Pyramiding resistance-conferring gene sequences in crops.

Plant viruses can cause devastating diseases in many crops around the world. Genetic resistance and the adoption of resistant crop cultivars is the most desirable strategy to manage viruses. Single or multiple sources of resistance derived from host and/or virus gene sequences are used to develop resistant crop plants. Pyramiding sources of resistance is essential for achieving broad-spectrum and durable resistance and for protecting crops from commonly occurring mixed virus infections. Stacking resistance-conferring gene sequences into single crop cultivars is achieved by first, conventional breeding and the use of dominant and recessive host genes; second, genetic engineering and the deployment of virus-derived gene sequences or modified small plant RNAs for antiviral RNA interference defense, or of programmable nucleases to target viral gene sequences or to alter host factors that are critical to complete the virus infection cycle; and third, a combination of conventional breeding and genetic engineering. These strategies are successfully used to mitigate the effect of viruses. It is anticipated that the development of virus resistant crops carrying multiple resistance-conferring gene sequences will be further facilitated by progress at unraveling underpinnings of virus-host interactions, and at determining the sequence of more crop genomes.