Evaluation of somatic embryogenesis and plant regeneration in tissue culture of ten sorghum (Sorghum bicolor L.) genotypes

Optimization of tissue culture conditions for Sorghum bicolor L. through somatic embryogenesis from immature embryos is important for the genetic manipulation and improvement of this agronomically valuable crop. In an attempt to develop a successfully reproducible in vitro regeneration protocol for a group of diverse sorghum genotypes, 10 sorghum lines including locally adapted and commercially important elite genotypes were assessed for their regeneration potential on different culture media–containing adequate growth regulators combinations. The maximum response of embryogenic callus induction was obtained from explants cultured on Murashige and Skoog (MS) medium supplemented with 1.5 mgL-1 of 2,4-dichlorophenoxyacetic acid (2,4-D) and 0.7 mgL-1 L-proline. The addition of kinetin to the MS-based culture media had a negative effect on the formation of embryogenic calli. The results reveal that embryogenic callus formation and regeneration were highly genotype dependent. The line LG3 revealed the highest mean number of embryogenic callus (47.5 ± 6.0%) across the media tested. On the other hand, SPP462 was the least responsive (13.4 ± 3.3%) to embryogenic callus induction. The regeneration percentage of the different genotypes ranged from zero to 22.1%. The lines LG3, LG4, Dorado, SPGM94021 and SPMD94001 succeeded to form shoots on the three tested regeneration media. Nevertheless, the genotypes LG8 and TX2794 produced shoots on only two out of the three media. Three lines failed to regenerate on any of the tested media. Adding 0.5 mgL-1 naphthalene acetic acid and 0.5 mgL-1 of indole-3-butyric acid (IBA) did not enhance the root induction. Regenerated shoots developed into normal mature plants. Regeneration of sorghum genotypes could be improved through the use of different auxins and cytokinins in callus induction and shoot formation media. The auxin, 2,4-D was critical for the induction of embryogenic calli. However, the addition of the cytokinin (kinetin) adversely affected the formation of embryogenic callus. On the other hand, the shoot induction was more influenced by the addition of indole-3-acetic acid (IAA), 6-benzylaminopurine (BA) and thidiazuron (TDZ). Key words: Sorghum, immature embryos, callus induction, regeneration, auxin, cytokinin.