The Effect of Irrigation Cut-off in Flowering Stage and Foliar Application of Spermidine on Essential Oil Quantity and Quality of Three Ecotypes of Cumin

Cumin (Cuminum cyminum L.) is an annual plant that commonly cultivated in arid and semiarid regions of Iran. The crop has a wide range of uses including medicinal, cosmetic and food industry. Cumin occupies about 26% of total area devoted to medicinal plants in Iran. However, cumin is seriously affected by the Fusarium wilt and blight diseases. The diseases usually increase under warm and wet conditions.
Control of the diseases incidence is a crucial factor for cumin production. Limited control of the diseases is provided by seed pre-sowing with certain fungicides such as benlate. Soil fumigation with methyle bromide can provide a control measure against the disease but may be limited application value for large scale production systems in the open field. In addition, methyle bromide is considered an ozone-depleting compound and has potential risk on the living environment and human health. Considering the environmental limitations of chemical fungicides, it seems appropriate to search for a supplemental control strategy .It was demonstrated that peak of the diseases incidence is occurred at flowering stage and irrigation cut-off in this time may be reduced the diseases density.
This experiment was conducted in a split-split-plot arrangement in randomized complete block design with three replications in research farm of Shahid Bahonar University of Kerman at 2014. The experimental treatments were irrigation (complete irrigation and cut-off the irrigation in flowering stage) assigned to main plots, foliar application of spermidine (0, 1 and 2 Mm) as subplot and cumin ecotypes (Kerman, Khorasan and Esfahan) that was randomized in sub-subplot. The seedbed preparation was made based on common practices at the location. Plots size under the trial was 4 m×3 m so as to get 50 cm inter row spacing in six rows. The ideal density of the crops was considered as 120 plant.m-2. As soon as the seeds were sown, irrigation continued every 10 days. Foliar application of spermidine was done at three stage (after thinning, before flowering stage and median of flowering stage). No herbicides and chemical fertilizers were applied during the course of the trials and weeding was done manually when necessary.
For extraction of cumin essential oil, from each plot, cumin seed were crushed at 50 g by electric grinder and suspended in 750 mL distilled water. Ground mass was subjected to hydro-distillation using Clevenger's apparatus. After 4 h, the essential oils were collected and dehydrated with Na2SO4 using the method of Guenther. Then essential oil yield and percentage was determined. GC/MS machine (Shimadzu GC/MS model QP5050) was used to specify the percentage of cumin essential oil components.
The results showed that irrigation and ecotype treatments had significant effect on essential oil percentage and yield, but there was not significant difference between foliar application levels in terms of the traits. The irrigation cut-off treatment caused to increase in percentage and decrease in yield of essential oil compared to complete irrigation conditions. The pharmaceutical value of medicinal plants depends on their secondary metabolite components and these materials are increased by stress. Therefore, drought stress caused to higher secondary metabolite including essential oil. The seed yield in comparison with essential oil percentage had more effect on essential oil yield. The traits were significantly higher in Kerman and Khorasan ecotypes than Esfahan. The highest essential oil yield (14.92 kg.ha-1) was gained in 1 Mm spermidine for Khorasan ecotype and the lowest (6.87 kg.ha-1) was observed in 0 Mm spermidine for Esfahan ecotype. p-Cymene, γ-Terpinene, Cuminaldehyde, p-Mentha-1,4-dien-7-ol and ɣ-Terpinene-7-al were contained the main components of essential oil in all the ecotypes. The most important component of essential oil in Kerman and Khorasan ecotypes was Cuminaldehyde and in Esfahan was ɣ-Terpinene-7-al. In essence, Kerman and Khorasan ecotypes had more similarity based on components of essential oil Similar compounds are reported by Iacobellis, (2005), Fanaei et al. (2006) and Jirovest and Buchbouer, (2005).
In essence, irrigation cut-off in flowering stage caused to significant increase in percentage and decrease in yield of cumin essential oil compared to complete irrigation conditions. Kerman and Khorasan ecotypes had higher essential oil percentage and yield than Esfahan. The most important component of essential oil in Kerman and Khorasan ecotypes was Cuminaldehyde and in Esfahan was ɣ-Terpinene-7-al.