Contribution to the assessment of the risk of spreading banana streak viruses (BSVs) in the Dominican Republic through the cultivation of banana interspecific hybrids harbouring infectious endogenous BSV sequences

Endogenous Banana streak viruses (eBSVs) are present in the genome of Musa balbisiana spp. Some eBSVs are infectious and their activation by biotic and abiotic stresses lead to spontaneous infections by several species of Banana streak virus (BSV) in triploid (AAB) and tetraploid (AAAB) interspecific hybrids harboring the M. balbisiana genome. Although interspecific hybrids are grown over important areas in several countries throughout the Caribbean, Latin America and Africa, the risk of spreading BSVs associated to large scale cultivation of these hybrids has never been assessed. This thesis focuses on the risk of spreading the three most widespread BSV species (BSOLV, BSGFV and BSIMV) in the Dominican Republic through the large scale cultivation of the two main banana hybrids that are grown in the country, Macho x Hembra, a natural triploid (AAB) plantain cultivar, and FHIA-21, a tetraploid (AAAB) hybrid. An unprecedented survey was conducted throughout all the Dominican banana producing areas in order to assess the prevalence levels of BSOLV, BSGFV and BSIMV in MxH and FHIA-21 plantations. It showed that BSOLV and BSGFV are widespread in both varieties, with BSGFV being the most prevalent species, and that BSIMV is not present. BSGFV prevalence level was significantly higher in FHIA-21 than in MxH. Analyses of molecular taxonomical data of the natural mealybug vectors of BSVs and eBSV patterns of MxH and FHIA-21 were carried out and pointed to a marginal role of mealybugs in the transmission of BSGFV and BSOLV in the Dominican Republic in MxH and FHIA-21. An experimental plot was set up and used for the first attempt ever made to monitor the kinetics of activation of infectious eBSOLV and eBSGFV in interspecific hybrids under field conditions. Results collected over a 15 months period showed that infectious alleles OL1 (eBSOLV) and GF7 (eBSGFV) are differentially expressed in MxH and FHIA-21, pointing to the existence of additional (plant) factors involved in the regulation of the expression of infectious eBSVs. They also showed that the mode of multiplication of the planting material influences activation levels. Preliminary results also suggest that BSV infection does not have a major effect on fruit production, although additional data are needed to reach definite conclusions in this regard. Overall, this thesis contributes significantly to the development and implementation of appropriate strategies for evaluating and mitigating the risks of spreading BSVs that are associated with the cultivation of banana interspecific hybrids. (Résumé d'auteur)