Search

Societal Impact Statement: Bananas are nutritious fruits of major importance worldwide. Characterizing their diversity is essential to ensure their conservation and use. A catalog showcasing cultivated bananas genomic diversity was compiled and is to be used as a tool to support the classification of banana cultivars. This research revealed that cultivated banana groups are not all made of identical clones. Materials from recent collecting missions indicated that more banana diversity is expected to be found as the exploration of the banana gene pool continues. These discoveries will drive dynamic conservation strategies for banana genetic resources and should increase their use. Summary: Banana is an important food crop cultivated in many tropical and subtropical regions around the world. Because banana cultivars often have low fertility, they are typically propagated clonally, which maintains desirable traits across generations. However, different factors, such as synonymy, incomplete passport data, and environmental effects, complicate the morphological‐based assignment of banana cultivars to specific clones or cultivar groups.In this study, we applied a previously developed genomic‐based tool for fine‐scale characterization of banana ancestry, known as in silico chromosome painting, to high‐throughput genotyping data from 317 banana accessions. This dataset covers most of the globally conserved, studied, and cultivated cultivar groups and includes both genebanks and new, uncharacterized materials.By comparing curated morphological assignation to the genomic patterns resulting from in silico chromosome painting, we compiled a diversity catalog referencing curated passport data, pictures, and chromosome painting patterns of the cultivar groups.Examining the genomic patterns obtained, intra‐cultivar group variability was discovered. In some cultivar groups, mitotic recombination or deletions accumulated clonally. In addition, at least four cultivar groups encompassed cultivars from distinct sexual events co‐existing, notably Pisang Awak with five distinct patterns across two ploidy levels. Finally, additional patterns were discovered in the newest materials of the set, showing that a wider diversity of clones still exists on farm. [ABSTRACT FROM AUTHOR]

SUMMARY: Hybridizations between Musa species and subspecies, enabled by their transport via human migration, were proposed to have played an important role in banana domestication. We exploited sequencing data of 226 Musaceae accessions, including wild and cultivated accessions, to characterize the inter(sub)specific hybridization pattern that gave rise to cultivated bananas. We identified 11 genetic pools that contributed to cultivars, including two contributors of unknown origin. Informative alleles for each of these genetic pools were pinpointed and used to obtain genome ancestry mosaics of accessions. Diploid and triploid cultivars had genome mosaics involving three up to possibly seven contributors. The simplest mosaics were found for some diploid cultivars from New Guinea, combining three contributors, i.e., banksii and zebrina representing Musa acuminata subspecies and, more unexpectedly, the New Guinean species Musa schizocarpa. Breakpoints of M. schizocarpa introgressions were found to be conserved between New Guinea cultivars and the other analyzed diploid and triploid cultivars. This suggests that plants bearing these M. schizocarpa introgressions were transported from New Guinea and gave rise to currently cultivated bananas. Many cultivars showed contrasted mosaics with predominant ancestry from their geographical origin across Southeast Asia to New Guinea. This revealed that further diversification occurred in different Southeast Asian regions through hybridization with other Musa (sub)species, including two unknown ancestors that we propose to be M. acuminata ssp. halabanensis and a yet to be characterized M. acuminata subspecies. These results highlighted a dynamic crop formation process that was initiated in New Guinea, with subsequent diversification throughout Southeast Asia. Significance Statement: Whole genome sequencing of wild and cultivated bananas suggested that banana domestication initiated in New Guinea and involved hybridization with M. schizocarpa, a species previously unsuspected to have importantly contributed to cultivars. Further diversification occurred through hybridizations with different local Musa sp. along Southeast Asia. This scenario resulted in banana cultivars having complex genomemosaics involving 3 to 7 ancestral genetic pools and several steps of meiosis, a much more complex scenario than previously thought. One of the recently reported unknown contributors was identified as M. acuminata ssp. halabanensis, a second one was found in many cultivars and remains to be discovered. [ABSTRACT FROM AUTHOR]

Societal Impact Statement: Global production of bananas, among the top 10 food crops worldwide, is under threat. Increasing the use of germplasm conserved in genebanks is crucial. However, the lack of or difficult access to genetic diversity information limits the efficient utilization of these valuable resources. Here, we present a digital catalog of high‐density markers for banana germplasm conserved at the international banana collection. By facilitating access to subsets of genetic diversity information, the catalog has potential to maximize conservation and use of climate‐ready varieties and to optimize breeding strategies. The catalog is extendable with data from any banana collection and the software is easily deployable in other crop genebanks. [ABSTRACT FROM AUTHOR]

Banana (Musa sp.) is a vegetatively propagated, low fertility, potentially hybrid and polyploid crop. These qualities make the breeding and targeted genetic improvement of this crop a difficult and long process. The Genome-Wide Association Study (GWAS) approach is becoming widely used in crop plants and has proven efficient to detecting candidate genes for traits of interest, especially in cereals. GWAS has not been applied yet to a vegetatively propagated crop. However, successful GWAS in banana would considerably help unravel the genomic basis of traits of interest and therefore speed up this crop improvement. We present here a dedicated panel of 105 accessions of banana, freely available upon request, and their corresponding GBS data. A set of 5,544 highly reliable markers revealed high levels of admixture in most accessions, except for a subset of 33 individuals from Papua. A GWAS on the seedless phenotype was then successfully applied to the panel. By applying the Mixed Linear Model corrected for both kinship and structure as implemented in TASSEL, we detected 13 candidate genomic regions in which we found a number of genes potentially linked with the seedless phenotype (i.e. parthenocarpy combined with female sterility). An additional GWAS performed on the unstructured Papuan subset composed of 33 accessions confirmed six of these regions as candidate. Out of both sets of analyses, one strong candidate gene for female sterility, a putative orthologous gene to Histidine Kinase CKI1, was identified. The results presented here confirmed the feasibility and potential of GWAS when applied to small sets of banana accessions, at least for traits underpinned by a few loci. As phenotyping in banana is extremely space and time-consuming, this latest finding is of particular importance in the context of banana improvement. [ABSTRACT FROM AUTHOR]

The production of bananas is threatened by rapid spreading of various diseases and adverse environmental conditions. The preservation and characterization of banana diversity is essential for the purposes of crop improvement. The world's largest banana germplasm collection maintained at the Bioversity International Transit Centre (ITC) in Belgium is continuously expanded by new accessions of edible cultivars and wild species. Detailed morphological and molecular characterization of the accessions is necessary for efficient management of the collection and utilization of banana diversity. In this work, nuclear DNA content and genomic distribution of 45S and 5S rDNA were examined in 21 diploid accessions recently added to ITC collection, representing both sections of the genus Musa. 2C DNA content in the section Musa ranged from 1.217 to 1.315 pg. Species belonging to section Callimusa had 2C DNA contents ranging from 1.390 to 1.772 pg. While the number of 45S rDNA loci was conserved in the section Musa, it was highly variable in Callimusa species. 5S rRNA gene clusters were found on two to eight chromosomes per diploid cell. The accessions were genotyped using a set of 19 microsatellite markers to establish their relationships with the remaining accessions held at ITC. Genetic diversity done by SSR genotyping platform was extended by phylogenetic analysis of ITS region. ITS sequence data supported the clustering obtained by SSR analysis for most of the accessions. High level of nucleotide diversity and presence of more than two types of ITS sequences in eight wild diploids pointed to their origin by hybridization of different genotypes. This study significantly expands the number of wild Musa species where nuclear genome size and genomic distribution of rDNA loci is known. SSR genotyping identified Musa species that are closely related to the previously characterized accessions and provided data to aid in their classification. Sequence analysis of ITS region provided further information about evolutionary relationships between individual accessions and suggested that some of analyzed accessions were interspecific hybrids and/or backcross progeny. [ABSTRACT FROM AUTHOR]