EVALUATION OF SALICYLIC ACID APPLICATION ON BIOMASS AND SOME MORPHOLOGICAL TRAITS OF DRAGONHEAD UNDER WATER DEFICIT CONDITIONS

Taha Izan¹, Yousef Nasiri², Farborz Shekari^2
1 Department of Natural Resources and Watershed of Piranshahr, Iran
² Department of Agronomy and Plant Breeding, Faculty of Agriculture, University of Maragheh, Iran

ABSTRACT

To investigate the effect of salicylic acid on some morphological traits and yield of dragonhead under water deficit conditions, a field experiment was done at Department of Natural Resource and Watershed of Piranshahr, Iran, in 2012. The experiment was arranged as a split plot, based on randomized complete block design with three replications. The experimental treatments consisted of three levels of irrigation after 40, 80 and 120 mm evaporation from pan as the main plots and three levels of the plant foliar application with salicylic acid as the subplots (0, 0.5 and 1 mM). The results showed that the irrigation treatments had significant effects on the plant height, the main stem diameter, number of lateral branches, floral branches length, number of leaves and biological yield. The maximum and minimum value of the mentioned traits respectively was obtained in the treatments of 40 and 120 mm. Salicylic acid effect on the biological yield was significant, so that the maximum biological yield (638 g·m^-2) belonged to the 1 mM salicylic acid application, while the control had 24.8 percent increase and had no significant difference with the 0.5 mM salicylic treatment. Interaction of the water deficit stress and salicylic acid on the number and length of floral branches in the plant was significant. The highest number of floral branches (mean 3.73 per plant) was observed in 40 mm evaporation from the pan with foliar application of 0, 0.5 and 1 mM salicylic acid and its lowest value was obtained with two levels, 80 and 120 mm, of evaporation from the pan without salicylic acid application.

Key words: Salicylic acid, Moldavian balm, yield, water stress, Flowering.

INTRODUCTION

Water deficit stress is one of the major limiting factors in the growth and production of agricultural products around the world. Drought, through the anatomical, morphological, physiological and biochemical changes, effects different aspects of the plant growth. The severity of the drought damage depends on the stress duration and growth stages. The drought stress reduces photosynthesis, stomata conductivity, biomass, growth and ultimately the plant yield [6, 8, 20]. Dragonhead (Moldavian balm) as an annual herbaceous plant from the Lamiaceae family and native of central Asia and domesticated in Central and Eastern Europe. All organs of the plant contain essence, nevertheless the flower and vegetative organs of dragonhead have more percent of essence. Dragonhead essence has antimicrobial and antitumor characteristics and it is used in pharmaceuticals, cosmetics and food industry. The dragonhead extract can be used to relieve headaches, colds, general body weakness and as a painkiller in neuralgia pains, gastric and renal spasms, to wash mouth and toothache treatment [19].

In drought stress conditions, turgor of cells is reduced since the development and growth of the cells is dependent on the turgor pressure, the growth of cells reduces and their size will be smaller [18]. As a result of water deficit, the plant height, dry weight of aerial organs, number of leaves and plant growth rate is reduced [1, 5, 14].

Salicylic acid is an important signaling molecule that makes the plant response to the environmental stresses. The substance as a non-enzymatic antioxidant plays an important role in the regulation of physiological processes in plants, and is involved as a messenger molecule in acquired resistance to the abiotic stresses such as drought, cold and heat [4, 23, 30]. The action mechanism of the salicylic acid against the stresses is related to its role in regulation of the antioxidant enzymes and the compounds containing active oxygen species in the plant [13, 26]. The salicylic acid use increases the value of polyamines in putrescine, spermidine and spermidine in plants that can help to integrate and maintain the cell membranes under the drought stress conditions [17].  Farooq et al. [10] reported that the use of salicylic acid with concentrations of 50, 100 and 150 ppm on the rice seeds in dry conditions increased the agricultural capacity of the plant up to 50 %. The use of salicylic acid in the wheat plant increased the photosynthesis [12] and chlorophyll content [27] under the drought conditions. Furthermore, salicylic acid increases the growth of barley shoot [21], wheat shoot [25], soybean roots and the concentration of lignin in the cell wall [11].

Given the importance of the medicinal plants cultivation and water resource constraints in most parts of Iran and the adverse effects of the water deficit stress on the plant growth and metabolism, study the possibility of the use of different ways to deal with the water deficit stress is necessary. Meanwhile, the use of plant growth regulators to improve and eliminate the effects of water deficit in plants is important. In this study, we aimed to investigate the effect of salicylic acid on some morphological, growth and yield traits of dragonhead as a medicinal plant under normal and water deficit conditions.

MATERIALS AND METHODS

The study was performed at the Department of Natural Resources and Watershed Research Station in Piranshahr-Iran with 51° and 36' longitude, 40° and 57' latitude and 1420 m height from the free water surface in 2012. The area has an annual average of 723 mm rainfall, the mean maximum and minimum temperature of 11 and 39° C respectively and a mean of 73% relative humidity. The experiment was conducted as split plots based on a randomized complete block design with three replications. The treatments consisted of three levels of water deficit stresses (40, 80 and 120 mm evaporation from pan) as the main plots and three levels of salicylic acid (SA) spray (0, 0.5 and 1 mM) as the subplots. The dragonhead seeds in six rows with a distance of 30 cm from each other and 15 cm on the row within the defined plots were planted in May of 2012. Irrigation was done immediately after the seeds planting. After full establishment of the plants in the ground (6 to 8-leaves stage of plants), the stress treatments were applied. The SA spray treatments were performed in two stages of stem elongation and before flowering. The studied traits such as plant height, number of lateral branches, number and length of flowering shoots, number of leaves in per plant, main stem diameter and biological yield. To calculate the biological yield, from each experimental plot a surface equal to one square meter was considered and all aerial parts of plants was taken and after dry them in the shade, weighed and recorded as a biological yield.

An analysis of variance was performed on all results using MSTAT-C software. The comparative of means was evaluated by Duncan's Multiple Range test (DMR) at a significance level alpha = 0.05.

RESULTS

The results of variance analysis showed that the effect of water deficit stress on the dragonhead plant height was significant (P<0.01). The mean comparisons showed that there was a significant difference in plant height among all drought stress treatments. The plant height was reduced by decrease of amount of water availability, so that the maximum height of the plant in the control and the least was observed in the severe stress treatment (Fig. 1). The results also showed that between the SA treatments and interaction of SA and drought stress levels were found no significantly difference (Tab. 1).

Based on the results, the water deficit stress had significant effect on the number of lateral branches per plant (Tab. 1). The sever water deficit stress (120 mm evaporation from pan) reduced the number of lateral branches, but the effect of the moderate stress (80 mm evaporation from pan) was not significant compared to the control. The minimum number of lateral branches (12 branches per plant), belonged to the severe stress that in compare to the control had 17.2% reduction (Fig. 2). The effect of SA and interaction of the SA and drought stress on the number of lateral branches in the plant were not significant.

 About the number of flowering stems, the results of analysis of variance showed that the main effects (P<0.01) and interactions (P<0.05) of drought stress and SA on this trait were significant. This means that the maximum number (73.3 flowering stem per plant), was attained in drought stress level after 40 mm evaporation from the pan and spray of zero, half and one mm values with no significant difference among them. The minimum amount of this trait was obtained in two levels of drought in 120 mm (31 flowering stem per plant), and 80 mm (33.6 flowering stem per plant), evaporation from the pan and without the use of SA (Fig. 3).

Based on the analysis of variance results (Tab. 1), the length of the flowering stem was significantly affected by the water deficit treatments, so that the length of the flowering stem under the moderate and severe stress was significantly reduced (Fig. 4). The last two treatments respectively, lead to 30.1 and 17.9 percent reduction of the flowering stem than the control. There was no significant difference between the two treatments of 80 and 120 mm evaporation from pan. The results also showed no significant effect of SA and its interaction with the drought stress on this trait.

According to the analysis of variance, the main stem diameter was significantly (P<0.05) affected by the water deficit stress (Tab. 1). So that the treatment of 120 mm evaporation from the pan, led to the significant reduction of the main stem diameter in compare to the control (Fig. 5). Although the 80 mm evaporation treatment led to 7.4 percent decrease of the stem diameter in compare to the control, but this difference was not significant. Two treatments of 80 and 120 mm evaporation from the pan had not significant difference. The results also showed non-significant effect of SA and its interaction with the drought stress on the defined trait.

The drought stress had significant effect (P<0.01) on the number of leaves in plan (Tab. 1). With increase of the water deficit stress, number of leaves of plant decreased, but this reduction only was significant in the severe stress. The highest and lowest number of leaves per plant belonged to control and 80 mm evaporation from the pan without significantly differences (1106 leaves per plant), and 120 mm evaporation from the pan (713 leaves per plant), respectively (Fig. 6). Effect of SA and its interaction with the water deficit stress on number of the leaves in this experiment was not significant.

The results of Table 1 showed that the effects of drought stress on biological yield was significant (P<0.01), so that with increase of stress, biological yield of dragonhead significantly reduced (Fig. 7). Biological yield average in the severe water deficit stress was 295.5 g·m^-2, the moderate drought stress 506 g·m^-2 and the control was 938.7 g·m^-2. On the other hand, the effect of SA on the biological yield was significant (P<0.05), so that the results of the means comparison showed that the use of 1 mM SA caused the maximum amount of biological yield (638 g·m^-2).

DISCUSSION

The results showed that the water deficit stress had significant effects on the morphological characteristics (plant height, number of lateral branches per plant, number of leaves, diameter of main stem, length of flowering stem, number of flowering stem), growth and biological yield of the dragonhead. The plant height, number and length of the flowering stems of dragonhead were decreased as a result of drought stress. Furthermore, the number of lateral stems, the main stem diameter and number of leaves were significantly decreased with increasing of stress intensity compared to the control. Similar results have been reported for sage [5], thyme [13] and chicory [28]. It is clear that the drought stress is a limiting factor in the early stages of the plant establishment. Since drought stress decreases the soil water content, the amount of water absorbed by the plants and plant leaf water content, so openness time of the stomata and the amount of the carbon dioxide uptake decreased and finally photosynthesis rate and plant growth reduced [22]. In addition to, water shortage in the plant leads to a reduction in cell turgor pressure. By reducing of the cell turgor pressure, the division, growth and development of cells particularly in the stems and leaves are reduced. The cell growth reduction leads to a decrease in the size of the plant organs, that it could be observed by the significant effect that it had on the plant height and on the number and the size of the plant leaves [1]. Water stress by reducing the soil water potential reduced the number, size and persistency of plant leaves [3].

Since the number of lateral branches per plant determines the number of leaves, thus reducing the number of lateral branches led to a reduction in the number of leaves on the plant. Emam and Rnjbar [9] have reported that in the drought stress conditions, stem diameter was decreased. Generally, the drought stress in vegetative stage reduces the size of the plant and therefore stem diameter reduces. The results also disclosed that the biological yield of the plant was significantly reduced under drought stress conditions. Since the whole shoot of dragonhead contains the essential oils, hence the biological yield of plant directly relates to the economic performance of the plant. So, every factor that reduce the biological yield of the dragonhead directly may reduce the worth of this plant. In general, the initial effect of drought stress in crop is biomass reduction [31].

Deficiency of water in plant reduces leaf water content and this reduction leads to diminution at the cell turgor pressure, stomatal conductance and leaf photosynthesis and finally decreases growth and yield [24]. It seems that a more transmission of produced assimilates from shoot to the roots, reduction of chlorophyll II and photosynthetic efficiency under water stress conditions could be another reason for the loss of biological yield in the plants [7, 29].

Based on the results, effect of salicylic acid and its interaction with the drought stress was significant on number of the flowering stems. Although under drought stress (Moderate or severe stress) conditions the number of the flowering stems significantly was decreased but the application of SA led to an increase in the number of flowering stems of dragonhead. The one of the reasons for this increase may be due to the osmotic pressure reduction after SA application in the plant cells [2]. It is reported that water content, dry weight, rubisco activity, superoxide dismutase activity and total chlorophyll in the plants that treated by SA was greater than untreated plants. Moreover, it is reported that at the drought stress conditions, SA had protected nitrate reductase activity, protein and nitrogen content of leaves of the plants compared to sufficient water conditions [27].

Also, our results discovered that application of 1 mM SA significantly increased the biological yield of dragonhead. Such a positive effect on the dry weight of marigold has also reported [16]. In the another study [15] it was reported that SA increased the number of leaves per plant and resulted to increase of amount of the absorbed radiation and photosynthetic rate and finally plant weigh had been increased.

CONCLUSIONS

Consequently the findings of present study revealed that the dragonhead plant as the most plants show appropriate physiological and morphological reaction to the water deficit stress. So that with occurrence of drought stress, the dry weight (biomass) decreased and some morphological and growth traits are affected. Although the use of SA could improve the plant growth and yield of dragonhead as well as its application especially with a concentration of 1 mM increased the number of flowering stems, as an effective characteristic on the quality of the dragonhead.

Accepted for print: 31.08.2015

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