Chitosan is a chitin-derived glosamine polysaccharide used as a bioelicitor to improve the biosynthesis of secondary metabolites. To investigate the effect of chitosan elicitor on the quantity and quality of essential oil of Hyssopus officinalis L. subsp. angustifolius Bieb. under different irrigation regimes, a factorial experiment was conducted in the Research Center for Medicinal Plants, I.A.U., Shahrekord in the crop year 2017-2018 in a RCBD with four replications. Experimental factors included different concentrations of chitosan at three levels of 0, 0.25 and 0.50 g/L and irrigation regimes including 4, 6, and 10-day intervals. The essential oil of the flowering branches of the plant was extracted by hydro-distillation using Clevinger apparatus and phytochemically analyzed by GC/MS. The main compounds of the hyssop essential oil were trans-pinocampone, cis-pinocampone, β-pinene, myrtenol, α-thujene, α-pinene, sabinene, delta-3-carcene and camphor. The results showed that the effect of different concentrations of chitosan and irrigation regimes on the yield of essential oil was significant (P <0.01). Different concentrations of chitosan had a significant effect (P <0.01) on the amount of some compounds essential such as trans-pinocampone, cis-pinocampone and myrtenol. In addition, different irrigation regimes had a significant effect on the amount of some compounds such as trans-pinocampone and cis-pinocampone (P <0.01) and sabinene, α-pinene and β-pinene (P <0.05). The results indicated that the maximum essential oil yield and pinocampone, as the most important consituent of hyssop is obtained from chitosan at 0.5 g/L and irrigation once every 10 days. It seems that chitosan foliar application and increasing the intervals of irrigation period can be effective in increasing the yield and quantitative and qualitative properties of hyssop essential oil.
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