Response of callus induction to light and regeneration system establishment offour alfalfa cultivars

In order to achieve the genetic improvement of alfalfa and establish the high frequency and stable regeneration system, the hypocotyls of 4 alfalfa cultivars (Medicago varia cv. Gannong No.1, M. sativa cv. Ameristand, M. sativa cv. WL324 and M. sativa cv. Sanditi) were cultured on 4 basal medium (MS, UM, modified HS and modified UM) containing 2,4D, KT and casein acid hydrolysate respectively. And the effect of light on callus induction and somatic embryo formation was studied. The result indicated that light showed no influence on callus induction and the callus rate was 100%. Callus induced under the lightdark alternation showed higher browning rate but rapid growth and more active, and showed light green or alternation of yellow and green. Callus induced from Gannong No.1 showed the highest somatic embryo developing rate which ranged from 20.83% to 56.25%. And it was easier to form somatic embryo under the lightdark alternation. The different medium were used to induce somatic embryo, UM + 0.1 mg/L NAA + 0.5 mg/L KT was the optimum medium and the rate of somatic embryogenesis was 56.25%.