Salinity resistance and plant growth revisited

This article reconsiders a recent hypothesis concerning the physiology of growth inhibition by salinity and its relevance to the breeding of salt-resistant crops (Munns 1993, Plant, Cell and Environment 16, pp. 15-24). The hypothesis states that the osmotic effects of salinity on water availability will strongly and equally inhibit the growth of related species and varieties. The genotypic diversity needed for breeding increased resistance to growth inhibition by salinity is only expected to appear after weeks or months. Higher rates of salt accumulation in more sensitive varieties then lead to accelerated leaf senescence. This further inhibits new growth, as compared with more resistant varieties. Accordingly, breeders aiming to increase crop growth under salinity should focus efforts on manipulating genes which can decrease rates of salt accumulation. However, the osmotic inhibition of growth by salinity appears to involve regulatory physiological changes. Thus, some genotypic diversity might be expected. Clear evidence is presented for genotypic diversity in early growth responses to salt or PEG-induced osmotic stress, in several species and varieties. The conclusion is that development of plants with increased resistance to inhibition of growth by the osmotic effects of external salinity (in addition to increased resistance to salt accumulation) is both feasible and desirable.