Highly efficient plant regeneration through somatic embryogenesis in 20 elite commercial cotton (Gossypium hirsutum L.) cultivars

A protocol was established for cotton somatic embryogenesis and plant regeneration. Using this protocol, highly efficient plant regeneration via somatic embryogenesis was obtained from more than 20 Chinese and Australian commercialized cotton cultivars including CCRI 12, CCRI 19, and Simian No 3. These three cultivars alone comprise more than 50% of the total cultivated cotton in China. Based on three criteria, the 20 tested cotton cultivars were classified into three different groups: easily embryogenesis-induced cultivars (such as CCRI 19, Simian No 3, Lumian 6, Sikral 1-3, Coker 201), moderately easy embryogenesis-induced cultivars (such as CCRI 16, CCRI 24, Simian No 4 and CCRI 29), and not easily embryogenesis-induced cultivars (such as CCRI 17, CCRI 30 and CCRI 27). The three criteria used included (1) the somatic embryogenesis ratios, (2) the time required to produce somatic embryogenesis, and (3) the number of the somatic embryos produced in each culture. Also, the plant hormone Zeatin (ZT) was used to induce direct somatic embryogenesis and had the highest induction ratio of 33.3%. Overall, this procedure simplifies cotton somatic embryogenesis from a multi-step culture process to a one-step culture process and shortens the culture cycle from 180 to 60-120 days. This protocol also makes it easier to control the somaclonal variation in plant tissue culture and facilitates the application of plant genetic engineering on cotton genetic improvement.