Development of polymorphic microsatellite markers in sesame (Sesamum indicum L.)

Fifty microsatellite sequences (SSRs) were isolated from an enriched library of sesame (Sesamum indicum L.) using a modified protocol. After screening, 10 polymorphic microsatellites were used to determine their usefulness in diversity analysis among 16 sesame accessions. The number of alleles ranged from three to six alleles per locus with an average of 4.6 alleles. The fragment size varied from 150 bp to 307 bp. Expected heterozygosites (H_E) and polymorphism information contents (PICs) ranged from 0.437 to 0.858 and 0.34 to 0.80, respectively, which indicates the highly informative nature of the microsatellites reported here. These microsatellite markers will be very useful in diversity analysis among a large germplasm collection of sesame present in our Korean gene bank and also in the establishment of its core collection.     

Evaluation of the genetic diversity and population structure of sesame (Sesamum indicum L.) using microsatellite markers

Sixteen polymorphic microsatellite (SSR) markers, developed from an SSR-enriched genomic DNA library of sesame (Sesamum indicum L.), were used to assess genetic diversity, phylogenetic relationships, and population structure among 150 sesame accessions collected from 22 countries. A total of 121 alleles were detected among the sesame accessions. The number of detected alleles varied from 2 to 18, with an average of 7.6 alleles per locus. Polymorphism information content values ranged from 0.03 to 0.79, with an average of 0.42. These values indicated an excess of heterozygous individuals at 16 loci and an excess of homozygous individuals at three loci. Of these, 32 genotype-specific alleles were identified at 11 of 16 polymorphic SSR markers. Cluster analyses were performed by accession and population, revealing a complex accession distribution pattern with mean genetic similarity coefficient of 0.45 by accession and 0.52 by population. The wide variation in genetic similarity among the accessions revealed by SSRs reflected a high level of polymorphism at the DNA level. Model-based structure analysis revealed the presence of three groups that were basically consistent with the clustering results based on genetic distance. These findings may be used to augment the sesame germplasm and to increase the effectiveness of sesame breeding.     

Study of genetic variation in sesame (Sesamum indicum L.) using agro-morphological traits and ISSR markers

This research was conducted to study the genetic variation among eighteen genotypes of sesame (Sesamum indicum L.) collected from various agro-climatic regions of Iran along with six exotic genotypes from the Asian countries using both agro-morphological and ISSR marker traits. The results showed significant differences among genotypes for all agro-morphological traits and a relatively high genetic coefficient of variation observed for number of fruiting branches per plant, capsules per plant, plant height and seed yield per plant. Cluster analysis based on these traits grouped the genotypes into five separate clusters. Larger inter- than intra cluster distances implies the presence of higher genetic variability between the genotypes of different groups. Genotypes of two clusters with a good amount of genetic divergence and desirable agronomic traits were detected as promising genotypes for hybridization programs. The 13 ISSR primers chosen for molecular analysis revealed 170 bands, of which 130 (76.47%) were polymorphic. The generated dendrogram based on ISSR profiles divided the genotypes into seven groups. A principal coordinate analysis confirmed the results of clustering. The agro-morphological traits and ISSR markers reflected different aspects of genetic variation among the genotypes as revealed by a non significant cophenetic correlation in the Mantel test. Therefore the complementary application of both types of information is recommended to maximize the efficiency of sesame breeding programs. The discordance among diversity patterns and geographical distribution of genotypes found in this investigation implies that the parental lines for hybridization should be selected based on genetic diversity rather than the geographical distribution.     

Genotypic effects on pollen morphology in sesame (Sesamum indicum L.)

Summary The morphology (shape, exine wall pattern, diameter, volume, surface area) of mature pollen grains from eight genotypes, four within each of two capsule types (dehiscent, indehiscent) was studied. The shape was a flattened sphere (oblate) with a P (polar axis diameter): E (equatorial axis diameter) ratio = 0.69. The exine wall pattern consisted of a series of furrows passing through the poles and intersecting the equatorial plane at right (90°) angles. In cross section, the furrows appeared to be associated with shallow U-shaped structures with the intine protruding between these structures. Over the eight genotypes, the diameter, volume, and surface area were 65 m, 147300 m³, and 13444 m², respectively. For all three related characters, highly significant differences between capsule type and genotypes within capsule type were obtained. For each character, the dehiscent capsule type mean was larger than the indehiscent capsule type mean with minimum overlap among the four genotype means within each capsule type. Possibly, the numerous and diverse pleiotropic effects associated with this simply-inherited recessive indehiscent capsule type character includes pollen dimensions.     

A genetic linkage map construction for sesame (Sesamum indicum L.)

Sesame (Sesamum indicum L.) is one of the oldest oilseed crops with high seed oil quality. The first sesame genetic linkage map based on F2 segregating population of an intraspecific cross between two cultivars was constructed. Using three types of PCR-based markers, 284 polymorphic loci including 10 EST-SSR marker, 30 AFLP marker and 244 RSAMPL marker, respectively, had been screened. Subsequently, a total of 220 molecular markers were mapped in 30 linkage groups covering a genetic length of 936.72 cM, and the average distance between markers was 4.93 cM. In this map, the linkage groups contained from 2 to 33 loci each and ranged in distance from 6.44 cM to 74.52 cM. Based on map information, sesame genome length was estimated to be approximately 1,232.53 cM, and genome coverage of this map was about 76.0%. As a starting point of sesame genome study, the genetic linkage map will be hopeful to tag traits of breeding interest and further aid in the sesame molecular breeding. Furthermore, RSAMPL marker had been also appreciated in this paper, for its first usage in genetic map construction and higher utilization potential in some crop species lacking much genome information.     

Transesterified sesame (Sesamum indicum L.) seed oil as a biodiesel fuel

The sesame (Sesamum indicum L.) oil was extracted from the seeds of the sesame that grows in Diyarbakir, SE Anatolia of Turkey. Sesame seed oil was obtained in 58wt/wt%, by traditional solvent extraction. The methylester of sesame (Sesamum indicum L.) seed oil was prepared by transesterification of the crude oil. Transesterification shows improvement in fuel properties of sesame seed oil. This study supports the production of biodiesel from sesame seed oil as a viable alternative to the diesel fuel.     

Biological effects of low-energy C ion implantation on sesame (Sesamum indicum L.)

Field cultivation experiments on white sesame (Sesamum indicum L.)seeds implanted with low-energy C ion showed that different dosages of C ion implantation produce different biological effects.Sesame plants in 6 different dosage groups with C ion density respectively at 1×1011,1×1012,1×1015,5×1015,1×1016,5×1016 ion/cm2 were superior to the control group in plant height,leaf number,stalk diameter and leaf size.Further,sesame plants in these groups flower and seed earlier than those in the control group,and single plant yield also increased.Of all the groups,the 5×1015 ion/cm2 dosage group yielded the best effect,whereas the 1×1017/cm2 dosage group showed an evident inhibitory effect of ion implantation on the germination and growth of the sesame seeds.     

Global gene expression responses to waterlogging in roots of sesame (Sesamum indicum L.)

Waterlogging stress lowers yields in sesame (Sesamum indicum L.). A major component of waterlogging stress is the lack of oxygen available to submerged tissues. Although the morphology and physiology of plants grown under anaerobic conditions have been studied in detail, limited work has been done to elucidate adaptations at the molecular level. To gain comprehensive insight into how sesame responds to hypoxia at the genome level, we performed gene expression profiling at two time points during a 36-h period following hypoxic treatment using a whole-genome RNA-Seq analysis. We identified sets of significantly positively and negatively expressed genes (induced and repressed, respectively) in response to hypoxia with distinct temporal profiles. The genes that were affected were associated with glycolysis, nitrogen metabolism, starch and sucrose metabolism and plant hormone signal transduction and indicated the upregulation of particular pathways (glycolysis/glycogenesis) in the Kyoto Encyclopedia of Genes and Genomes. Moreover, significant changes in the expression of genes were found for pathways, including flavone and flavonol biosynthesis, steroid biosynthesis, photosynthesis, cysteine and methionine metabolism, glutathione metabolism, as well as phenylpropanoid biosynthesis, spliceosome, circadian rhythm. This study helps in elucidating the molecular mechanisms of waterlogging tolerance and provides a basis for the genetic engineering of sesame.     

The amino acid sequence of sesame (Sesamum indicum L.) and castor (Ricinus communis L.) cytochrome c

The amino acid sequences of sesame (Sesamum indicum L.) and castor (Ricinus communis L.) cytochrome c were determined by using 1.5mumol of protein from each species. Both molecules consist of a single chain of 111 amino acid residues and are homologous with other mitochondrial cytochrome c molecules. Both have an N-acetylated ;tail' of eight amino acids and two in-N-trimethyl-lysine residues, as also reported for wheat germ (Delange, Glazer & Smith, 1969) and mung-bean cytochrome c (Thompson, Laycock, Ramshaw & Boulter, 1970). Two different preparations of castor cytochrome c differed by one residue. This was glutamic acid for glutamine in position 100. The results for sesame and castor cytochrome c led to a re-examination and subsequent correction to the N-terminal region of the mung-bean cytochrome c sequence, as given by Thompson et al. (1970).     

Comparative analysis of genetic diversity of sesame (Sesamum indicum L.) from Vietnam and Cambodia using agro-morphological and molecular markers

The purpose of this study was to comparatively analyze the genetic diversity of sesame (Sesamum indicum L.) using agro-morphological and molecular markers. Twelve sesame populations collected from three regions in Cambodia and Vietnam were used in this study. A high genetic variation was revealed both by agro-morphological and RAPD markers within and among the 12 sesame populations. The range of agro-morphological trait based average taxonomic distance among populations (0.02 to 0.47) was wider than that of RAPD based genetic distance (0.06 to 0.27). The mean distance revealed by agro-morphological markers (0.23) and RAPD markers (0.22) was similar. RAPD based analysis revealed a relatively higher genetic diversity in populations from South Vietnam as compared to the other two regions. Interestingly, populations from this region also had higher values for yield related traits such as number of capsules per plant, number of seeds per capsule, and seed yield per plant suggesting positive correlation between the extent of genetic variation within population and yield related traits in sesame. A highly significant positive correlation (r = 0.88, P < 0.001) was found between agro-morphological and RAPD markers in estimating the genetic distance between populations. Both methods suggested the existence of a substantial amount of genetic diversity both in the Vietnamese and Cambodian populations. Although both agro-morphological and RAPD markers were found to be useful in genetic diversity analysis in sesame, their combined use would give superior results.     

Incidence and severity of foliar diseases of sesame (Sesamum indicum L.) intercropped with maize (Zea mays L.)

This study evaluates the effects of different row arrangements on incidence and severity of Cercospora leaf spot (CLS) and Alternaria leaf blight (ALB) diseases and seed health of sesame intercropped with maize. Row arrangements were: sesame intercropped with maize in alternate pair of rows (2:2), two rows of sesame intercropped with one row of maize (2:1), sesame intercropped with maize in single alternate rows (1:1) with sole sesame as control. Intercropping maize with sesame reduced the incidence and severity of diseases. Sesame intercropped with maize in a (1:1) ration recorded a significantly lower number of infected leaves by CLS and ALB incidence than other row arrangements. ALB lesion number was between 17 and 20 in the (1:1) arrangement relative to 65–104 and 28–43 in the sole crop and other row arrangements, respectively. ALB lesion size was also reduced in the (1:1) than other row arrangements. Fungal infection of harvested sesame seeds was significantly reduced in the intercrop relative to the sole crop. CLS incidence was significant and negatively correlated with seed weight while defoliation was significant and positively correlated with ALB or CLS incidence. Rainfall was significant and positively correlated with CLS or ALB incidence while intercropping induced microclimatic effects that influenced disease incidence. Grain yield, weight of 1000-seed, number of capsules/plant and weight of seed/plant were significantly higher in the (1:1) row arrangement than the sole crop or other row arrangements. The study demonstrates that intercropping sesame with maize in a single alternate row (1:1) arrangement can be used to reduce foliar diseases of sesame.     

A comparison of the effects of physical and chemical mutagens in sesame (Sesamum indicum L.)

Three sesame genotypes (Rama, SI 1666 and IC 21706) were treated with physical (γ-rays: 200 Gy, 400 Gy or 600 Gy) or chemical (ethyl methane sulphonate, EMS: 0.5%, 1.0%, 1.5% or 2.0%) mutagens and their mutagenic effectiveness and efficiency were estimated in the M (2) generation. The M (3) generation was used to identify the most effective mutagen and dose for induction of mutations. The average effectiveness of EMS was much higher than γ-rays. The lowest dose of γ-rays (200 Gy) and the lowest concentration of EMS (0.5%) showed the highest mutagenic efficiency in all genotypes. Analysis of the M (3) generation data based on parameters such as the variance ratio and the difference in residual variances derived from the model of Montalván and Ando indicated that 0.5% concentration of EMS was the most effective treatment for inducing mutations.     

In vitro regeneration of sesame (Sesamum indicum L.) from seedling cotyledon and hypocotyl explants

The goal of this study was to develop an efficient regeneration protocol to be used for genetic transformation of sesame. Published regeneration methods using benzyladenine (BA) and 1-naphthalene acetic acid (NAA) were unsuccessful for the cultivars used herein. Experiments were carried out using cotyledon and hypocotyl explants from the cultivar Mtwara-2. Later the optimised culture conditions were used to investigate the regeneration response of different genotypes. There was significant interaction between hormone treatments and macronutrients for shoot and root regeneration. Results also showed that shoot regeneration was significantly influenced by explant type. Shoots were only obtained from cotyledons whereas both cotyledons and hypocotyls could produce roots. Modified Murashige and Skoog (MS) medium with N6 macronutrients resulted in twice the shoot regeneration frequency obtained with ½MS macronutrients in the presence of thidiazuron (TDZ). The shoot regeneration frequency was significantly reduced when BA was used in place of TDZ. On shoot regeneration medium containing BA and NAA, only roots were formed. Replacing NAA with indole-3-acetic acid (IAA) greatly improved the regeneration of shoots. The optimum growth regulator combination for shoot regeneration was 20 μM TDZ together with 2.5 μM IAA, which gave a frequency of 63% and 4.4 shoots per regenerating explant for the best cultivar Ex-El. Genotypic differences were significant both for the number of explants regenerating shoots and the number of shoots produced per regenerating explant.     

Effects of germination on chemical composition and functional properties of sesame (Sesamum indicum L.) seeds

The changes of chemical composition and functional properties of derooted sesame (Sesamum indicum L.) seeds (DSS) before, during, and after germination were investigated. Sesame seeds germinated in dark chambers maintained near 100% relative humidity at 35 degrees C without presoaking reached >99% germination rate in 4 days with the final moisture content stayed ca. 2% (w/w), characterizing sesame seeds as orthodox seeds that are suitable for long term storage at low temperature and humidity under defined environment. With noticeable reduction in fat content (23%), germinated DSS were found rich in linolenic acid, P, and Na, increasing from 0.38% (w/w), 445 mg/100 g, and 7.6 mg/100 g before germination to 0.81% (w/w), 472 mg/100 g, and 8.4 mg/100 g after germination, respectively. DSS after germination contained considerable amount of Ca (462 mg/100 g), higher than that of soybean. Germinated DSS presents an excellent source of sesamol (475 mg/100 g), a potent natural antioxidant, and alpha-tocopherol (32 mg/100 g), the most active form of vitamin E.     

Changes in leaf cuticular waxes of sesame (Sesamum indicum L.) plants exposed to water deficit

Sesame (Sesamum indicum L.) is one of the most important oilseed crops, having seeds and oil that are highly valued as a traditional health food. The objective of this study was to evaluate leaf cuticular wax constituents across a diverse selection of sesame cultivars, and the responses of these waxes to drought-induced wilting. Water-deficit was imposed on 18 sesame cultivars by withholding irrigation for 15d during the post-flowering stage, and the effect on seed yield and leaf waxes compared with a well-watered control. Leaf cuticular waxes were dominated by alkanes (59% of total wax), with aldehydes being the next-most abundant class. Compared to well-irrigated plants, drought treatment caused an increase in wax amount on most cultivars, with only three cultivars having a notable reduction. When expressed as an average across all cultivars, drought treatment caused a 30% increase in total wax amount, with a 34% increase in total alkanes, a 13% increase in aldehydes, and a 28% increase in the total of unknowns. In all cultivars, the major alkane constituents were the C27, C29, C31, C33, and C35 homologs, whereas the major aldehydes were the C30, C32, and C34 homologs, and drought exposure had only minor effects on the chain length distribution within these and other wax classes. Drought treatments caused a large decrease in seed yield per plant, but did not affect the mean weight of individual seeds, showing that sesame responds to post-flowering drought by reducing seed numbers, but not seed size. Seed yield was inversely correlated with the total wax amount (-0.466*), indicating that drought induction of leaf wax deposition does not contribute directly to seed set. Further studies are needed to elucidate the ecological role for induction of the alkane metabolic pathway by drought in regulating sesame plant survival and seed development in water-limiting environments.     

Identification of sesame (Sesamum indicum L.) chromosomes using the BAC‐FISH system

• Sesame (Sesamum indicum L.; Pedaliaceae) is a commercially valuable oilseed crop with high oil content. Its small genome size favours the genomic analysis of key biological processes, such as oil synthesis and metabolism. However, the 13 chromosome pairs of sesame have not been characterised because of technological limitations and their small size.
• We constructed a BAC library comprising 57,600 BAC clones for sesame. The estimated genome coverage of the sesame BAC library was 13.8×. The successive double colour fluorescence in situ hybridisation (FISH) with bacterial artificial chromosomes (BACs) for sesame was established in this study.
• Subsequently, the 13 sesame chromosome pairs were individually differentiated using 17 specific BACs for the first time. The schematic of the sesame chromosome set was drawn according to the chromosome relative length and relative position of the BAC signal. The cytogenetic characteristics of sesame chromosomes were also explored.
• The results provide the technical background required for further cytogenetic map construction, genome assembly and localisation of the DNA sequence in sesame.

     

Characterization and genetic mapping of a novel recessive genic male sterile gene in sesame (Sesamum indicum L.)

Male sterile mutants play a very important role in the utilization of crop heterosis. A recessive genic male sterile (RGMS) two-type line 95ms-5AB was derived from a male sterile mutant of common white sesame (Sesamum indicum L.) cultivar Yuzhi 4 by treatment with gamma rays from ⁶⁰Co. Male sterile 95ms-5A plants did not show any other obvious differences from the male fertile 95ms-5B plants, except for having greenish, shriveled and slim anthers with few, small and degenerative pollens. Genetic analysis indicated that the male sterility of 95ms-5A was controlled by a single RGMS gene, Sims1 (Sesamum indicum male sterility 1). An allelic test with a previously identified RGMS mutant, ms86-1, confirmed that Sims1 in 95ms-5A is different from Sims2 in ms86-1. Amplified fragment length polymorphism markers linked to SiMs1 were screened using bulked segregant analysis. A genetic linkage map of the SiMs1 gene was constructed using 237 plants derived from the sib-mating between the near-isogenic lines 95ms-5A and 95ms-5B. The SiMs1 gene was found to be located in a region of 8.0 cM, at a distance of 1.2 cM from P06MG04 and 6.8 cM from P12EA14. In this genetic region, another marker P01MC08 was identified to be co-segregated with SiMs1. The linkage map constructed in this study will be very useful for marker-assisted selection and map-based cloning of SiMs1 as well as for hybrid breeding in sesame crop.