Determination of salinity stress tolerance threshold of quinoa genotypes under field conditions

Quinoa (Chenopodium quinoa Willd.) is a beneficial plant with high nutritional value with high tolerance to salinity and drought stress. Most of the experiments performed on the study of quinoa salinity stress tolerance in pot and greenhouse conditions were not comparable to the results of cereal experiment such as wheat and barley performed in field conditions. The purpose of this experiment is to determine the threshold value of quinoa to salinity stress under field conditions.

An experiment was performed as a split plot in a randomized complete block design with three replications on August 7, 2017 at Sadough Salinity Research Station of Yazd National Salinity Research Center. Experimental treatments including five quinoa genotypes including three quinoa lines (NSRCQE, NSRCQB, NSRCQC) with Titicaca and Sadough cultivars as subplots and irrigation water salinity at five levels of 2, 5, 10, 15 and 17 dS m-1 in the main plot. During the growing season, soil samples were taken from the plant root development area. Seed yield and yield components were measured. The percentage of saponin, seed vigor, 1000-seed weight and grain size were also measured.

The results of analysis of variance of the measured traits showed that the effect of salinity stress on plant height, 1000-seed weight and grain yield was significant at the level of 1%. The effect of salinity stress on grain size was not significant. Differences between genotypes in terms of plant height, grain yield, 1000-seed weight, biomass and grain size were significant at the level of 1% and panicle length and number of lateral panicles at the level of 5%. The interaction effect of genotype and salinity on biomass was not significant at 5% level and on other traits was not significant. The percentage of saponin between genotypes was significant at the level of 5%. The interaction effect of salinity and genotype on biomass and saponin percentage was significant at 5% level. The percentage of grain saponin increased significantly with increasing salinity in NSRCQB genotype and was not affected by salinity stress in other genotypes. Biomass of all genotypes except Titicaca was not significantly different up to salinity of 10 dS m-1. The highest biomass production in non-saline conditions was related to NSERCQE and Sadough cultivar and These two genotypes had the lowest decrease in biomass production with increasing salinity. Seed viability was not affected by salinity increase except in NSRCQB genotype seed vigour decreased by 15%. The lowest 1000-seed weight in non-saline conditions was related to NSRCQB genotype and the trend of 1000-seed weight loss with increasing salinity was similar to all genotypes and decreased by an average of 16%. The results of mean comparison showed that the highest yield at all salinity levels was observed in Sadough cultivar. Based on the results of the fitted linear equation, changes in quinoa seed yield to salinity showed that the salinity tolerance thresholds of quinoa genotypes were 4.3, 8.7, 4.1, 4.8, and 6.8 dS m-1 of electrical conductivity of saturated soil extracts, respectively. The soil and slope of the line were 3.5, 2.4, 0.1, 0.7 and 0.9%. Fifty percent reduction in wheat yield of Kavir and barley cultivars of Marvdasht cultivar has been reported at 15 and 20 dS m-1  of soil salinity, while Quinoa Sadough cultivar at 24 dS m-1  of electrical conductivity of soil saturated extract was 80% seed yield in non-saline conditions. Sadaogh cultivar not only have suitable agronomic characteristics and high production potential in saline conditions, but also has a higher salinity tolerance.

Quinoa has a higher tolerance to salinity stress than wheat and barley and can be a promising plant for using saline water and soil resources that are not economically viable for crop production. There is also a good variety among quinoa genotypes to select for using saline water.
Acknowledgments
This project has been done with the financial support of the Researchers Support Fund and the Agricultural Education and Extension Research Organization (AREEO).