عنوان مقاله [English]
Introduction: Iran’s climate is mostly arid and semi-arid, where water availability is a major problem. Water stress substantially alters plant metabolism, decreasing plant growth and photosynthesis and profoundly affecting ecosystems and agriculture, as well as human societies. Unfortunately, water deficiency is increasingly becoming a serious problem in agriculture in Iran whereas the national average annual precipitation is less than 249 mm. Recently, medicinal and aromatic plants have received much attention in several fields such as agroalimentary, perfumes, pharmaceutical industries and natural cosmetic products. Although, secondary metabolites in the medicinal and aromatic plants impressed conventionally by their genetic makeup; moreover their biosynthesis is strongly influenced by environmental factors. It means biotic and abiotic environmental factors affect growth parameter, essential oil yield and constituents. Abiotic environmental stresses like drought have the most effect on medicinal plants. In arid and semi-arid regions like south of Iran where water availability is a major limitation, using plants with low water consumption is one way to manage available water efficiently. Chamomile (Matricaria recutita L.) and chicory (Cichorium intybus) are annual plants belonging to Asteraceae family naturally widespread in west, northwest and south of Iran and their consumption has a long history in Iranian folklore medicine. Over 120 components have been identified in these plants essential oil, while, chamazulene, camphor, bisabolol oxides A and B, farnesene and ά- bisabolonoxide are the most important ones.
Materials and Methods: This study was conducted in Research Farm of Islamic Azad University, Shoshtar Branch, Iran during 2010-2011 in order to evaluate the effects of water stress levels on growth, photosynthesis and essential oil yield of German chamomile (Matricaria recutita L.) and chicory (Cichorium intybus). Two water stress levels viz. medium at 75% field capacity (FC) (I 75) and sever at 55% FC (I 55) were included in the study, while 90% FC (I 90) was taken as control. The experiment was laid out based on a randomized complete block design (RCBD) with four replications. Net plot size was 2 m × 2 m having plants density of 120 chamomile m-2 and 100 chicory m-2. Sowing was done manually on well prepared seedbed in November 2010 and plants were harvested in June 2011. Irrigation treatments were started three weeks after seed sown when seedling started their growth and development. Chamomile and chicory essential oil percentage, essential oil yield, dry weight, photosynthesis and chlorophyll content were assayed in this research.
Results and Discussion: Results showed that drought stress had significant effect on photosynthesis, chlorophyll a concentration, plant height and dry matter yield of chamomile and chicory. The Lowest flowers dry yield of chamomile and leaf dry weight of chicory obtained from severe drought stress level (47 and 195 gr m-2). The highest essential oil yield of chamomile (56.6 g m-2) and chicory (226.9 gr m-2) showed in mild drought stress treatment. Results indicated that medium drought stress increased seconds’ metabolites concentration and essential oil yield of chamomile and chicory. Important second compound in chamomile and chicory essential oil were camphor, α-pinene, β-pinene, ά-bisabolol and chamazulene. Drought stress decreased photosynthesis rate and minimum photosynthesis rate in chamomile and chicory were 9.0 mgl CO2 m-2 s-3 and 12.0 mgl CO2 m-2 s-3 under severe drought stress treatment. In chamomile the lowest chlorophyll a content showed in mild and severe drought stress treatments (1.1 and 1.2 mg g-1). Minimum chlorophyll a and b content of chicory obtained from severe drought stress treatment (0.7 and 1.02 mg g-1 respectively).Results of the study clearly elaborate that severe drought stress hampered the growth, photosynthetic rate and lowered the oil yield of chamomile, whereas medium drought stress (irrigation at 75% of FC level) improved the growth and oil productivity even more than well watered conditions. Although, severe water stress observed sizeable rise in essential oil contents but due to drastic reduction in flower or leaf dry weight, severe drought stress exhibited lowest oil yield in chamomile and chicory.
Conclusion: The results of the study clearly elaborated that medium drought stress (irrigation at 75% of FC) enhanced the essential oil productivity, while severe water stress (55% FC) decreased chamomile and chicory growth, photosynthesis rate and essential oil yield. Moreover, under drought stress quantity of chamomile and chicory oil was improved. Therefore, chamomile and chicory should be irrigated at 75% FC level to attain higher essential oil yield.