Identification of genetic markers linked to banana streak disease expression in inter-specific Musa hybrids

Recently-introduced inter-specific #Musa# hybrids, bred for improved yield and resistance to diseases, have been found to be widely infected with banana streak virus (BSV), the causal agent of banana streak disease (BSD). One hypothesis suggests: (1) that BSD occurrence in these inter-specific hybrids results from activation of BSV-01 endogenous pararetrovirus sequences (EPRV) integrated into the #Musa# genome rather than from external sources of infection, and (2) that the process of genetic hybridisation may be one factor involved in triggering episomal expression of the BSV integrants. In order to test this hypothesis we carried out a genetic analysis of BSD incidence in a F1 triploid (#Musa# AAB) population produced by inter-specific hybridisation between virus and disease-free diploid #Musa balbisiana# (BB) and tetraploid #Musa acuminata# (AAAA) parents. Half of the F1 progeny of this cross expressed BSV particles. Using PCR amplification to determine the presence or absence of BSV-01 EPRVs, it was determined that this endogenous sequence was specific to the #M. balbisiana# genome and occurred in a homozygous state. Using bulk segregant analysis, ten AFLP markers co-segregating with the absence and/or presence of BSV infection were identified in the #M. balbisiana# genome, but were absent from the #M. acuminata# genome. Seven of these markers segregated with the presence of a BSV particle and three with the absence of BSV particles. Analysis of the segregation of these markers using a test-cross configuration allowed the construction of a genetic map of the linkage group containing the locus associated with BSV infection in the F1 hybrid population. These data indicate that a genetic mechanism is involved in BSV appearance, and suggest that a monogenic allelic system confers the role of carrier to the #M. balbisiana# parent.