistance genes in this agriculturally important group of plants.”

Their study contributes valuable knowledge on plant disease resistance gene function and evolution, which can facilitate the improvement of crops against agriculturally important diseases, such as stem rust. To learn more, read “Extensive Genetic Variation at the Sr22 Wheat Stem Rust Resistance Gene Locus in the Grasses Revealed Through Evolutionary Genomics and Functional Analyses” published in the November issue of the MPMI journal. 

More news fromAPS – American Phytopathological Society


Published: December 8, 2020

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Photo: Jaspreet Kindra/IRINWheat under threat

JOHANNESBURG, 2 April 2014 (IRIN) – Outbreaks of a deadly fungal disease in wheat crops in Germany and Ethiopia in 2013 have had the scientific community buzzing over the threat posed to global food security.

Wheat stem rust, also known as wheat black rust, is often referred to as the “polio of agriculture”: The rapidly mutating fungal disease can travel thousands of kilometres and wipe out crops.

Wheat farmers and scientists at a recent summit hosted by the Mexico-based International Maize and Wheat Improvement Center (CIMMYT ) have been examining outbreaks of different strains of wheat stem rust in the two countries to identify any similarities.

In Germany “the occurrence of stem rust was favoured by a period of unusually high temperatures… and an unusually late development of the wheat crop due to cold spring and early summer temperatures,” explained Kerstin Flath, senior scientist at Germany’s Federal Research Centre for Cultivated Plants at the Julius Kuehn-Institut. The outbreak occurred in June in central Germany, a mainly wheat producing area, and was the first in the country in several decades.

“A changing climate will ‘definitely’ favour this thermophilic fungus” Scientists noted that the rust came so late that even the fungicides sprayed earlier to prevent leaf rust epidemics proved ineffective.

Then in November 2013 the disease struck a popular variety of wheat in Ethiopia called digalu, used to make bread, said Bekele Abeyo, a senior scientist and wheat breeder at CIMMYT.

What was particularly disconcerting for the scientists was that digalu had been bred with inherent resistance to certain strains of stem rust and another wheat disease called “yellow rust” or “stripe”.

The fact that the fungus has been rapidly mutating has prompted scientists to study the two cases with a view to helping with the preparation of new wheat varieties.

David Hodson, a senior scientist with the Global Cereal Rust Monitoring Program at CIMMYT, says the analysis presented on the German outbreak showed “there were some clear specific differences between the races present in Germany compared to Ethiopia, although the races were similar and fitted into the same race group.”

In Ethiopia, he said, the season had also been favourable for rusts, with above-average and well distributed rainfall – conditions similar to those in 2010 when wheat crops there were affected by yellow rust.

However, said Hodson, “the key factor was the presence of a suitable host and the appearance of a race that was able to attack this host.”

Flath said the big question on the German outbreak was whether it “was a unique situation or if it will repeat this year” – particularly because they had had a rather mild winter, so the spores might have survived.

She reckons a changing climate will “definitely” favour this thermophilic fungus. In the last two years two new aggressive variants of the yellow rust-causing fungus have made huge inroads in central and northern Europe.


Fungicides are the first line of defence. A longer term solution is replacing the world’s entire wheat varieties with those that contain several minor rust-resistant genes, which are pooled together to counter the infection, giving them an edge over single rust-resistant genes in combating various mutated variants of the fungus. Digalu contains single rust-resistant genes.

There are 20 new stem-rust-resistant varieties of wheat available. But getting the new seeds to farmers has been a problem, mainly due to poor distribution networks and cost.

Industrialized countries have an edge in terms of resources, said Flath. But even developing countries, realizing that food security is at stake, are beginning to make massive investments, says Abeyo. For instance, after the outbreak in Ethiopia in 2010, the government invested US$3 in fungicides, which helped contain the fungus in 2013.

With global wheat supplies vulnerable to changing weather patterns, Abeyo says developing countries are realizing the need to become self-sufficient in grain.

“Countries are now making the investment in infrastructure and research to develop better varieties.” But they still have a long way to go. Better partnerships with the developed world in sharing information and skills to monitor and protect their crops are also proving to be effective, he added.


All wheat varieties will have to be replaced
Two new wheat varieties offer hope against stem rust
Mutant wheat killer on the prowl
Another strain of deadly wheat fungus in South Africa

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