Evaluation of Drought Tolerance in Some Sesame (Sesamum indicum L.) Genotypes Based on Stress Tolerance Indices

Sesame is one of the oldest crops. Ethiopia is commonly accepted as the origin of domestic sesame. Sesame is a diploid (2n = 26) plant that grows as a bush. Sesame has a special place among oil plants due to its high oil content and quality as well as its high oil durability. Drought stress is a condition that cells and tissues are in a state where their inflammation is incomplete. In other words, dehydration occurs when the amount of transpiration exceeds the amount of water absorbed. Drought is one of the most important causes of declining agricultural productivity worldwide. Drought has destructive and detrimental effects on different stages of plant growth and reduces yield and yield components in sesame genotypes. Due to the serious problem of limited water resources and drought and its effect on yield reduction, this study to evaluate drought tolerance of sesame genotypes based on tolerance indices to identify and group sensitive, tolerant and resistant genotypes and select resistant genotypes and identify correlations of related traits. Drought tolerance was performed through field studies.

In order to evaluate the genetic diversity of different sesame genotypes under non-stress and drought stress conditions, an Augmented design was conducted in three blocks on 32 genotypes in the southeastern fields of Bojnourd in 2018. Genotypes used were obtained from Karaj Seed and Plant Breeding Research Institute in the amount of 1.5 grams per sample. In this experiment, one plot of land was allocated to the drought stress environment and the other to the stress-free environment. The distance between these two environments was considered to be five meters so that the humidity of the two adjacent environments did not affect each other. With the onset of stress flowering on the target medium, application and irrigation of the dry stress plot based on 200 mm and the non-stress plot based on 100 mm evaporation from the pan was performed. Cumulative evaporation from the pan determined the arrival time of irrigation in each of the environments. SAS PLUS software for calculating variance analysis, principal component analysis and mean comparison, S-PLUS software for drawing 3D and bipod diagrams, SPSS software for calculating the correlation of traits and correlation of tolerance indices and cluster tolerance analysis, respectively, from EXCEL Action was taken.

The studied genotypes showed a significant difference at the level of 1% probability in terms of traits measured under non-stress and drought stress conditions, which indicated genetic diversity and the possibility of selecting drought tolerant genotypes. Darab 14 genotype with 2344 kg.ha-1 had the highest grain yield and the Markazi genotype with 1148 kg.ha-1 had the lowest grain yield in non-stress conditions. Under drought stress conditions, Darab 14 genotype with 1360 kg.ha-1 had the highest grain yield which showed a 58% decrease compared to non-stress conditions. Also, the lowest grain yield was observed in Pakistani genotype with 624 kg.ha-1, which was 53% less than non-stress conditions. Based on the results, Darab 14 genotype showed the highest values of MP, GMP, TOL and STI tolerance indices and the correlation analysis between yield under stress and non stress conditions with drought tolerance indices also showed that STI, GMP, MP and TOL indices the most suitable indices are for screening sesame genotype. Using three-dimensional diagrams of YS, YP and STI, the genotypes were divided into two groups A and C under drought stress conditions. In order to investigate the correlation between different agronomic traits in comparing the grain yield of genotypes and determine their relationships, a simple correlation was calculated in both non-stress and drought stress environments, which showed a positive and significant correlation between yield and yield components in both conditions.

This study showed that comparison genotypes significant differences in terms of measurable traits in non-stress and drought stress conditions. Using MP, GMP, TOL, SSI and STI indices, genotypes can be separated to a large extent based on stress tolerance. Based on these indices and considering the performance in two environmental conditions Darab 14, Shaban and Yekehsaud is were identified as the most tolerant.