In vitro chromosome doubling potential of colchicine, oryzalin, trifluralin, and APM in Brassica napus microspore culture

The potential of colchicine and the microtubule depolymerizing herbicides trifluralin, oryzalin, and amiprophos-methyl (APM) for in vitro chromosome doubling during B. napus microspore culture was studied. Colchicine was administered during the first 6, 12 or 24 h of culture with 8 different concentrations up to 3 mM, and herbicides at 6 different concentrations up to 30 mu M for 12 h. Treatments with moderate concentrations of colchicine (3-100 mu M) Produced a small increase in embryo production, while concentrations above 300 mu M were toxic. Colchicine treatment for 12 h resulted in higher embryo production than treatment for 6 and 24 h. Duration of treatment and concentration of colchicine both had a significant effect on the chromosome doubling. The highest diploidization rates (94% diploid regenerants) were seen after 24 h treatment with 1 mM colchicine. All three herbicides were similar to colchicine in terms of their effect on embryo formation and chromosome doubling comparable to the one of colchicine, but at concentrations approximately 100 times lower. APM was less toxic than trifluralin and oryzalin, but no significant difference in chromosome doubling efficiency was detected between the compounds. The 12 h treatment resulted in a maximum of approximately 65% diploid regenerants with all three herbicides, but APM may have an advantage because of its less toxic effects. Prolonged treatment with APM (20-24 h) may produce 95-100% diploid regenerants.