Genetic diversity among watermelon (Citrullus lanatus and Citrullus colocynthis) accessions

Genetic diversity was estimated among 42 U.S. PlantIntroduction (PI) accessions of the genusCitrullus (of these, 34 PIs are reported tohave disease resistance), and 5 watermelon cultivars, using 30RAPD primers. These primers produced 662 RAPD markers that could berated with high confidence. Based on these markers, geneticsimilarity coefficients were calculated and a dendrogram wasconstructed using the unweighted pair-group method witharithmetic average (UPGMA). The analysis delineated threemajor clusters. The first cluster consisted of a group of fivewatermelon cultivars, a group of C.lanatus var. lanatusaccessions, and a group of C.lanatus var. lanatusaccessions that contained some C.lanatus var. citroidesgenes. The second cluster consisted of the C.lanatus var. citroidesaccessions, while the third cluster consisted of theC. colocynthis accessions.The two C. lanatus clustersdifferentiated from each other and from the C.colocynthis cluster at the level of 58.8%and 38.9% genetic similarity, respectively. Assessment ofgenetic diversity among accessions that have been reported to havedisease resistance indicated that resistance to either anthracnose,downy mildew, powdery mildew, or watermelon mosaic virus is foundamong all major groups of Citrullus PIs.Additionally, resistance to gummy stem blight or Fusarium wilt mayexist among C. lanatus var.citroides PIs. This study demonstrates thatmolecular markers can be useful in assessing genetic diversity, andin sorting Citrullus PIs into phylogeneticgroups prior to their evaluation for disease or pestresistance.     

Genetic diversity and phylogenetic relationship of <Emphasis Type="Italic">Tadehagi</Emphasis> in southwest China evaluated by inter-simple sequence repeat (ISSR)

There are many valuable Tadehagi accessions in southwest China, but it is unknown that the genetic diversity and phylogenetic relationship of these Tadehagi resources. This report is the first study in which 41 primers of inter-simple sequence repeat (ISSR) were used to assess the genetic diversity of 36 Tadehagi accessions from 3 provinces in the southwest of China. Totally, 30 usable ISSR primers detected 163 polymorphic bands among the 36 accessions, which suggested high utility of ISSR primers in the genetic analysis of Tadehagi accessions. Genetic similarity coefficients among all of the accessions ranged from 0.54 to 0.92 with the average of 0.79 based on the ISSR data, indicating high level of genetic variation in Tadehagi resources from the southwest of China. As for the 3 population, Hainan population had the maximum average genetic similarity coefficients of 0.81, while similarity coefficient of Guangxi and Yunnan population was 0.75 and 0.74, respectively. All the 36 Tadehagi accessions were divided into 4 groups in the UPGMA dendrogram constructed from genetic similarity coefficients. The Tadehagi accessions from Yunnan and Guangxi provinces showed more genetic variation and occupied the bottom of the dendrogram. On the contrary, those from Hainan Province had less genetic variation and clustered in the middle and top of the dendrogram. The information on the genetic diversity and phylogenetic relationship from this study is propitious to construct a core germplasm collection and develop novel Tadehagi cultivars with desired economic traits.     

Geographic Pattern of Genetic Diversity Among 43 Ethiopian Mustard(Brassica carinata A. Braun) Accessions as Revealed by RAPD Analysis

As an oilseed crop, the cultivation of Ethiopian mustard (Brassica carinata) is restricted only to Ethiopia. Even though geographic diversity is a potent source of allelic diversity, the extent of genetic diversity among germplasm material of Ethiopian mustard from different countries has not been assessed. Forty-three accessions, comprising 29 accessions from eight different geographic regions of Ethiopia and 14 exotic accessions from Australia, Pakistan, Spain, and Zambia were analysed for their genetic diversity using random amplified polymorphic DNA (RAPD) technique. A set of 50 primers yielded a total of 275 polymorphic bands allowing an unequivocal separation of every Ethiopian mustard accession. The usefulness of the 50 RAPD primers in measuring heterozygousity and distinguishing accessions was variable such that polymorphic information content (PIC) varied from 0.05 to 0.40, band informativeness (BI) from 0.05 to 0.65 and primer resolving power (RP) from 0.15 to 6.83. Jaccard's similarity coefficients ranged from 0.44 to 0.87 indicating the presence of a high level of genetic diversity. On the average, Australian and Ethiopian accessions were the most similar while, Spanish and Zambian accessions were the most distant ones. Cluster analysis grouped the 43 accessions into four groups, which has quite a high fit (r = 0.80) to the original similarity matrix. With no prior molecular information, the RAPD technique detected large genetic diversity among the 43 accessions from five different countries and their grouping by dendrogram and principal coordinate analysis (PCoA) was inclined towards geographic differentiation of RAPD markers. Conversely, RAPD differentiation along geographic origin was not apparent within the Ethiopian accessions.     

Polymorphisms Among Chloroplast and Mitochondrial Genomes of <Emphasis Type="Italic">Citrullus</Emphasis> Species and Subspecies

Twelve and six DNA clones representing various parts of chloroplast and mitochondrial genomes, respectively, were used to detect polymorphism among five watermelon cultivars and 21 U.S. Plant Introductions (PIs) collected from diverse geographical locations and representing major groups of Citrullus species. Cluster analysis based on 20 chloroplast DNA (cpDNA) and 10 mitochondrial DNA (mtDNA) restriction fragment length polymorphism (RFLP) markers differentiated the accessions into three major phenetic groups: PIs and watermelon cultivars of Citrullus lanatus subsp. vulgaris (Schrad. ex Eckl. et Zeyh.) Fursa (also designated as C. lanatus var. lanatus) (group I), PIs of C. lanatus var. citroides (of C. lanatus subsp. lanatus Schrad. ex Eckl. et Zeyh.)(group II), and C. colocynthis (L.) Schrad. PIs (group III). The chloroplast and mitochondrial genomes of watermelon cultivars are distinct, but closely related to those of the C. lanatus var. lanatus PIs. On the other hand, the chloroplast and mitochondrial genomes of the wild species C. colocynthis are more similar to those of C. lanatus var. citroides. Polymorphic cpDNA and mtDNA markers identified in this study can complement isozyme and nuclear DNA data used in earlier phylogenetic and phenetic classifications of Citrullus PIs. These cpDNA and mtDNA markers are being used in experiments designed to enhance watermelon cultivars by replacing the chloroplast and mitochondrial genome of cultivated watermelon with those of the wild species C. colocynthis.     

Analysis of Genetic Diversity in Colonial Bentgrass (<Emphasis Type="Italic">Agrostis capillaris</Emphasis> L.) using Randomly Amplified Polymorphic DNA (RAPD) Markers

Colonial bentgrass (Agrostis capillaris L.) is a cool-season grass, native to temperate Asia and Europe. It has good tolerance to low temperatures and partial shade and is well suited to golf course fairways and tees. Little information is available regarding levels and patterns of genetic variation among populations of colonial bentgrass, which would be useful for breeding programs. To study the genetic relationships among 27 colonial bentgrass accessions obtained from the US National Plant Germplasm System (NPGS), randomly amplified polymorphic DNA (RAPD) markers were scored and analyzed. Out of 80 primers screened, 16 were selected for further analysis, which yielded a total of 120 polymorphic bands used to differentiate the accessions. Dice's similarity coefficients for pair-wise comparisons ranged from 0.23 to 0.84 based on the RAPD data. Since there was no similarity coefficient value close to 1 between any two accessions, there was no apparent duplication among the sampled accessions. A dendrogram constructed on the basis of the Unweighted Pair Group Method with Arithmetic average (UPGMA) clustering algorithm clearly separated 26 of the accessions into three clusters with one accession distinct from the rest. The least similar pair of accessions was PI 204397 from Turkey and PI 628720 from Bulgaria, and the most similar pair was PI 509437 from Romania and PI 491264 from Finland. Clustering patterns based on principal components analysis (PCA) corresponded well with the dendrogram. A high cophenetic correlation (r = 0.82) was found between the RAPD data matrix and cophenetic matrix. The accession PI 628720, from Bulgaria, did not cluster with any other accessions.     

Genetic diversity of <Emphasis Type="Italic">Nelumbo</Emphasis> accessions revealed by RAPD

Total 65 lotus accessions in genus Nelumbo mainly collected from China, were subjected to random amplified polymorphic DNA (RAPD) markers to estimate the genetic diversity and to test the genetic basis of the relationships between morphotypes and molecular markers. Seventeen primers generated a total of 195 highly reproducible and discernible loci, among which 173 were polymorphic. Percent polymorphism varied from 66.7 to 100 with an average of 88.72, and five primers out of them, OPC05, OPG10, OPN20, OPP09 and OPS17, showed 100% polymorphism. A relatively high genetic diversity was detected among all the samples with the similarity coefficient values ranging from 0.45 to 0.85, and Nei’s gene diversity (h) 0.30, and Shannon index (I) 0.46. The UPGMA dendrogram clustered 65 accessions in four clusters and the clustering pattern showed two groups, N. nucifera ssp. nucifera and those accessions related to the American lotus, and some special cultivars, landraces, hybrids and the American lotus. Principal Coordinate Analysis (PCA) further indicated that the genetic diversity of Nelumbo accessions was not evenly distributed, instead, was presented by a clustered distribution pattern. Similar to the results revealed by the dendrogram, two main groups representing the two subspecies of N. nucifera, as well as some special landraces, cultivars of Chinese lotus, the Japanese lotus and hybrids out of the two groups were obtained. Neither the UPGMA dendrogram nor the PCA analysis exhibited strict relationship with geographic distribution and morphotypes among the accessions.     

Assessment of genetic variation in a working collection of Vigna vexillata (L.) A. Rich. by isozyme and RAPD analyses

Genetic variation based on isozyme and RAPD analyses was investigated in 47 and 34 accessions respectively of Vigna vexillata from different geographical origins and belonging to three botanical varieties. A total of 9 enzyme systems were studied, accounting for 14 putative loci, 8 of which were polymorphic. The analysis of genetic diversity revealed a low level of within accession variation (H_S=0.013), while between accession diversity (D_ST) was 0.120. Coefficient of gene differentiation (G_ST) was 0.905, indicating that most variation was among accessions. Nei's genetic distances were calculated on the basis of allelic frequencies and a UPGMA dendrogram was constructed. Twenty arbitrary 10-mer oligonucleotides were used in RAPD analysis. Amplification profiles disclosed a higher level of polymorphism than isozymes. Based on amplification patterns, the similarity index of Jaccard was calculated and a dendrogram constructed on the basis of the similarity matrix. The final clustering based on RAPD data was similar to the one obtained using isozyme allelic frequencies. The classification in botanical varieties did not reflect the allelic constitution of the different samples. On the other hand, referring to geographical origin, most accessions from Africa and from Latin America were distributed respectively in two distinct clusters in the dendrogram. This grouping might also reflect the differences observed in the germination behaviour of V. vexillata from the two continents.     

High frequency oligonucleotides: targeting active gene (HFO-TAG) markers revealed wide genetic diversity among Citrullus spp. accessions useful for enhancing disease or pest resistance in watermelon cultivars

There is a continuous need to enhance watermelon cultivars for disease and pest resistance. Different U.S. Plant Introductions (PIs) of Citrullus lanatus subsp. lanatus var. lanatus [also known as C. lanatus (Thunb.) Matsum. et Nakai subsp. lanatus var. citroides (Bailey) Mansf. ex Greb.] (CLC) collected in southern Africa are a useful source for enhancing disease or pest resistance in watermelon cultivars. They are also valuable as rootstocks for grafted watermelon, particularly in fields infested with root-knot nematodes or Fusarium wilt. However, there is little information about genetic relationships among these PIs. In this study, genetic diversity was examined among 74 CLC PIs collected from their center of origin in southern Africa. Also, 15 Citrullus lanatus subsp. lanatus (CLL) PIs and the American heirloom cultivars Charleston Gray and Black Diamond (Citrullus lanatus subsp. vulgaris (Schrader ex Eckl. et Zeyh.) Fursa) (CLV) and five Citrullus colocynthis (L.) Schrader (CC) PIs collected in different locations throughout the world were used as out-groups in the phylogenetic analysis for the CLC PIs. Twenty-three high frequency oligonucleotides—targeting active gene (HFO-TAG) primers were used in polymerase chain reaction (PCR) experiments to produce a total of 562 polymorphic markers among the Citrullus PIs and cultivars. Cluster and multidimensional scaling plot analysis produced distinct groups of CLC, CLL, and CC PIs. Several PIs that were designated as CLC or CLL were in transitional positions, indicating that they are the result of gene flow between the major Citrullus groups or subgroups. Population structure analysis indicated that CLC comprises two subgroups; each containing a set of unique alleles. Also, unique alleles exist in the CLL and the CC genotypes. Overall, broad genetic diversity exists among the Citrullus PIs. The data in this study should be useful for identifying PIs with a wide genetic distance between them that could be used in breeding programs aiming to develop heterotic F₁ hybrid rootstock lines for grafted watermelon.     

The Genetic Diversity and Similarities Among <Emphasis Type="Italic">Kengyilia</Emphasis> Species Based on Random Amplified Microsatellite Polymorphism (RAMP)

The genetic diversity and similarities among 32 Kengyilia accessions, distributed to 14 species and one variety were analyzed by using random amplified microsatellite polymorphism (RAMP) markers. Of the 160 RAMP primer combinations tested, 40 (25%) produced polymorphic and clear bands. A total of 264 bands were produced by 40 primer combinations, among which 231 out of 264 bands (87.5%) were polymorphic. Two to 11 polymorphic bands could be amplified from each primer combination, with an average of 5.8 bands. The data of 264 bands were used for RAMP assay. By NTSYS-pc program, genetic similarity coefficients were generated and dendrogram was constructed using UPGMA. The genetic similarity coefficients ranged from 0.477 to 0.965 with the mean of 0.714. The results showed as follows: (1) distinct genetic differences were present among the different species; (2) the different accessions in a species were clustered together, respectively, which had larger genetic similarities and closer relations; (3) the species with similar morphological characters and the species from the same areas or neighboring geographical regions were clustered together; (4) the lowest genetic similarity was found between K. hirsuta (PI531618) and K. laxiflora (PI531631), while the highest genetic similarity was observed between K. hirsuta (Y2364) and K. hirsuta (Y2368); (5) RAMP results are basically comparable with those obtained from studies on morphology and cytology. It is a useful method for analysis of the genetic diversity and similarities in Kengyilia.     

Genetic Diversity of Asian Cotton (Gossypium arboreum L.) in China Evaluated by Microsatellite Analysis

Asian cotton (Gossypium arboreum L.) was once widely cultivated in China. It has also been a valuable source of genetic variation in modern cotton improvement. In this study, the genetic diversity of selected G. arboreum accessions collected from different regions of China was evaluated by microsatellite (simple sequence repeats, SSRs) analysis. Of the 358 microsatellite markers analyzed, 74 primer pairs detected 165 polymorphic DNA fragments among 39 G. arboreum accessions examined. Twelve accessions could be fingerprinted with one or more SSR markers. With the exception of two accessions, DaZiJie and DaZiMian, genetic similarity coefficients among all accessions ranged from 0.58 to 0.87 suggesting high level of genetic variation in the G. arboreum collections. The UPGMA dendrogram constructed from genetic similarity coefficients revealed positive correlation between cluster groupings and geographic distances. In addition, comparison of the microsatellite amplification profiles of the diploid G. arboreum and tetraploid Gossypium hirsutum L. found that size distribution of amplified products in G. arboreum was dispersive and that of G. hirsutum was relatively concentrated. The information on the genetic diversity and SSR fingerprinting from this study is useful for developing mapping populations for constructing diploid cotton genetic linkage map and tagging economically important traits.Diqiu Liu, Xiaoping Guo: These two authors contributed equally to this work.     

RAPD and ISSR fingerprinting in cultivated chickpea (<Emphasis Type="Italic">Cicer arietinum</Emphasis> L.) and its wild progenitor <Emphasis Type="Italic">Cicer reticulatum</Emphasis> Ladizinsky

Detection of genetic relationships between 19 chickpea cultivars and five accessions of its wild progenitor Cicer reticulatum Ladizinsky were investigated by using RAPD and ISSR markers. On an average, six bands per primer were observed in RAPD analysis and 11 bands per primer in ISSR analysis. In RAPD, the wild accessions shared 77.8% polymorphic bands with chickpea cultivars, whereas they shared 79.6% polymorphic bands in ISSR analysis. In RAPD analysis 51.7% and 50.5% polymorphic bands were observed among wild accessions and chickpea cultivars, respectively. Similarly, 65.63% and 56.25% polymorphic bands were found in ISSR analysis. The dendrogram developed by pooling the data of RAPD and ISSR analysis revealed that the wild accessions and the ICCV lines showed similar pattern with the dendrogram of RAPD analysis. The ISSR analysis clearly indicated that even with six polymorphic primers, reliable estimation of genetic diversity could be obtained, while nearly 30 primers are required for RAPD. Moreover, RAPD can cause genotyping errors due to competition in the amplification of all RAPD fragments. The markers generated by ISSR and RAPD assays can provide practical information for the management of genetic resources. For the selection of good parental material in breeding programs the genetic data produced through ISSR can be used to correlate with the relationship measures based on pedigree data and morphological traits to minimize the individual inaccuracies in chickpea.     

DNA markers and pollen morphology reveal that <Emphasis Type="Italic">Praecitrullus fistulosus</Emphasis> is more closely related to <Emphasis Type="Italic">Benincasa hispida</Emphasis> than to <Emphasis Type="Italic">Citrullus</Emphasis> spp.

The round melon Praecitrullus fistulosus (Stocks) Pangalo has been cultivated in Asia since ancient times and has been considered an underexploited crop in the western world. In the USA, there is an increased interest in using P. fistulosus as a commercial vegetable, and possibly as a rootstock for grafting watermelon, melon, or cucumber. However, the taxonomic classification of P. fistulosus is incomplete and for many years it has been considered a close relative of watermelon [Citrullus lanatus subsp. vulgaris (Schrad. ex Eckl. et Zeyh.) Fursa] and was previously classified as Citrullus lanatus subsp. fistulosus (Stocks) Duthie et J.B. Fuller. Here, we used two sets of DNA markers to assess the genetic similarity of P. fistulosus in relation to Citrullus spp. {including Citrullus lanatus subsp. vulgaris, C. lanatus subsp. lanatus, Citroides group [also known as C. lanatus (Thunb.) Matsum. et Nakai subsp. lanatus var. citroides (Bailey) Mansf. ex Greb.], and C. colocynthis (L.) Schrad.}, Cucumis spp. (including C. melo, C. sativus, C. anguria, C. meeusei, C. zeyheri), Benincasa hispida (Thunb.) Cogn., Lagenaria siceraria (Mol.) Standl. and Cucurbita spp. (including C. moschata Duchesne and the winter squash C. maxima Duchesne). The first marker set comprised 501 markers that were produced by 38 primer pairs derived from watermelon expressed sequenced tags (ESTs) containing simple sequence repeat (SSR) motifs (designated as EST-SSR primers; produced 311 markers), and by 18 primer pairs derived from ESTs that do not contain SSR motives (designated here as EST-PCR primers; produced 190 markers). The second marker set comprised 628 markers that were produced by 18 sequence related amplified polymorphism (SRAP) primer pairs. The phylogenetic data indicated that among these cucurbit species, the wax gourd B. hispida is the closest to the P. fistulosus. Pollen observations, using light microscopy, indicated that each of the cucurbit genera examined here has unique pollen morphology. The Cucurbita spp. have globular pollen grains with a stigmatic surface. The L. siceraria has polygonal pollen grains with symmetrical boundaries, while the Citrullus spp. and Cucumis spp. have ovular (conical) and triangular shaped pollen grains (respectively). The B. hispida and P. fistulosus have spherical or semispherical pollen grains. These pollen features appear to be in agreement with the phylogenetic relationships of these two species based on DNA markers. Analysis with 12 SRAP primer pairs revealed low genetic diversity among 18 United States Plant Introductions (PIs) of P. fistulosus, indicating the need to expand the germplasm collection of this cucurbit crop.     

Assessment of genetic diversity and genetic relationships among 29 populations of <Emphasis Type="Italic">Azadirachta indica</Emphasis> A. Juss. using RAPD markers

Randomly amplified polymorphic DNA (RAPD) analysis was employed to assess genetic divergence among 29 neem accessions collected from two agro-ecological regions of India (11 agro-climatic sub-zones), which cover three states, Punjab, Haryana and Rajasthan. Out of 24, 10-mer random primers used for studying genetic divergence, 14 were polymorphic, generating a total of 73 amplification products with an average of 5.21 products per polymorphic primer and estimated gene diversity of 0.49. Genetic relationships among accessions were evaluated by generating a similarity matrix based on Jaccard’s coefficient, ranging from 0.70 to 0.96. The phenetic dendrogram generated by UPGMA analysis grouped accessions into five clusters. RAPD performed within accessions (individual seedlings collected from the same mother plant) showed no variation indicating homogeneous population within accessions. Primers OPA-18, OPC-08 and OPI-03 were found most informative based on their resolving power. The degree of genetic variation detected among the 29 accessions with RAPD analysis suggests that RAPD can be used for studying genetic diversity in neem. The study also demonstrated that neem germplasm collected from northwestern plains of India shows no eco-geographical isolation based on sub-zones because accessions collected from different sub-regions are grouping together in the genetic tree.     

RAPD polymorphisms in Aegilops geniculata Roth (Ae. ovata auct. non L.)

Genetic diversity of eighteen accessions of Ae. geniculata (2n=28; UUMM) was assessed using the random amplified polymorphic DNA (RAPD) technique. We optimized RAPD conditions including the template DNA, the concentration of AmpliTaq DNA polymerase Stoffel fragment, and MgCl₂ concentration for revealing polymorphisms. Thirty-eight decamer oligonucleotides were individually used as primers under optimized conditions. Seventeen of these primers produced polymorphic RAPDs among the 18 accessions of Ae. geniculata. Polymorphisms were recorded by noting presence or absence of an amplification product from the total genomic DNA. Comparisons of unique and shared amplification products of each pair of accessions were used to generate genetic similarity coefficients (GSCs). These GSCs were used to construct a phenogram using an unweighted pair-group method with arithmetical averages (UPGMA). The phenogram shows that RAPD data is useful in the measurement of genetic variation or similarity within a species. It also indicates that we can select eight or nine accessions of the eighteen accessions to maintain at least 80% genetic variability of the Chinese collection of Ae. geniculata. Address for correspondence: Dr X-Y. Zhang, USDA-ARS-FRRL, Utah State University, Logan, UT 84322-6300, who is visiting the USA under an agreement between USDA-ARS and CMA-CAAS on germplasm resources.     

Set up of simple sequence repeat markers and first investigation of the genetic diversity of West-African watermelon (<Emphasis Type="Italic">Citrullus lanatus</Emphasis> ssp. <Emphasis Type="Italic">vulgaris</Emphasis> oleaginous type)

Citrullus lanatus ssp. vulgaris oleaginous type (West-African watermelon) is a crop cultivated in sub-Saharan Africa for its dried seeds reported to be rich in nutrients. In previous studies, little polymorphism was found in watermelon—cultivated for its flesh with the use of microsatellite (SSR) markers. Such study has never been applied to the oleaginous type until now. The objectives of the present study were firstly to apply the SSR markers set up for watermelon to the West-African watermelon and secondly to study the genetic structure of this type in Ivory Coast. For the first objective, 37 markers were studied on eight plants pertaining to four accessions. For the second objective, the polymorphic markers were applied on three morphologically and geographically separated accessions with twenty plants per accession. Multiple correspondence analysis (MCA), unweighted pair-group method with arithmetic averaging (UPGMA), molecular analysis of variance (AMOVA) and assignments test structure were applied. The optimal annealing temperature varied from 49 to 59°C according to the markers. Thirty-two markers that proved to amplify their respective loci were selected, but only nine of them appeared to show polymorphism on the set of 8 plants studied. The application of these markers on the three accessions revealed several features. No stucturation into sub-populations was observed inside a given accession. The genetic variance proved to be substantially higher between the different accessions than inside a given accession. Moreover this analysis is a first hint that the morphology classification does not match the genetic structure of C. lanatus. The results of this work provide the first quantitative information regarding the genetic variability of Citrullus lanatus oleaginous type. In order to sharpen our understanding of the mechanisms responsible for the genetic variance inter/intra accessions, further studies based on a larger sample of plants and accessions are required.     

Genetic variation in wild and cultivated artichoke revealedby RAPD markers

Determination of intraspecific genetic diversity is an important first step for the utilization of genetic resources and canprovide useful information on crop evolution. A living collection of Italian and foreign artichoke varieties and ecotypes is maintained at the Germplasm Institute, Bari, Italy. A total of 32 accessions of cultivated (Cynara cardunculus L. var.scolymus (L.) Fiori), three of wild (Cynara cardunculus var.cardunculus L.) artichoke and two ofcultivated cardoon (Cynara cardunculus var.altilis L.) were analysed in order to studygenetic variation and relationships within the species, using RAPDmarkers. Cultivated accessions were selected according tomorphological variation and geographical distribution available inthe collection. Fifty arbitrary decamer primers were initially tested, 18 ofwhich showed from 3 to 10 unambiguously interpretable fragments. Anintra-accession analysis using 4 varieties and 8 polymorphicprimers revealed that no RAPD variation was detected amongindividuals. Jaccard's similarity index (JSI) was comprisedamong 1 and 0.693 when all accessions were considered, on the otherhand, within the cultivated artichoke, JSI ranged between 1 and0.817. A UPGMA dendrogram based on the similarity matrix showed thatwild artichokes were clearly separated from cultivated accessions.Moreover, within cultivated artichokes, several groups could bedistinguished.     

A study of genetic diversity of sesame (<Emphasis Type="Italic">Sesamum indicum</Emphasis> L.) in Vietnam and Cambodia estimated by RAPD markers

Sesame (Sesamum indicum L.) is a traditional oil crop cultivated throughout South East Asia. To estimate the genetic diversity of this crop in parts at the region, 22 sesame accessions collected in Vietnam and Cambodia were analyzed using 10 RAPD markers. The 10 primers generated 107 amplification products of which 88 were polymorphic fragments (83%). Genetic diversity of all populations was H_t = 0.34 when estimated by Nei’s genetic diversity and species diversity was H′_sp = 0.513 when estimated by Shannon diversity index. Genetic distance ranged from 0.03 to 0.43, with a mean genetic distance of 0.23. The unweighted pair group method with arithmetic averages (UPGMA) cluster analysis for the 22 accessions divided the material in four groups. The dendrogram revealed a clear division among the sesame accessions based on their geographical region. Interestingly, some geographically distant accessions clustered in the same group, which might indicate the human factor involved in the spreading of sesame varieties. The high level of polymorphism shown suggests that RAPD techniques can also be useful for the selection of parents in sesame (Sesamum indicum L.) breeding program and for cultivar differentiation.     

Diversity analysis of <Emphasis Type="Italic">Aegilops</Emphasis> species from Morocco using RAPD markers

The diversity of 51 representative populations of the 5 Aegilops species from Moroccan collection was analyzed using 22 RAPD primers. We investigated the associations among these 5 Aegilops species (A. geniculata Roth (UUMM), A. triuncialis L. (UUCC), A. ventricosa Tausch (DDNN), A. peregrina (Hackel) Maire et Weiller (UUMM) and A. neglecta Req. ex Bert. subsp. recta (Zhuk.) K. Hammer (UUMMNN)); some diploid species considered as their ancestors; accessions of some neighboring countries and also accessions of Triticums. A total of 650 polymorphic RAPD fragments were amplified. A dendrogram was constructed using the un-weighed pair group method arithmetic average (UPGMA) and Jaccard`s similarity coefficient. The UPGMA clustering showed a regrouping to the level species with high level of the structuration of the diversity at A. geniculata. We confirm as reported by other authors, the proximity of N genome to U genome and C genome to M genome and also the difference between the genomes M and N. Thus, the phylogeny between the species and the different genomes were retracted.     

Analyses of genetic diversity and population structure of anchote (Coccinia abyssinica (Lam.) Cogn.) using newly developed EST-SSR markers

Anchote (Coccinia abyssinica (Lam.) Cogn.) is a perennial root crop belonging to Cucurbitaceae family. It is endemic to Ethiopia and distributed over wide range of agro-ecologies. For further improvement and efficient conservation of this crop, characterization of its genetic diversity and its pattern of distribution is a vitally important step. Expressed sequence tags-simple sequence repeats (EST-SSRs) markers were developed from publicly available watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] ESTs in the GenBank database. Among those novel markers, eight were polymorphic and subsequently used for genetic diversity and population structure analyses of 30 anchote accessions collected from western Ethiopia. A total of 24 alleles were obtained across the eight polymorphic loci and 30 accessions that revealed moderate level of genetic diversity in this minor crop. Among the eight loci, locus CA_06 was the most informative with six alleles and polymorphic information content (PIC) of 0.76. The accessions showed about threefold variation in terms of genetic diversity, with expected heterozygosity (He) ranging from 0.15 (accession An) to 0.44 (accession Dg). Other accessions with higher genetic diversity include Ar and Gu (He?=?0.43 and 0.41, respectively). Analysis of molecular variance (AMOVA) revealed that the variation within accessions and among accessions accounted for 84.7% and 15.3% of the total variation, respectively. The study revealed low but significant population differentiation in this crop with no clear pattern of population structure. The EST-SSR markers developed in this study are the first of their kind for anchote and can be used for characterization of its wider genetic resources for conservation and breeding purposes.

     

A phenetic analysis of morphological variation in Citrullus lanatus in Namibia

Morphological data recorded from field trials using Citrullus lanatus germplasm collected in Namibia were used to analyse and compare the various morphotypes of this species. The experiment comprised wild types and local landraces as well as commercial cultivars. Cluster analysis supported the indigenous classification system used in Namibia, in which Citrullus types are distinguished based on gross morphology, ecology and usage and grouped into seed, cooking and fresh-eating (watermelon) types. Commercial watermelon cultivars formed a distinct cluster. Wide variation was found within the local types whereas the genetic basis of the commercial type appears to be narrow. The commercial cultivars were most closely related to local watermelon types and more distantly related to the wild types, whereas the cooking melons form an intermediate group.