Résumé
Two viruses are systematically involved in banana bract mosaic disease, BBrMD: a potyvirus, BBrMV, responsible for the disease and uncharacterized filamentous viral particles identified as potexvirus. The potyvirus was the only one transmitted by Pentalonia nigronervosa to healthy banana plants. It is pathogenic and induces typical symptoms of the disease (Fig. 1).Antisera were developed against it and reacted with one protein of an estimated size of 36kD in western blot. No reaction was obtained with the specific monoclonalpotexvirus, confirming infection by the potyvirus alone (Fig. 2). Because of these observations, this strain is considered the reference strain -"Ref" strain - of BBrMD in the Philippines. Molecular analysis of the CP gene and UTR region was conducted (Fig. 3). Comparisons with other BBrMV isolates (Philippines and India) and with the potyvirus gene data bank showed the "Ref" strain and the BBrMV isolates to be the same virus and the "Ref" strain a different potyvirus from the other potyviruses analysed (Fig. 4). Three couples of primers defined from the "Ref" sequence were used to study the molecular variability of BBrMV in the field. The expected amplified fragments were obtained for 5 differents isolates. No significant variability was observed between the isolates and the "Ref" strain after sequencing. The "Ref" strain was thus representative of BBrMD in the field. The identification of specific primers for molecular detection is in progress. The presence of the potexvirus in BBrMD remains unexplained. (Résumé d'auteur)