Increasing salinity of soil and water threatens agriculture in arid and semiarid regions. By itself, the traditional engineering approach to the problem is no longer adequate. Genetic science offers the possibility of developing salt-tolerant crops, which, in conjunction with environmental manipulation, could improve agricultural production in saline regions and extend agriculture to previously unsuited regions.

Salt buildup in agricultural soils threatens irrigation agriculture in arid and semiarid regions of the world. Development of salt resistant crops may allow increased production in areas plagued by salt. Although ample sources of genetic diversity exist for most of the major crops, adequate screening methods for isolating salt‐resistant lines have yet to be developed. Wheat was chosen as a test case to investigate the current availability of salt‐resistant germplasm in the world collection. Over 5000 accessions of hexaploid wheat were screened in solution culture salinized with sea salt. Screening at 85% seawater yielded 312 individual selections capable of vigorous growth at germination and emergence. These were recovered and transferred to nonsaline conditions for seed multiplication. Subsequent screening of the next generation was done over the entire life cycle at 50% seawater, resulting in the isolation of 29 salt‐resistant lines. Salt‐sensitive lines were visually evaluated for uniformity of leaf damage at 25% seawater. Three resistant and two sensitive selections were compared with ‘Anza’ and ‘Kharchia’ for biomass production in solution cultures salinized to 20, 40, and 60% seawater. At the highest salinity, average biomass production was 6.4% of the controls for the resistant selections, 5.9% for ‘Kharchia’, 3.7% for ‘Anza’, and 1.6% for the sensitive selections. These results indicate that screening wheat at high salinities over a single generation can be effective in identifying salt‐resistant genotypes.

Two selections of bread wheat, Triticum aestivum L, differing in their relative salt resistance, were grown in salinized solution culture, and relative growth rates, osmotic adjustment, ion accumulation, and photosynthesis were monitored to study the responses of the plants to salinity.Differences in water relations were minimal and were only apparent for 3 days following salinization. The lines differed substantially in their relative growth rates and photosynthetic responses for several weeks following salinization, despite full osmotic adjustment. Concentrations of major cations and Cl in the plant organs were remarkably similar in both lines, indicative of minimal differences in gross ion absorption and translocation.The authors interpret these results to suggest that the major difference between these two lines of wheat was their response to specific ion effects, at the level of the organ, tissue, cell, and subcellular entities. Superior compartmentation oftoxic ions by the more salt-tolerant line, presumably in the vacuole, might have enabled it to maintain its cytoplasmic metabolic apparatus in a stabler and more nearly normal state than the sensitive line was able to do; a measure of true cytoplasmic toleration of salt may also be a factor.Salinity is a major problem in today's irrigation agriculture, as millions of tons of salt are annually dumped onto the soil from the irrigation water. Plants vary, however, in their ability to cope with salinity, as is evidenced by the wide diversity of plant habitats, ranging from nonsaline environments to the extreme salinities of the sea, salt marshes, and saline deserts. For crop plants, differences in salt resistance exist not only among different genera and species, but even within a species which may on the whole be considered salt sensitive (Ref. 6, Refs. 8,9, and 18). These observations support two arguments: (a) crop plants can be adapted to saline environments, and (b) intraspecific variation can be exploited to investigate the nature of salt resistance or sensitivity (9). It is the second of these claims that is addressed in the current study.The reduction in yield of many crops by salinity is well documented (18 mechanisms of salt tolerance (7,(10)(11)(12)19).In this paper, we report the results of a study of the physiological responses to salinity, comparing a salt-resistant line of hexaploid wheat with one which is salt-sensitive. The use of intraspecific selections in comparative studies should provide a powerful tool to unveil the genetically based mechanisms of salt resistance (9). This investigation was not meant to be exhaustive, but rather exploratory in nature, as an attempt to find the areas of greatest difference between the selections which might relate to the observed differences in salt resistance. MATERUILS AND METHODS Selection and Culture of Salt-Resistant and Salt-SensitiveWheat. Details of the selection procedures have been reported elsewhere (15). In general, lines from the world collection of wheat, Triticum aestivum L., were ...

ABSTRACrTwo selected lines of bread wheat, Triticum aestivum L, differing in their relative salt resistance, were grown in isosmotic solutions ofdifferent ionic compositions to investipte sensitivity to specific ions. Growth rates and ion accumulation were determined. The salt composition of the various solutions had little effect on the growth of the salt-resistant line, but significantly affected that of the salt-sensitive line. Specifically, solutions containing high Na' concentrations were more toxic than those containing high Cl concentrations or high concentrations of nutrient ions. There were few differences in ion accumulation between lines in a given treatment, although the sensitive line tended to accumulate more Na' than the tolerant line in the salt treatments with high Na concentrations. The (2,3,9,17,27). Examples of intraspecific variation in response to salinity have been noted in many crops (6,7,24,26,28,29). This genetic variation can provide an added tool in physiological investigations of this problem. In an earlier study (14) we compared two selections of wheat deliberately selected for salt resistance and sensitivity, respectively, to provide a high degree of contrast for physiological experiments. The study showed minimal differences between selections in water relations and gross ion accumulation, but major differences in photosynthetic and growth rates. We interpreted these results as indicative of differential responses of the two lines to specific ions, possibly related to different capabilities in ion compartmentation.The principal objective of the present study was to determine which of the two ions most frequently implicated in salinity, Na+ and Cl-, is most toxic to wheat. Attention was also paid to the effects of Ca2" and Mg2". MATERIALS AND METHODSDetails of the selection procedures used to identify saltresistant and salt-sensitive wheat, Triticum aestivum L., have been reported elsewhere (13). Fifty grams of seed from the saltresistant line (P. I. 178704) and the salt-sensitive line (P. I. 94341) were surface-sterilized by a 20-min wash in 10% bleach (NaOCl). Germination and transplantation of seedlings were carried out following standard procedures for solution culture as described previously (14) Table I. All solutions had a background of modified Hoagland solution. The solutions were as follows (parentheses indicate abbreviated designations used hereafter). The control was modified Hoagland solution (Control). The other solutions, all at an osmotic potential equal to that of 28% seawater, contained, in addition, concentrated Hoagland solution 2 (10) macronutrient salts (Hoagland); concentrated macronutrient anions, in the same proportion as in Hoagland, with Na+ as the countercation (NaHoagland); concentrated macronutrient cations, in the same proportion as in Hoagland, with Cl-as the counteranion (Hoagland-Ca); NaCl (NaCl); and Rila Marine mix, obtained from Rila Products, Teaneck, NJ (Seawater). The solutions were made up in this fashion in order to attempt to separate ...

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