Dissecting QTLs for tolerance to drought and salinity

Compared to conventional breeding approaches, the dissection of the genetic basis of quantitative traits into their single components (i.e. Quantitative Trait Loci: QTLs) provides a more direct access to valuable allelic diversity at the loci governing the adaptive response to drought and salinity. Genomics and post-genomics platforms offer unprecedented opportunities to map, clone and manipulate the suite of QTLs affecting tolerance to drought and salinity in model species and crops. New high-throughput platforms capable of reducing the cost of molecular profiling coupled with a rapidly expanding amount of sequence information will streamline QTL dissection and the identification of superior alleles to enhance tolerance to drought and/or salinity. Therefore, it is expected that yield improvement under drought and/or saline conditions will increasingly benefit from the manipulation of QTLs through marker-assisted selection and, following QTL cloning, genetic engineering. Approaches based on the screening of wild relatives will unveil new allelic variants lost during domestication and early selection. Allelemining (e.g. association mapping, TILLING) in germplasm and mutant collections coupled with marker-assisted backcrossing and/or genetic engineering will further expand the possibilities to improve elite materials. QTL-based modelling approaches will contribute to better understand ‘Genotype x Environment’ interactions and to single out the most promising genotypes based upon the available QTL information. The impact of QTL-based approaches on the release of improved cultivars more resilient to drought and salinity will depend on their successful integration with conventional breeding methodologies and a thorough understanding of the biochemical and physiological processes limiting yield under such adverse conditions.