Histological analysis of direct organogenesis from micro-cross-sections of cultures of the banana

The histological origin of organogenesis was studied during plant regeneration of banana (Musa AAA cv. Williams) via direct organogenesis from micro-cross-sections of the rhizome in modified Murashige–Skoog (MS) medium (including 10 µm 6-BAP, 1 µm IAA and 50 µm KN). The frequency of the organogenesis was dependent on the position from where the explant was cut. Generally, more adventitious shoots were obtained from explants cut from regions close to apical meristem. The origin of adventitious shoots was multicellular, from cell layers with active cell division in the epidermis of the rhizome axis. After 24 h of culture, a layer of epidermal cells close to the leaf sheath base was actively dividing, and as the time in culture increased, regions containing actively dividing cells became enlarged. By the fifth day of culture, regions of actively dividing cells covered the whole peripheral zone of cortex. Several meristemoid structures were formed from the peripheral zone of cortex after 7 days of culture. These structures developed into adventitious shoots by the ninth day of culture. Vigorous plantlets could be regenerated from the shoots when they were transferred to rooting medium containing MS basal salts supplemented with 30 g L–1 sucrose, 6.5 g L–1 agar, a vitamin/amino acid mixture, 1 µm NAA and 1 µm 6-BAP.