Factors Influencing Agrobacterium-Mediated Transformation of Shoot Apex- Derived Calli Explants of Sorghum

Sorghum bicolor is an agronomical cereal crop providing food security to millions in tropics especially Africa, Asia and Central America. Generation of transgenic sorghum for insect resistance through Agrobacterium is a challenging task as there are several factors that determine the efficiency of successful transformation. The objective of the study was to evaluate the effect of critical factors such as the use of shoot apex explants for generating embryogenic calli as target tissue for transformation, the effect of combination of the transgene Bt cry2A with two different promoters –d35S and ST-LS1 respectively in pCAMBIA 1305.1 construct, the duration of co-cultivation and the concentration of acetosyringone during co-cultivation on transformation. The results showed that the transformation frequency was influenced by the above factors and the gus expression studies revealed that cry 2A gene driven by d35S promoter in pCAMBIA 1305.1, 3 days of co-cultivation of calli explants with Agrobacterium strain LBA4404 and a concentration of 200 µM acetosyringone in the co-cultivation medium was found to be optimal in increasing the transformation frequency.