A robust tissue culture system for sorghum [Sorghum bicolor (L.) Moench]

• No phenolic has been observed in the optimized tissue culture system.
• Callus induction rates up to 100% have been routinely achieved from Tx430.
• Callus regeneration rates at 100% have been routinely obtained from SA281 and 91419R at optimal callus age.
• The optimal callus age has been identified at two weeks in the tissue culture system.

Sorghum tissue culture has been challenged by three predominant obstacles for decades, namely toxic pigments (phenolics), low regeneration frequencies and short duration of callus regenerability. Here, we report a robust tissue culture system for sorghum, which has minimized these major impediments. To optimize media, different concentrations of various plant growth regulators, such as 2,4-dichlorophenoxyacetic acid (2,4-D), N6-benzyladenine (BA), indole-3-acetic acid (IAA), indole-3-butyric acid (IBA) and α-naphthaleneacetic acid (NAA) were evaluated. Additional ingredients, including KH2PO4, CuSO4·5H2O, l-asparagine, l-proline and polyvinylpyrrolidone (PVP) were also assessed. Results showed that callus age had a conspicuous effect on its growth and regenerability, with callus weekly growth ratio and regenerability peaked at two weeks after induction. A callus induction rate up to 100% was achieved in inbred line Tx430, whereas regeneration rates up to 100% were obtained from SA281 and 91419R. This highly efficient system has been utilized for sorghum transformation for several years and has been proven to be reliable and reproducible.