Genetic identity and relationships of Iranian apple (Malus?×?domestica Borkh.) cultivars and landraces, wild Malus species and representative old apple cultivars based on simple sequence repeat (SSR) marker analysis

In order to shed light on the role of Iran in apple evolution and domestication, we chose to investigate the relationships of a collection of 159 accessions of wild and domesticated apples including Iranian indigenous apple cultivars and landraces, selected wild species, and old apple scion and rootstock cultivars from different parts of the world. The majority of the wild species belonged to M. sieversii, which is widely believed to be the main maternal wild ancestor of domestic apples, from Kazakhstan and M. orientalis, which is one of the probable minor ancestors of domestic apples, from Turkey and Russia located on the east and west of Iran, respectively. The accessions were assigned into six arbitrary populations for the purpose of generating information on genetic parameters. Nine simple sequence repeat (SSR) loci selected from previous studies in apple were screened over DNA extracted from all the accessions. Results showed that all SSR loci displayed a very high degree of polymorphism with 11–25 alleles per locus. In total, there were 153 alleles across all loci with an average of 17 alleles per locus. The SSR allelic data were then used for estimation of population genetic parameters, including genetic variation statistics, F-statistics, gene flow, genetic identity, genetic distance and then cluster analysis using POPGENE 1.32 software. The F-statistics and gene flow in particular, showed that there was more intra-population than between population variation. The genetic identity and genetic distance estimates, and the dendrogram generated from the un-weighted pair group arithmetic average (UPGMA) method of cluster analysis showed that the Iranian cultivars and landraces were more closely related to M. sieversii from Central Asia (east of Iran) and M. orientalis native to Turkey and Russia than to other accessions of Malus species. Also, the old apple cultivars from different parts of the world have a closer genetic relationship to M. sieversii, M. orientalis and the Iranian apples, than to other wild species. Based on these results, we suggest that the Iranian apples may occupy an intermediate position between the domesticated varieties and wild species. We propose that Iran could be one of the major players in apples’ domestication and transfer from Central Asia to the western countries.     

Variation in melon (<Emphasis Type="Italic">Cucumis melo</Emphasis>) landraces adapted to the humid tropics of southern India

We present here the first comprehensive genetic characterization of melon landraces from the humid tropics of southern India. The genetic diversity among 50 melon landraces collected from 3 agro-ecological regions of southern India (6 agro-ecological sub-regions) was assessed by variation at 17 SSR loci, morphological traits of plant habit and fruit, 2 yield-associated traits, pest and disease resistance, biochemical composition (ascorbic acid, carotenoids, titrable acidity) and mineral content (P, K, Fe, Zn). Differences among accessions were observed in plant and fruit traits. Melon germplasm with high titrable acidity, higher than average amounts of mineral content and resistance to Cucumber mosaic virus, Zucchini yellow mosaic virus, powdery mildew (races 1, 2, 3, 5), Fusarium wilt (races 1, 2), Aphis gossypii and leafminer was recorded in the collection. A high level of genetic variability in melon germplasm was suggested by the SSR analysis. Comparative analysis using SSRs of the genetic variability between Indian melons from north, south, and east regions and reference accessions of melon from Spain, France, Japan, Korea, Iraq, Zambia showed regional differentiation between Indian melon accessions and that Indian germplasm was weakly related to the melon accessions from other parts of the world, suggesting that an important portion of the genetic variability found within this melon collection has not been used yet for the development of new cultivars. Additional collections of acidulus melon germplasm should be made in southern India and adequate management of this important genetic resource is clearly a necessity.     

Molecular characterization of mulberry genetic resources indigenous to India

Mulberry (Morus L.) is essential for the sericulture industry as the primary feed for the silkworm Bombyx mori L. in India, with its long tradition of practicing sericulture, has a large number of indigenous cultivars. Since knowledge on the genetic divergence of these cultivars/varieties is essential for proper conservation and utilization, Inter Simple Sequence Repeat (ISSR) profiling was employed to assess genetic relationships among 34 mulberry accessions, collected from different regions of India. By using 12 ISSR primers, which produced 72 markers displaying a high degree of polymorphism (94.4%), genetic dissimilarity coefficients were calculated for each pair of the accessions and clustering of the accessions with Unweighted Pair Group Method using Arithmetic average (UPGMA) analysis was done to unravel the genetic diversity among the accessions. The dissimilarity coefficients varied from 0.111 to 0.692. UPGMA analysis generated a dendrogram with six groups and five isolates. Clustering of the accessions did not correspond with the information on the geographic origin of many of the accessions. Two-dimensional representations of the relative positions of the accessions with regards to divergence using the first two canonical variates as co-ordinate axes revealed considerable variability among the cases in each group. Further, Discriminant Function Analysis (DFA) showed changes in the geographic origin of 11 accessions and species status of 20 accessions.     

Genetic Diversity Among Brazilian Cultivars and Landraces of Tomato Lycopersicon Esculentum Mill. Revealed by RAPD Markers

Random amplified polymorphic DNA markers (RAPD) were used to estimate the variability of 35 tomato accessions (Lycopersicon esculentum Mill.). A total of 257 reproducibly scorable bands were obtained from 20 primers, 78.6% of which were polymorphic. The percentage distribution of RAPD markers shows a bimodal distribution, and the frequency of rare alleles is similar in commercial and landrace accessions. Genetic distances among accessions were calculated and a dendrogram showing the genetic relationships among them was constructed allowing for the separation of four groups. Twenty out of 23 Brazilian landraces fell within one group, whereas commercial cultivars were distributed in the four groups. AMOVA analysis of RAPD data showed that, despite the high within Brazilian landraces and commercial cultivars variation, these two groups are significantly different, indicating that landraces can be a source of variation for breeding programs.     

Comparison of isozyme and random amplified polymorphic DNA data for determining intraspecific variation in Cucumis

Variation at isozyme and random amplified polymorphic DNA (RAPD) loci in eight cucumber and seven melon cultivars, breeding lines, and plant introductions were used to determine the utility of these markers for assessing genetic variation among populations of each species. Although dendrograms derived from cluster analyses using species' variation at marker loci were dissimilar, these disparities were consistent with differences in the pedigrees and/or other information (e.g., morphological) known about each accession and species. Empirical estimations of variances associated with each marker type in the cucumber and melon accessions examined indicate that, per band, lower coefficients of variation can be attained in the estimation of genetic difference when using RAPDs compared to isozymes. The disparity between the marker analyses made may be related to the amount of genome coverage characteristic of a particular marker system in a species and its efficiency in sampling variation in a population.     

Identification of intra-accession genetic diversity in selfing crops using AFLP markers: implications for collection management

Germplasm conserved as seeds in genebanks requires regular regeneration. In this process, selection and genetic drift may cause loss of genetic diversity from accessions. In the case of selfing crops, separation of distinct lines into different accessions may be an efficient strategy to avoid these negative effects. In order to evaluate the applicability of this method for collection management, knowledge about the level of intra-accession genetic diversity is required. By means of AFLP analysis intra-accession variation was investigated in two cultivars, two landraces and two wild populations of ex situ conserved barley germplasm. In the total sample of 216 individuals analysed (36 per accession), 22 genotypes were observed based on 104 polymorphic loci. The number of genotypes detected ranged from 1 to 3 per accession, except for a Nepalese landrace that revealed 12 genotypes. An UPGMA cluster analysis grouped the genotypes unambiguously into the accession they belonged to and genotypes within accessions were generally found to be closely related. In order to determine the repeatability of the results obtained, 11 individuals belonging to 4 genotypes from the Nepalese landrace were scored for a second set of AFLP markers. Matrices of genetic distances calculated for the two AFLP datasets were found to be highly correlated (r = 0.9346, P < 0.001). Separation of genotypes into different accessions was considered a relevant option only for the Nepalese landrace. Analysis of molecular variance indicated that this accession could be well divided into 8 distinct lines. Further implications of the results for genebank practices are discussed.     

Molecular Markers for the Classification of Switchgrass (Panicum virgatum L.) Germplasm and to Assess Genetic Diversity in Three Synthetic Switchgrass Populations

Information regarding the amount of genetic diversity is necessary to enhance the effectiveness of breeding programs and germplasm conservation efforts. Genetic variation between 21 switchgrass genotypes randomly selected from two lowland (‘Alamo’ and ‘Kanlow’) and one upland (‘Summer’) synthetic cultivars were estimated using restriction fragment length polymorphism (RFLP) markers. Comparison of 85 RFLP loci revealed 92% polymorphism between at least two genotypes from the upland and lowland ecotypes. Within ecotypes, the upland genotypes showed higher polymorphism than lowland genotypes (64% vs. 56%). ‘Kanlow’ had a lower percent of polymorphic loci than ‘Alamo’ (52% vs. 60%). Jaccard distances revealed higher genetic diversity between upland and lowland ecotypes than between genotypes within each ecotype. Hierarchical cluster analysis using Ward's minimum variance grouped the genotypes into two major clusters, one representing the upland group and the other the lowland group. Phylogenetic analysis of chloroplast non-coding region trnL (UAA) intron sequences from 34 switchgrass accessions (6 upland cultivars, 2 lowland cultivars, and 26 accessions of unknown affiliation) produced a neighbor-joining dendrogram comprised of two major clusters with 99% bootstrap support. All accessions grouped in the same cluster with the lowland cultivars (‘Alamo’ and ‘Kanlow’) had a deletion of 49 nucleotides. Phenotypic identification of greenhouse-grown plants showed that all accessions with the deletion are of the lowland type. The deletion in trnL (UAA) sequences appears to be specific to lowland accessions and should be useful as a DNA marker for the classification of upland and lowland germplasm.     

Genetic relationships and diversity among Brazilian cultivars and landraces of common beans (Phaseolus vulgaris L.) revealed by AFLP markers

The genetic variation and relationships among 31 accessions of Phaseolus vulgaris L., and two representatives of Vigna unguiculata L., were evaluated by AFLP analysis. A total of 263 DNA fragments across all materials were scored using nine primer combinations, averaging 32 per primer. More than 95% of the amplification products showed polymorphism, indicating high variation at the DNA level among these accessions. Pair-wise genetic similarity (Jaccard's coefficient) ranged from 0.553 to 0.840, with a mean of 0.765. Twenty-three accessions (70%) clustered into three groups. A majority of the commercial cultivars (91%) clustered within a single group, whereas the landraces were distributed along all the variation. An apparent correlation with phaseolin types was detected. Results of this study suggest that Brazilian landraces truly represent the overall genetic variability of Phaseolus vulgaris, confirming the multiple origins of these materials, and their potential as a source of variation for breeding programs.     

Application of random amplified polymorphic DNA to study genetic diversity in Paspalum scrobiculatum L. (Kodo millet, Poaceae)

Summary Genetic diversity and patterns of geographic variation among collections of Paspalum scrobiculatum (kodo millet) and P. polystachyum were studied using molecular markers generated through the random amplified polymorphic DNA (RAPD) method. A high level of polymorphism in RAPD markers was observed among the individual accessions, demonstrating the high genetic diversity of the crop. The markers obtained from the RAPD method were analyzed with the cluster analysis, principal coordinates and minimum spanning tree methods. Three major groups were resolved, one representing the African accessions, and two for the Indian accessions. The accessions of the north African kodo millet and P. polystachyum (considered conspecific with P. scrobiculatum) were quite distinct. The Australian kodo millet showed higher affinity to the African types. The study demonstrated that the RAPD technique can be applied to resolving degrees and patterns of genetic variation at the population and species levels, identifying cultivars, and defining gene pools of this crop.     

Genetic diversity of some accessions of Cucurbita maxima from Spain using RAPD and SBAP markers

Increasing the knowledge of the molecular diversity of a crop is essential for extending its genetic base, identifying cultivars and selecting parental varieties for breeding programs. In this sense, Cucurbita maxima Duch. is poorly characterised. Nineteen accessions of this species and 8 related Cucurbita accessions were included in a genetic diversity analysis. For this purpose, Random Amplified Polymorphic DNA markers (RAPDs), which analyse neutral variability, and Sequence-Based Amplified Polymorphism (SBAPs), which preferentially amplify coding regions of the genome, were used. While the UPGMA cluster and the principal coordinates analysis obtained using RAPDs did not group the different accessions according either to fruit morphological criteria or to passport data (origin and agro-climatic conditions), the principal coordinates analysis obtained using SBAPs grouped the different pumpkin accessions fundamentally according to the type of use (human consumption, animal fodder or ornamental). This passport trait is reported to be associated with agronomic breeding characters of interest. The usefulness of both types of markers for discriminating accessions of breeding interest is discussed.     

PCR Marker-based Analysis of Wild and Cultivated Yams (<Emphasis Type="Italic">Dioscorea</Emphasis> spp.) in Nigeria: Genetic Relationships and Implications for <Emphasis Type="Italic">ex situ</Emphasis> Conservation

Reliable characterization of the variation among wild and cultivated yams in Nigeria is essential for improved management and efficient utilization of yam genetic resources. RAPD and double stringency PCR (DS-PCR) analyses were used to investigate genetic relationships and the extent of redundancy among 30 accessions of two cultivated, and 35 accessions of four wild yam species collected from Nigeria. Twenty-five selected random decamer and two microsatellite primers were used individually and in combination to generate DNA profiles for each accession of the six Dioscorea species. The number of amplified fragments varied from 7 to 18 fragments per primer/primer combination. Different levels of intraspecific genetic diversity were found, with Dioscorea rotundata Poir. being the most variable. Based on identical profiles for the RAPD and DS-PCR primers, 12 duplication groups consisting of a total number of 37 accessions were observed in the present study. An UPGMA analysis grouped the majority of plants according to the species. Cultivated yams belonging to the D. cayenensis–rotundata species complex, which were classified into seven morphotypes/varietal groups, could be clearly separated into two major groups corresponding to D. rotundata Poir. and D. cayenensis Lam. D. cayenensis cultivars exhibited a low level of intraspecific variation and were genetically close to the wild species Dioscorea burkilliana J. Miège. D. rotundata cultivars classified into six varietal groups showed a high degree of DNA polymorphism and were separated into two major groups that appeared most closely related to Dioscorea praehensilis Benth. and Dioscorea liebrechtsiana de Wild. We propose, based on these results, that cultivars classified into D. cayenensis should be considered as a taxon separate from D. rotundata. The implications of intraspecific variability for the ex situ conservation of wild and cultivated yam germplasm in Nigeria are discussed.     

南瓜栽培品种的SSR分子标记分析及农艺性状多样性研究

为了研究南瓜栽培品种的遗传多样性,本研究利用43个简单序列重复(SSR)分子标记,对35份南瓜育成品种及地方品种进行了分子标记分析,并调查了农艺性状。结果表明,43个SSR标记均能扩增出多态性条带,共检测到155个等位基因,平均每个标记能检测到3.6个等位基因,多态性信息含量(PIC)为0.130 8~0.775 4,平均值为0.487 2。利用非加权组平均法(UPGMA)进行聚类分析,结果表明35份材料可分为三大类,分别与中国南瓜、印度南瓜和美洲南瓜三个种吻合,且印度南瓜与美洲南瓜之间的亲缘关系较近。农艺性状调查结果表明,不同栽培种之间以及同一栽培种内的不同品种之间,都发现有农艺性状差别明显的情况。本研究为南瓜种质资源的保护、品种指纹图谱的建立及分子育种提供了理论依据。     

Genetic Diversity and Relationships of Japanese Peach (<Emphasis Type="Italic">Prunus persica</Emphasis> L.) Cultivars Revealed by AFLP and Pedigree Tracing

To evaluate the genetic diversity and to clarify the genetic relationships of Japanese peach cultivars, we analyzed the amplified fragment length polymorphism (AFLP) and traced the pedigree of 17 Japanese commercial peach cultivars and six traditional accessions. Sixteen AFLP primer combinations produced a total of 837 fragments and 146 polymorphic bands with a polymorphism percentage of 17.5%. All of the peach accessions could be identified from differences in at least 10 polymorphic bands. A cluster analysis showed that all the Japanese commercial peach cultivars, except ‘Kiyomi’ and ‘Jichigetsuto’, formed a major group consisting of three sub-groups. Of the six traditional accessions, four were genetically distant from the Japanese commercial peach cultivars while two accessions from China were classified into the Japanese commercial peach cultivars group. Both the AFLP analysis and pedigree tracing suggested that Japanese commercial peach cultivars are mainly derived from ‘Shanhai Suimitsuto’, one of the traditional accessions from China. Although the genetic relationships revealed by AFLP were generally in agreement with those shown by the pedigree information, some contradictions were found. Combining the AFLP results and pedigree information can provide a better understanding of the genetic relationships of Japanese peach cultivars.     

Genetic diversity and structure of Ethiopian,Yemen and Brazilian C<Emphasis Type="Italic">offea arabica</Emphasis> L. accessions using microsatellites markers

Genetic diversity among 115 coffee accessions from the Coffea Germplasm Collection of IAC was assessed using SSR markers. The germplasm represents 73 accessions of Coffea arabica derived from spontaneous and subspontaneous plants in Ethiopia and Eritrea, species center of origin and diversity, 13 commercial cultivars of C. arabica developed by the Breeding Program of IAC, 1 accession of C. arabica cv. ‘Geisha’, 13 accessions of C. arabica from Yemen, 5 accessions of C. eugenioides, 4 accessions of C. racemosa and 6 accessions of C. canephora. Genetic analysis was performed using average number of alleles per locus (A), proportion of polymorphic loci (P), Shannon’s genetic index (H′ and G′_ST) and clustering analysis. All evaluated species were distinguished by a cluster analysis based on Jaccard’s coefficient. Differentiation between the cultivated plants of C. arabica and accessions derived from spontaneous and subspontaneous plants was observed. Spontaneous and subspontaneous accessions from Ethiopia were separated according to the geographical origin: east and west of the Great Rift Valley. Cultivated plants showed a low genetic diversity with a division in two groups: accessions from Yemen (H′=0,028) and Brazilian commercial cultivars (H′=0,030). The results agreed with previously reported narrow genetic basis of cultivated plants of C. arabica and supported the hypotheses about domestication of the species. This study also showed a significant genetic diversity among accessions from Ethiopia and Eritrea present in the Germplasm Collection of IAC. This diversity is specially observed in accessions from Sidamo (H′=0,143), Kaffa (H′=0,142) and Illubabor (H′=0,147) indicating their importance as source of genetic variability for coffee breeding programs.     

AFLP analysis of genetic diversity in five accessions of Polish runner bean (<Emphasis Type="Italic">Phaseolus coccineus</Emphasis> L.)

Runner bean (Phaseolus coccineus L.) is traditionally cultivated in Poland for dry seeds. The national collection of runner bean maintained in the National Center for Plant Genetic Resources gathers 152 accessions, which are mainly landraces originated in Poland (68%), Ukraine (17%) and Slovakia (10%). The collection contains valuable genetic resources for bean breeders and research. The aim of this study was to describe the level and structure of genetic diversity of three landraces and two commercial cultivars of runner bean from the national collection in order to assess their genetic potential for breeding. Amplified Fragment Length Polymorphism analysis included five combinations of selective primers. Analysis of seven genetic diversity parameters reveled fair amount of genetic variation both in landraces and cultivars. High genetic diversity of commercial cultivars relative those of landraces suggests that the breeding process leading to their release was rather moderate and most likely included domestic gene pool of runner bean. Low gene diversity and low Nei’s genetic distance values as well as intergradations among accessions in the PCoA may indicate reduced variability P. coccineus grown in Poland as a result of its migration pathways.     

DNA fingerprinting sheds light on the origin of introduced mulberry (Morus spp.) accessions in Italy

Mulberries are members of the genus Morus L., a taxonomic group showing a great genetic variability and adaptability to different environmental conditions. This study deals with the use of AFLP-based fingerprints as a tool for estimating genetic variability within as well as among three different mulberry species (i.e., M. alba L., M. latifolia Poir. and M. bombycis Koidz.). A high level of polymorphism (72.2) was found over all the 48 accessions analyzed. Genetic similarity (GS) within single Morus species ranged from 0.845 (M. bombycis) to 0.884 (M. alba) being intermediate in M. latifolia (0.869). The between-species mean genetic similarity estimates based on pair-wise AFLP marker fingerprint comparison were very similar ranging from 0.861 to 0.874. The partition of the genetic variation over the three Morus species was unexpected a proportion of the among-species genetic diversity as low as GST= 0.084 pointed out that about 92% of the total genetic diversity found among Morus accessions is due to DNA polymorphisms within a species, while only 8% of the total variation was highlighted among species. Our data indicate that some of the introduced accessions showing distinctive phenotypes, clearly differentiated from those revealed in the original habitat where they have been selected and adapted, hide an identical genotype.     

Molecular Characterization of the USDA White Clover (Trifolium repens L.) Core Collection by RAPD Markers

White clover is one of the most important forage legume species worldwide, playing an important role in Southern Brazil temperate cultivated pastures. This work was aimed to characterize the genetic variability of the USDA white clover core collection formed by 78 accessions representing 50 countries, together with two very well known cultivars (Huia and Ladino Regal), using RAPD (Random Amplified Polymorphic DNA) markers to produce genetic fingerprints. There were used DNA bulks formed by the extraction and mixture of 20 random individuals from each accession. Twenty four primers were used, which revealed from 3 to 29 bands, forming a total of 371 polymorphic bans and only one monomorphic, ranging from 50 to 3098 bp. The results showed a genetic similarity among the accessions, ranging from 0.18 to 0.58 (Jaccard’s index), with an average of 0.24, allowing the identification of each individual accession using just three primers. The results also showed a large genetic variability within the white clover core collection, probably due to its reproduction mode and ploidy level, which could be used in plant breeding program.     

Evaluation and utilization of <Emphasis Type="Italic">Aegilops</Emphasis> and wild <Emphasis Type="Italic">Triticum</Emphasis> species for enhancing iron and zinc content in wheat

Grains of 80 accessions of nine species of wild Triticum and Aegilops along with 15 semi-dwarf cultivars of bread and durum wheat grown over 2 years at Indian Institute of Technology, Roorkee, were analyzed for grain iron and zinc content. The bread and durum cultivars had very low content and little variability for both of these micronutrients. The related non-progenitor wild species with S, U and M genomes showed up to 3–4 folds higher iron and zinc content in their grains as compared to bread and durum wheat. For confirmation, two Ae. kotschyi Boiss. accessions were analyzed after ashing and were found to have more than 30% higher grain ash content than the wheat cultivars containing more than 75% higher iron and 60% higher zinc than that of wheat. There were highly significant differences for iron and zinc contents among various cultivars and wild relatives over both the years with very high broad sense heritability. There was a significantly high positive correlation between flag leaf iron and grain iron (r = 0.82) and flag leaf zinc and grain zinc (r = 0.92) content of the selected donors suggesting that the leaf analysis could be used for early selection for high iron and zinc content. ‘Chinese Spring’ (Ph ^I ) was used for inducing homoeologous chromosome pairing between Aegilops and wheat genomes and transferring these useful traits from the wild species to the elite wheat cultivars. A majority of the interspecific hybrids had higher leaf iron and zinc content than their wheat parents and equivalent or higher content than their Aegilops parents suggesting that the parental Aegilops donors possess a more efficient system for uptake and translocation of the micronutrients which could ultimately be utilized for wheat grain biofortification. Partially fertile to sterile BC₁ derivatives with variable chromosomes of Aegilops species had also higher leaf iron and zinc content confirming the possibility of transfer of required variability. Some of the fertile BC₁F₃ and BC₂F₂ derivatives had as high grain ash and grain ash iron and zinc content as that of the donor Aegilops parent. Further work on backcrossing, selfing, selection of fertile derivatives, leaf and grain analyses for iron and zinc for developing biofortified bread and durum wheat cultivars is in progress. Nidhi Rawat, Vijay K. Tiwari, and Neelam Singh have contributed equally to the work.     

Phenotypic biodiversity of an endemic wild pear, Pyrus mamorensis Trab., in North-Western Morocco using morphological descriptors

In this paper, we report on morphological diversity, ecology and flowering phenological records of an endangered and an endemic species of Morocco Pyrus mamorensis Trab. For this study, a survey was undertaken in North-Western Morocco (Mamora forest and Zaër region) whereby 67 accessions of P. mamorensis were sampled. A set of 33 genotypes of Pyrus spp. from the international collection INRA-Angers (France) of the genus Pyrus were also analyzed. The variability of the total of 100 accessions was assessed by twenty-six characters including fourteen qualitative and twelve quantitative traits. The results demonstrated high levels of morphological variation in the sampled accessions of P. mamorensis and established the relationships among the local germplasm using the UPGMA cluster analysis and the factorial discriminant analysis. Furthermore, we were able to distinguish three types of flowering in the Mamora forest: early, intermediate and late flowering type. Otherwise, the UPGMA classification comparing local accessions of P. mamorensis to the international collection led to the formation of four major groups showing the closest correspondence to their geographical origins: (1) The North African species represented by P. mamorensis, (2) The East Asian pea species, (3) The West Asian species and (4) The European species. These findings suggest the importance of implementing a conservation strategy preserving the genetic resources of wild pear in North-Western Morocco.     

Genetic diversity within a range of cultivars and landraces of flax (Linum usitatissimum L.) as revealed by RAPDs

Analysis of the extent and distribution of genetic diversity incrop plants is essential for optimizing sampling and breedingstrategies. We used random amplified polymorphic DNA (RAPD)markers to assess genetic diversity and relationships in 22 Canadiancultivars, 29 selected world cultivars and 10 landraces of flax(Linum usitatissimum L.). RAPDvariation was generally low and more variation was detected among,than within, the investigated flax accessions. Based on 53 variableRAPD loci observed for the 61 accessions, the landraces had a lowerproportion of fixed recessive RAPD loci (0.427) (i.e.,more genetic variation) than all of the flax cultivars examined(0.492). The linseed cultivars had a lower proportion ofrecessive loci (0.469) than the fiber flax cultivars(0.529). Canadian linseed cultivars had a lower proportionof recessive loci (0.465) than the selected world flaxcultivars (0.512). A trend was also observed that the rateof loss in genetic variation in Canadian flax breeding programs overthe last fifty years was approximately two variable loci per 100 lociper 10 years. Clustering analyses based on similarity estimatesshowed that the fiber cultivars were more related (or similar toeach other) and were classified as a homogeneous group. All ofthe linseed cultivars were clustered in diverse groups with the ninelandrace accessions. Implications of these findings for flax breedingand germplasm management are discussed.