description
- Wheat is arguably the most important cereal crop in the world, with more than 600 million tons produced annually, supplying greater than nineteen percent of human dietary calories. The limited genetic diversity of wheat however renders it vulnerable to new diseases. The wheat stem rust fungus, known as the 'polio of agriculture', has caused repeated widespread crop failures throughout recorded history in North America, Europe, Asia and Australia. In the 1950s Norman Borlaug, father of the Green Revolution, successfully bred for resistance to the disease. This resistance held until the end of the '90's, when a new, super-virulent race of wheat stem rust called Ug99 emerged in Africa. Ug99 is capable of causing disease on greater than ninety percent of the world's wheat varieties. First detected in Uganda, it has spread at an alarming rate through sub-Saharan Africa and across the Arabian Peninsula, appearing in Iran in 2008. Because wind-borne rust spores can travel long distances, it is only a matter of time before this scourge reaches Pakistan and India, the source of nineteen percent of the world's wheat and home to 1 billion people. Changing climate will expose Europe to enhanced risk of the disease. New sources of stem rust resistance are urgently needed. Although traditional breeding can introduce new genes into wheat from other related species, this process is laborious, time-consuming, and difficult to control, often causing the simultaneous introduction of deleterious characteristics along with the desired trait ('linkage drag'). Moreover, when new resistance genes are deployed one-at-a-time, the pathogen typically overcomes the resistance gene within one or two growing seasons, rendering it useless. This problem can be alleviated by introducing more than one resistance gene at a time, but that turns out to be impractical if not impossible by conventional breeding methods. The work proposed here aims to identify new resistance genes from a wild relative of wheat, Aegilops sharonensis. This grass, native to the Levant, is closely related to one of wheat's progenitors, and contains a rich trove of new, unexploited resistance genes. Our long-term strategy is to isolate, by molecular cloning, as many new resistance genes as possible from this species, and introduce them in combinations using GM methods. Molecular cloning makes it possible, indeed straightforward, to put several new genes together in the same location in the genome, allowing breeders to work with them as a 'single' gene. This holds tremendous advantages for disease resistance breeding, and is a clear case where GM technology is not only vastly superior to conventional breeding, but indeed required for sustainable food security. Our proposal has the specific goals of i) cloning the first of these genes, based on preliminary genetic mapping information already in hand, and ii) developing a novel method for quickly identifying the position in the genome of any gene of interest. This novel method will use a combination of classical genetics and 'next-generation' ultra-high-throughput sequencing technology, which now makes experiments that would have been prohibitively expensive only a few years ago both feasible and affordable. The platform we are developing will have as a primary output new lines of wheat that harbour three or more new stem rust resistance genes at a single genetic locus. These lines will be made available to public breeding programs that develop new breeding material for developing countries in harm's way from stem rust. Aegilops also harbors genetic diversity for other useful traits, including water and nitrogen use efficiency. Thus, the genomic data and methodology we will develop in this project will benefit wheat improvement generally.