Improvement of cassava shoot organogenesis by the use of silver nitrate in vitro

To improve the regeneration efficiency of cassava (Manihot esculenta Crantz) in vitro, the effect of silver nitrate (AgNO3) on shoot organogenesis from somatic cotyledons was assessed. Adding AgNO3 to the regeneration medium improved the regeneration frequency and reduced callus formation in all tested cultivars. Both the extent of the response to and the optimum concentration of AgNO3 were cultivar dependent. In the model cultivar MCol22, the use of AgNO3 at concentrations between 4 and 12 mg l−1 increased shoot organogenesis frequency and the number of shoot primordia per explant, the maximum effect being observed on a medium containing 12 mg l−1 AgNO3. At this concentration, the frequency of shoot organogenesis was enhanced from 60 to 90%, while callus formation decreased from 100 to 5%. The highest shoot organogenesis rates were obtained by supplementing the medium with 2 and 1 mg l−1 AgNO3 in KU50 and Hanatee, respectively, while cultivar T5 showed an optimum response at 4 mg l−1. The shoots regenerated from explants cultured on a medium containing AgNO3 were more elongated than those cultured on a medium without AgNO3. The application of AgNO3 did not change the dose response of shoot organogenesis for the selective agents hygromycin and mannose.