Abstract
Field evaluation of plants produced in vitro initiated from a phenotypically distinct, apparently healthy dwarf `French-type' plantain clone `Dwarf Superplátano' ( Musa `AAB') was carried out at three sites in Puerto Rico. The use of the floral axis tip from a `mother plant' versus vegetative apices from lateral buds of the same plant as a source of the primary explant was compared and contrasted. Material from floral axis tip consistently showed high phenotypic uniformity whereas materials from vegetative apices of `sword' suckers were less so. `Virus-like symptoms' that became apparent in much of the material just before flowering (shooting stage) were determined to be due to the badnavirus banana streak virus (BSV), a dsDNA pararetrovirus. The `good news' is that a primary explant taken from the floral axis tip was quicker in its initial response to yield a multiplication system in vitro, and produced significantly fewer virus-infected plants, ca. 5%. By contrast, primary explants obtained from the vegetative sucker-derived apices were later in their production of initial buds, and produced many more virus-infected plants, an average of 32%. Comparison of vegetative-apex-derived plants and floral axis tip-derived plants disclosed no evidence that apices from vegetative suckers or floral stem tips gave rise to genetic off-types due to mutations were brought about by the in vitro process per se. Phenotypic differences were due to virus infestation. The `bad news' is that this dwarf plantain clone of considerable interest and potential in Puerto Rico can show very severe BSV symptoms. The occurrence of BSV infection in tissue culture-derived plants may be related to the presence of viral sequences integrated into the host genome, in which case there is no apparent strategy to rid the clone of this `virus'.
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