Two large reciprocal translocations characterized in the disease resistance-rich burmannica genetic group of Musa acuminata

BACKGROUND AND AIMS: Banana cultivars are derived from hybridizations involving Musa acuminata subspecies. The latter diverged following geographical isolation in distinct South-east Asian continental regions and islands. Observation of chromosome pairing irregularities in meiosis of hybrids between these subspecies suggested the presence of large chromosomal structural variations. The aim of this study was to characterize such rearrangements. METHODS: Marker (single nucleotide polymorphism) segregation in a self-progeny of the ‘Calcutta 4’ accession and mate-pair sequencing were used to search for chromosomal rearrangements in comparison with the M. acuminata ssp. malaccensis genome reference sequence. Signature segment junctions of the revealed chromosome structures were identified and searched in whole-genome sequencing data from 123 wild and cultivated Musa accessions. KEY RESULTS: Two large reciprocal translocations were characterized in the seedy banana M. acuminata ssp. burmannicoides ‘Calcutta 4’ accession. One consisted of an exchange of a 240 kb distal region of chromosome 2 with a 7.2 Mb distal region of chromosome 8. The other involved an exchange of a 20.8 Mb distal region of chromosome 1 with a 11.6 Mb distal region of chromosome 9. Both translocations were found only in wild accessions belonging to the burmannicoides/burmannica/siamea subspecies. Only two of the 87 cultivars analysed displayed the 2/8 translocation, while none displayed the 1/9 translocation. CONCLUSION: Two large reciprocal translocations were identified that probably originated in the burmannica genetic group. Accurate characterization of these translocations should enhance the use of this disease resistance-rich burmannica group in breeding programmes.