Diploids are not suitable as end products of breeding: generally less productive and less vigorous than triploids, the bunches are smaller and sometimes contain seeds in the fruit. Although some diploid varieties are in notable trade, the vast majority of varieties grown for local consumption or marketing are triploid. Therefore, all breeding programs aim to select improved triploid varieties, whether by conventional (crosses) or non-conventional (mutagenesis, genetic transformation and genome editing) methods.

The cross-breeding strategy developed at CIRAD, called ‘reconstructive breeding’, aims at creating triploid hybrids directly from diploid germplasm. Our approach is based on the search for the best combining abilities between two diploids, one of which is a diplo-gamet donor. As diplo-gametes are quite rare in diploid clones, the chromosome stock of one of the two parents is doubled by a colchicine treatment, ensuring the regular production of diplo-gametes. This approach aims to combine the favorable traits contributed by both parents and to maximize heterozygosity in triploid progenies.

After a primary phase of evaluation of agronomic traits and pathogen resistance and fertility tests, mono- or interspecific diploids are selected. Genotypes intended for chromosome doubling are selected according to their agronomic characteristics, their behavior towards diseases and their paternal and/or maternal fertility. The doubled diploids are then crossed with complementary diploid parents leading to essentially triploid progenies subject to selection. Upstream, a pre-breeding phase aiming at increasing gamete fertility and combining favorable traits at the diploid level is conducted by hybridization between wild and cultivated diploid varieties and also includes the selection of Musa balbisiana-derived parents lacking infectious eBSV alleles for the creation of AxB interspecific hybrids.

The advantages of this approach are many: the genetic combinations selected at the diploid level are largely preserved by the diploid gametes and globally transferred to the final triploids. Moreover, these hybrids being triploid present the desired sterility. This strategy makes it possible to exploit the great diversity of the diploid complex. By combining new parents, it is thus possible to combine new selection criteria at any time in order to respond rapidly either to the emergence of new races of pathogens (such as FOC TR4) or to other selection objectives.

Key publications

Bakry F., Horry J.P., Jenny C.. 2021. Making banana breeding more effective. In : Kema Gert H.J. (ed.), Drenth André (ed.). Achieving sustainable cultivation of bananas. Volume 2 - Germplasm and genetic improvement. Cambridge : Burleigh Dodds Science Publishing, p. 217-256. (Burleigh Dodds Series in Agricultural Science, 86).
https://doi.org/10.19103/AS.2020.0070.12

F Salmon,, F Bakry, JC Efile, S Ricci, L Toniutti, JP Horry (à paraître) Banana breeding at CIRAD: Creating resistant new varieties to avoid the use of pesticides. Acta Horticulturae