Oilseed rape (Brassica napus L.) is an important oilseed crop worldwide. The objective of this research was to study the genetic diversity and relationships of B. napus accessions using simple sequence repeat (SSR). A set of 217 genotypes was characterized using 37 SSR markers of mapping on the B. napus genome. The detected alleles were 2 to 11 at each of the 37 markers, with an average of 5.29 per marker. Unweighted pair group method with arithmetic mean (UPGMA) clustering enabled the identification of two general groups with increasing genetic diversity as follows: (1) group I was further divided into three groups (A, B and C), group A included 121 accessions, and consisted of the yellowseeded and black-seeded cultivars and breeding lines. The group B included 70 accessions and consisted mainly of the yellow-seeded cultivars and breeding lines, which were mostly cultivated in China. The group C included 10 accessions and consisted of the black-seeded cultivars and breeding lines with low levels of erucic acid. (2) Group II included 16 accessions consisted mainly of breeding lines and German cultivars, which were black-seeded lines with high levels of oleic acid (>80%) and low erucic acid and seed glucosinolate. The grouping of accessions by cluster analysis was generally consistent with known pedigrees, which included the grouping of lines derived both by backcrossing or self-pollination with their parents. The molecular genetic information gained enables also help breeders and geneticists to understand the structure of B. napus germplasm and to predict which combinations would produce the best offspring which is potentially interesting with respect to increasing heterosis in oilseed rape hybrids.
Domestication process and the subsequent breeding may result in a genetic mutation and selection pressures that possibly contributed to the emergence of two phenotypes of barley spikelets, namely six-row and two-row barley. The present study used microsatellite genetic markers to investigate the population genetics of a selected set of accessions of domesticated barley representing different populations of Jordan, to identify a signature of selection resulted from domestication process. Genomic and statistical approaches, such as the analysis of molecular variance (AMOVA) and the so-called hierarchical "outlier" tests, were utilized to identify signatures of selection. Generally, there was a high level of polymorphisms in all the studied populations, which ranged from 19.23 for Ramtha to 69.23 (%) for Zarga, with an average of 53.61 (%). The average number of allele per locus for the entire sample set was of 9.346 and it ranged 2 occurring at [(Bmag0136), (EBmac0970_a), (EBmac0970_c) loci], to 27 at (Bmac0040) locus. The results of AMOVA showed that the main portion (~72%) of total diversity was attributed to differentiations within populations. Other portions of diversity (11.040%) were explained by the diversity among populations. As revealed by the hierarchical outlier tests and AMOVA results, 9 microsatellites were identified to be under possible selection pressures, possibly indicates that these loci were important in the past improvement of barley by early cultivators. In conclusion, the present study shows that barley landraces of Jordan possess high levels of genetic diversity and allelic richness that could be utilized in barley improvement and breeding program.
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