Application of knockout rape Far-Red Elongated Hypocotyl 3 in regulation and control of size of rape petals

The invention relates to a method for regulating and controlling the sizes of rape petals, belongs to the field of genetic engineering, and provides application of knockout rape Far-Red Elongated Hypocotyl 3 in regulating and controlling the sizes of the rape petals. In the rape, the BnaFHY3 is totally provided with four homologous copies, the four homologous copies are respectively positioned on chromosomes A01, C01, A05 and C05, and the four homologous copies are respectively a gene BnaA01G0219400WE/BnaA01. FHY3, a gene BnaA05G0289800WE/BnaA05. FHY3, a gene BnaC01G030800WE/BnaC01. FHY3 and a gene BnaC05G0342900WE/BnaC05. FHY3. According to the application, four copies on BnaFHY3 gene loci of A01, C01, A05 and C05 in rape are knocked out by utilizing a gene editing technology, so that a bnafhy3 homozygous mutant is obtained. The petals of the mutant are smaller than those of a normal wild type during flowering. In the rape, the petal area is related to individual energy conservation and consumption reduction