عنوان مقاله [English]
Introduction: Water deficit is one of the major abiotic stresses, which adversely affects crop growth and yield. Plants use two different strategies, including drought avoidance and drought tolerance to grow under drought stress. Drought avoidance species are able to have a normal growth, which is due to: 1) efficient and fast metabolism, 2) high uptake of water and nutrients, and 3) little production of secondary metabolites under deficient water conditions. While drought tolerance species maintain their regular growth, under drought stress, by: 1) adjustment of osmotic potential, 2) changes in cell wall properties, and 3) production of antioxidants and secondary metabolites, these species under prolong drought, and irrespective of plant type, plant produces higher rate of secondary metabolites, as a non-enzymatic mechanism. Such products are able to maintain plant activities, under oxidative stress, and in the presence of high rate of reactive oxygen species. Medicinal plants, including Balangu (Lallemantia royleana Benth.), are cultivated across different parts of the world including Iran for food and biodiesel purposes. Investigating the effects of drought stress on the production of secondary compounds by medicinal plants is an important issue. According to the previous studies drought stress increases the production of secondary compounds affecting the quality of medicinal plants. This must be considered when developing tolerant medicinal plants under stress, especially if the quality of medicinal plants is of higher importance than their quantity. The tolerance of medicinal plants is different under stress. Due to the importance of drought and its effects on the growth and the quality of medicinal plants, in this research the effects of stress intensity and plant species on the growth and physiology (including the medicinal contents) of Balangu plants were investigated. To our knowledge, there are not much data on such effects. The objectives of this study were to investigate the effects of drought stress on: 1) Balangu growth and yield, and 2) Balangu physiology including the activities of morphological traits, yield components and oil yield and the production of antioxidant enzyme affecting plant medicinal content.
Materials and Methods: This study was conducted to investigate grain yield, yield components, and superoxide dismutase enzyme in three populations of Balangu (Lallemantia royleana Benth.) under drought stress. This study was conducted as a split plot experiment based on randomized complete block design with three replications at the experimental field of Shahed University during 2013-2014 growing season. The main factor consisted of four levels of drought stress (soil moisture content of -0.5, -3.5, -6.5 and -9 atm) and three Balangu Shirazi populations (Mashhad, Kerman and Taleghan) as sub-factors were considered. The main factor included drought stress levels at four levels (soil moisture content of -0.5, -3.5, -6.5 and -9 atm) and three Balangu Shirazi populations (Mashhad, Kerman and Taleghan) were considered as sub-plots. Measured traits were included root length, plant height, fresh and dry weight per plant, grain yield, grain yield components, mucilage percent and yield. In order to study the morphological traits, seven plants of each plot were selected with consideration of marginal impacts. About four square meters of each plot was harvested at maturity for determination of yield and its components.. The analysis of variance was does through SAS 9.12 statistical program and the means were compared by Duncan's multiple range test in 5% level.
Results and Discussion: A set of yield and biochemical properties of three different species of Balangu which were affected by drought levels were determined. According to the analysis of variance the yield and biochemical properties of Balangu were significantly affected by drought, and there were significant differences between three species. The results showed that drought stress had a significant effect on growth components, yield components, grain yield, and oil yield and superoxide dismutase enzyme. With decrease of soil water content, plant height traits (24.73 cm), the number of branches (5.44), fresh (17.36 g) and dry (3.80 g) weight of plant, 1000-grain weight (1.51 g), harvest index (6.41 %), grain yield (157 kg.ha-1) and oil yield (37.77 kg.ha-1) decreased. Root length and superoxide dismutase content increased by 24.02 and 66.63% under severe stress compared to no stress condition, respectively. The highest grain and oil yield was obtained in Mashhad population under drought stress. In relatively severe stress conditions, the grain and oil yield of Taleghan population increased with the mean of 315.75 and 86.5 kg.ha-1, respectively. Under drought stress levels, the lowest reduction was observed in some growth characteristics and grain yield of Kerman population.
Conclusion: Overall, the results of this study demonstrated that drought stress at flowering stage increased root length and superoxide dismutase enzyme of the studied populations. Furthermore morphological traits, grain yield components, harvest index, relative water content, grain yield and seed oil of Balangu populations were decreased. The highest seed and oil yield gained under moderate stress which belongs to Taleghan population and Mashhad population revealed the highest seed and oil yield under mild stress. Therefore, given the high stresses, introducing high-yielding populations under relatively severe stresses can lead to water use efficiency and irrigation management. Finally, the production of Taleghan population under relatively severe conditions such as arid and semi-arid cropping systems is recommended.