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lary rise and evaporation of soil water during the dry season or from salinity of irrigation waters. Salinity tolerance during germination and early seedling growthSalinity impairs seed germination, reduces nodule forwas evaluated for 24 accessions representing four wild Phaseolus mation, retards plant development and reduces crop species (P. angustissimus A. Gray, P. filiformis Bentham, P. leptostayield (Greenway and Munns, 1980). One approach to chyus Bentham, and P. microcarpus Mart.) and four accessions of cultivated common bean (P. vulgaris L.) at 0, 60, 120, and 180 m M reducing the deleterious effects of soil salinity on crop NaCl. Salinity stress delayed germination in all accessions to varying production is the development of salt-tolerant cultivars degrees. Eight accessions of P. filiformis germinated fastest under (Epstein et al., 1980). In certain species, this may be high salinity (120 mM NaCl). Additional wild accessions exhibiting achieved by exploiting intraspecific variability. Howrapid germination at 120 m M NaCl were P. angustissimus, PI535272, ever, when such variability is limited, as occurs in many P. leptostachyus, PI535336, and P. microcarpus, PI430196. Among crop species, genes may be transferred from closely reaccessions, median germination time (days to 50% germination, T50) lated wild species adapted to high salinity (Austin, at 120 mM NaCl was correlated positively (r 2 ϭ 0.55, P Յ 0.01) with 1993). Legumes are considered a relatively salt sensitive germination in the control treatments. Seeds that germinated rapidly family (Maas and Hoffman, 1977) within which limited at 60 m M NaCl also germinated rapidly at 120 m M NaCl. At 180 variability for salinity tolerance has been detected (Garg m M NaCl, several accessions reached 50% germination by 6 d, demonstrating high genetic potential within Phaseolus for salinity toler-and Gupta, 1997; Johansen et al., 1990). In contrast ance during germination. The biomass of radicles plus hypocotyls to the cultivated legumes, the genetic diversity of wild decreased with increasing salinity. Cluster analysis separated the acrelatives may provide useful genes for improving tolercessions into three groups. Group I included salt sensitive accessions ance. For example, there are several wild relatives of with late germination, high sensitivity index (ratio of median germina-

eno-Limó n et al., 2000). However, few salt-tolerant genotypes were identified in these studies. The genus Phaseolus includes important cultivated species as wellIn some crops, wild species have been identified as as wild species with diverse ecological adaptations. Characterization good genetic resources for biotic and abiotic stress tolerof the ecological adaptations of the wild species would be useful for ance (Harlan, 1976). For example, there are several wild improved understanding, conservation, and utilization of these genetic resources. Salinity tolerance during vegetative growth was evaluated species of tomato (Lycopersicon cheesmanii, L. perufor 132 accessions for 14 wild Phaseolus species (P. acutifolius A. vianum,andSolanum pennellii) (Tal and Shannon, 1983), Gray, P. angustissimus A. Gray, P. carteri Freytag & Debouck, P. wheat (Triticum spp.) (McGuire and Dvorak, 1981), filiformis Bentham, P. glabellus Piper, P. leptostachyus Bentham, barley (Hordeum spontaneum K. Koch) (Mano and P. lunatus L., P. micranthus Hook & Arnold, P. microcarpus Mart, Takeda, 1998), soybean (Glycine spp.) (Pantalone et P. mcvaughii A. Delgado, P. oligospermus Piper, and P. vulgaris L.) al., 1997), and cowpea [Vigna unguiculata (L.) Walp.] and 11 accessions representing five cultivated species (P. acutifolius, (Gulai and Jaiwal, 1996), which exhibit a wide variation P. coccineus L., P. lunatus L., P. polyanthus Greenman, and P. vulin their salinity tolerance compared to their cultivated garis ) in nutrient solution containing 0 and 180 m M sodium chloride species. In addition, some wild relatives of pigeonpea for 21 d. When plants were salinized after the emergence of the first [Cajanus cajan (L.) Millse.] including Atylosia, Rhyntrifoliate leaf, wild accessions of P. acutifolius, P. filiformis, P. lunatus, and P. vulgaris showed a wide range of variation in their salinity chosia, and Dunbaria were observed in salt affected, tolerance as defined by total dry weight reduction (PR) as a percentage dry land habitats (Subbarao et al., 1991), and these genof the unsalinized controls, salt susceptibility index (SSI), and root: era could be a useful source of tolerance to salt stress shoot ratio (RSR). SSI and PR were correlated positively, indicating via genetic transformation. either trait could be used to select salt-tolerant accessions. ClusterCharacters such as yield, survival, vigor, leaf damage, analysis revealed substantial intraspecific and interspecific variation and plant height, have been the most commonly used in salinity tolerance. Salinity tolerance was observed in wild P. micrancriteria for identifying salinity tolerance (Maas and thus, P. mcvaughii, P. lunatus, cultivated P. coccineus, and several Hoffman, 1977;Shannon, 1984). Other indices of toleraccessions of wild P. filiformis, and P. vulgaris. Of these, P. filiformis ance have been proposed that are based on specific was noteworthy in having 9 of 11 accessions rated as highly tolerant.physiological characteristics, for instance, accumulation Wild P. vulgaris ...

This paper reports the changes on growth, photosynthesis, water relations, soluble carbohydrate, and ion accumulation, for two salt-tolerant and two salt-sensitive Phaseolus species grown under increasing salinity (0, 60 and 90 mM NaCl). After 20 days exposure to salt, biomass was reduced in all species to a similar extent (about 56%), with the effect of salinity on relative growth rate (RGR) confined largely to the first week. RGR of salt-tolerant species was reduced by salinity due to leaf area ratio (LAR) reduction rather than a decline in photosynthetic capacity, whereas unit leaf rate and LAR were the key factors in determining RGR on salt-sensitive species. Photosynthetic rate and stomatal conductance decreased gradually with salinity, showing significant reductions only in salt-sensitive species at the highest salt level. There was little difference between species in the effect of salinity on water relations, as indicated by their positive turgor. Osmotic adjustment occurred in all species and depended on higher K + , Na + , and Cl − accumulation. Despite some changes in soluble carbohydrate accumulation induced by salt stress, no consistent contributions in osmotic adjustment could be found in this study. Therefore, we suggest that tolerance to salt stress is largely unrelated to carbohydrate accumulation in Phaseolus species.