Evidence that the proliferation stage of micropropagation procedure is determinant in the expression of Banana streak virus integrated into the genome of the FHIA 21 hybrid (Musa AAAB)

Banana streak virus (BSV) is causing increasing concern in almost every pro ducing area of banana and plantain (Musa spp.) worldwide. This situation ap peared partially linked to some breeding lines and micropropagated hybrids. A complete BSV sequence integrated into the genome of a triploid plantain has been recently characterised and it has been hypothesised that it could give rise to infectious virus via recombination. In this study, we evaluate d the effect of a routine micropropagation procedure on the expression of B SV in the FHIA 21 tetraploid hybrid. The widespread presence of integrated sequences and the absence of episomal BSV in thirty FHIA 21 "mother plants" selected for micropropagation were first confirmed by specific PCR and IC- PCR tests. The proliferation stage of the procedure, characterised by an in tensive production of neoformed buds, appeared determinant in BSV expressio n whereas the rooting and acclimatisation stages had little or no effect. T he duration in culture and the way of subdividing the clumps of proliferati on influenced greatly the percentage of episomal BSV infections, reaching 5 8% of infected micropropagated lines after six in vitro subcultures. These data suggest that the expression of episomal BSV observed during the in vit ro procedure is correlated with the presence of an integrated form.