Abstract: 【Objective】Garlic is a vegetative crop. It is difficult to use conventional method to breed new varieties. Chemical mutagenesis plays an important role in germplasm innovation, and the effect is admirable in some crops. This paper mainly discussed the mutagenic effect of colchicine on in vitro shoot-tips of garlic with the aim at finding a theoretical and methodical basis for obtaining new garlic germplasm. 【Method】 Garlic cultivars of Cangshan Puke, Zhengyuezao, and Xinjiang purple were collected from different regions. After dormancy broken, the selected shoot-tips from bulbs of garlic were cultured in different media and proceeded to plant regeneration. The rate of plantlet regeneration and tetraploid in vitro shoot-tips were studied in three garlic varieties induced by colchicine exposure. Correlative model of different colchicine concentrations and time duration was established by applying D-optimal design, so as to determine the optimum scheme of the tetraploid induction of garlic. The plant ploidy was identified by Flow Cytometry Analysis and chromosome counts of the root-tips.【Result】The result showed that the DNA content of tetraploid garlic leaf was twice that of diploid garlic Cangshan Puke by flow cytometry analysis. The diploid chromosome number was 2n=2x=16 and the tetraploid chromosome number was 2n=4x=32 by chromosome counting. In colchicine treatment process, the rate of plantlet regeneration was significantly decreased when treated with colchicine at higher concentration and after longer duration. And the concentration of colchicine had a stronger effect on plantlet regeneration than time duration. The difference among the three garlic varieties was significant. As an outstanding example, the plantlet of Cangshan Puke survived significantly fewer than Zhengyuezao and Xinjiang purple. And the plantlet rates were 41.83%, 48.69% and 46.73%, respectively. The concentration of colchicine had a more significant effect on tetraploid induction than the treatment duration. The difference of tetraploid rate among the three varieties was also significant. The tetraploid rates were 15.69%, 15.69% and 23.53% for Cangshan Puke, Zhengyuezao, and Xinjiang purple, respectively. Among the cultivars, the tetraploid rate of Zhengyuezao was the highest (9.15%), Cangshan Puke took the second place (7.84%), and Xinjiang purple was in third place (6.53%). By applying simulation technology, the results showed that over 50% of plantlets had been regenerated and survived when all the varieties were treated by colchicine at a concentration of 0.268%-0.694% after 61.1-113.8 h. While the tetraploid rate was more than 5% when treated at a concentration of 0.531%-0.580% after 79.8-112.2 h. 【Conclusion】 Garlic varieties showed different reactions when treated at various colchicine concentrations and time durations. The difference of mutagenic effect among these was significant. It showed that immersion concentration affected more apparently than the immersion time did. Mutual effect between the concentration and treatment time of colchicine was found. By applying intersection method analysis, the result showed that when treated with colchicine at concentration of 0.531%-0.580% and after 79.8 h-112.2 h duration, more than 50% of plantlets were regenerated and survived, while the tetraploid rate was more than 5%.

Key words: garlic , in vitro plantlet , colchicine , tetraploid