Evaluation of relationships between some developmental and biochemical traits of soybean under salt stress by canonical correlation analysis and ideal genotype selection index at seedling stage

Introduction

Soybean, like other legumes, is in the group of plants sensitive to salinity, and considering that, like other crops, it faces a decrease in yield under salinity stress conditions, therefore, it is important to discover the mechanisms that control the response of soybean to salinity and to select cultivars that do not face a decrease in yield under salinity conditions, from the aspect of agricultural and economic productivity. This study aimed to determine the relationships between traits related to seedling growth and biochemical traits and identify soybean genotypes that are tolerant to salt stress.

Materials and methods

Two separate randomized complete block designs, one for the control treatment with zero salinity and the other for the salinity treatment with 150 mM sodium chloride, were used to evaluate 30 soybean genotypes under hydroponic culture under greenhouse conditions at the seed and plant improvement institute, Karaj, Iran, in 2016. In this study, the following traits related to seedling growth and biochemical traits were investigated: leaf area index, stem height, root length, fresh and dry weight of both shoots and roots, chlorophyll content, salt injury index, the amount of sodium and potassium in shoots and roots, the ratio of potassium to sodium in shoots and roots, and the transfer ratio of sodium and potassium from roots to shoots.

Results and discussion

AMMI variance analyses showed that genotype, environment (salinity treatments), and their interactions significantly affected soybean shoot weight changes. The results showed that the effect of the environment on the shoot fresh weight was high. The changes in traits under stress conditions with normal conditions showed that we observed a decrease in most traits, except for the salt injury index, amount of sodium and potassium in shoots, amount of sodium in roots, and the transfer ratio of sodium and potassium from roots to shoots. Fresh and dry weight of shoots in both conditions had a positive and significant correlation with shoot height, root length, leaf area, fresh and dry weight of roots, and potassium to sodium ratio of shoots under stress conditions, and they also had a significant negative correlation with salt injury index and root sodium content under stress conditions. Canonical correlation analysis under salt stress conditions for the set of traits related to seedling growth in contrast to the set of biochemical traits led to the creation of a significant non-correlated variable, the first pair of variables were called "shoots characteristics" and "amount of sodium accumulation in shoots and the salt injury index" respectively. To select the best genotypes using all the examined traits under stress conditions, the selection index of ideal genotypes was used. Based on the SIIG index, the genotypes Lee, Vernal, LYON, l504, Crawford, and Douglas, which had the highest SIIG value, were among the genotypes that were tolerant to salinity.

Conclusion

When separating genotypes into tolerant and sensitive categories, both the canonical correlation analysis and ideal genotype selection index methods were very similar. Based on these traits, the genotypes were divided into tolerant and sensitive groups. Except for the chlorophyll content trait, the reactions of the remaining traits in the tolerant and sensitive genotypes were the same. The results showed that soybean genotypes tolerant to salinity have higher seedling height, leaf area, and shoot weight; on the other hand, they often have a lower salinity injury index and lower sodium content in the shoot.