Breeding for improved drought tolerance

Abstract

The combination of a changing global climate and an increasing world population requires that crops for food, fibre and fuel need to be more resilient to hotter and drier conditions than they have been in the past. Given the years required to develop and release new varieties, breeders have been working hard to achieve this goal. Various strategies being used to counteract drought stress and some examples of successes will be reviewed. These include improvements in maize yield stability, due in part to improved drought tolerance; new varieties of wheat with increased water use efficiency; upland rice with deeper roots, and pearl millet with better yields in arid areas. While most of the selections are based simply on yield, greater emphasis is being placed on morpho-physiological traits associated with greater stress tolerance. Molecular markers based on QTLs linked to these traits also have been used, although less than the number of papers published in this area would suggest. There is promise in candidate genes that have been highlighted by 'omic studies, and great hope has been placed on transgenic approaches, but few of these have yet borne fruit in the field. The rapidly advancing genomic technologies and ready access to cheap sequence data are accelerating the breeding process. However, the ability to obtain relevant, high quality phenotypic information is the rate-limiting process; new innovations in 'high-throughput' phenotyping may provide solutions. Improved characterisation of test environments in multi-location trials combined with advanced statistical dissection of G x E interactions is helping breeders to improve target varieties. The use of models for predicting gene effects, particularly when combining multiple traits, will find greater application as these tools are developed further. Teams of breeders, physiologists, molecular geneticists, agronomists, pathologists, modellers and statisticians, who can communicate across disciplines, are required to tackle the challenge of producing enough food in a world where production is often constrained by insufficient water resources.