Phytochemical and morpho-physiological changes of hyssop in response to chitosan-spraying under different levels of irrigation

Hyssop [Hyssopus officinalis L. subsp. angustifolius (Bieb.)] well-known for bearing essential oil-producing glands is a medicinal and aromatic plant with valuable properties for pharmaceutical, aromatic, and flavoring. The volatile oil from the aerial parts of hyssop harvested at flowering stage of growth is broadly applied in the cosmetics, pharmaceutical, and food industries In order to improve the growth, yield, and secondary metabolites production or active substances in hyssop, the experiment was done with factorial arrangement in randomized complete block design during two years (2016 and 2017). The Experimental treatments were three levels of the foliar spraying of chitosan at 0.0, 2.5, and 5.0 g/L under three levels of irrigation frequencies (6, 8, and 10 every days based on irrigation at 80-85% field capacity or F.C., 65-70% F.C., and 45-50% F.C., respectively). Results indicated that the chitosan-spraying at 2.5 g/L meaningfully raised the values of the canopy diameter, plant height, inflorescence height, numbers of auxiliary and flowering branches, dry herbal weight, and the concen-trations of photosynthesis pigments (Chl a, and Chl b) under different levels of irrigation frequencies. Increasing interval irrigation decreased some physiological characteristics such as biomass and photosynthesis pigments, however, the amounts of proline and carotenoid in both experimental years increased when the hyssop plants irrigated under reduced irrigation treatment. The highest values of the volatile oil content and yield were ob-tained from chitosan-spraying in reduced irrigation condition. The major constituents of the hyssop volatile oils analyzed by GC-FID and GC/MS were cis-pinocamphone, 8-pinene, trans-pinocamphone, myrtenol, bornyl ace-tate, 8-caryophyllene, and germacrene D, which the elicitation of hyssop with chitosan had positive impacts on the percentage of (cis- and trans-) pinocamphone, as the predominant compounds of the hyssop volatile oil, under reduced irrigation condition. In final, it can be concluded that the applied of chitosan decrease the negative effects of water shortages and improve the quantity and quality yield of H. officinalis under reduced irrigation condition.