Introduction
Sesame (Sesamum indicum. L) belongs to the Pedaliaceae family and is an annual and thermophilic plant known as the queen of oilseeds. Sesame is compatible with the climatic conditions of Iran, and due to its unique characteristics, it is possible to cultivate it second after wheat in arid and semi-arid regions. To utilize the maximum production capacity of sesame, implementing the proper agronomic practices such as plant density, optimal planting arrangement and selecting the appropriate genotype is inevitable.
 
Materials and Methods
To investigate the effect of planting arrangement and planting density on grain yield of two sesame genotypes, a factorial experiment based on a randomized complete block design with three replications was carried out in a hot and dry region situated in Behbahan (30° 36’ N; 50° 14’ E) in 2017 and 2018. The region is characterized as arid, and the average yearly precipitation (over a 30-yr period), which occurs mostly during the autumn and winter months, is 345 mm for the site. The annual mean temperature is 24 °C. The average temperature in 2017 was similar to the long-term meteorological data trend, while in 2017, the average temperature (22 °C) was lower. In this experiment, three factors included planting arrangement (cultivation of one and two rows on the ridge), planting density per unit area (including 20, 30 and 40 plants per square meter) and sesame genotypes Behbahan (local name) and Shavin cultivar were investigated. Data were subjected to ANOVA using SAS software (9.4 version). Because Bartlett’s test revealed homogeneity in the variance of all studied traits, data were presented as the mean values for both years. When an F-test showed statistical significance at, the protected LSD was used to separate the main effects, and the significant interaction effects were separated by the slicing method.
 
Results and Discussion
The results of grain yield, as the most important trait, indicated that in single-row cultivation, the maximum yield of the Behbahan genotype (1068 kg ha^-1) was obtained at a density of 20 plants per square meter. An increase in planting density caused a significant reduction in grain yield when Behbahan genotype was sown as single-row arrangement. In two-row cultivation, the Behbahan genotype responded positively to an increase in plant density and an increase in planting density was associated with a significant increase in grain yield. However, the maximum grain yield obtained in two-row cultivation with a density of 40 plants per square meter (919 kg ha^-1) was 16% lower compared to the superior treatment (single-row cultivation with a density of 20 plants per square meter). In the Shavin cultivar, the maximum grain yield was obtained in single-row (683 kg ha^-1) and two-row (610 kg ha^-1) arrangements at densities of 40 and 20 plants per square meter. The results showed that the average grain yield of the Behbahan genotype (851 kg ha^-1) was significantly higher than the Shavin cultivar (561 kg ha^-1).
 
Conclusion
Overall, in the Behbahan region and for the local genotype of Behbahan, as the superior genotype, a single-row arrangement and plant density of 20 plants per square meter is recommended.