Evaluation of biochemical and agronomic traits of sesame cultivars under application of phosphorus nano-chelate and chitosan fertilizers under irrigation cut-off

Introduction Drought is a major environmental stress affecting plant morphology, physiology, and biochemistry. Two management strategies for controlling drought stress include the use of nutrients and planting resistant plants. Chitosan, known as elicitors, is considered a natural biopolymer modified from chitin, which is the main structural component of squid pens, cell walls of some fungi and crab shells. Nanotechnology provides a new interdisciplinary venture into agriculture and food sciences by converging science and engineering. In addition, nanoparticles have potential applications in agriculture system, viz., the pollutants detection, plant diseases, pests, and pathogens, controlled delivery of pesticide, fertilizers, nutrients, and genetic material, and can act as nano architects in forming and binding soil structure. Sesame (Sesamum indicum L.) is a source of excellent vegetable oil (35-63%). Sesame is considered as drought tolerant crop, the productivity is heavily affected by severe drought stress mainly when it occurs during anthesis. Restricted water resources are considered as a limiting factor for irrigation applications around the world. Therefore, the present study aimed to evaluate the changes in the quality and yield traits of two sesame genotypes under drought stress and foliar application of chitosan and phosphorus nano-chelate in second cultivation. Material and methods The present study was conducted to investigate the changes in the quality and yield traits related to two sesame genotypes under irrigation cut-off and foliar application of chitosan and phosphorus nano-chelate in the second cultivation at research field of Shahed University in Tehran, Iran, during 2015-16 and 2016-17. The experiment was conducted during a two-year factorial split plot experiment based on completely randomized block design with three replications. The research farm is located at geographical characteristics of latitude 31° and 36’ and longitude 48° and 53’ and the height of this area from sea level is equal to 1050 m. The experimental factors including irrigation treatments at normal irrigation as control (non-stress), mild stress (irrigation cut-off at 50% seed ripping) and severe stress (irrigation cut-off at 50% flowering) were in the main plots and spraying treatments including non-spraying (control), phosphorus nano-chelate (2 ppt), chitosan (3 g.L-1), and the combination of phosphorus nano-chelate + chitosan and Oltan, and Naz single branch sesame cultivars were in the subplots. Number of capsules per plant, number of grain per plant, 1000-grain weight, grain yield, biological yield, oil percentage and yield, and fatty acids composition (oleic, linoleic, palmitic, and stearic contents) was investigated. Result and discussion The results showed that the highest 1000-grain weight was obtained in the first year of experiment and Oltan genotype (3.10 g) and the lowest mean was in the first year in Naz single branch genotype (2.51 g). The highest grain yield was observed in the second year of the experiment under without stress and mild stress conditions (irrigation up to seed ripening) and foliar application of phosphorus nano-chelate alone or combined with chitosan. In general, between different levels of irrigation treatments, severe stress (irrigation up flowering) resulted in a significant reduction in the grain yield, but mild drought stress (irrigation up to seed ripening), especially in terms of using chitosan and nano-fertilizer compounds, had a good grain yield. In the interactions effects of the year in drought stress, the highest seed oil percentage was obtained in the non-drought stress (normal irrigation) during the second year of the experiment (57.02%) and the lowest mean of this trait was observed in the second year under severe drought stress condition. Compared to the two cultivars, the highest oil yield was in Naz single branch cultivar (858.4 kg/ha) and the lowest mean of Oltan cultivar (731.7 kg/ha) was observed. The highest amount of saturated fatty acids (palmitic and stearic) was achieved in Oltan cultivar under non-foliar aplication. In contrast, the lowest content of linoleic fatty acid (unsaturated fatty acid) was observed in this treatment. In general, the application of phosphorus nano-chelate with chitosan increased the quantitative and qualitative characteristics of sesame seed yield and resulted in increased growth and quality growth factors in drought stress conditions. Summer planting of sesame plant is recommended in warm and dry climatic conditions (with end session drought stress) along with chitosan and phosphorus nano fertilizer. Conclusion Based on the aim of this research, the results showed that planting both Oltan and Naz single branch cultivars in the south Tehran climatic after wheat harvesting (as the second crop) had favorable results for grain and oil yield. In general, the results showed that co-application of phosphorus nano-chelate and chitosan fertilizers under mild drought stress (irrigation up to seed ripening) resulted in the moderate negative effect of drought stress and produced grain and oil yield. Also, the cultivation of this plant in warm and dry climates (similar to southern Tehran) under the mentioned conditions (co-application of phosphorus nano-chelate and chitosan fertilizers) is recommended under limited irrigation conditions (end of season drought stress).