Abstract
BackgroundOilseed Brassica represents an important group of oilseed crops with a long history of evolution and cultivation. To understand the origin and evolution of Brassica amphidiploids, simple sequence repeat (SSR) markers were used to unravel genetic variations in three diploids and three amphidiploid Brassica species of U’s triangle along with Eruca sativa as an outlier.ResultsOf 124 Brassica-derived SSR loci assayed, 100% cross-transferability was obtained for B. juncea and three subspecies of B. rapa, while lowest cross-transferability (91.93%) was obtained for Eruca sativa. The average % age of cross-transferability across all the seven species was 98.15%. The number of alleles detected at each locus ranged from one to six with an average of 3.41 alleles per primer pair. Neighbor-Joining-based dendrogram divided all the 40 accessions into two main groups composed of B. juncea/B. nigra/B. rapa and B. carinata/B. napus/B. oleracea. C-genome of oilseed Brassica species remained relatively more conserved than A- and B-genome. A- genome present in B. juncea and B. napus seems distinct from each other and hence provides great opportunity for generating diversity through synthesizing amphidiploids from different sources of A- genome. B. juncea had least intra-specific distance indicating narrow genetic base. B. rapa appears to be more primitive species from which other two diploid species might have evolved.ConclusionThe SSR marker set developed in this study will assist in DNA fingerprinting of various Brassica species cultivars, evaluating the genetic diversity in Brassica germplasm, genome mapping and construction of linkage maps, gene tagging and various other genomics-related studies in Brassica species. Further, the evolutionary relationship established among various Brassica species would assist in formulating suitable breeding strategies for widening the genetic base of Brassica amphidiploids by exploiting the genetic diversity present in diploid progenitor gene pools.
Highlights
Oilseed Brassica represents an important group of oilseed crops with a long history of evolution and cultivation
simple sequence repeat (SSR) marker variability/transferability across Brassica species Of the 124 Brassica-derived SSR loci assayed, 100% cross-transferability had been obtained for B. juncea and all three subspecies of B. rapa, while the lowest crosstransferability (91.93%) was obtained for Eruca sativa, where 114 SSRs showed successful amplification (Fig. 2, Additional file 1: Table S1)
In conclusion, the high level of SSR marker crosstransferability observed in this study demonstrated the usefulness of various Brassica-derived SSR markers for the analysis of genetic relationship and provided insights into the genomic evolution of various diploid and amphidiploids Brassica species
Summary
Oilseed Brassica represents an important group of oilseed crops with a long history of evolution and cultivation. The relationship between the six major cultivated Brassica species was originally described by U [2], who associated the diploid Brassica species including B. rapa, B. nigra and B. oleracea with the amphidiploid B. juncea, B. carinata and B. napus (Fig. 1). B. napus (AACC) is a recent allotetraploid species, obtained as a result of spontaneous hybridization between the diploid species B. rapa (AA) and B. oleracea (CC). B. carinata had been obtained by hybridization between B. nigra (BB) and B. oleracea (CC) and is cultivated in African countries. Since their parental genome species were thought to exist in diploid form and in different hemispheres, it became a hot research topic to explore the true progenitors for amphidiploid Brassica species. It is imperative to find out how their genome got modified during the course of evolutionary process
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