Abstract: A new method of improving induction rate of polyploid through chemical induction combined with physical mutation were proposed by using the diploid Astragalus membranaceus(Fisch.) Bge. var. mongholicus(Bge.) Hsiao seeds as the materials and N⁺ beam as the mutagenic agent. The results indicated that N⁺ implantation showed significant biological effects. The effects of N⁺ implantation combined with colchicine on inducing polyploidy of Astragalus were obvious, 44.4% doubling rate was obtained by being treated by the combination of N⁺ ion implantation dose 2.6×10¹⁶ N⁺/cm² and colchicine concentration 100 mg·L^-1 for 5 d. The best result of 46.2% was obtained by using the combination of N⁺ implantation dose 5.2×10¹⁶ N⁺/cm² and colchicine concentration 100 mg·L^-1 for 10 d. They were higher than the control group of maximum induction rate 13.9% of colchicine concentration 100 mg·L^-1, treatment time 15 d. Cell chromosome identification results showed that the polyploid is tetraploid.

Key words: Astragalus membranaceus(Fisch.) Bge. var. mongholicus(Bge.) Hsiao, N⁺ implantation, colchicine, polyploidy induction