Research Programs |
Wheat Stem Rust Resistance
Wheat stem rust, caused by the fungus Puccinia graminis f. sp. tritici (Pgt), is a devastating disease that has caused multiple epidemics and associated crop failures throughout recorded history. Resistance to stem rust was a top priority in the “green revolution” wheat varieties bred by Norman Borlaug and coworkers beginning in the 1950s, and the combinations of resistance genes they created remained effective until the last decade. In 1998-9, a new strain of Pgt was identified from Africa that overcomes the major resistance genes used to combat stem rust. Commonly called Ug99, it has given rise to new strains to which 90% of the world’s commercial wheat varieties are susceptible. This pathogen, now spreading from sub-Saharan Africa across the Arabian peninsula, is predicted to move into central and south Asia, an area that produces 20% of the world’s wheat and is home to 1 billion people, most of whom depend on the wheat crop for nutrition.
Throughout his career and right up until his passing in 2009, Dr. Borlaug had raised the alarm to mobilize the global plant breeding community to reinvigorate breeding for stem rust resistance. This activity has been supported through the Borlaug Global Rust Initiative, including the Durable Rust Resistance in Wheat project, funded by the Bill and Melinda Gates Foundation, and also the Food and Agriculture Organization. It is hoped that these on-going efforts in conventional breeding will result in new wheat varieties resistant to Ug99 and its progeny.
2Blades shares these concerns about stem rust and is working on a comprehensive transgenic solution that complements the breeding efforts described above. Our goal is to identify many new resistance (R) genes from species closely related to wheat and deploy them in combinations as transgenic cassettes. This strategy has the combined advantages of:
accessing novel sources of resistance not otherwise available in the wheat germplasm pool
deploying them only in combinations in order to sustain their durability in the field
placing them at a single locus for ease of introgression into locally adapted varieties
eliminating “linkage drag,” the negative contribution of genomic regions linked to desirable genes that often results from introducing traits by traditional breeding
2Blades also carries out and funds work to identify the effector proteins for Pgt that are recognized by R genes in wheat and related species. Understanding the effector complement of Pgt will allow us to:
identify components of the pathogen essential for virulence, which are priority targets for R genes
understand variation in the pathogen population, to anticipate deployment of additional R genes
create facile phenotyping tools for breeding based on delivery of single effectors
identify R gene candidates in grass species that are complete non-hosts for Pgt
ultimately engineer improved R genes, with specificities directed toward variant forms of conserved effectors
In parallel, 2Blades is investigating the genetics of resistance to wheat stripe rust, Puccinia striiformis f. sp. tritici, a second major rust pathogen of the wheat crop.
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