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Research Project: Genetic Improvement of Crop Plants for Use with Low Quality Irrigation Waters: Physiological, Biochemical and Molecular Approaches

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Title: Variable salinity responses of 12 alfalfa genotypes and comparative expression analyses of salt-response genes

Author
item Sandhu, Devinder
item CORNACCHIONE, MONICA - National Institute Of Agricultural Technology(INTA)
item Ferreira, Jorge
item Suarez, Donald

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/17/2017
Publication Date: 2/22/2017
Citation: Sandhu, D., Cornacchione, M.V., Ferreira, J.F., Suarez, D.L. 2017. Variable salinity responses of 12 alfalfa genotypes and comparative expression analyses of salt-response genes. Scientific Reports. 7:42958. doi: 10.1038/srep42958.

Interpretive Summary: Salinity is one of the most important abiotic stresses that adversely affect plant growth and productivity globally. In order to tackle this complex problem, it is important to link the biochemical and physiological responses with the underlying genetic mechanisms. We selected 12 genotypes based on biomass yield and ion composition, cloned them and evaluated them for their salt tolerance under long-term salinity stress. The most salt tolerant genotypes were top performers for shoot biomass accumulation and exhibited the least effect on shoot number and height. There was a net reduction in shoot Ca, Mg, P, Fe, and Cu, while shoot Mn and Zn increased significantly under salinity. Some salt tolerant genotypes accumulated low level of Na and Cl, but ionic composition alone could not explain plant performance under salinity. Salinity reduced leaf area and stomatal conductance. Interestingly, salinity increased chlorophyll and antioxidant capacity in all genotypes. Antioxidant activity, however, did not correlate well with salt tolerance. Genotypes that displayed the highest salt tolerance, showed increased expression of important genes involved in various components of salt stress mechanism. Expression analysis allowed us to partition complex salt tolerance mechanism into individual components, which may provide better precision in manipulating salt tolerance in alfalfa. Combining different components of the salt tolerance mechanism may lead to development of superior salt tolerant cultivars. Improving salt tolerance in alfalfa will not only improve biomass yield, but also will provide incentives to expand the use of alternative/degraded waters and saline soils unfit for traditional crops, thus allowing alfalfa to be cultivated in new lands. Our results will help alfalfa breeders and geneticists to develop new salt-tolerant alfalfa varieties, which in turn will allow farmers to increase crop yield in marginal lands, and to use cheaper recycled waters.

Technical Abstract: Twelve alfalfa genotypes that were selected for biomass under salinity, differences in Na and Cl concentrations in shoots and K/Na ratio were evaluated in this long-term salinity experiment. The selected plants were cloned to reduce genetic variability within each genotype. Salt tolerance (ST) index of the genotypes ranged from 0.39 to 1. The most salt-tolerant genotypes SISA14-1 (G03) and AZ-90ST (G10), the top performers for biomass, exhibited the least effect on shoot number and height. SISA14-1 (G03) accumulated low Na and Cl under salinity. Most genotypes exhibited a net reduction in shoot Ca, Mg, P, Fe, and Cu, while Mn and Zn increased under salinity. Salinity reduced foliar area and stomatal conductance; while net photosynthetic rate and transpiration were not affected. Interestingly, salinity increased chlorophyll and antioxidant capacity in most genotypes; however neither parameter correlated well to ST index. Salt-tolerant genotypes showed upregulation of the SOS1, SOS2, SOS3, HKT1, AKT1, NHX1, P5CS1, HSP90.7, HSP81.2, HSP71.1, HSPC025, OTS1, SGF29 and SAL1 genes. Gene expression analyses allowed us to classify genotypes based on their ability to regulate different components of the salt tolerance mechanism. Pyramiding different components of the salt tolerance mechanism may lead to superior salt-tolerant alfalfa genotypes.