Organ Formation from Callus Cultures of Bananas and Plantains
Spherical swellings which resembled globular embryos developed on the surface and within leaf base expiants of banana (Musa acuminata Colla. cvs. Dwarf Cavendish and Valery), plantain (Musa × paradisiaca L. cvs. Mysore and Apple), and bluggoe-type cooking banana (Musa × paradisiaca L. cv. Chato) when cultured without illumination for 30 to 60 days on a basal medium containing Murashige and Skoog (MS) salts, i-inositol (100 mg/1), thiamine-HCl (0.4 mg/1), sucrose (30 g/1), supplemented with 0.1% (w/v) activated charcoal, various concentrations of 2-methoxy-3,6-dichlorobenzoic acid (dicamba), and solidified with 0.3% (w/v) agar. Inclusion of kinetin or N -benzyl-adenine (BA) in addition to dicamba during culture initiation suppressed the formation of these structures. Transfer of leaf base expiants to hormone-free basal medium or to MS with a lowered concentration of dicamba resulted in the rapid enlargement and elongation of the globular masses. Small pieces of callus which were shaken free after transfer to liquid medium continued to divide, and eventually organized into discrete structures resembling those which arose from the globular swellings. In both instances the structures closely resembled those described elsewhere as “somatic embryos.” However, shoot formation from these structures was never observed. Root elongation occurred. Histological examination revealed these structures to be unipolar and without typical embryo anatomy. Swellings in the basal area, presumed to be nascent shoot axes, were identified as secondary root axes.