Iranian seedless barberry is a species with high degree of contamination in in vitro culture. The current study was aimed to investigate the effects of mercuric chloride (HgCl2), sodium hypochlorite (NaOCl) and HgCl2, HgCl2 and 8-hydroxyquinoline, cefotaxime and streptomycin, HgCl2 and shoot type, HgCl2 and explant position, and HgCl2 and shoot color on the reduction of contamination. The results showed that the combined use of NaOCl and HgCl2 was more effective than single use of HgCl2, but the contamination rate was relatively high. Interestingly, the results showed that explants sterilized with 100 mg L-1 HgCl2 and cultured in media containing 150 mg L-1 8-hydroxyquinoline exhibited the lowest fungal contamination (15%), while those treated with 50 mg L-1 HgCl2 and cultured in 8-hydroxyquinoline-free media showed the highest fungal contamination (96%). Furthermore, treatment of 75 mg L-1 cefotaxime + 70 mg L-1 streptomycin exhibited no bacterial contamination compared to control with 58% bacterial contamination. Explants prepared from sucker and treated with 150 mg L-1 HgCl2 showed the lowest rates of fungal (16%) and bacterial (13%) contamination. The results also showed that explants collected from upper position had the lowest rates of fungal (20.86%) and bacterial (18.4%) infection. Explants taken from pinkish-colored shoots showed surprisingly the lowest rates of fungal contamination (13.33%), bacterial contamination (10%) and bud mortality (36.46%). In general, choice of explants from upper position of pinkish-colored sucker, sterilization of them with 100 mg L-1 HgCl2 for 5 min and their culture in medium containing 150 mg L-1 8-hydroxyquinoline can be recommended for reducing contamination.

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