Breeding for salinity resistance in crop plants: Where next?

Soil salinity is widely reported to be a major agricultural problem, particularly in irrigated agriculture, and research on salinity in plants has produced a vast literature. However, there are only a handful of instances where cultivars have been developed which are resistant to saline soils. Reasons for the lack of success in developing salt-resistant genotypes, and for the low impact that plant physiological research has made, are explored. We conclude that soil salinity has not yet become a sufficient agricultural problem, other than on a local scale, to make salt resistance a high priority objective for plant breeders. The limited success of simple selection, where this has been practised in breeding programs, can be accounted for by the fact that research has consistently shown salt resistance is a complex character controlled by a number of genes or groups of genes and involves a number of component traits which are likely to be quantitative in nature. We also conclude that the results of physiological research have been poorly marketed by physiologists and, understandably, have failed to impress plant breeders. We anticipate that the importance of salinity as a breeding objective will increase in the future. Our assessment of reports of the degradation of irrigation systems, together with projections of the future demands of irrigated agriculture, is that enhancing the salt resistance of at least some crops will be necessary. Salinity resistance will both help provide stability of yield in subsistence agriculture and, through moderating inputs, help limit salinisation in irrigation systems with inadequate drainage. It is emphasised that plant improvement and drainage engineering should be seen as partners and not alternatives. We conclude with a personal view of one way forward for developing salt-resistant genotypes, through the pyramiding of physiological characters.