Investigating the effect of different humidity conditions on some morphological traits of the root and shoot in sesame (Sesamum indicum L.)

Drought stress has great effect on the yield and quality of agronomy crops and increasing the world population and global changing of the climate, on the other hand, making this more important. Sesame (Sesamum indicum L.), is one of the most important oil crops that is planting in many rejoins of the world. There is no detailed study about sesame interaction against drought. In this study, the shoot and root morphological traits of two sesame genotypes, which were sensitive and tolerant against drought stress, was investigated in different humidity condition.

two sesame genotypes Darab1 (tolerant) and Moghan (sensitive), were planted in PVC tubes with the height of 100 cm and diameter of 30 cm and after perfect establishment (35 days after planting) of plants up to maturation, humidity treatments were carried out as the amount of 100, 50 and 25 percent of the field capacity. The factorial experiments on the base of complete randomized design with three replications and three plant per replication were carried out. Traits under investigating were contain: plant height, capsule number, stem diameter, length and diameter of capsules biomass of the shoot, and 100 seeds weight, also root traits such as root length and diameter under the crown, volume and fresh and dry weight of the root were measured.

Reciprocal effect of irrigation and genotype, was significant for all traits related to the both of shoot and root. Also, drought stress caused decrease in the value of traits plant height, capsule diameter, capsule length and number, fresh weight of the stem and also, fresh weight and dry weight of the root. In genotype of Darab1, root volume and diameter indicated no significant decrease compared with the control at irrigation treatment of the amount of 50 percent of the FC, and in irrigation treatment as the amount of 25 percent of the FC, Darab1 showed higher values of the volume and diameter of the root compared with Moghan. Root length, had its maximum value at irrigation regimes as the amount of 50 and 25 percent of FC, and in trait of root area at irrigation treatment of 50 percent, this genotype had the maximum value. Results showed that genotype Darab1, with compatibility of root system against drought stress, was able to tolerance unfavorable condition.

Considering the result of this study and the previous ones about the role of the root system in plant tolerance against drought, root characters are good criterion in selecting plant genotypes suitable for planting in water deficit condition and using in breeding programs of the sesame. Genotype of Darab1 owing favorable root system was able to tolerance unfavorable humidity condition and preserving the yield in stress condition.