INTRODUCTION

Salinity is a major environmental stress affecting plant growth and productivity. Salinity effects are more conspicuous in arid and semi-arid areas where 25% of the irrigated lands are affected by salts. The ability of plants to cope with salt stress is an important determinant of crop distribution and productivity. An excess of soluble salts in the soil leads to osmotic stress, specific ion toxicity and ionic imbalances (Munns, 2002) and the consequences of these can be plant death or yield losses in both crop species and medicinal plants (Rout and Shaw, 2001).

Ashraf et al. (2004) found that increasing salt concentrations caused a significant reduction in the fresh and dry masses of both shoots and roots as well as seed yield of Ammolei majus while reduced plant fresh and dry weight in Hyoscyamus niger. It was reported that salinity increased phenolic acids in Matricaria chamomilla plants (Kovaciket al., 2009). Belaqziz et al. (2009) showed that the aerial part oil content of Thyme species did not change with increase in external salt level. In Iran (mostly arid and semi-arid with saline-alkaline soil), there are >7500 plant species which most of them have valuable active substances. One of the most important species of them is Chamomile, an annual plant belongs to Asteraceae family, grows widely in various ecological zones of Iran (Afzali et al., 2006). Chamomile flowers have active substance that is called essential oil in which the most important constituent is chamazulene that is used widely in pharmaceutical, food, perfumery and flavouring industry (Glambosi and Holm, 1991). The annual world consumption of chamomile flowers is >4000 ton (Franz et al., 1986). Recently, its cultivation in some part of Iran such as Tehran, Lorestan, Khozestan, Fars and Isfehan provinces has started and several drugs have produced from its essential oil. This is very important to reduce, chemical drugs and increase individual health. In view of importance of Chamomile as potential medicinal herb which is being used for treatment a number of diseases. An experiment was conducted to assess the effect of salt stress on growth and essential oil of chamomile plants.

MATERIALS AND METHODS

This study was carried out at the Department of Medicinal Plants, Shirvan College of Agriculture, Ferdowsi University of Mashhad, Iran. Pot experiment based on randomized complete block design was carried out in green house conditions with six replications. Seed of chamomile (Matricaria chamomilla) were kindly provided by the Agricultural Research Center of Isfehan and were sown 1 mm deep in plastic containers filled with sand. After emergence, seedlings were transplanted to 15 cm diameter plastic pots containing one part loamy soil and two parts sand. Four levels of salinity including control (0 mM), 50, 150 and 250 mM NaCl and CaCl₂ in a 5:1 molar ratio were added to the modified Hogland nutrient solution (Maas and Poss, 1989). About 2 weeks after transplanting, seedlings were irrigated with saline water. To prevent shock to plants, irrigation started with 50 mM saline water and was increased by 50 mM every other day until reaching each salinity level.

In addition, the pots were flushed out with saline water every week to ensure homogeneity of salinity and nutrient supply in growth medium. This was checked by measuring the Electrical Conductivity (EC) of the drainage water. Water lost by evapo-transpiration of plants and pots was replaced by tap water. Plant height, plant dry weight, the number of branches per plant, the number of flower per plant and dry weight of flowers per plant were measured. Flowers dried at room temperature. A 10 g sample of dried and threshed flowers was mixed with 500 mL of distilled water in flask and mixture was distilled for 8 h using a clevenger type apparatus. The essential oil content was measured. Data were analyzed using SAS statistical program. Means were compared by Duncan’s multiple range tests at the 0.01 probability level for all comparisons.

RESULTS AND DISCUSSION

Salinity affects all growth traits of chamomile plant but the response of them varied. Plant height was greatly reduced by salinity (Fig. 1). Plant height at low (50 mM) and high level of salinity (250 mM) was decreased 12.6 and 44% compared to plant height of non-stressed plants at the end of season (Fig. 1).

The number of branch per plant significantly decreased as salinity increased. The number of branch at highest salinity (250 mM) was decreased 63% compared to control plants (non-stressed plants) (Fig. 2). The number of flower per plant also was reduced by salinity. The number of flowers per plant at low (50 mM) and high (250 mM) levels of salinity decreased by 16 and 69.2% compared to control plants, respectively (Fig. 3). Salinity had significant effect on flower dry weight per plant (Fig. 4). The effect of salinity on flower dry weight is greater than the effect of salinity on other traits so that flower dry weight of plants treated with 250 mM salinity decreased by 79.8% compared to non-stressed plants. Reduction in flower dry weight due to salinity may be a cumulative effect of decline in the number of flowers per plant.

Fig. 1:	Effect of different salinity concentration on plant height of chamomile plants. Each bar is the average of six replications. Vertical lines are standard error of the means

Fig. 2:	Effect of different salinity concentration on number of branches per plant of chamomile plants. Each bar is the average of six replications. Vertical lines are standard error of the means

Fig. 3:	Effect of different salinity concentration on number of flower per plant of chamomile plants. Each bar is the average of six replications. Vertical lines are standard error of the means

Salinity affects flowering time of plants. Flowering time of non-stressed plants started 50 days after plant transplanting while flowering time of plants treated by 250 mM salinity started 64 days after seedlings transplanting to pots.

Fig. 4:	Effect of different salinity concentration on flower dry weight of chamomile plants. Each bar is the average of six replications. Vertical lines are standard error of the means

Although, low level of salinity appeared to stimulate essential oil content, higher salt concentrations significantly decreased essential oil content (Fig. 5). Low level of salinity stimulates essential oil content.

However, higher salt concentrations significantly decreased essential oil content from 1.1% in control treatment to 0.6% at 250 mM salinity level. The results showed that plant height, number of branches per plant and flowers dry weight per plant was adversely affected with increasing salinity. Such an adverse effect of salt stress on growth traits has been observed in many plants. This reduction was closely linked to slower cell production and development of smaller stems. This is consist with the result of previous research which showed that high levels of salinity decreased plant growth due to a combination of a decrease in cell number and in cell size (De Herralde et al., 1998). Munns (2002) reported that suppression of plant growth under saline conditions may either be due to decreased availability of water or to the toxicity of sodium chloride.

It was hypothesized that growth reduction in response to salt stress was related to the restriction of the synthesis of plants growth promoters such as cytokinine and the increase in the production of the inhibitors such as abscisic acid (Ungar, 1991). Razmjoo and Sabzalian (2008) reported that the reduction in dry weight under saline condition may be attributed to inhibition of hydrolysis of reserved foods and their translocation to the growing shoots.

Other researchers have suggested that the reduction in growth parameters would be due primarily to the reduction of the water absorption and nutrient deficiencies (Bajji et al., 2002). Pessarakli and Tucker (1988) reported that a possible reason for growth reduction could be the grater reduction in uptake and utilization of mineral nutrients by plants under salt stress.

Fig. 5:	Effect of different salinity concentration on essential oil content of chamomile plants. Each bar is the average of six replications. Vertical lines are standard error of the means

They found that total nitrogen uptake of cotton plants decreased with increasing salinity reflecting primarily a dry matter reduction. The uptake of N in salt stressed plant might be competitively limited by Cl¯ (Michael et al., 1986). The essential oil content increased from 1.1% in control treatment to 1.3% (18% increasing) at low level (50 mM) of salinity (Fig. 5). Holtzer et al. (1988) believed that depending upon the plant species and plant genotype, stress can increase, decrease or have no effect on the levels of metabolites. Fatima et al. (1999) reported, limited stressful environments may stimulate the production of secondary metabolites such as essential oil. However, higher salt concentration significantly decreased essential oil content. Ashraf et al. (2004) showed that oil content in seed of medicinal plant Ammolei majus was decreased consistently with increasing salinity. The reduction in essential oil content may be due to disturbance in photosynthesis and carbohydrate production under stress condition and suppression of the plant growth (Flexas and Medrano, 2002). Dadkhah (2010) reported that salinity caused a significant reduction in leaf net photosynthesis consequently total carbon fixed in leaves of plant. Salinity stress imposes additional energy requirements on plant cells and less carbon is available for growth and flower primordial initiation and then less essential oil may be synthesized (Cheeseman, 1988).

CONCLUSION

Chamomile was moderately tolerant to salinity because salinity inhibited various growth parameters of this plant to various degrees. The flower dry weight per plant indicates a greater reduction due to increased salinity than other traits. Salinity >50 mM may reduce plant growth. Even if the production of the, essential oil was not affected by salinity, it was not recommended to cultivated chamomile exceed the critical values (50 mM in this study).

ACKNOWLEDGEMENTS

The researcher would like to express his appreciation for research deputy of the Ferdowsi University of Mashhad for financial support. The researcher is grateful to Mr. Hamid Eskandari BSc student of Medicinal Plant Production for his excellent assistance.