Plants with properly developed leaves and stems were derived from bright green calluses with dark green meristematic structures inside callus tissue. No shoots were regenerated from white and yellow calluses without meristematic zones. In total, only sixteen calluses of genotypes BC-1, BC-6 and BN-OP-01 regenerated shoots; several previously mentioned calli produced more than one shoot. All regenerated plants were characterized by certain level of hyperhydricity; such type of plants was described also by Jourdan and Earle (1989) in the protoplast culture of four Brassica species, Hu et al., 1999 in Brassica napus and B. juncea. This undesirable physiological state was eliminated by repeated subcultivation on MS medium without growth regulators. It is evident, that only the proper combination of PEG 6000 concentrations and time durations can provide satisfactory fusion frequency. From results can be concluded that all the 30 % PEG solutions provided good results (about 8% of fusants) together with 25% PEG solution with the period of 20 minutes. The efficiency of these combinations is comparable with the results, obtained by Gurel et al. (2002). Even higher frequency of fusants was observed by Beranek et al. (2006) on protoplast fusions between B. carinata and B. rapa, where the 30% PEG 6000 MW treatment for 10 minutes achieved about 25% of fusants. Both 20% PEG concentrations and shorter period of 25% concentration showed rather low efficiency. However, both combinations with 30% PEG solution increased the number of multifusants, unfavourable for practical applications. Analogous to the production of calli, significant differences between biological replicates in fusion frequency were detected as well. These circumstances might be explained by the heterogeneity of fused material during experiments even if all measurable environmental conditions were maintained. Protoplasts of fused cultures regenerated cell walls and first divisions were observed after 4th day of the culture. Small calli, approx. 1-2 mm in diameter turned brown-yellow and did not develop desired callus structures. Similar results were defined by Beranek et al. (2007) in Brassica carinata and Brassica rapa genotypes.
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