Changes in the oil fatty acids composition of rapeseed cultivars under drought stress conditions

Plants are exposed to various environmental stresses, such as drought, salinity and high or low temperatures. Amongst, drought is the most serious problem for global agriculture, approximately affecting 40% of the world’s land area (Zhang et al., 2014). Furthermore, climate change is likely to lead to changes in global temperature and precipitations patterns in some parts of the world, which will have a dramatic impact on crop growth and productivity (Trenberth et al., 2014). Thus, there is an urgent need to develop varieties that can maintain optimum yield levels under drought conditions. Water is one of the major limiting factors affecting plant growth, development and yield, especially in arid and semi-arid regions, where plants are often exposed to periods of water shortage (drought stress).Iran is a vast country with different of climate conditions. It is estimated that approximately 85% of Iran is located in arid, semi-arid or hyper arid regions. It has been reported that annual rainfall, number of rainy-days and monthly rainfall have been significantly decreased in the last few decades, in arid and semi-arid regions of the world and Iran (Modarres & da Silva, 2007). Among the oilseed crops, Brassica species are more affected by drought, as these crops are mainly grown in arid and semiarid areas. Oilseed rape growth and seed production decrease by drought stress. Under drought stress, the percentage of saturated fatty acids decreased, that could be explained by a shorter growing period, and oil yield also decreased. Fatty acid metabolism may be involved in plant adaptation to drought stress. The objective of the present study was to evaluateoil fatty acids composition of Rapeseed cultivars under drought stress conditions in different growth stages
The experiment was conducted as a split-plot based on a randomized complete block design with three replications at Yazd, Iran in 2011-2012 growing season. Irrigation treatments including control (irrigation after 80 mm evaporation from evaporation pan class A) and drought stress (irrigation withholding starting from stem elongation, flowering and silique formation stages until physiological maturity stages) were allocated to the main plots and three winter type rapeseed cultivars (GKH2005, Opera and Okapi) were considered as the subplots. The measured traits included Oil percentage, Oleic acid, Linoleic acid, Linolenic acid Palmitic acid, Palmitic acid, Gadoleic acid, Stearic acid, Arachidonic acid, Palmitoleic acid, Erucic acid, seed yield and oil yield.SAS statistical software used for data analysis and means were compared with LSD test at 5% probability level.
The results showed that oleic acid content of rapeseed oil varied from 64 to 68 percent and linoleic acid varied from 15 to 18 percent. Among the three saturated fatty acids (palmitic, stearic and Arachidonic), the irrigation effect was only on Arachidonic acid and among the six unsaturated fatty acids (Palmitoleic, oleic, linoleic, linolenic, Gadoleic and Erucic) the effect of irrigation only on oleic fatty acids, Linoleic and linolenic were meaningful. Irrigation withholding from developmental stages significantly increased oleic acid compared to control treatment, while the amount of linoleic acid decreased significantly. The response of three rapeseed cultivars to irrigation levels for Linoleic fatty acid was different and GKH2005 had the higher linoleic acid, under all of drought stress treatments. Among three cultivars, the highest seed yield was observed in GKH2005 (2211 kg.ha-1).
In general, it seems the withholding irrigation resulted in enhanced oleic acid compared to linoleic, in fatty acids composition of rapeseed oil. Moreover, among rapeseed varieties, there was a significant difference in oil fatty acids content. Our findings indicated that GKH2005 had higher seed yield and good quality of fatty acid oils in drought stress than other cultivars.