Investigate the effects of drought stress on some physiological parameters, percentage and yield of essential oil of Salvia sahendica

IntroudationSalvia sahendica is a perennial native odorant plant of Iran with a right stem, crustal and about 90-40 cm height. Due to the importance of the use of Salvia sahendica in various pharmaceutical, food and sanitary industries, and because of its potential for cultivation in stressful climates, this plant has attentions to cultivate in low-yielding lands. Until now, there is not a comprehensive study on the response of Salvia sahendica to drought stress. Therefore, in order to evaluate the possibility of production and development of its cultivation under drought stress conditions, this research was carried to investigate the effects of drought stress on some physiological parameters, percentage and yield of essential oil of Salvia sahendica and determining the tolerance threshold of this plant to stress in 1395 in field conditions. Material and MethodsThis experiment was conducted at the research farm of Mobarakeh steel complex which located at 40th kilometers of southwest of Isfahan, at latitude of 32˚ 21′ northern and longitude of 51˚ 27′ eastern. After field preparation, the plants were cultivated in plots with size of 1.5 × 1.5m by 50 × 50 cm spacing in a randomized complete block design with three replicates and 9 plants per replicate. At the beginning of planting, all plots were irrigated three times a week for two weeks until the plants were established. Then, the effect of various irrigation intervals including 4 (as control, which is traditionally the optimum irrigation rate of plant in studied area), 8, 12 and 16 days intervals were applied. At the end of the summer, a sample was taken from the cultivated plant. The plants were fractioned to roots and shoots and some physiological and biochemical indices including, relative water content of leaves (RWC), water potential of leaves, total chlorophyll and chlorophyll a and b, proline and soluble sugars contents, electrolyte leakage, the essential oil percentage and yield were determined. Statistical analysis was performed on the data using MSTAT-C software at 5% level and the correlation between traits was determined by SPSS software. Results The results of analysis of variance showed that the effects of different levels of irrigation intervals on water potential of leaves, relative water content of leaves, soluble sugars, electrolyte leakage, percentage and essential oil yield were discriminated at 1% statistical level while on proline and total chlorophyll, chlorophyll a and b contents at 5%. Based on the results of the comparison of the mean, by increasing irrigation interval from 4 to 8 and 12 days, the differences in the means of all investigated parameters were not significant and only in 16 days irrigation interval the noted parameters differed significantly(pr<0.05). The highest amount of RWC (95%), chlorophyll a, b and total chlorophyll were 2.47, 1.32, and 0.98 mg.g-1 respectively in control treatment. The highest water potential of leaves (-1.78 MPa), proline accumulation (3.1 mg.g-1) and electrolyte leakage (57.7%) were observed in16- day irrigation interval. Maximum amount of soluble sugar, percentage and essential oil yield by the mean of 2.55 mg.g-1, 0.3% and 14.3 kg.ha-1 respectively were obtained in the 12-day irrigation interval. The correlation of traits showed a negative relationship between chlorophyll a, chlorophyll b with proline, soluble sugars, percentage and essential oil yield. Conclusion By considering that non-significant differences were observed in stress resistance indices of this plant up to 12-days interval in comparison with control, it can be concluded with 95% confidence that an optimal irrigation interval for using of this plant in areas arid and semi-arid regions is 12 days irrigation interval, which saves irrigation water. Also, the results of this study showed that Salvia sahendica resisted to water stress by increasing accumulation of proline and soluble sugars (osmotic regulation). Therefore, the accumulation of proline and soluble sugars can be considered as a sensitive indicator for determining the degree of leaf turgidity. Also, in order to produce the highest amount of essential oil from Salvia sahendica, the mild stress (12-day irrigation) can be used.