Expressed Sequence Tag-simple Sequence Repeat Research Articles

Mining and characterization of novel EST-SSR markers of Parrotia subaequalis (Hamamelidaceae) from the first Illumina-based transcriptome datasets.

Parrotia subaequalis is an endangered Tertiary relict tree from eastern China. Despite its important ecological and horticultural value, no transcriptomic data and limited molecular markers are currently available in this species. In this study, we first performed high-throughput transcriptome sequencing of two individuals representing the northernmost (TX) and southernmost (SJD) population of P. subaequalis on the Illumina HiSeq 2500 platform. We gathered a total of 69,135 unigenes for P. subaequalis (TX) and 84,009 unigenes for P. subaequalis (SJD). From two unigenes datasets, 497 candidate polymorphic novel expressed sequence tag-simple sequence repeats (EST-SSRs) were identified using CandiSSR. Among these repeats, di-nucleotide repeats were the most abundant repeat type (62.78%) followed by tri-, tetra- and hexa-nucleotide repeats. We then randomly selected 54 primer pairs for polymorphism validation, of which 27 (50%) were successfully amplified and showed polymorphisms in 96 individuals from six natural populations of P. subaequalis. The average number of alleles per locus and the polymorphism information content values were 3.70 and 0.343; the average observed and expected heterozygosity were 0.378 and 0.394. A relatively high level of genetic diversity (HT = 0.393) and genetic differentiation level (FST = 0.171) were surveyed, indicating P. subaequalis maintained high levels of species diversity in the long-term evolutionary history. Additionally, a high level of cross-transferability (92.59%) was displayed in five congeneric Hamamelidaceae species. Therefore, these new transcriptomic data and novel polymorphic EST-SSR markers will pinpoint genetic resources and facilitate future studies on population genetics and molecular breeding of P. subaequalis and other Hamamelidaceae species.

New Somatic Hybrid Mandarin Tetraploids Generated by Optimized Protoplast Fusion and Confirmed by Molecular Marker Analysis and Flow Cytometry

Six mandarin cultivars, Ponkan (Citrus reticulata), Willowleaf (Citrus deliciosa), Kinnow (Citrus nobilis × C. deliciosa), Murcott (purported C. reticulata × Citrus sinensis), W. Murcott [purported (C. reticulata × C. sinensis) × C. reticulata)], and Snack (purported C. reticulata hybrid), were used in protoplast fusion with different parental combinations to generate somatic hybrids. Sixty-five somatic regenerants were obtained using optimized formulation of enzymes and molecular weight of polyethylene glycol for improved protoplast yield and heterokaryon fusion rate, respectively. Flow cytometry was used to determine the ploidy level of somatic regenerants, and nuclear expressed sequence tag–simple sequence repeat (EST-SSR) markers to determine their parental source. Of the 65 somatic regenerants, 46 were identified as autotetraploids, 18 allotetraploids, and one undefined. The EST-SSR markers also revealed that some ‘W. Murcott’ embryogenic callus lines that were presumed to be of nucellar origin were actually derived unexpectedly from individual ovules of zygotic origin. These mandarin-derived tetraploids are valuable as potential breeding parents for interploid crosses with an aim at seedlessness and easy-peeling traits.

Antioxidant properties and structured biodiversity in a diverse set of wild cranberry clones

Wild germplasm with elevated antioxidants are a useful resource for using directly and in a breeding program. In a study with 136 wild clones and two cranberry cultivars, phenolic, flavonoid and anthocyanin contents varied 2.79, 2.70 and 17.46 times, respectively. The antioxidant activity ranged from 1.17 ± 0.01 to 2.53 ± 0.05 mg/g and varied 2.16 times. Seventy-five of wild clones and the cultivar Franklin were grouped into five distinct classes by molecular structure analysis using inter simple sequence repeat (ISSR), expressed sequence tag-simple sequence repeat (EST-SSR) and EST-polymerase chain reaction (PCR) markers. Grouping with DNA markers did not coincide with that of based on antioxidant properties. Present study indicates that genetic diversity analysis combined with antioxidant properties of wild germplasm play a significant role for conservation and in selecting diverse genotypes for future berry crop improvement.

De novo assembly of transcriptomes, mining, and development of novel EST-SSR markers in Curcuma alismatifolia (Zingiberaceae family) through Illumina sequencing

Curcuma alismatifolia widely used as an ornamental plant in Thailand and Cambodia. This species of herbaceous perennial from the Zingiberaceae family, includes cultivars with a wide range of colours and long postharvest life, and is used as an ornamental cut flower, as a potted plant, and in exterior landscapes. For further genetic improvement, however, little genomic information and no specific molecular markers are available. The present study used Illumina sequencing and de novo transcriptome assembly of two C. alismatifolia cvs, ‘Chiang Mai Pink’ and ‘UB Snow 701’, to develop simple sequence repeat markers for genetic diversity studies. After de novo assembly, 62,105 unigenes were generated and 48,813 (78.60%) showed significant similarities versus six functional protein databases. In addition, 9,351 expressed sequence tag-simple sequence repeats (EST-SSRs) were identified with a distribution frequency of 12.5% total unigenes. Out of 8,955 designed EST-SSR primers, 150 primers were selected for the development of potential molecular markers. Among these markers, 17 EST-SSR markers presented a moderate level of genetic diversity among three C. alismatifolia cultivars, one hybrid, three Curcuma, and two Zingiber species. Three different genetic groups within these species were revealed using EST-SSR markers, indicating that the markers developed in this study can be effectively applied to the population genetic analysis of Curcuma and Zingiber species. This report describes the first analysis of transcriptome data of an important ornamental ginger cultivars, also provides a valuable resource for gene discovery and marker development in the genus Curcuma.

Development of a Core Set of SSR Markers for Cultivar Identification and Seed Purity Tests in Oriental Melon (Cucumis melo L. var. makuwa)

Oriental melon (Cucumis melo L. var. makuwa), also called ‘Korean melon’ or ‘Chamoe’, is widely grown in East Asia, including Korea, Japan, and China. We used 521 simple sequence repeats (SSRs) to develop a core set of SSR markers as an effective tool for cultivar identification and seed purity tests in oriental melon. The polymorphism test using a subset of seven cultivars identified 20 expressed sequence tag SSR (EST-SSR) and 23 genomic SSR markers that showed high levels of polymorphism and simple segregation patterns. These SSR markers were used for DNA fingerprinting in additional 46 commercial cultivars. The average number of alleles per marker was 2.95 and 4.61 for the EST-SSR and genomic SSR markers in the 53 cultivars, respectively. For polymorphic information content (PIC), we found 0.411 to 0.816 with an average of 0.536 for the EST-SSR markers and 0.453 to 0.862 with an average of 0.568 for the genomic SSR markers. The unweighted pair group mean algorithm (UPGMA) dendrograms with the three sets of SSR markers (20 EST-SSR, 23 genomic SSR, and all 43 SSR markers) revealed that the 53 cultivars were separated into 4 to 5 major clusters. Furthermore, the set of all SSR markers was more effective at identifying the 53 cultivars relative to the other two marker sets. Therefore, the 43 SSR markers as a core set will be a valuable tool for several applications, including cultivar identification and seed purity tests in oriental melon.

Development and Characterization of EST-SSR Markers From RNA-Seq Data in Phyllostachys violascens.

Bamboo are woody grass species containing important economic and ecological values. Lei bamboo (Phyllostachys violascens) is a kind of shoot-producing bamboo species with the highest economic yield per unit area. However, identifying different varieties of Lei bamboo based on morphological characteristics is difficult. Microsatellites play an important role in plant identification and genetic diversity analysis and are superior to other molecular markers. In this study, we identified 18,356 expressed sequence tag-simple sequence repeat (EST-SSR) loci in Lei bamboo transcriptome data. A total of 11,264 primer pairs were successfully designed from unigenes of all EST-SSR loci, and 96 primer pairs were randomly selected and synthesized. A total of 54 primer pairs were used for classifying 16 Lei bamboo varieties and 10 different Phyllostachys species. The number of polymorphism alleles among the 54 primer pairs ranged from 3 to 12 for P. violascens varieties and 3 to 20 for Phyllostachys. The phylogenetic tree based on polymorphism alleles successfully distinguished 16 P. violascens varieties and 10 Phyllostachys species. Our study provides abundant EST-SSR resources that are useful for genetic diversity analysis and molecular verification of bamboo and suggests that SSR markers developed from Lei bamboo are more efficient and reliable than ISSR, SRAP or AFLP markers.

SRAPs and EST-SSRs provide useful molecular diversity for targeting drought and salinity tolerance in Indian mustard.

Abiotic stress tolerance is one of the target trait in crop breeding under climate change scenario. Selection of suitable gene pools among available germplasm is first requisite for any crop improvement programme. Drought and salinity traits, being polygenic, are most difficult to target. The present investigation aimed at exploring and assessment of the genetic variability in Indian mustard at molecular level. A total of twenty-five genotypes and five related species were used. Sixty-three molecular markers including sequence related amplified polymorphism (SRAP) markers along with twenty-three expressed sequence tag-simple sequence repeats (EST-SSRs) were used for diversity analysis. Thirty-seven SRAPs and 18 EST-SSRs showed amplification producing a total of 423 alleles of which 422 were polymorphic. These markers gave an overall polymorphism of 99.78%, with 99.67% polymorphism in SRAPs and 100% polymorphism in EST-SSRs. The study revealed the genetic relationships among different genotypes of B. juncea and related species which could be used for Indian mustard improvement for targeting drought and salinity tolerance in future. Four SRAP and two EST-SSRs identified unique bands which may be related to abiotic stress tolerance. EST sequence BRMS-040 (IM7) was similar to Brassica and radish sequences related to PR-5 (pathogenesis-related) protein.

Development and characterization of EST-SSR markers for Vitex negundo var. heterophylla (Lamiaceae).

Premise of the Study Vitex negundo var. heterophylla (Lamiaceae) is a dominant shrub in the warm temperate zone of northern China. Expressed sequence tag–simple sequence repeat (EST‐SSR) markers were developed to investigate its genetic diversity and structure.Methods and ResultsWe detected 12,075 SSRs in V. negundo var. heterophylla using transcriptome sequencing. Primer pairs for 100 SSR loci were designed and amplified in three populations of V. negundo var. heterophylla. Sixty loci were amplified, of which 14 were polymorphic. The number of alleles per locus ranged from two to 15, and levels of observed and expected heterozygosity ranged from 0.241 to 0.828 and from 0.426 to 0.873, respectively. All primer pairs amplified PCR products from V. rotundifolia but only four of them amplified products from Leonurus japonicus.ConclusionsThe identified EST‐SSR markers will be useful for future molecular and reproductive ecology studies of V. negundo var. heterophylla and V. rotundifolia.

Characterization and novel Est-SSR marker development of an important Chinese medicinal plant, Morinda officinalis How (Rubiaceae)

Morinda officinalis How (Rubiaceae) is well known as one of the four most popular medicinal plants in the southern region of China. In order to assess its genetic diversity and assist the development of its molecular assisted-selection breeding in China, we constructed the transcriptome database of M. officinalis using fresh leaf material and developed novel expressed sequence tag–simple sequence repeat (EST-SSR) markers for this important medicinal plant species. Our study identified 8064 potential EST-SSRs from 6668 unigenes. For perfect repeat motifs, the mononucleotide repeats were most abundant (4221; 52.34%), followed by the trinucleotide repeats (1588; 19.69%), and the dinucleotide ones (1040; 12.90%). The seven most commonly occurring repeat motifs were A/T (4661), AG/CT (588), AAG/CTT (408), AC/GT (353), ATC/ATG (338), AT/AT (296) and AGG/CCT (277). Of a total of 5605 SSR primer sets that were successfully designed de novo, 100 were selected for validation analysis. There, 24 primer sets were polymorphic across the 96 M. officinalis individuals collected from four different populations in Guangdong province. Based on cross-species transferability test, 19 and 22 primer sets produced successful amplification in M. umbellata subsp. obovata and M. parvifolia, respectively. These novel EST-SSR markers with high cross-species transferability between M. officinalis and its closely-related species could serve as aids to future studies in genetic diversity, conservation, assisted-selection breeding and genes associated with the medical uses of the genus.

The first transcriptome sequencing and analysis of the endangered plant species Picea neoveitchii Mast. and potential EST-SSR markers development

Picea neoveitchii Mast. is a rare and endangered evergreen coniferous tree species in China. P. neoveitchii grows within a specific ecological and geographical range. Here, we performed transcriptome sequencing of P. neoveitchii using the Illumina high-throughput deep sequencing technology with the following aims: (i) to perform de novo transcriptome assembly, (ii) to perform transcriptome assembly with functional annotation, (iii) to study the candidate genes involved in the biosynthesis of cellulose and lignin, (iv) to identify and analyse the transcription factors, and (v) to develop potential expressed sequence tag–simple sequence repeat (EST-SSR) markers for future population genomic and genome-wide association studies in P. neoveitchii. This is, to the best of our knowledge, the first study to provide a comprehensive transcriptome of P. neoveitchii. The transcriptome data contained 12.97 gigabase pairs (Gbp) for a total of 120,951 different transcripts belonging to 66,022 unigenes. In addition, we classified enzymes involved in the biosynthesis of cellulose and lignin and identified and analysed the transcription factors involved in stress responses, growth and development. Based on the larger than 1 kb unigenes, 1,814 EST-SSR markers were shown. Our results demonstrated that the transcriptome analysis is a valuable technology for non-model species with large genomes and this dataset will be an essential resource for future genetic and genomic research in P. neoveitchii.

Characterization of 20 new EST-SSR markers for northern red oak (Quercus rubra L.) and their transferability to Fagus sylvatica L. and six oak species of section Lobatae and Quercus

Northern red oak (Quercus rubra L.) is widely distributed in the eastern United States and southeastern Canada. It has also been introduced to Europe, where it has become an economically important plantation species now. Despite growing genomic resources, the number of available EST-SSR (expressed sequence tag – simple sequence repeat) markers for Q. rubra is still limited. Here, we used existing sequence information to provide a new set of EST-SSRs for northern red oak. In total, we report 20 polymorphic EST-SSRs, for which performance was evaluated in three Q. rubra populations from different regions in Michigan. We further tested the transferability of these markers to six additional oak species of section Lobatae (Quercus ellipsoidalis E.J. Hill, and Quercus georgiana M.A. Curtis) and Quercus (Quercus robur L., Quercus alba L., Quercus pedunculiflora K. Koch, and Quercus petraea (Matt.) Liebl.), as well as to European beech (Fagus sylvatica L.). The reported markers can be used in future population genetic studies.

A High-Density EST-SSR-Based Genetic Map and QTL Analysis of Dwarf Trait in Cucurbita pepo L.

As one of the earliest domesticated species, Cucurbita pepo (including squash and pumpkin) is rich in phenotypic polymorphism and has huge economic value. In this research, using 1660 expressed sequence tags-simple sequence repeats (EST-SSRs) and 632 genomic simple sequence repeats (gSSRs), we constructed the highest-density EST-SSR-based genetic map in Cucurbita genus, which spanned 2199.1 cM in total and harbored 623 loci distributed in 20 linkage groups. Using this map as a bridge, the two previous gSSR maps were integrated by common gSSRs and the corresponding relationships around chromosomes in three sets of genomes were also collated. Meanwhile, one large segmental inversion that existed between our map and the C. pepo genome was detected. Furthermore, three Quantitative Trait Loci (QTLs) of the dwarf trait (gibberellin-sensitive dwarf type) in C. pepo were located, and the candidate region that covered the major QTL spanned 1.39 Mb, which harbored a predicted gibberellin 2-β-oxidase gene. Considering the rich phenotypic polymorphism, the important economic value in the Cucurbita genus species and several advantages of the SSR marker were identified; thus, this high-density EST-SSR-based genetic map will be useful in Pumpkin and Squash breeding work in the future.

Application of EST-SSR markers developed from the transcriptome of Torreya grandis (Taxaceae), a threatened nut-yielding conifer tree.

Torreya grandis (Taxaceae) is an ancient conifer species endemic to southeast China. Because of its nutrient-rich and delicious seeds, this species has been utilized for centuries by the Chinese. However, transcriptome data and transcriptome-derived microsatellite markers for population genetics studies are still insufficient for understanding of this species’ genetic basis. In this study, a transcriptome from T. grandis leaves was generated using Illumina sequencing. A total of 69,920 unigenes were generated after de novo assembly, and annotated by searching against seven protein databases. In addition, 2,065 expressed sequence tag–simple sequence repeats (EST-SSRs) were detected, with the distribution frequency of 2.75% of total unigenes and average number of 0.03 SSRs per unigene. Among these EST-SSRs, 1,339 primer pairs were successfully designed, and 106 primer pairs were randomly selected for the development of potential molecular markers. Among them, 11 EST-SSR markers revealed a moderate level of genetic diversity, and were used to investigate the population structure of T. grandis. Two different genetic groups within this species were revealed using these EST-SSR markers, indicating that these markers developed in this study can be effectively applied to the population genetic analysis of T. grandis.

Microsatellite markers of finger millet (Eleusine coracana (L.) Gaertn) and foxtail millet (Setaria italica (L.) Beauv) provide resources for cross-genome transferability and genetic diversity analyses in other millets

The cross-genome transferability of 101 simple sequence repeats (SSR) markers of finger millet and 26 SSR markers of foxtail millet were analyzed in 8 other millets. In total, 33 finger millet and 2 foxtail millet SSR markers showed 100% cross-genome transferability in other millets. The cross-genome transferability of 101 finger millet and 26 foxtail millet SSR markers ranged from 47.52% to 61.38% and from 30.76% to 69.23% respectively. Expressed sequence tags SSR (EST-SSR) markers of finger millet showed higher level of cross-genome transferability than genomic SSR (gSSR) markers. The observed polymorphic information content (PIC) values were the same for finger millet and foxtail millet SSR markers which ranged from 0.14 to 1.00. Further, these data were also used for genetic diversity analysis among 8 millets using the software version 2.1 of NTSYSpc tool and PAST version 2. All millet species were grouped into one major cluster based on finger millet SSR markers, through UPGMA analysis. But two major clusters were observed by the analysis using foxtail millet SSR markers. Similarity value ranged from 0.238 to 0.714. Higher bootstrap values were observed in all cluster nodes. Successful analysis of genetic diversity was also confirmed by PCO and PCA analyses. This study would pave the way to understand the genetic structure of many nutritionally important millets lacking genomic resources. The SSR markers can also be used for further studies on analysis of genetic variation, population structure and germplasm characterization of millets.

Morphological and Genetic Diversity of Sea Buckthorn (Hippophae rhamnoides L.) in the Karakoram Mountains of Northern Pakistan

Sea buckthorn (Hippophae rhamnoides L.) is a dioecious, wind-pollinated shrub growing in Eurasia including the Karakoram Mountains of Pakistan (Gilgit-Baltistan territory). Contrary to the situation in other countries, in Pakistan this species is heavily underutilized. Moreover, a striking diversity of berry colors and shapes in Pakistan raises the question: which varieties might be more suitable for different national and international markets? Therefore, both morphological and genetic diversity of sea buckthorn were studied to characterize and evaluate the present variability, including hypothetically ongoing domestication processes. Overall, 300 sea buckthorn individuals were sampled from eight different populations and classified as wild and supposedly domesticated stands. Dendrometric, fruit and leaf morphometric traits were recorded. Twelve EST-SSRs (expressed sequence tags-simple sequence repeats) markers were used for genotyping. Significant differences in morphological traits were found across populations and between wild and village stands. A significant correlation was found between leaf area and altitude. Twenty-two color shades of berries and 20 dorsal and 15 ventral color shades of leaves were distinguished. Mean genetic diversity was comparatively high (He = 0.699). In total, three distinct genetic clusters were observed that corresponded to the populations’ geographic locations. Considering high allelic richness and genetic diversity, the Gilgit-Baltistan territory seems to be a promising source for selection of improved germplasm in sea buckthorn.

Development of EST-SSR markers in Larix principis-rupprechtii Mayr and evaluation of their polymorphism and cross-species amplification

We developed and validated a new set of polymorphic EST-SSR markers across Larix species and evaluated genetic diversity in a clonal seed orchard of Larix principis-rupprechtii Mayr. Prince Rupprecht’s larch (Larix principis-rupprechtii Mayr) is an important deciduous conifer species that has been widely planted in North China due to its major ecological and commercial value. However, the paucity of genomic data and robust molecular markers has hampered genetic and genomic studies. Here, transcriptome sequencing of L. principis-rupprechtii callus was performed using the Illumina platform. By mining 43,753 assembled unigenes, 1418 expressed sequence tag-simple sequence repeats (EST-SSRs) derived from 1300 unigenes were identified. A total of 1065 primer pairs were designed and 240 of these selected at random for validation among 24 L. principis-rupprechtii individuals. Of these, 52 primer pairs were scored as polymorphic, and 20 polymorphic EST-SSR markers were further selected to genotype 66 clones deployed in a clonal seed orchard of L. principis-rupprechtii; these exhibited a moderate level of genetic diversity, as reflected by the mean values of the number of alleles (Na = 3.85) and polymorphism information content (PIC = 0.424). Additionally, all of the 20 EST-SSR markers could amplify clear and stable bands across three related Larix species. A neighbor-joining (NJ) clustering tree uniquely distinguished 66 clones and distributed these into three main clusters, which was further validated by principal coordinate analysis (PCoA). The developed EST-SSR markers will serve as valuable tools for future genetics and breeding research in larch species. The evaluation of genetic diversity among 66 clones will provide important information for efficient management and utilization of genetic material in L. principis-rupprechtii breeding programs.

Influence of radiation on Hemarthria compressa's genetic variations

AbstractUsing the material of Hemarthria compressa (L.F.) R.Br. cv. YA’AN, we carried out this research to study the influence of radiation on the genetic variation of plants. Genetic difference was analyzed with expressed sequence tag‐simple sequence repeat (EST‐SSR) molecular marker through the comparison of 60Co‐γ radiation on H. compressa seed stems and original variety. By using 20 primer pairs, 176 polymerase chain reaction (PCR)‐amplifications with clear and consistent bands were obtained. The results showed that 155 of 176 bands were polymorphic, which indicating an 88.07% polymorphism rate, and each pair of primers had 8.8 amplified bands on average; the amplitude of polymorphism information content was 0.4709–0.6952 with an average value 0.6081. The genetic similarity coefficient of H. compressa and its mutants ranged from 0.4318 to 0.8239 with an average of 0.6671. As a consequence, existence of genetic differences between the mutants and the basic material was proved.

Evaluation of genetic variability within actual hop (Humulus lupulus L.) cultivars by an enlarged set of molecular markers

Traditional hop (Humulus lupulus L.) cultivars have been used in the brewing industry for a long time. Globally, about ten new breeding lines were released to the market in each decade from ~1970 to 1999. Since 2006, the rate of release of new cultivars has increased tenfold. It is, therefore, important to identify their genotype and origin. Molecular genetic methods based on DNA are the most appropriate technology for this purpose. Recently, we developed an efficient marker system for the authenticity control of hop genotypes based on expressed sequence tag-simple sequence repeats (EST-SSR). In the present study, we enlarged the previously established EST-SSR set with 27 new polymorphic markers and evaluated molecular genetic variability within 135 traditional and new world hop cultivars. Two sets of 10 markers effectively differentiated all used cultivars, with the exception of cultivars derived from the same original genotype such as Saaz, Spalt, Tettnang and Nadwislawsky. Results of molecular genetic variability analyses corresponded with the genealogical and geographical origin of the key cultivars.

Genetic diversity and virulence of Striga hermonthica from Kenya and Uganda on selected sorghum varieties

Joel KA, Runo S, Muchugi A. 2018. Genetic diversity and virulence study of Striga hermonthica from Kenya and Uganda on selected sorghum varieties. Nusantara Bioscience 10: 111-120. Parasitic weeds pose a severe problem in agricultural production, causing massive crop losses in many regions of the world and especially Africa. One example to be considered the most significant biological constraint to food production in sub-Saharan Africa (SSA) is Striga hermonthica, the most widespread among the Striga species in the semi-arid tropical African zones. The wide geographical distribution set conditions for genetically structured populations. The genetic variations among the weed populations allow for the quick breakdown of resistance in crops hence making control of the weed difficult. Efficient and effective control of S. hermonthica demands knowledge on inherent genetic variability within local and regional races of the weed. However, the genetic diversity and virulence of S. hermonthica ecotypes in Kenya and Uganda on selected sorghum varieties remain unknown. This study aimed at evaluating the genetic diversity among seven S. hermonthica populations from locations in Kenya and Uganda using 5 primer sets of Expressed Sequence Tags-Simple Sequence Repeats (EST-SSR). The genetic diversity was moderate as shown by the Nei’s genetic distance values. AMOVA measured low genetic differentiation among the populations. This study also investigated twelve sorghum varieties for their response to S. hermonthica infection. The result demonstrated that the varieties resistance responses to S. hermonthica varied widely. The phenotype of resistant interaction was characterized by the inability of the weeds haustoria to penetrate the sorghums root endodermis due to severe necrosis and in rare cases the parasites radicle growing away from the host root. The resistant sorghum varieties were the Asareca W2, Asareca AG3, N13 and the Wild-type which had low mean number of S. hermonthica plantlets growing on their roots, while the most susceptible varieties were Sap 027, Epurpur which had the highest mean number of S. hermonthica plantlets growing on their roots. There was a highly significant difference in the means of the number of Striga growing on the roots of sorghum varieties, Striga dry biomass and S. hermonthica length between the susceptible and resistant ones. This knowledge holds unique potentiality since resistant sorghum germplasm tested will be sourced and targeted to the seven specific geographical areas where virulence of the particular S. hermonthica populations was characterized.

English

Development of improved varieties of sweet potato to meet specific end users in the sub-Saharan African region has the potential of transforming the crop’s market, consumption and health benefits. Molecular biology techniques such as fingerprinting are key to crop improvement, and critical for numerous genetic studies. This study, carried out in Ghana, seeks to determine genetic relatedness among two populations of sweet potato (released and elite), as well as to identify polymorphic and informative markers for diversity studies. Twenty expressed sequence tags-simple sequence repeat (EST-SSR) markers were used for analysis of DNA assembled. A total of 169 alleles were obtained, with an average of 8.5 alleles per locus. Pairwise genetic distance among genotypes ranged from 12 – 89. GenAlex v6.4 analysis showed that a higher genetic diversity existed within elite genotypes than the released lines. Results analyzed using Popgene version 1.31 software indicated that on the basis of both populations studied, EST-SSR markers utilized were very polymorphic (95%) and showed genetic diversity (I =0.888, He= 0.548) suggesting high heterozygosity in the collected varieties. The overall Fit (0.372%) and Fis (0.088%) suggest high genetic diversity within populations, and gene flow (1.95) indicate an exchange of genes between released sweet potatoes and elite ones. Ewens-Watterson test was conducted to test the neutrality. From the results obtained, markers CB329940, CB330477 and CB330936 showed high allelic polymorphism among varieties used and were recommended to be included in diversity studies. Key words: Genetic diversity, genetic relatedness, expressed sequence tags-simple sequence repeat (EST-SSR), populations, released sweet potato, elite sweet potato.