The effects of different plant growth regulators on micropropagation of Juniperus excelsa L.

Background and objectives
Juniperus excelsa L. is one of the most important coniferous species that has wide habitats in Iran. J. excelsa is habitats in large areas of the mountains of Iran at the altitudes 750 to 3400 m. The juniper habitats of the world are mostly spread in semi-arid areas with limited humidity, and this condition also prevails for juniper habitats in Iran. High tolerance in the most difficult climatic, geological and hydrological conditions is one of the distinctive features of J. excelsa and it has high medicinal, antimicrobial, antifungal and antibacterial properties. Environmental studies of juniper habitats report the cessation or insufficient regeneration of juniper in many of its habitats. The seed production cycle (seeding period) of juniper is long and usually between 4 and 8 years, and as a result, seeds are produced every year. It is not produced and is not available in sufficient quantities. Also, factors such as poor pollination, high amount of empty and dead seeds and low percentage of survival and growth of seeds, long period of dormancy in seeds, and non-establishment of remaining juniper seedlings due to excessive livestock grazing, have put the regeneration of this species in jeopardy. As a result, the vegetative reproduction of this organism is crucial, and according to global studies, it seems that this important forest species is on the verge of extinction. By reviewing the literature, it seems that plant tissue culture is an efficient tool for the continuous production of valuable and endangered forest species. Also, this method may be the only alternative that allows the simulation of rare and endangered populations of woody plants, including J. excelsa. The use of new technologies for the reproduction of J. excelsa based on micropropagation is of particular importance today in the face of climate change, which is a great threat to natural forest ecosystems. Therefore, the main goal of this research is to optimize salt concentration and plant growth regulators in the regeneration and rooting of J. excelsa in vitro and its mass production in a short time.
Methodology
In this study, the effect of plant growth regulators BAP, KIN and TDZ at four levels (0, 1, 2 and 5 mg L-1) separately and in combination with IAA at three levels (0, 1/ 0 and 0.5 mg L-1) were investigated in MS culture medium. In addition, for rooting, the effects of 6 different basic media (OM, MS, DKW, WPM, 1/2 MS, and 1/4 MS) containing IBA (0.5 mg L-1) were investigated.
Results
The results showed that the maximum regeneration for J. excelsa area (94.43%) was achieved in the MS culture medium and in the combination of KIN (1 mg L-1) with IAA (0.1 mg L-1). Also, the maximum average number of branches was observed in the culture medium without cytokinin in the MS culture medium for J. excelsa. The maximum shoot length was recorded in the combination of KIN (1 mg L-1) and IAA (0 mg L-1). The highest rooting percentage (33.33%) was obtained under the conditions of induction of plant growth regulator IBA (0.5 mg L-1) and cultivation in OM culture medium for one week.
Conclusion
Some woody plants, especially the endangered species, are facing reproductive and regeneration problems in their natural habitats. Conventional vegetative and reproductive methods do not lead to successful propagation of these species. The results showed that DKW culture medium supplemented with BAP (1 mg L-1) and IAA (0.1 mg L-1) is the best and most effective culture medium for the propagation of J.excelsa branch. In addition, the best culture medium for J.excelsa rooting is related to the induction of plant growth regulator IBA (0.5 mg L-1) in OM culture medium for one week.