Establishment Of High-Frequency In Vitro Regeneration System And Polyploid Induction Of Onion

The onion (Allium cepa L.), biennial herbs, belonging to the genus Allium and the family Alliaceae, is an important vegetable crop in the world. In vitro culture and plant regeneration from Allium explants have been widely reported.Polyploids often generate variants that may contain favorable horticultural characteristics, such as a large fruit size, sturdiness and high productivity. Recent progress showed great potential for induced polyploid plant during the in vitro culture. The in vitro chromosome doubling technique has been used to produce polyploid plant artificially in vegetable crops and has been successful in several species. The onion bulb was the product, and polyploid breeding have great significance in breeding. In addition, by doubling the gene products, polyploids provide a wider germplasm base breeding studies.The main results of this article are as follows:Base on the explant of young umbels and different young buds, a high frequency in vitro regeneration system of onion was established through examining effect of inducing callus, differentiate shoot and rooted with different plant growth regulator combinations and concentration. Calli were induced from young umbels on B5medium with1.0mg·L-12,4-D+1.0mg·L-16-B A, the rate reaching100%. The optimum hormone concentration of getting high-frequency regeneracy shoot from callus was1.0mg·L-1TDZ on B5medium,78.13%. All shoots rooted on1/2MS medium with0.01mg·L-1NAA, the regenerated plantlet were domesticated and transplanted in greenhouse. The survival rate was95%.Calli were induced from immature inflorescence cultivar’W645’, based on onion regeneration system. These calli were treated with colchicines as a chemical mutagen. We studied the induction effect of colchicine with different concentrations and treatment duration on callus. The results showed that the death rate of callus grew up, differentiation decreased significantly with increased concentration and duration of colchicines. The optimal formula is obtained by the treatment of0.10%colchicines with24hours, callus surviving rate is60.00%, the inducible rate is high, regenerated plants were obtained by tissue culture. The ploidy level was identified by morphological trait, chromosome counting number and comparison of epidermal stomata size. In this treatment, we obtained three tetraploidy plantlets from four regenetated plants, no chimera. The choromosome number of tetraploids was2n=4x=32, the plants showed some general characteristics of tetraploids, such as darker leaf color, larger stomata, fewer stomata per unit area. This study will supply an important tool for onion ploidy breeding.In this study, the onion immature inflorescence as explants, high frequency in vitro regeneration system was established. Based on the protocol we can study on genetic transformation and polyploid induced of onion. Callus from immature inflorescence were induced with the combination of tissue culture and colchicines. We obtained tetraploids and provided technical support for the polyploid induction of onion.