Abstract
This study assessed the responses of four local Spanish cultivars of Phaseolus lunatus (lima bean) to moderate salinity. For three weeks, plants were exposed to increasing salinity (50–150 mM NaCl) under greenhouse conditions. At the end of the experiment, several growth and biochemical parameters were determined. Salt stress reduced the fresh weight of aerial organs, allowing us to rank the four genotypes according to their tolerance to salinity. The concentration of most photosynthetic pigments remained unaltered, except carotenoids that were reduced in the least salt-tolerant cv. (cultivar) VPH-79. Leaf Na+ and Cl− concentrations increased with increased salt concentration of irrigation water, but K+ either remained constant, as in the most tolerant ‘BGV-15410’, or increased in the other cultivars, resulting in an unchanged K+/Na+ ratio under stress in two of the selected cultivars. Moreover, proline increased in all cultivars, most notably in cv. VPH-79, with the highest absolute concentrations registered in the more salt tolerant cultivars. Interestingly, these cultivars already had a relatively higher proline concentration in non-stressed plants. These findings indicate that P. lunatus is moderately salt tolerant and that its main mechanisms to adjust to salinity stress are the maintenance of high concentrations of K+ and proline accumulation in leaves.
Highlights
Lima bean, Phaseolus lunatus L., is an important crop, which ranks second among beans—only superseded by common beans, Phaseolus vulgaris—regarding consumption and cultivated land [1].Though originating from Mesoamerica and the Andes [2], its area of cultivation has spread over time, covering many tropical and subtropical areas around the world, notably in Africa and North America, with the United States the leading producer of P. lunatus [3]
electrical conductivity (EC) was registered in the pots watered with 150 mM NaCl, recording about a four-fold increase in comparison with EC measured in the respective controls
P. lunatus could tolerate three weeks of exposure to salinities as high as 150 mM NaCl, in agreement with previous reports indicating that this crop could be moderately salt-tolerant
Summary
Phaseolus lunatus L., is an important crop, which ranks second among beans—only superseded by common beans, Phaseolus vulgaris—regarding consumption and cultivated land [1].Though originating from Mesoamerica and the Andes [2], its area of cultivation has spread over time, covering many tropical and subtropical areas around the world, notably in Africa and North America, with the United States the leading producer of P. lunatus [3]. Agriculture 2018, 8, 201 the need to acclimate to different climatic and ecologic conditions [4]. This diversity is being threatened by contamination, climate change, and changes in land use (urbanisation, industrialisation, or cultivation of other more valuable crops). As traditional farming methods are being replaced by industrialised cultivation led by large agricultural companies, the maintenance of local varieties and, diversity is being lost [5]. This loss is irreversible, affects the stability of agro-ecosystems, and increases the vulnerability of crops. The reduction of genetic diversity decreases the chance of adapting agriculture to future challenges triggered mostly by climate change [6], especially since the genotypes used extensively in agriculture were selected for their high productivity or resistance to some diseases and pests, but not bred for increased tolerance to abiotic stresses [7]
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