Irrigation of Mediterranean crops with saline water: from physiology to management practices

Salinity is currently one of the most severe abiotic factors limiting agricultural production. The high rates of population growth and global warming are expected to further exacerbate the threat of salinity, especially in areas with a semi-arid climate as in the Mediterranean region. Salinity affects plant performance through the development of osmotic stress and disruption of ion homeostasis, which in turn cause metabolic dysfunctions. Particular emphasis is given on the impacts of salinity on photosynthesis because of its potential restrictions on plant growth and yield. The inhibition of photosynthesis under low to moderate salinity stress appear to be mainly attributed to diffusional limitations (stomatal and mesophyll conductance), even for salt-sensitive fruit trees such as citrus trees. In contrast, biochemical limitations to photosynthesis appear to occur only when stress becomes heavy. A thorough understanding of the mechanisms conferring salt tolerance is therefore essential under the expected climatic change, as it will enable the selection of salt-tolerant genotypes and the adoption of appropriate practices to alleviate salinity impacts on agricultural production. In fruit trees, salt tolerance is mainly associated with their ability to restrict salt accumulation in the leaves. Cell features of specific tissues, morphological factors and water-use efficiency regulate salt accumulation in the shoot. Furthermore, most fruit trees display a rapid osmotic adjustment in response to salinity, which is mainly attributed to the accumulation of inorganic ions and carbohydrates. Little information is available about the ability of horticultural crops to detoxify reactive oxygen species and to synthesize compatible solutes and hence on the potential contribution of these mechanism to induce salt tolerance in horticultural crops. (c) 2004 Elsevier B.V. All rights reserved.