The chemical composition of culture growth media to micropropagate plants should be devised to allow the best quality and high production of plant material. One of the challenges is to optimize the ionic balance involving mineral nutrients. As banana (Musa sp.) requires high levels of potassium, the optimum level was investigated. Shoot apexes of two banana cultivars 'Nanica' and 'Prata Anã' were cultivated in asseptic conditions in modified MS media for 90 days in the presence of six different concentrations of K: 5, 10, 15, 20, 25 and 30 mM. The concentration of 20 mM is found in the basic MS medium. The cultures were then transferred to rooting media with the same concentrations of K. Dry matter weight and k concentration in shoots, roots and the whole plantlet, and number of plantlets produced were determined. Visual symptoms of K deficiency, such as chlorosis and necrosis in older leaves, were observed in all plantlets under low concentration of K. Quantitative differences were observed between the two cultivars in relation to dry matter weight and number of in vitro regenerated banana plantlets; K concentration was optimum around 15-20 mM.
Musa; banana plant; ionic balance; potassium; in vitro