Nowadays mass reproduction of many species of ornamental plants, e.g. chrysanthemums, is conducted in in vitro cultures. Plants are propagated in specific laboratories under strictly controlled light and temperature conditions, irrespective of season and climate zone. Micropropagation is performed under sterile conditions, on an autoclaved nutrient medium poured into glass vessels or plastic containers. Plant parts which are transferred on the medium are known as explants. Work with disinfected plant material is only possible under aseptic conditions under HEPA filtered air in laminar flow cabinets. For this reason also the initial plant material collected from the place of cultivation (garden, greenhouse) needs to be disinfected before the initiation of an in vitro culture and micropropagation. Ethanol, sodium or calcium hypochlorite or mercuric chloridesolutions are the most frequently used sterilizing agents. However, these chemical compounds often damage the plant tissue or are ineffective in the elimination of bacterial and fungal contaminations. Silver and copper nanocolloids also present antibacterial, antifungal and antiviral activities. The aim of this research was to develop an effective disinfection protocol of Chrysanthemum × grandiflorum /Ramat./ Kitam. ‘Falco’ explants during initiation of in vitro cultures. The explants - shoot tips were first rinsed under running water. Then they were incubated in 5% detergent solution for 5 minutes. Next they were transferred into 70% ethanol solution for 5 seconds. After that the explants were immersed in Ag, Cu or Ag+Cu nanocolloids at the concentration of 5 or 10 ppm for 5 or 10 minutes. Then they were rinsed for 5 minutes in sterile distilled water. The explants were dried on sterile paper and inoculated on the universal MS medium. During four successive weeks observation were made for the appearing of bacterial and fungal contaminations. The share of disinfected cultures in each research object was determined. For this data the Freeman-Tukey transformation was used and next the analysis of variance for a three-factor experiment was performed. Means were evaluated with the Tukey test at the significance level of 5%. The share of sterile cultures, depending on the research object, ranged from 70 to 100%. The statistical analysis did not demonstrate significant differences between the used nanocolloid type, its concentration and the time of explant disinfection on the percentage of disinfected cultures. Nevertheless, the research confirmed the usefulness of Ag and Cu nanocolloids for the elimination of bacterial and fungal contaminations in chrysanthemum in vitro cultures. The nanocolloids demonstrated satisfying antibacterial and antifungal activity even at low concentration and short time of disinfection. Additionally no plant tissue damage was observed.

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