The genus Rosa has involved about 200 species, only a few species among hundreds in the genus Rosa are scented, which involve Rosa damascenaMill., R. gallicaLinn., R. centifoliaLinn., R. moschataHerrm., R. bourbonianaDesportes., R. chinensisJacq., and R. alba Linn.Rosa has sixteen wild species in Iran of whichR. moschatawith the common names of Persian Musk rose, Nastrane Shiraz and Rose Anbar isdistributed in many local regions of the Iran [1-8].In addition,the Damask rose (R. damascena) is the most important species used to produce rose water, attar of rose, and essential oils in the perfume industry [6,9]. In Iranian traditional medicine, water rose of Damask rose and Persian Musk rose have been used to sedative, strengthen heart muscles, stomach, liver, spleen, nerves and intelligence [4,6]. This study aimed to evaluate and compare the floral scent headspace compounds and their content in Persian Musk rose vs. Damask rose as well as to provide useful information regarding the elucidation of biosynthetic pathways.

Plant materials

Flowers of Damask rose and Persian Musk rose were harvested from plants grown in Eram Botanical Garden (Shiraz – 57° 32' E, 29°37' N, Altitude 1486 m).

The headspace volatiles extraction

The headspace proceeded on the Combi PAL System that was provided with headspace auto-sampler, heater and agitator. The vial was heated to 45°C and retained for 20 min while being agitated; the temperature of the sampling needle and transmission line was 85°C.

Volatile oil analysis procedure

GC analysis was done using an Agilent gas chromatograph series 7890- A with a flame ionization detector (FID). GC-MS analysis was completed by using Agilent gas chromatograph, equipped with fused silica capillary HP-5MS column (30 m × 0.25 mm i.d.; film thickness 0.25 m) and coupled with 5975-C mass spectrometer. The constituents of the VOCs were identified by calculation of their retention indices under temperatureprogrammed conditions for n-alkanes (C8-C25) and the volatile oil on a HP-5 column under the same chromatographic conditions.

The chemical compositions of the volatile oils isolated from two species of Rosa including R. damascenaand R. moschata var. nastaranaflowers by using headspace extraction are presented in Table 1. The applied headspace GC-MS metabolite profiling resulted in the identification of a total of 31 and 21 compounds in Damask rose and Persian Musk rose respectively. The relative percentage of Phenylethyl alcohol wasas main compound in the both of rose species.The relative percentage of Phenylethyl alcohol was significantly increased to peak (54.15 ± 1.34%) at the full bloom stage of Persian Musk rose, but the highest quantity of this compound was 36.6 ± 2.05% in Damask rose. These results were in agreement with previous studies, who found a similar evolution of phenyl ethyl alcohol in the flower of R. hybrid and other genotypes of R. damascena[1,2,5,6,9,10].In the same way, Phenyl ethyl alcohol (2-Phenylethanol) is a prominent scent compound released from flowers of Damask roseand some hybrid roses such as Rosa ‘Hoh-Jun’ and Rosa ‘Yves Piaget’ [1,4,5].In the wild roses, from which R. hybridais resulting, floral scent are notice to be chemical signals between the plant and insects, the second including both pollinators and predators [9]. In previously study, it was show that the petal aroma such as Phenyl ethyl alcohols, which are known insect attractants for seed formation and dispersers [2,6].

Table 1: Chemical compositions of floral scent of two Roses.

The percentages of β-citronellol(35.53 ± 1.82%)were observed as second major component of Damask rose by headspace methods;however this compound was not detected in Persian Musk rose.α-Pinene was the representative monoterpene hydrocarbons detected in the floral volatile and accumulated in Damask rose (14.15 ± 1.02%), however a trace amount (0.56 ± 0.15%) of this compound was found in Persian Musk rose.Acetate esters such as geranyl acetate are important contributors to the aroma of different rose flowers. The highest geranyl acetate(4.9 ± 0.83%) was detected in Damask rose. No quantity of this compound was detected in Persian Musk rose.During flower opening, the level of emission of acetate esters (geranyl acetate) reached to maximal levels at full bloom stage, and decreased in the last stages [6].

In general, the present investigation showed that the flowers of Damask rose differed in fragrance characteristics compared to Persian Musk rose. In addition, it was shown that in both of rose species, petal aromas are dominated by Phenyl ethyl alcohols, which are known insect attractants for seed formation and dispersers. In conclusion, the genetic factors affect volatile oil composition in rose. Consequently, there was high variation in floral scent levels in the different rose genotypes suggesting a key role of the genotype in the biosynthesis of secondary metabolites.