Disease Resistance

Abstract

Wheat plants are infected by diverse pathogens of economic significance. They include biotrophic pathogens like mildews and rusts that require living plant cells to proliferate. By contrast necrotrophic pathogens that cause diseases such as tan spot, Septoria nodurum blotch and spot blotch require dead or dying cells to acquire nutrients. Pioneering studies in the flax plant-flax rust pathosystem led to the ‘gene-for-gene’ hypothesis which posits that a resistance gene product in the host plant recognizes a corresponding pathogen gene product, resulting in disease resistance. In contrast, necrotrophic wheat pathosystems have an ‘inverse gene-for- gene’ system whereby recognition of a necrotrophic fungal product by a dominant host gene product causes disease susceptibility, and the lack of recognition of this pathogen molecule leads to resistance. More than 300 resistance/susceptibility genes have been identified genetically in wheat and of those cloned the majority encode nucleotide binding, leucine rich repeat immune receptors. Other resistance gene types are also present in wheat, in particular adult plant resistance genes. Advances in mutational genomics and the wheat pan-genome are accelerating caus­ative disease resistance/susceptibility gene discovery. This has enabled multiple dis­ease resistance genes to be engineered as a transgenic gene stack for developing more durable disease resistance in wheat.