Natural and culture-induced genetic variation in plantains ( Musa spp. AAB group)

Random amplified polymorphic DNA (RAPD) analysis of 15, mostly African, plantain land races revealed a very low proportion of polymorphic bands (13 of 276). However, further examination of these 13 marker bands demonstrated that they varied within land races and could not be used to distinguish between land races. In many cases, this could be directly associated with tissue culture treatment of the material. In order to investigate tissue culture effects in more detail, a single meristem of the West African plantain Agbagba was introduced into axenic culture and subjected to three cycles of micropropagation. A total of 48 regenerated plants were established under field conditions and subjected to RAPD analysis. By using 40 arbitrarily selected primers, about 400 bands were scored across this population of in vitro -derived plants. Sixteen of the bands were polymorphic within the population of Agabgba plants, distinguishing 13 genotypes. The pattern of relationships of these genotypes was established by cluster analysis; field characterisation of the plants supported the relationships revealed by RAPD data. The high level of RAPD polymorphism (4% of bands polymorphic), along with a clear correlation between the genotypic classification of individual plants and their tissue culture pedigree, suggests that a substantial amount of genetic variation existed within the original cultured meristem. On this basis, a putative Agbagba meristem representing an apparent sectoral chimera has been constructed. A model is presented that takes account of the persistence and high rate of somaclonal variation and proposes that the mother Agbagba plant comprised a periclinal chimera.