Genetics and diversity of Indonesian bananas

Chapter 1 is an introductory section and describes the aim of this thesis with a focus on providing insight into the rich genetic diversity of wild bananas in the center of diversity to eventually contribute to overall sustainability of global banana production.

Chapter 2 describes an exploration of wild Musa acuminata on Sumatra, one of the largest islands of the Indonesian archipelago and the world. In total 164 accessions from 164 locations in eight provinces of Sumatra and of 20 wild banana accessions in the collection of the Research Center for Biology (LIPI), originating from other regions of Indonesia were studied using morphological characteristics and multilocus genotyping. Analysis of the data revealed five types of wild M. acuminata on Sumatra. A principle component analysis showed that these were distributed over three major clusters. Based on these data it seems appropriate to merge the previously described var. halabanesis (Meijer) Nasution and var. alasensis Nasution into one subspecies halabanesis (Meijer) Hotta and to consider var. sumatrana (Becc.) Nasution as a subspecies. The multilocus genotyping showed a high genetic diversity of M. acuminata across Sumatra, often in isolated subpopulations of each subspecies.

Chapters 3 and 4 detail the cytogenetic complexity of bananas by describing the optimization of a chromosome spreading protocol for pollen mother cells and demonstrates its benefits by studying the meiotic features of five wild diploid M. acuminata bananas and the diploid (AA) cultivar banana “Rejang”, with particular attention on pairing configurations and chromosome transmission. Pollen analyses suggested partial sterility and unreduced gamete formation that likely resulted from restitutional meiotic divisions. How this affects breeding efforts is further described in a literature study in Chapter 4.

In chapter 5, the mapping of a resistance gene to the so-called Race 1 Fusarium strains is described, based on the genotyping and phenotyping of a selfed M. acuminata ssp. malaccensis population. The combined analyses of these data indicate a single dominant resistance locus near the distal part of chromosome 10. Graphical genotyping revealed molecular markers flanking a 360 kb genetic region associated with the resistance locus. The mapped region contains 165 putative genes on the reference genome, including 19 leucine-rich repeat receptor-like kinase-like genes. These data are the basis for a fine-mapping strategy towards cloning the resistance gene. Chapter 6 is a general discussion, which puts the data of the entire thesis in perspective of the urgently required diversification of the banana crop and how this can be achieved to eventually contribute to a sustainable banana production. This study supports millions of small holders in their livelihoods and consumers that need banana as a staple crop or fruit snack.