Why does Yellow Rust resistance ‘break down’?
When the pathogen spores land on the wheat plant and begin to infect, it releases hundreds of compounds as part of the infection process. The plant ‘recognises’ this and deploys its defence response i.e. resistance. As the pathogen replicates, random errors occur when copying its genetic material; it just takes an error in the code of the compound that is recognised by the plant, and the plant no longer recognises the pathogen and so will not initiate the resistance response. Also, with the ever-changing Yellow Rust pathogen population, new pathotypes are appearing, and often avoid the plant’s defence response.
What are plant breeders doing to develop resistant varieties?
We are constantly looking for novel resistance genes which we can breed into our new varieties in combinations. Using molecular marker technology, we can combine multiple resistance genes in a single variety. By having more than one resistance gene, we reduce the risk of the resistant variety becoming susceptible.
Are all resistance genes equal?
No. Some resistance genes provide juvenile resistance, whilst others work in adult plants. Some provide ‘full resistance’, whilst others reduce the severity of the Yellow Rust symptoms. It’s worth noting that it costs the plant to deploy its resistance response, and this can often be seen as a reduction in yield. Our job as breeders, is to find effective resistance gene combinations that do not come with negative side effects.