Effect Mycorrhizal Fungi on Reduction of Drought Stress Effect in Some Growth Traits of Sesame (Sesamum indicum L.) Genotypes

Introduction Sesame (Sesamum indicum) plays an important role in human health because of its high oil capacity (47 - 52%).. Arbuscular mycorrhizal symbiosis protects host plants against the detrimental effects of drought stress through mechanisms of drought avoidance. Strategies of drought avoidance in mycorrhizal plants rely on the ability to maintain an adequate hydration status on the level of whole plants as characterized by relative water content. So the aim of current study was to evaluate the symbiosis effect of two different species of mycorrhizae fungi on yield and physiological characteristics of sesame landraces under different drought stress levels in Urmia. Materials and Methods This experiment was conducted in 2014-2015 by using factorial split plot based on randomized complete block design with three replications in the research field of Urmia agricultural high school with 12 Km distance from Urmia. The main plot factor was consisted of different irrigation levels: normal irrigation (irrigation after 70 mm evaporation of crop (ETC)), moderate drought stress (irrigation after 90 mm evaporation of crop (ETC)) and severe drought stress (irrigation after 110 mm evaporation of crop (ETC)). Also three levels of Sub plot factors included two species of mycorrhizae fungi) Glomus mosseae, Glomus intraradices) and no -inoculation (control). Sub-sub plot factorss consisted of eight landraces of sesames (named Jiroft13, Zanjan Tarom landrace, Moghan landrace, Naz of several branches, TC-25,TS-3, Darab 14 and Dashtestan 5). Then Leaf Area Index (LAI), Total Dry Matter (TDM), Leaf relative water content (RWC), Specific leaf area (SLA), Specific leaf weight (SLW), Leaf Area Ratio (LAR), Leaf Weight Ratio (LWR) of different landraces calculated using SAS and MSTATC. To compare the means, Tukey's test at 5% probability level was used. Results and Discussion The results of the experiment showed that with increasing the levels of drought stress, RWC, LAI, seed yield and LAR decreased significantly. Severe drought stress reduced RWC, LAI and LAR about 30 and 75 and 50 percent, respectively. The reason of LAI reduction in drought stress conditions was due to decreasing cellular turgecense and falling leaves at the onset of reproductive growth stage. By inoculation with mycorrhizal fungi species Glomus mosseae and Glomus intraradices in compare to non-inoculation, seed yield improved about 33 and 11 percent, respectively. It may be due to the effects of mycorrhizae on absorption of phosphorus and sulfur, lasting more leaves on the plant, maintaining and increasing the leaf size and improving the photosynthesis by more chlorophylls. Mycorrhizae application caused an increase in seed yield and improvement of physiological traits in compare to no inoculation (control). Among different sesame landraces studied in this research, Moghan and Zanjan Tarom landraces showed a superiority in seed yield, LAI, RWC, LWR and the first lateral stem above ground in compare to other landraces. It was also found that a significant proportion of seed yield reduction caused by drought stress was due to deterioration of physiological traits studied in this study. Conclusion The results showed that increasing LAI caused more absorption of light and ultimately seed yield incensement. Among different sesame landraces studied in this research, Moghan and Zanjan Tarom landrace showed a superiority in yield and physiological indices in compare to other landraces. Also it was found that a significant proportion of yield reduction caused by drought stress was due to deterioration of physiological indices studied in this study. Based on the results of this study, application of Mycorrhizae species, especially G. mosseae, is recommended as an effective approach for increasing seed yield and improvement physiological traits in sesame