Abstract :
[en] The Bioversity International Transit Center (ITC) for banana hosts more than
1500 accessions largely covering the genetic diversity of the genus Musa. Its
objective is to conserve this genetic diversity and to supply plant materials to
users worldwide. All the Musa accessions must be tested for virus presence
and, if infected, virus elimination must be attempted, to enable the supply
of virus-free plant material. An international collaborative effort launched
under the auspices of Bioversity International (2007–2013) finally led to the
implementation of a two-step process to test the accessions. The first step, called
pre-indexing, involved only molecular tests and was designed as a pre-screen
of new germplasm lines or existing accessions to reduce the need for post-entry
virus therapy and repeated virus indexing. The second step, called full indexing,
was performed on either older existing accessions or newer accessions which
tested negative during pre-indexing, and involvedmolecular tests, transmission
electron microscopy (TEM) and symptom observation. In total, 270 germplasm
lines (434 samples) were pre-indexed; while full indexing was carried out on
243 accessions (68 of which had been pre-indexed). A significant proportion
of the samples tested during pre-indexing was infected with at least one virus
(68%), showing the utility of this early pre-screening step. Banana streak OL
virus and Banana mild mosaic virus were the most commonly detected viruses
during both pre- and full indexing. For 22 accessions, viral particles were
observed by TEM in full indexing while the molecular tests were negative,
underlining the importance of combining various detection techniques. After
full indexing, viruses were not detected in 166 accessions, which were then
released for international distribution from the ITC. This publication exemplifies
how the practical application of diagnostic protocols can raise fundamental
questions related to their appropriate use in routine practice and the need for
their continuous monitoring and improvement after their first publication.
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