Enhancing the quality of crop plants by obtaining more fertile varieties is an important task in world agriculture, and progress in this area is possible thanks to work aimed at improving the adaptive capacity of plants in response to environmental changes. Interesting techniques used in agriculture include biological and biotechnological methods, leading to the induction of genomic mutations by chemical polyploidization using antimitotics.

The aim of thisexperiment is to develop an effective method of inducing polyploidy inSilybum marianum (milk thistle, SILMA variety IWNiRZ-PIB), which is an important medicinal plant of high economic, horticultural and pharmaceutical importance.

In our study, colchicine and oryzalin in various concentrations (0.01%, 0.1%, 0.5%, 1%, 3%) were tested. Seeds and young plants were soakedin solutions of antimitotics in different time periods (48 and 20 h for seeds and 20 and 120 min for young plants). Seed germination and plant survival were observed in terms of the type of antimitotic and its concentration, the exposure time to antimitotics and the plant material. Polyploidization was tested by using flow cytometry.

Results showed that 100% of plants soaked in colchicine and oryzalin (0.1% and 0.01%) survived after minutes, and 80% of plants soaked in colchicine (0.1%) and oryzalin (0.1%) survived for 60 and 120 minutes, respectively. However only 42% and 40% of seeds sprouted after soaking in colchicine in concentrations at 0.5% and 1%, respectively (100% in control group). The epidermal cells and stomata did not show any negative changes, with a tendency to increase the number of stomata (digital and scanning microscopy). Cytometric analysis showed that in 21.52% of plants with an altered genome (2x + 4x and 4x + 8x and 2x + 4x + 8x), including 17.72% of mixoploid plants, polyploid chimeras (sectoral and mericlinal plants) were obtained. The method using colchicine is more effective for seeds than for young plants (11:3).