The shoot tip explants of the tillered onion line Z-018 were used as experimental materials. The effects of colchicine
and pendimethalin on the induction of polyploid tillered onion were studied in vitro with different concentrations and
treatment time. Treatment with 250 μmol/L colchicine for 4 days caused a variant rate of 42.22% and a mortality rate
of 36.67%, whereas treatment with 30 μmol/L pendimethalin for 6 days caused a variant rate of 41.11% and a mortality
rate of 24.44%. Subsequent cytological identification showed that tetraploid plants were successfully induced by both
mutagens. Compared with the diploid plants, the tetraploid plants exhibited slower growth, thicker leaves, stems and
roots, larger stomatal apparatus and increased number of chloroplasts. In addition, the obtained tetraploid plants have
thicker tubular leaves, decreased number of tillers, larger bulbs and increased yield of the products. This provides the
basis for future research on tillered onion germplasm resources.