TDZ and 4-CPPU Induce Embryogenic Response on Scalps of Recalcitrant East African Highland Banana

Breeding of banana conventionally is very difficult due to high levels of sterility arising from aneuploidy. Transformation of East African highland banana (EA-AAA banana) has been limited by difficulties in induction of embryogenic callus and/or embryogenic cell suspension (ECS), a requirement for efficient genetic transformation. In this study N-phenyl-N’-1,2,3-thidiazol-5-ylurea (TDZ) and N-(2-chloro-4-pyridyl)-N’-phenylurea (4-CPPU) that are highly active in regulating morphogenesis in tissue culture of many plant species were tested for enhancing embryogenic callus induction in recalcitrant EA-AAA banana through scalps. In vitro derived shoot-tips of banana cultivars Mbwazirume, Mpologoma, Nakabululu, Nakinyika and Nfuuka were subcultured on various combinations of TDZ and 4-CPPU till scalps were formed. In all the cultivars, ideal scalps for callus induction were achieved in over 50% of the shoot-tip cultures within four subculture cycles in the medium containing equal proportions of 9–13 µM of TDZ and 4-CPPU, and 26 µM of each. Embryogenic callus was formed on 2.5–20% of the scalp cultures depending on cultivar and, TDZ and 4-CPPU combination. Cultivars Nakinyika, Nakabululu, Mbwazirume and Nfuuka developed regenerable embryogenic callus. Of the plantlets regenerated 5 out of 12 and 4 out of 5 plantlets of cultivars Nakinyika and Mbwazirume, respectively, developed normal roots and were weaned onto soil. These results suggest that TDZ and 4-CPPU increases embryogenic response from scalps of EA-AAA banana which can enhance their genetic transformation.