FIELD: agriculture. SUBSTANCE: method involves transforming basic diploid sorts to tetraploid level by colchicinization or other known method; separating reversing diploid plants by morphological and other economically valuable features and using said plants as basic material; growing produced tetraploids for several generations and simultaneously selecting in each generation recombined tetraploid forms different from basic tetraploid morphological type; multiplying each individual selected form during several generations; separating from each generation forms with reversibly multiple-reduced ploidy (reploids), whose ploidy is determined by morphological features and by direct calculation of chromosomes; evaluating reploids by fatty-acid content of oil and separating forms differing from plants with basic ploidy by altered or novel fatty-acid content of oil. EFFECT: provision for creating soya without using mutagenes. 3 cl, 1 tbl
