The triploid East African Highland Banana (EAHB) genepool is genetically uniform arising from a single ancestral clone that underwent population expansion by vegetative propagation

Abstract

All East African Highland Banana varieties are genetically uniform having arisen from a single clone introduced to Africa. East African Highland bananas (EAHBs) are a subgroup of triploid (AAA genome) bananas of importance to food security in the Great Lakes region of Africa. Little is known about their genetic variation, population structure and evolutionary history. Ninety phenotypically diverse EAHB cultivars were genotyped at 100 SSR microsatellite markers to investigate population genetic diversity, the correlation of genetic variability with morphological classes, and evolutionary origins since introduction to Africa. Population-level statistics were compared to those for plantain (AAB) and dessert (AAA) cultivars representing other M. acuminata subgroups. EAHBs displayed minimal genetic variation and are largely genetically uniform, irrespective of whether they were derived from the distinct Ugandan or Kenyan germplasm collections. No association was observed between EAHB genetic diversity and currently employed morphological taxonomic systems for EAHB germplasm. Population size dynamics indicated that triploid EAHBs arose as a single hybridization event, which generated a genetic bottleneck during foundation of the EAHB genepool. As EAHB triploids are sterile, subsequent asexual vegetative propagation of EAHBs allowed a recent rapid expansion in population size. This provided a basis for emergence of genetically near-isogenic somatic mutants selected across farmers and environments in East Africa over the past 2000 years since EAHBs were first introduced to the African continent.

Suitability of existing Musa morphological descriptors to characterize East African highland ‘matooke’ bananas

“…However, Creste et al (2003), using SSR to analyze 35 polyploid banana cultivars (3x AAA, AAB; 4x AAAA, AAAB) grown in Brazil, concluded that their phenetic analysis based on the Jaccard similarity index highly agreed with the morphological classification. Kitavi et al (2016) used 100 SSR markers to investigate the genetic diversity of 90 phenotypically diverse EAHB cultivars collected from Kenya and Uganda and compared them with plantain (AAB) and dessert (AAA) cultivars. They found out that EAHB cultivars had minimal genetic variation and were largely genetically uniform, irrespective of source of collection.…”

Molecular and cytological characterization of the global Musa germplasm collection provides insights into the treasure of banana diversity

“…The existence of a previously assumed fifth clone set (Mbidde), containing only bananas for beer making, has recently been abandoned (Kitavi et al 2016), its cultivars being morphologically and genetically indistinguishable from one or other of the aforementioned clone sets. Our results are in line with Kitavi et al (2016) findings that the four clone sets are part of a single subgroup stemming from a single original AAA hybrid that has probably been formed in eastern Indonesia (Perrier et al 2011) and diversified subsequently by multiple somatic mutations. A similar conclusion can be made for the subgroup of AAB 'African Plantains' that is subdivided into three clone types: Horn, False Horn and French, based on inflorescence morphology .…”

“…Risterucci et al 2009). Yet SSR markers are still used as an effective tool in elucidating the genetic diversity in many plant species, including bananas (Nicolai et al 2013;Mbanjo et al 2012;Gross-German and Viruel 2013;Liu et al 2015;Kitavi et al 2016). The main advantage of the SSR genotyping approach resides in its capability of systematically adding new information to existing data sets.…”

Trait variation and genetic diversity in a banana genomic selection training population

“…Variation in rainfall patterns impacts banana production by causing drought stress because most farmers in the region rely on rain for agricultural production. Although phenotypic variation is observed in EAHB, their genetic variation is low [9, 10] making them all susceptible to biotic and abiotic stress. Adaptation of cultivated banana varieties to changing environment is limited because while some are capable of sexual reproduction, they are all propagated clonally.…”