Polyploidisation is an important process in the evolution of many plant species. An additional set of chromosomes can be derived from intraspecific genome duplication (autopolyploidy) or hybridising divergent genomes and chromosome doubling (allopolyploidy). Special forms of polyploidy are autoallopolyploidy and segmental allopolyploidy. Polyploidy arises from two basic processes: spontaneously occurring disturbances of meiotic division and induced by antimitotic agents’ disruption of mitosis. The first involves the induction and fusion of unreduced gametes, resulting in the formation of triploids and tetraploids. The second process uses antimitotics that disrupt cellular microtubules and prevent chromosome’s sister chromatids motion during anaphase. Colchicine, oryzalin, and trifluralin are the most commonly used antimitotics for inducing polyploids in plants. The exposure time and concentration of the antimitotics and the species, cultivar, genotype, and tissue type affect the efficiency of genome duplication. Polyploids are distinguished from diploids by increased cell size and vegetative parts of plants and increased content of secondary metabolites. Genome duplication generates several changes at the epigenetic level resulting in altered gene expression. Polyploidisation is used in plant breeding to overcome the non-viability and infertility of interspecific hybrids, obtain seedless polyploid cultivars and increase resistance/tolerance to biotic and abiotic factors.

The aim of the study was to determine the breeding value of advanced lines of fibrous flax and oilseed flax (linseed) on the basis of comparative experiments with reference varieties. In field experiments conducted in 2019–2020, the HDH line of fibrous flax and the R26 linseed line were assessed in terms of significant phenotypic traits and also traits affecting the yield structure. Due to the fundamentally different weather conditions in the growing seasons of 2019 and 2020, it was also possible to determine the susceptibility of the studied genotypes of flax to climatic stress factors. The obtained results showed the high breeding value of the HDH line as a potential new variety of fibrous flax. The R26 line did not exceed the reference varieties in terms of the traits essential for the oily form of the cultivated flax cultivars, but it was characterized by a favorable morphological and yield-forming structure for dual purpose varieties. Moreover, both assessed lines showed high resistance to unfavorable climatic conditions.

Flax is one of the few plants that are entirely a source of raw materials for further production. Promising directions for the use of flax biomass may be the production of bioenergy in the form of 2G biofuels and the production of “green” composites. The aim of the study is to compare the biomass of fiber flax, linseed and dual-purpose varieties of cultivated flax (Linum usitatissimum L.) susceptibility to the biorefining processes. In the first stage of the research, based on the results of yield structure features and biometric measurements of plants, the most optimal flax line was selected for the fiber flax, linseed and dual purpose. Next, the forms of flax were pretreated with sodium hydroxide (NaOH), the chemical composition was determined and SEM images were taken. The obtaining of bioethanol process SFF (simultaneous saccharification and fermentation) was carried out. In addition, biodegradable polymers were modified with flax biomass, shapes were prepared, and the rheological and mechanical properties, as well as microbiological activity of biocomposites, were determined. The highest concentration of ethanol (8.72 g·L⁻¹) and the greatest susceptibility to mold fungi of the biocomposites were obtained for the fiber flax variety PET 16/20.