Ground Cover Supplement : GC Supplement - Cereal foliar fungal diseases
3 Disease resistance PACKAGED GENES OFFER DURABLE RESISTANCE csiro research through the grdc-funded australian cereal rust control Program will make it easier and less costly for breeders to develop wheat varieties with durable rust resistance THE MOST COMMON loss of rust resistance in wheat occurs when the rust pathogen evolves to overcome a single resistance gene. For each additional resistance gene added to a variety there is a massive increase in the durability of the resistance trait because it is extremely difficult for rust to overcome several resistance genes in a single evolutionary step. The 'Holy Grail' of wheat rust resistance would be a new variety carrying a package of as many as five effective resistance genes in one compact and connected genetic unit, so that wheat breeders could simply and continuously transfer the whole package into new wheat varieties coming out of breeding programs. While there is no shortage of rust- resistance genes among wheat's wild relatives, isolating and transferring several of these at the same time into new varieties in a cost-effective and time-efficient way is difficult. This is because plant breeders must prioritise many other traits -- particularly yield -- as they develop new wheat varieties to meet growers' needs. If a series of rust-resistance genes could be isolated and then 'sewn' together into a neat unit and spliced into a wheat breeding line it would make the job of developing wheat varieties with durable and robust rust resistance much easier. Such a gene unit would stay permanently together so breeders would only have to keep track of one large resistance gene stack rather than many single genes spread, as they now are, over different chromosomes. It would also thwart the rust pathogen's unending propensity to evolve to overcome the single rust-resistance genes present in modern wheat varieties. CSIRO scientist Dr Peter Dodds and colleagues in the GRDC-funded Australian Cereal Rust Control Program (ACRCP) are on their way to achieving such a genetic feat by using rapidly developing gene- cloning technologies to deliver resistance genes into genetically modified wheat. The research team has so far successfully isolated and cloned three rust-resistance genes and are close to cloning others. This is about the same number of rust-resistance genes that have been cloned worldwide. Sewing the cloned genes together and inserting them into wheat is the next hurdle. To do this, the researchers are investigating newly developed technologies to stack multiple resistance genes and insert them into chosen locations in wheat chromosomes. Using the new method, Dr Dodds has shown that single resistance genes can be transferred into wheat chromosomes in a stable way. The next step will be to demonstrate the stability of multiple gene stacks in experimental breeding programs. The scientific challenge is great but so are the rewards. With an estimated 20 per cent of the world's wheat production under threat from the advancing and ever- evolving Ug99 stem rust pathotype, Dr Dodds and his colleagues are committed to success and believe developing durable forms of rust resistance is critical to global food security. Meanwhile, using the conventional approach, the GRDC partnership and co-investments with CSIRO and the University of Sydney through the ACRCP that involve the International Maize and Wheat Improvement Center continue to make significant strides using the conventional approach that significantly reduces costs to growers and improves environmental footprints. To date, the group has characterised four distinct adult plant multi-pathogen resistance genes that are being deployed as 'backbone' genes to complement major gene combinations. These are Lr46/ Yr29/Sr58/Pm39/Ltn2 on chromosome 1BS, Sr2/Yr30/Lr27/Pm on 3BL, Lr678/ Yr46/Pm46/Sr55/Ltn3 on 4DS and Lr34/ Yr18/Pm38/Sr57/Pbc/Ltn1 on 7DS. Knowledge from the cloning of some of these is contributing to the development of robust diagnostic markers thereby facilitating immediate, effective and efficient deployments in breeding programs to develop cultivars with potential durability against rust diseases in wheat. Uptake of these markers by breeding entities in Australia has been 100 per cent with strong and heightened interest internationally. The leveraging of the GRDC investment into the international arena will contribute to the potential reduction in rust epidemics globally, thereby preventing potential epidemics into Australia. □ grdc research codes csP00161, cim00017, csP00164 more information: Dr Peter Dodds, CSIRO Plant Industry, 02 6246 5039, firstname.lastname@example.org PHOTO: CARL DAVIES, CSIRO Australian Cereal Rust Control Program research is attempting to develop wheat varieties with long- lasting rust resistance by cloning and packaging several resistance genes into a single, transferrable genetic unit.
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