Diverged subpopulations in tropical Urochloa (Brachiaria) forage species indicate a role for facultative apomixis and varying ploidy in their population structure and evolution

Background Urochloa (syn. Brachiaria) is a genus of tropical grasses sown as forage feedstock, particularly in marginal soils. We aimed to clarify the genetic diversity and population structure in Urochloa species to understand better how population evolution relates to ploidy level and occurrence of apomictic reproduction. Methods We explored the genetic diversity of 111 accessions from the five Urochloa species used to develop commercial cultivars. These accessions were conserved from wild materials collected at their centre of origin in Africa, and tentatively represent the complete Urochloa gene pool used in breeding programmes. We used RNA-seq to generate 1.1 million SNP loci. We employed genetic admixture, principal component, and phylogenetic analysis for defining subpopulations. Results We observed three highly differentiated subpopulations in U. brizantha, which were unrelated to ploidy; one intermixed with U. decumbens, and two diverged from the former and the other species in the complex. We also observed two subpopulations in U. humidicola, unrelated to ploidy; one subpopulation had fewer accessions but included the only characterised sexual accession in the species. Our results also supported a division of U. decumbens between diploids and polyploids, and no subpopulations within U. ruziziensis and U. maxima. Conclusions Polyploid U. decumbens are more related to polyploid U. brizantha than to diploid U. decumbens, which supports the divergence of both polyploid groups from a common tetraploid ancestor and evidences of the hybridisation barrier of ploidy. The three differentiated subpopulations of apomictic polyploid U. brizantha accessions constitute diverged ecotypes, which can be likely utilised in hybrid breeding. Subpopulations were not observed in non-apomictic U. ruziziensis. Sexual Urochloa polyploids were not found (U. brizantha, U. decumbens) or were limited to small subpopulations (U. humidicola). The subpopulation structure observed in the Urochloa sexual–apomictic multiploidy complexes supports geographical parthenogenesis, where the polyploid genotypes exploit the evolutionary advantage of apomixis, i.e. uniparental reproduction and clonality, to occupy extensive geographical areas.

Bibliographic Details

Main Authors:	Higgins, Janet, Tomaszewska, Paulina, Pellny, Till K., Castiblanco, Valheria, Arango, Jacobo, Tohme, Joe, Schwarzacher, Trude, Mitchell, Rowan A., Heslop-Harrison, J.S., Vega, Jose J. de
Format:	Journal Article biblioteca
Language:	English
Published:	Oxford University Press 2022-11-17
Subjects:	grasslands, plant breeding, forage, rna sequence, apomixis, parthenogenesis, polyploidy, praderas, fitomejoramiento, forrajes, secuencia de arn,
Online Access:	https://hdl.handle.net/10568/125352 https://doi.org/10.1093/aob/mcac115
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