Application of molecular markers to assess genetic relationships among accessions of wild oat,Avena sterilis

Summary The Avena sterilis collection in the National Small Grains Collection (NSGC) is an invaluable source of genetic variation to be exploited by oat breeding programs. Prior knowledge of the structure and distribution of genetic variation within the A. sterilis collection would be useful to efficiently screen the collection for valuable traits. To determine genetic structure within a subset of the collection, restriction fragment length polymorphisms were analyzed in a stratified sample of 173 accessions originating in eight countries of Africa and Southwest Asia. Of the 48 probes used for this study 43 detected polymorphism among accessions. The average number of RFLP patterns per probe ranged from 2.9 among Ethiopian accessions to 3.7 among those from Iran. Genetic variation, as measured by genetic distances and polymorphic indexes, was highest in Iran and lowest in Ethiopia. The probability of drawing a genotype from Iran or Iraq that is not present in the more western regions was high, indicating large genetic divergence of the Iran-Iraq accessions from the other regional collections surveyed. Cluster analysis of genetic distances and probabilities of unique genotypes clearly differentiated the eastern region (Iran and Iraq) from the western region (Algeria, Ethiopia, Israel, Lebanon, Morocco, and Syria). The western region could be further subdivided into two clusters, an African cluster (Algeria, Ethiopia, and Morocco) and a southwestern Asia cluster (Israel, Lebanon, and Syria). Genetic distances were generally related to but not proportional to geographical distances.     

Microsatellite variation in <Emphasis Type="Italic">Avena sterilis</Emphasis> oat germplasm

The Avena sterilis L. collection in the Plant Gene Resources of Canada (PGRC) consists of 11,235 accessions originating from 27 countries and is an invaluable source of genetic variation for genetic improvement of oats, but it has been inadequately characterized, particularly using molecular techniques. More than 35 accessions have been identified with genes for resistance to oat crown and stem rusts, but little is known about their comparative genetic diversity. This study attempted to characterize a structured sample of 369 accessions representing 26 countries and two specific groups with Puccinia coronata avenae (Pc) and Puccinia graminis avenae (Pg) resistance genes using microsatellite (SSR) markers. Screening of 230 SSR primer pairs developed from other major crop species yielded 26 informative primer pairs for this characterization. These 26 primer pairs were applied to screen all the samples and 125 detected alleles were scored for each accession. Analyses of the SSR data showed the effectiveness of the stratified sampling applied in capturing country-wise SSR variation. The frequencies of polymorphic alleles ranged from 0.01 to 0.99 and averaged 0.28. More than 90% of the SSR variation resided within accessions of a country. Accessions from Greece, Liberia, and Italy were genetically most diverse, while accessions from Egypt, Georgia, Ethiopia, Gibraltar, and Kenya were most distinct. Seven major clusters were identified, each consisting of accessions from multiple countries and specific groups, and these clusters were not well congruent with geographic origins. Accessions with Pc and Pg genes had similar levels of SSR variation, did not appear to cluster together, and were not associated with the other representative accessions. These SSR patterns are significant for understanding the progenitor species of cultivated oat, managing A. sterilis germplasm, and exploring new sources of genes for oat improvement.     

Patterns of AFLP variation in a core subset of cultivated hexaploid oat germplasm

Many core collections have been developed from large collections of crop germplasm, but most of these have not been characterized, particularly using molecular techniques, for germplasm management and utilization. We have attempted to characterize a structured sample representing a world collection of 11,622 cultivated hexaploid oat accessions in the hope of understanding the genetic structure of the world collection. The amplified fragment length polymorphism (AFLP) technique was applied to screen 670 accessions representing 79 countries and one group of uncertain origin. For each accession, 170 AFLP polymorphic bands detected by five AFLP primer pairs were scored. Analyses of the AFLP data showed the effectiveness of the stratified sampling applied in capturing country-wise AFLP variation. The frequencies of polymorphic bands ranged from 0.11 to 0.99, with an average of 0.72. The majority (89.9%) of the AFLP variation resided within accessions of each country, and only 6.2% of the AFLP differences existed among accessions of major geographic regions. Accessions from the Mediterranean region were the most distinct, while those from Russia and the USA were the most diverse. The two distinct groups that were observed were separated largely on the basis of common oat and red oat. Red oat was genetically more diverse than its common and hull-less counterparts, and hull-less oat was more related to common oat than red oat. Landrace and non-landrace accessions displayed similar AFLP variation patterns. These patterns are significant for understanding the domestication of cultivated oat and are useful in classifying the intraspecific diversity of oat germplasm, developing specific core subsets of the oat collection, and exploring new sources of genes for oat improvement.     

Comparative analyses of RFLP diversity in landraces of Triticum aestivum and collections of T. tauschii from China and Southwest Asia

 Chinese accessions of Triticum tauschii and T. aestivum L. from the Sichuan white (SW), Yunnan hulled (YH), Tibetan weedrace (TW), and Xinjiang rice (XR) wheat groups were subjected to RFLP analysis. T. tauschii and landraces of T. aestivum from countries in Southwest Asia were also evaluated. For T. tauschii, a west to east gradient was apparent where the Chinese accessions exhibited less diversity than those from Southwest Asia. Compared to the Southwest Asian gene pool, the Chinese T. tauschii was highly homogeneous giving a low frequency of polymorphic bands (16%) and banding patterns (1.33 per probe) with 75 RFLP probe-HindIII combinations. Accessions of T. tauschii from Afghanistan and Pakistan were genetically more similar to the Chinese T. tauschii than those from Iran. Of 368 bands found for 39 Chinese hexaploid wheat accessions with 63 RFLP probe-HindIII combinations, 28.3% were polymorphic with an average of 2.6 banding patterns per probe and 5.0 bands per genotype. The individual Chinese landrace wheat groups revealed less variation than those from Afghanistan, Iran, and Turkey. When classified into country based groups, however, the diversity level over all Chinese landraces was greater than that of some Southwest Asian landraces, especially those from Afghanistan and Iran . The XR wheat group was genetically distinct from the other three Chinese landrace groups and was more related to the Southwest Asian landraces. The TW group was genetically similar to, but more diverse than, the SW and YH groups. The Chinese landraces had a higher degree of genetic relatedness to the Southwest Asian T. tauschii, particularly to accessions from Iran, rather than to the Chinese T. tauschii. ‘Chinese Spring’ was most related to ‘Chengdu-guang-tou’, a cultivar from the SW wheat group. Received: 13 May 1997 / Accepted: 19 September 1997     

Genetic diversity in inter‐simple sequence repeat profiles across natural populations of Indian pomegranate (Punica granatum L.)

Pomegranate (Punica granatum L.), in the monogeneric family Punicaceae, is found in Iran, Afghanistan, India and Mediterranean countries. Iran is considered to be its primary centre of origin. In India, pomegranate occurs naturally only in the Western Himalayan regions of Jammu and Kashmir, Himachal Pradesh and Uttarakhand States. However, there is no information about genetic variation in wild pomegranate at population level. In this paper, we describe genetic diversity across natural populations of Indian pomegranate based on inter‐simple sequence repeat (ISSR) markers. Forty‐nine accessions representing eight populations from two regions were analysed using ISSR. Seventeen ISSR primers resulted in 268 polymorphic bands, with 87.01% polymorphism throughout the accessions. Pair‐wise population genetic distances ranged from 0.05 to 0.45, with a mean of 0.25 between populations. amova and Nei’s genetic diversity analyses revealed higher genetic variation within populations than among populations. A higher genetic differentiation (G_ST) was observed between the spatially distant populations, indicating a low level of genetic exchange (Nm) among these populations. However, clustering of populations was not in accordance with their geographical affiliations in the tree. The results indicate that the ISSR method is sufficiently informative and powerful to assess genetic variability in pomegranate, and that patterns of genetic variability observed among populations of wild pomegranate from the Western Himalaya differ. Estimation of genetic variation reported here provides a significant insight for in situ conservation and exploitation of genetic resources for this economically important species as potential breeding material.     

Molecular diversity and landscape genomics of the crop wild relative Triticum urartu across the Fertile Crescent

Modern plant breeding can benefit from the allelic variation that exists in natural populations of crop wild relatives that evolved under natural selection in varying pedoclimatic conditions. In this study, next‐generation sequencing was used to generate 1.3 million genome‐wide single nucleotide polymorphisms (SNPs) on ex situ collections of Triticum urartu L., the wild donor of the A^u subgenome of modern wheat. A set of 75 511 high‐quality SNPs were retained to describe 298 T. urartu accessions collected throughout the Fertile Crescent. Triticum urartu showed a complex pattern of genetic diversity, with two main genetic groups distributed sequentially from west to east. The incorporation of geographical information on sampling points showed that genetic diversity was correlated to the geographical distance (R² = 0.19) separating samples from Jordan and Lebanon, from Syria and southern Turkey, and from eastern Turkey, Iran and Iraq. The wild emmer genome was used to derive the physical positions of SNPs on the seven chromosomes of the A^u subgenome, allowing us to describe a relatively slow decay of linkage disequilibrium in the collection. Outlier loci were described on the basis of the geographic distribution of the T. urartu accessions, identifying a hotspot of directional selection on chromosome 4A. Bioclimatic variation was derived from grid data and related to allelic variation using a genome‐wide association approach, identifying several marker–environment associations (MEAs). Fifty‐seven MEAs were associated with altitude and temperature measures while 358 were associated with rainfall measures. The most significant MEAs and outlier loci were used to identify genomic loci with adaptive potential (some already reported in wheat), including dormancy and frost resistance loci. We advocate the application of genomics and landscape genomics on ex situ collections of crop wild relatives to efficiently identify promising alleles and genetic materials for incorporation into modern crop breeding.     

Morphological and molecular genetic variations of oat genotypes grown in Kermanshah,Iran

Morphological traits and molecular markers are two common methods for genetic variation studies. Molecular markers, morphological traits methods and relationship between the two were used to study genetic variation among 43 oat genotypes and varieties. For this purpose, an augmented design was conducted in three replicates at 2008–2009 cropping season in the experimental field of Campus of Agriculture and Natural Resources of Razi University, Kermanshah, Iran. Four wild oat accessions (Avena sterilis) were added to evaluated genotypes in molecular experiment. Results showed a significant variation among genotypes for all morphological traits and they were classified based on this variation in four groups by WARD cluster analysis. In molecular experiment, 28 inter simple sequence repeat (ISSR) primers amplified 206 polymorph bands. Based on Jaccard similarity matrix, similarity among genotypes was varied from 0.23 to 0.66 and cluster analysis classified genotypes in seven groups by complete linkage method. The correlation between ISSR marker and morphological traits classifications was not significant. ISSR showed to be a helpful marker for genotype identity and separation as it put wild accessions in a group.     

Intraspecific karyotype divergence inTriticum araraticum (Poaceae)

Karyotypes of 185 accessions ofTriticum araraticum Jakubz. (2n = 28 = 4x = A^tA^tGG) from Iraq, Iran, Turkey, and Transcaucasia were analyzed using C-banding technique. All accessions showed a certain degree of C-banding polymorphism and further karyotypic diversity was generated by structural rearrangements, mainly translocations. Eighty-one accessions had the normal karyotype similar to that ofT. timopheevii (cultivation), i.e., they showed C-banding polymorphism but no chromosomal rearrangements based on the resolving power of the C-banding technique. One-hundred four accessions showed 34 karyotypic variants, 31 had reciprocal translocations with the breakpoints in the centromeric regions of chromosomes. Three showed reciprocal translocations with the breakpoints in intercalary regions of chromosomes. A paracentric inversion for 7A^t chromosome was observed in some accessions. The rearranged karyotypes differed from the normal by one translocation in 21 variants, by two in 9 variants, by three in 1 variant, and by four in 2 variants of karyotypes. Translocations occurred more frequenty in the chromosomes of G-genome than of A^t-genome. Individual chromosomes differed in the frequencies of their involvement in translocations. Each geographical region contained a unique spectrum of translocations. Karyotypic diversity was the highest in Iraq followed by Transcaucasia and Turkey. Iran showed little karyotypic variation. Based on karyotypic analysis, Iraq should be considered as a centre of origin and primary centre of diversity ofT. araraticum.     

A comparison of RAPD and isozyme analyses for determining the genetic relationships among Avena sterilis L. accessions

Isozyme analysis is a valuable tool for determining genetic relationships among breeding lines and populations. The recently developed DNA technologies which can assay a greater proportion of the plant genome are providing a plentiful array of additional genomic markers. The objective of this research was to compare random amplified polymorphic DNA (RAPD) versus isozyme-based estimation of relationships among 24 accessions of a hexaploid wild oat, Avena sterilis L. The accessions were evaluated for variation in 23 enzyme systems and by 21 10-mer primers. A total of 77 polymorphic isozyme bands and 115 polymorphic RAPD bands were observed. Two matrices of genetic distances were estimated based on band presence/ absence. These matrices were subsequently utilized in cluster analysis and principal coordinate analysis. Both isozymes and RAPDs were proficient at distinguishing between the 24 accessions. The correspondence between the elements of both distance matrices was moderate (r=0.36**). Nevertheless, the overall representation of relationships among accessions by cluster analysis and ordination was in considerable agreement. The two techniques contrasted most notably in pair-by-pair comparisons of relationships. RAPD analysis resulted in a more definitive separation of clusters of accessions. The most significant impact of the DNA-based markers probably will be the more accurate determination of relationships between accessions that are too close to be accurately differentiated by isozymes.The research reported in this publication was funded by the North Carolina Agricultural Research Service, the North Carolina Biotechnology Center, and by a Heisenberg Fellowship (HE 1497/3-2) provided by the German Research Council to Manfred Heun     

Assessment of genetic diversity among and within Achillea species using amplified fragment length polymorphism (AFLP)

Amplified fragment length polymorphism (AFLP) markers were used to assess the genetic diversity of 57 Achillea accessions belonging to five species, A. millefolium, A. filipendulina, A. tenuifolia, A. santolina and A. biebersteinii. Nine AFLP primer combinations were used, which produced 301 polymorphic bands. In most species, a high level of genetic variation was detected among the genotypes. The Jaccard's similarity indices (J), based on AFLP profiles, were subjected to UPGMA cluster analysis. Application of Mantel's test for cophenetic correlation to the cluster analysis indicated the high fitness of the accessions to a group (r = 0.918). The dendrogram generated revealed five major groups corresponding to five species. The principle coordinate analysis (PCoA) data confirmed the results of the clustering. Among the species, A. teunifolia and A. santolina showed the greatest and the least genetic diversity, respectively. A. filipendulina accessions were acquired primarily from the same ecological regions of western Iran. Accessions belonging to A. biebersteinii originated from the Isfahan province and were separated from other species at the root of the dendrogram. The results of the clustering method, based on AFLP markers, corresponded closely with the geographical origins of the genotypes. The results of the present study could contribute to a better understanding and management of conservation and exploitation of the Achillea germplasm.     

Genetic diversity of Dioscorea dumetorum (Kunth) Pax using Amplified Fragment Length Polymorphisms (AFLP) and cpDNA

We have utilized Amplified Fragment Length Polymorphisms (AFLP) in conjunction with chloroplast DNA (cpDNA) sequence data to study the genetic diversity in 53 accessions of Dioscorea dumetorum from six countries in West and Central Africa. Our results provide a comparison of the two marker systems with regards to their applicability to differentiate intraspecific genotypes and the grouping of the accessions based on localities of collection. A total of 1052 AFLP fragments (of which 94.1% were polymorphic) produced from twelve primer combinations indicate a relatively high level of polymorphism among the accessions. Three major genetic groups that do not strictly follow a geographic distribution pattern were identified using Neighbour-joining and the principal coordinate (PCo) analyses. Accessions from Togo showed higher numbers of private fragments and the highest percentage polymorphism (59.4%). The detection of highest genetic diversity in accessions from Nigeria and Togo and their relationship to other accessions suggest that these countries are the centre of origin and diversity of D. dumetorum. The moderately high genetic diversity (average of 61%) is suggesting great influence on the D. dumetorum germplasms through exchange and transfer of cultivars among local farmers in the sub-region. In contrast, DNA sequence data from the psbA-trnH and the rpoB-trnC chloroplast regions revealed no variation among accessions from the different localities and clearly differentiated by AFLP patterns. The results demonstrate the usefulness of the AFLP marker in generating high polymorphism in the D. dumetorum accessions from West and Central Africa and hence may be used for agronomic purposes.     

AFLP analysis of Cynodon dactylon (L.) Pers. var. dactylon genetic variation.

Cynodon dactylon (L.) Pers. var. dactylon (common bermudagrass) is geographically widely distributed between about lat 45 degrees N and lat 45 degrees S, penetrating to about lat 53 degrees N in Europe. The extensive variation of morphological and adaptive characteristics of the taxon is substantially documented, but information is lacking on DNA molecular variation in geographically disparate forms. Accordingly, this study was conducted to assess molecular genetic variation and genetic relatedness among 28 C. dactylon var. dactylon accessions originating from 11 countries on 4 continents (Africa, Asia, Australia, and Europe). A fluorescence-labeled amplified fragment length polymorphism (AFLP) DNA profiling method was used to detect the genetic diversity and relatedness. On the basis of 443 polymorphic AFLP fragments from 8 primer combinations, the accessions were grouped into clusters and subclusters associating with their geographic origins. Genetic similarity coefficients (SC) for the 28 accessions ranged from 0.53 to 0.98. Accessions originating from Africa, Australia, Asia, and Europe formed major groupings as indicated by cluster and principal coordinate analysis. Accessions from Australia and Asia, though separately clustered, were relatively closely related and most distantly related to accessions of European origin. African accessions formed two distant clusters and had the greatest variation in genetic relatedness relative to accessions from other geographic regions. Sampling the full extent of genetic variation in C. dactylon var. dactylon would require extensive germplasm collection in the major geographic regions of its distributional range.     

Siberian wild rye (Elymus sibiricus L.): Genetic diversity of germplasm determined using DNA fingerprinting and SCoT markers

Elymus sibiricus is a perennial, self-pollinating, allotetraploid grass native to northern Asia. It is widely used in cultivated pastures and natural grassland due to excellent cold and drought tolerance, good forage quality, and adaptability to a variety of habitats. Information on the genetic diversity and variation among worldwide E. sibiricus germplasm is limited but necessary for germplasm collection, conservation and effective commercial use. In this study we ana lyzed genetic diversity and variation of 69 E. sibiricus accessions from the species range and constructed DNA fingerprinting profiles of 24 accessions using SCoT markers. A total of 173 bands were generated from 16 SCoT primers, 154 of which were polymorphic with 89.0% of polymorphic bands (PPB) occurring at the species level. The PPB within 8 geographical regions ranged from 2.3 to 54.3 %. Genetic variation was greater within geographical regions (57.9%) than between regions (42.1%). The 24 accessions from Qinghai-Tibet Plateau, Mongolia Plateau, Kazakhstan, and Russia were distinguished by their unique fingerprinting. This is the first report using SCoT markers for identifying cultivars and accessions of E. sibiricus. The DNA fingerprinting profiles of E. sibiricus were useful in germplasm collection and identification. The genetic diversity of worldwide E. sibiricus germplasm has been substantially affected by ecogeographical factors. Our results suggest that collecting and evaluating E. sibiricus germplasm from major geographic regions and unique environments broadens the available genetic base and illustrates the range of variation.     

Genetic diversity among East Asian accessions of the barley core collection as revealed by six isozyme loci

 Studies of allelic variations at six isozyme loci revealed genetic diversity of 380 East Asian accessions of the Barley Core Collection. Genetic variation was found in both cultivars and landraces in different regions. Allelic variations at the Aco-1 and Aco-2 loci were detected for East Asian barley for the first time. Moreover, the Aco-1 locus displayed the highest genetic diversity among the six loci assayed. Indian cultivars showed the highest diversity, followed by Korean and Chinese cultivars. Landraces from Bhutan and Nepal showed the lowest diversity. Cultivars had generally higher diversity than landraces within as well as among regions. The cluster analysis of genetic identity showed that all landraces from different countries can be placed in one group; the cultivars from Japan, India and Korea each form independent groups. Gpi-1 Gu, Pgd-1 Tj, Aco-1 Si, Ndh-2 D and Aco-2 A were rare alleles found in only a few accessions of 6-rowed barley. The Pgd-2 Tn allele was very rare in East Asian accessions. Received: 29 July 1998 / Accepted: 2 November 1998     

粗山羊草种质遗传多样性及群体结构的ISSR分析

粗山羊草分布范围广,遗传变异丰富,被认为是改良普通小麦的重要基因源。为深入了解不同来源粗山羊草种质的遗传多样性和群体结构,该研究利用ISSR分子标记对56份粗山羊草种质进行了遗传多样性和群体结构分析。结果表明:(1)16个ISSR引物共检测170条多态性位点,每个ISSR引物多态性位点为3～18条,平均为10.63条; 多态性信息(PIC)变异范围为0.17～0.85,平均为0.67。(2)粗山羊草4个群体的遗传多样性比较显示,中亚粗山羊草的群体遗传多样性水平最高(H_e=0.225 4,I=0.355 7),群体间的基因流较低(N_m=1.638 6)。(3)聚类结果在遗传相似系数约0.67处,来源于塔吉克斯坦6份和土库曼斯坦2份粗山羊草种质材料聚成一类(Group 2); 其他48份种质材料形成一大类(Group 1),其中Group 1可进一步分成3个Sub亚类,呈现出来源相同的粗山羊草种质材料倾向聚在一起。(4)群体结构分析将56份粗山羊草种质分为5个群体,其中,来源于西亚伊朗V群体种质材料遗传背景比较一致,混杂程度相对较低; 进一步分析各群体Q值,发现IV群体种质材料亲缘关系的来源相对复杂,遗传多样最为丰富。该研究结果可为粗山羊草种质亲缘关系解析、种质多样性保护提供重要参考依据,为其科学利用以及进化研究奠定基础。     

Isozyme analysis of genetic variability and population structure of Lactuca L. germplasm

Isozymes were used to investigate the genetic variability, population structure, and relationships of Lactuca germplasm. The isozyme systems revealed 16 putative loci of a total of 31 alleles. Out of these 16 loci, 11 were polymorphic. The average values of expected heterozygosity (H_e), observed heterozygosity (H_o), mean number of alleles per locus (A) and effective number of alleles per locus (A_e) were 0.2227, 0.266, 1.3005 and 1.369, respectively. The average fixation indices were lower than zero for most of the accessions studied, indicating an excess of heterozygotes. Genetic differentiation among accessions (F_ST) exhibited that 51.3% of the isozyme variation was recorded among accessions, and 48.7% of the genetic variation resided within accessions. The average values of total heterozygosity (H_T) and intra-accessional genetic diversity (H_S) were 0.352 and 0.171, respectively. Moreover, the inter-accessional genetic diversity (D_ST) ranged from 0 to 0.424 with an average of 0.18. Cluster analysis revealed that L. sativa cultivars were distributed throughout different Lactuca species. Thereby, isozymes results confirms the hypothesis of the polyphyletic origin of L. sativa. This high level of genetic variation proved that isozymes are efficient for polymorphism analysis of Lactuca germplasm.     

RAPD markers on seed bulks efficiently assess the genetic diversity of a Brassica oleracea L. collection

 The concept of a core collection was elaborated to fit the necessity of optimizing the management, for both conservation and use, of genetic resources in sizeable collections. This approach requires an analysis of how the genetic variability is structured among the accessions. The large number of heterogeneous populations in our collection of Brassica oleracea makes genetic diversity studies based on plant-to-plant analysis impracticable. To overcome this limitation, the variability analysis by RAPD on seed bulks was investigated for its efficiency in assessing the structure of the genetic diversity of this collection. The optimal bulk size and the bulking or sampling variation were evaluated with bulks of different size and with replicated samples. A mixture of known genotypes was also used to characterise the band detection in bulks, and to compare the plant-to-plant and the bulk methods. Forty seeds were chosen to represent each population. In such a bulk, the detection of bands depended on the proportion of the genotype they were derived from in the mixture. Intense and frequent bands were detected in the bulk with a 15% detection limit. The observed bulking or sampling variation within populations was smaller than the variation between populations, leading to an efficient separation of populations with a clustering of all samples of the same population. The distances calculated from bulk data were highly correlated with the distances based on the plant-to-plant analysis. We demonstrated that RAPD on seed bulks can be used to describe the genetic diversity between populations. Received: 27 August 1998 / Accepted: 29 September 1998     

Allozyme and morphological variability,outcrossing rate and core collection formation in lentil germplasm

Summary A survey of qualitative genetic variation at 3 morphological trait loci, 17 isozyme loci and a putative isozyme locus (amylase) was made for 105 lentil (Lens culinaris Medikus) germplasm accessions from Chile, Greece and Turkey. New alleles were found for Lap-1, Me-2, Pgm-c, Pgm-p and 6-Pgd-c. The average proportion of polymorphic loci per population was 0.19, with a range of 0 to 0.42 over populations. Germplasm from Chile was equally variable to that from Greece and Turkey on the basis of individual loci and in a multilocus sense, despite its post-Columbus introduction to the New World. Evidence was found from associations between allelic states at different loci of a complex multilocus structure of lentil populations. A single multilocus genotype represented 10.2% of all plants sampled. The rate of outcrossing varied from 2.2% and 2.9% in Turkish and Greek landraces to 6.6% among Chilean populations. Using the survey data, a random sampling strategy for core collection formation was compared with two stratified sampling methods. The advantage of stratified sampling over random sampling was only significant at P=0.28.     

DNA restriction fragment length polymorphisms correlate with isozyme diversity in Phaseolus vulgaris L.

Summary Genetic variation in Phaseolus vulgaris L. (P. vulgaris) was investigated at the isozyme and DNA levels. We constructed a library of size-selected Pst I clones of P. vulgaris nuclear DNA. Clones from this library were used to examine 14 P. vulgaris accessions for restriction fragment length polymorphisms (RFLPs). DNAs from each accession were analyzed with three restriction enzymes and 18 single copy probes. The same accessions were also examined for variability at 16 isozyme loci. Accessions included four representatives of the T phaseolin group and five representatives each of the C and S phaseolin groups. One member of the S group (the breeding line XR-235-1-1) was derived from a cross between P. vulgaris and P. coccineus. Isozymes and RFLPs revealed very similar patterns of genetic variation. Little variation was observed among accessions with C and T phaseolin types or among those with the S phaseolin type. However, both isozyme and RFLP data grouped accessions with S phaseolin separately from those accessions with C or T phaseolin. The highest degree of polymorphism was observed between XR-235-1-1 and members of the C/T group. RFLP markers will supplement isozymes, increasing the number of polymorphic loci that can be analyzed in breeding, genetic, and evolutionary studies of Phaseolus.     

Simple sequence repeat marker diversity in cassava landraces: genetic diversity and differentiation in an asexually propagated crop

Cassava (Manihot esculenta) is an allogamous, vegetatively propagated, Neotropical crop that is also widely grown in tropical Africa and Southeast Asia. To elucidate genetic diversity and differentiation in the crop's primary and secondary centers of diversity, and the forces shaping them, SSR marker variation was assessed at 67 loci in 283 accessions of cassava landraces from Africa (Tanzania and Nigeria) and the Neotropics (Brazil, Colombia, Peru, Venezuela, Guatemala, Mexico and Argentina). Average gene diversity (i.e., genetic diversity) was high in all countries, with an average heterozygosity of 0.5358 ± 0.1184. Although the highest was found in Brazilian and Colombian accessions, genetic diversity in Neotropical and African materials is comparable. Despite the low level of differentiation [F_st(theta) = 0.091 ± 0.005] found among country samples, sufficient genetic distance (1-proportion of shared alleles) existed between individual genotypes to separate African from Neotropical accessions and to reveal a more pronounced substructure in the African landraces. Forces shaping differences in allele frequency at SSR loci and possibly counterbalancing successive founder effects involve probably spontaneous recombination, as assessed by parent-offspring relationships, and farmer-selection for adaptation.Communicated by H.C. Becker