Assessment of the genetic diversity and pattern of relationship of West African sorghum accessions using microsatellite markers

An understanding of the extent, distribution and patterns of genetic variation is useful for estimation of any possible loss of genetic diversity and assessment of genetic variability and its potential use in breeding programs, including establishment of heterotic groups. This study assessed patterns of genetic diversity and relationships among 30 West African sorghum accessions using 22 microsatellite markers. Population structure and within population genetic diversity was also assessed using the same markers. Genotypic data was generated using the ABI Prism 3730 and alleles called and sized using genemapper software version 3.7. Molecular data was analyzed using DARwin 4.0, powermarker 3.0 and Arlequin version 3.11. The average marker quality index was 0.27 while a mean PIC of 0.54 was observed across the 22 SSR markers. Among the 30 accessions, the markers detect a total of 146 alleles with an average of 6.6 alleles per marker. Results from the various statistical analyses performed revealed a wide range of polymorphism from 22.7 to 86.4%. The mean heterozygosity was relatively low at 0.28 while the average Nei’s genetic diversity among the 30 populations was 0.57. The within population Nei’s genetic diversity assessed from 49 individuals in 10 populations was lower at 0.54 and the average heterozygosity was also lower at 0.21. Cluster and principal coordinate analysis of the 30 populations revealed two distinct groups independent of their geographic origins The examination of the hierarchical partitioning of genetic variation by AMOVA demonstrated that genetic differentiation was significant at P < 0.00. Of the total diversity, 8.9% was attributed to country differences, 54.11% was attributed to population differences within the countries while 36.99% was attributed to differences within populations. The FST value (0.63) indicated a very high genetic differentiation as expected for selfing species. This study demonstrates the utility of SSR markers in detecting polymorphism, estimating genetic diversity and establishment of genetic clusters for heterotic studies.Keywords: Genetic diversity, heterozygosity, SSR microsatellites, heterotic grouping, alleles, polymorphismAfrican Journal of Biotechnology, Vol 13(14), 1503-151

Full Length Research Paper - Analysis of genetic structure in Melia volkensii (Gurke.) populations using random amplified polymorphic DNA

Melia volkensii   (Gurke.) is a popular fast growing agro forestry tree species in the East Africa's arid and semi arid lands (ASALs). The species is valued for its high quality termite resistant timber. In addition, its fruits are eaten by livestock thus making it the species of choice by small-scale farmers. However, the species has been overexploited and information on its existing gene pool is currently lacking. The present work was therefore carried out using random amplified polymorphic DNA (RAPD) markers to assess genetic diversity within and between populations in order to suggest appropriate conservation and management strategies. Eight RAPD primers generated 38 scorable polymorphic bands which were used to estimate genetic distances between populations and for construction of neighbour-joining phenograms. Analysis of Molecular Variance (AMOVA) indicated significant genetic differentiation between populations in the eastern and the coastal regions with 21.1%, (P < 0.0002) of the total variation attributed to differences between these regions. There was a clear split between populations from Eastern and Coastal populations of Kenya. These differences may be due to ecogeographical association with genetic variation and should be conserved to retain the full breadth of genetic variation of the species

Construction of a SSR-based genetic map and identification of QTL for domestication traits using recombinant inbred lines from a cross between wild and cultivated cowpea (V. unguiculata (L.) Walp.)

Cowpea (Vigna unguiculata (L.) Walp.) is a grain legume commonly grown and consumed in many parts of the tropics and subtropics. A genetic linkage map was constructed using simple sequence repeat (SSR) markers and a recombinant inbred (RI) population of159 individuals derived from a cross between the breeding line 524B, a California Blackeye, and 219-01, a perennial wild cowpea from Kenya. Out of 912 primer combinations predicted to amplify SSRs in cowpea, 639 reliably produced amplification products in PCR assays and 202 (31.6%) were polymorphic between the two parents. These polymorphic SSRs were used to construct a genetic map consisting of 11 linkage groups (LGs) spanning 677 cM, with an average distance between markers of 3 cM. Agronomic traits related to domestication (seed weight, pod shattering) were analyzed together with the genotypic data. Six quantitative trait loci (QTL) for seed size were revealed with the phenotypic variation ranging from 8.9 to 19.1%. Four QTL for pod shattering were identified with the phenotypic variation ranging from 6.4 to 17.2%. The QTL for seed size and pod shattering mainly cluster in two areas of LGs 1 and 10, facilitating the use of marker-assisted selection to eliminate undesirable wild phenotypes in breeding activities involving introgression of traits from wild germplasm. The generation of an SSR-based molecular map and additional trait-linked markers also contributes to the expanding tool kit available to cowpea breeders, especially in Africa

Molecular mapping of QTLs for domestication-related traits in cowpea (V. unguiculata (L.) Walp.)

Understanding the genetic basis underlying domestication-related traits (DRTs) of cowpea (Vigna unguiculata (L.) Walp.) is important since the genome has experienced divergent domestication and in addition it is also useful to utilize the wild germplasm efficiently for improving different traits of the cultivated cowpea. Quantitative trait loci (QTLs) for DRTs were identified in a population of 159 F-7 recombinant inbred lines derived from a cross between a domesticated cowpea (V. unguiculata (L.) Walp.) variety, 524B, and a wild accession, 219. Using the constructed linkage map, QTLs for 10 DRTs were analysed and mapped. QTLs for seed, pod and flower related traits were detected. Subsequently, QTL for ovule number was also identified. To our knowledge, this is the first time a QTL for this trait has been observed. QTLs for DRTs show co-localization on three linkage groups and pleiotropy or close linkage of genes for the traits is suggested in these chromosome regions. The information gained in this study can be used for marker-assisted selection of domestication-related QTLs in cowpea and enhance understanding of domestication in the genus Vigna

Mapping of quantitative trait loci for floral scent compounds in cowpea (Vigna unguiculata L.)

Floral scent is a very important trait in plant evolution. Currently, little is known about the inheritance of floral scent in cowpea (Vigna unguiculata L.) or changes that might have occurred during its domestication. Therefore, we analysed scent volatiles and molecular markers in a population of 159F(7) recombinant inbred lines derived from a cross of a domesticated blackeye cowpea cultivar, 524B' and a wild accession 219-01'. Using gas chromatography-mass spectrometry (GC-MS) 23 volatile compounds were identified that fall into five general functional categories. Twenty-two of the compounds displayed quantitative variation in the progeny, and a total of 63 QTLs influencing the amounts of these volatiles were mapped onto the cowpea genetic marker map. Although QTLs for volatile compounds putatively involved in cowpea flower scent were found on 9 of the 11 cowpea chromosomes, they were not evenly distributed with QTLs mainly clustered on LGs 1, LGs 2 and LG 4. Our results serve as a starting point for both more detailed analyses of complex scent biosynthetic pathways and the development of markers for marker-assisted breeding of scented rose varieties

Assessment of the genetic diversity and pattern of relationship of West African sorghum accessions using microsatellite markers

An understanding of the extent, distribution and patterns of genetic variation is useful for estimation of any possible loss of genetic diversity and assessment of genetic variability and its potential use in breeding programs, including establishment of heterotic groups. This study assessed patterns of genetic diversity and relationships among 30 West African sorghum accessions using 22 microsatellite markers. Population structure and within population genetic diversity was also assessed using the same markers. Genotypic data was generated using the ABI Prism 3730 and alleles called and sized using genemapper software version 3.7. Molecular data was analyzed using DARwin 4.0, powermarker 3.0 and Ariequin version 3.11. The average marker quality index was 0.27 while a mean PIC of 0.54 was observed across the 22 SSR markers. Among the 30 accessions, the markers detect a total of 146 alleles with an average of 6.6 alleles per marker. Results from the various statistical analyses performed revealed a wide the average Nei's genetic diversity among the 30 population was lower at 0.54 and the average heterozygosity was also lower at 0.21. Cluster and principal cooridinate analysis of the 30 populations revealed two distinct groups independent of their geographic origins The examination of the hierarchical partitioning of genetic variation by AMOVA demonstrated that genetic differentiation was siginficant at P<0.00. Of the total diversity, 8.9% was attributed to country difference, 54.11% was attributed to population differences within the countries while 36.99% was attributed to differences within populations. The Fst value (0.63) indicated a very high genetic differentiation as expected for selfing species. This study demonstrates the utility of SSR markers in detecting polymorphism, estimating genetic diversity and establishment of genetic clusters for heterotic studie

Analysis of genetic diversity in Eucalyptus grandis (Hill ex Maiden) seed sources using inter simple sequence repeats (ISSR) molecular markers

Eucalyptus grandis is an economically important tree species that is native to the Australian continent and its northern neighbours, where it is grown primarily for its hard wood timber and pulp for paper industries. It is widely grown in tropical countries such as South Africa, Kenya, Angola, Ghana, and Zimbabwe. Five ISSR primers generated 41 scorable polymorphic bands which were used to analyse genetic diversity between and within the seed sources and for construction of neighbour-joining phenogram. Mean Genetic Diversity per each primer loci based on Nei (1987) statistics indicated significant genetic variation between seed sources with 26.4%, (Gst = 0.264) of the total variation attributed to differences between seed sources. The variation between populations could be due to ecological, geographical association and gene flow rates and hence they should be conserved to retain the full breadth of genetic variation of the species. Thus, ISSR-PCR technology is a reliable, rapid (high throughput) and cost effective marker system that can be used to study genetic variation and genetic relationships among E. grandis seed sources