Improving resistance to drought and salinity in plants

Abstract

As has been reported previously (Parry et al., 2004), a European Commission sponsored conference on the “Optimisation of Water Use by Plants in the Mediterranean, OPTIMISE” (INCOMED ICA3-CT-2002-50005) was held in Palma de Mallorca, Balearic Islands, Spain in March 2003. Water is a scarce commodity in Mediterranean countries. Agriculture accounts for 75% of the total water consumption, but drought is the major limitation for growing many crops. The predicted change in climate, greater use through tourism, industrialisation and salinisation of water supplies, will further exacerbate the situation (Araus, 2004; Clary et al., 2004). There is therefore an important requirement to improve the drought and salinity tolerance of agricultural crops. Considerable advances have been made in the selection of crop varieties that are able to tolerate drought and salinity. These have been through traditional breeding (Araus et al., 2003; Munns et al., 2003; Slafer, 2003), mutant selection (Mahar et al., 2003; Ahloowalia et al., 2004) and more recently QTL analysis (Baum et al., 2003; Thomas 2003; Foolad, 2004; Forster et al., 2004; Talame et al., 2004). The identification of wild relatives (e.g. Porteresia coarctata for rice), that are able to grow in saline soils, may also provide a useful supply of new germplasm for future breeding (Latha et al., 2004). Molecular approaches have identified a large number of genes that are induced following the application of drought or saline conditions. These genes and the proteins that they encode can be divided into three categories: (1) signalling and transcriptional control; (2) the protection of membranes and proteins and (3) water and ion transport (Shinozaki et al., 2003; Wang et al., 2003). As a result of these studies there have been a number of attempts to genetically manipulate plants to become more tolerant to drought and salinity stresses. Potential candidate genes have included those encoding: (1) transcription factors; (2) compatible solutes (e.g. proline); (3) antioxidants and detoxifying enzymes; (4) ion transport and (5) heat shock and late embryogeneis abundant proteins. A number of articles have discussed at length the results obtained from the laboratory testing of transgenic plants containing such potentially useful genes (Yoshida 2002; Chaves et al. 2003; Figueras et al., 2004; Wang et al., 2004). As yet we are awaiting evidence from major field trials to establish if such genetic manipulation will eventually lead to useful drought and salinity tolerant crop plants that are safe and acceptable to the public.