A Simple and Cost-effective Approach for Salt Tolerance Evaluation in Cowpea (Vigna unguiculata) Seedlings

in HortScience

Little has been done with respect to breeding for salt-tolerant cowpea (Vigna unguiculata) cultivars despite of salt stress being a growing threat to cowpea production. Seedling stage is one the most susceptible stages to salt stress in cowpea. Establishing a streamlined methodology for rapidly screening a large number of genotypes will significantly contribute toward enhancing cowpea breeding for salt tolerance. Therefore, the objective of this study was to establish and validate a simple approach for salt tolerance evaluation in cowpea seedlings. A total of 30 genotypes including two controls (PI582468, a salt-tolerant genotype, and PI255774, a salt-sensitive genotype) were greenhouse-grown under 0 mm and 200 mm NaCl. A total of 14 above-ground traits were evaluated. Results revealed: (1) significant differences were observed in average number of dead plants per pot, leaf injury scores, relative salt tolerance (RST) for chlorophyll, plant height, and leaf and stem biomass among the 30 genotypes; (2) all PI255774 plants were completely dead, whereas those of PI582438 were fully green after 2 weeks of salt stress, which validated this methodology; (3) RST for chlorophyll content was highly correlated with number of dead plants and leaf injury scores; (4) RST for leaf biomass was moderately correlated with number of dead plants and leaf injury scores; and (5) RST in plant height was poorly correlated with number of dead plants and leaf injury scores Therefore, less number of dead plants per pot, high chlorophyll content, and less leaf injury scores were good criteria for salt tolerance evaluation in cowpea. This study provided a simple methodology and suggested straightforward criteria to evaluate salt tolerance at seedling stage in cowpea.

Contributor Notes

This work is supported, in part, by the U.S. Department of Agriculture National Institute of Food and Agriculture Hatch project accession number 1002423.

Corresponding authors. E-mail: Beiquan.Mou@ARS.USDA.GOV or ashi@uark.edu.

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    Phenotyping of salt tolerance in cowpea at seedling stage 14 d of salt stress. (R) Salt-tolerant genotype, PI582468, and (S) salt-sensitive genotype, PI255774, used as controls. Salt treatment was conducted by irrigating each plastic pot from the bottom.

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    Differences in aboveground traits between salt-tolerant and salt-sensitive genotypes 14 d of salt stress. R = salt-resistant; S = salt-sensitive.

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    Foliar injury due to salt stress: 1 = healthy plants, 2 = first sign of leaf chlorosis, 3 = expansion of chlorosis on leaf surface, 4 = totally chlorotic leaf, 5 = first sign of necrosis, 6 = expansion of necrosis on leaf surface, and 7 = completely dead plants.

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    Distributions of the average number of dead plants per pot and leaf injury score.

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    Independent replicated trial involving the tolerant check (Tc: PI582468), the susceptible check (Sc: PI255774), and one of the salt-tolerant genotypes (T: PI349674) and salt-susceptible ones (S: PI582573) as identified in the previous experiment. The results from the independent replicated trials showed that the current methodology was stable.

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    Distributions of chlorophyll content of non–salt-stressed and salt-stressed plants, and relative salt tolerance for chlorophyll content.

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    Distributions of plant height of non–salt-stressed and salt-stressed plants, and relative salt tolerance for plant height.

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    Distributions of leaf biomass of non–salt-stressed and salt-stressed plants, and relative salt tolerance for leaf biomass.

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    Distributions of stem biomass of non–salt-stressed and salt-stressed plants, and relative salt tolerance for stem biomass.

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    Network analysis between traits evaluated under salt stress and non-salt conditions. Pathways were shown using solid lines when absolute value of Pearson's correlations was greater than 0.65.

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