Increasing crop yields to ensure food security is a major challenge. Mutagenesis is an important tool in crop improvement and is free of the regulatory restrictions imposed on genetically modified organisms. The forward genetic approach enables the identification of improved or novel phenotypes that can be exploited in conventional breeding programmes. Powerful reverse genetic strategies that allow the detection of induced point mutations in individuals of the mutagenized populations can address the major challenge of linking sequence information to the biological function of genes and can also identify novel variation for plant breeding. This review briefly discusses recent advances in the detection of mutants and the potential of mutagenesis for crop improvement.

We describe a novel method, agrosuppression, that addresses the need for an assay of the hypersensitive response (HR) in intact plants that is rapid and adapted to high-throughput functional screening of plant and pathogen genes. The agrosuppression assay is based on inoculation of intact plants with a mixture of Agrobacterium tumefaciens strains carrying (i) a binary plasmid with one or more candidate HR-inducing genes and (ii) a tumor-inducing (oncogenic) T-DNA. In the absence of HR induction, tumor formation is initiated, resulting in a typical crown gall phenotype. However, upon induction of the HR, tumor formation by the oncogenic T-DNA is suppressed, resulting in a phenotype that can be readily scored. We tested and optimized agrosuppression in Nicotiana benthamiana using the inf1 elicitin gene from the oomycete pathogen Phytophthora infestans, which specifically induces the HR in Nicotiana spp., and the gene-for-gene pair Avr9/Cf-9 from the fungal pathogen Cladosporium fulvum and Lycopersicon pimpinellifolium (currant tomato), respectively. Agrosuppression protocols that can be rapidly performed using simple mechanical wounding of petioles of intact N. benthamiana plants were developed and appeared particularly adapted to intensive high-throughput screening. This assay promises to greatly facilitate the cloning of novel plant R genes and pathogen Avr genes and to accelerate functional analyses and structure-function studies of these genes.