Determination of genetic variability by RAPD markers in cauliflower,cabbage and kale local cultivars from France

RAPD markers were used to analyse the genetic variability among a cole crop cultivar collection from France and to identify possible duplicate accessions for facilitating the germplasm multiplication. We surveyed 24 cauliflower, 24 cabbage and 48 kale populations using 62, 100 and 89 RAPD markers respectively on 40 seed bulk samples per accession. Genetic distances were calculated on the basis of these markers. Using the phylogenetic package PAUP we compared the genetic clusters obtained for the RAPD markers with the groups based on morphologic and agronomic data. For cauliflowers and cabbages a drastic selection by growers led to an extensive differentiation of morphologic and precocity traits related to geographic origin, which matches the grouping based on RAPD markers. Furthermore, RAPDs detected in some cases misclassification of accessions in the collection. Kales formed an homogeneous group probably due to extensive genetic exchanges leading to a continuous diversity. For the other crops, different horticultural types were separated in several subgroups by the RAPD markers suggesting different genetic origins. RAPD markers provide a rapid and informative approach to analyze the genetic variability in a collection. It can be applied to autogamous (spring cauliflower) or allogamous (winter cauliflower) crops, even in cases where the intra-population diversity is extensive (cabbages).     

Genetic diversity in African cucumber (Cucumis sativus L.) provides potential for germplasm enhancement

Genetic diversity among 26 cucumber (Cucumis sativus L. var. sativus) accessions from five African countries [Algeria (1), Egypt (21), Ethiopia (2), Kenya (1), and Libya (1)] present in the U.S. National Plant Germplasm System (NPGS) were examined by assessing variation at 71 polymorphic random amplified polymorphic DNA (RAPD) loci. Genetic distances (GD; simple matching coefficient) were estimated among these African accessions and a reference array (RA) of 21 accessions representative of the genetic variation in cucumber. GD among African accessions ranged between 0.41 and 0.97. GD among accessions in the reference array ranged between 0.36 and 0.88. Multivariate analysis identified three distinct groupings (1–3) of African accessions; Group 1 contained 21 accessions (Egypt, Ethiopia and Libya), Group 2 consisted of two accessions (Kenya, Algeria), and Group 3 possessed three accessions (Egypt). These groupings were distinct from each other (P > 0.001). Accessions in Group 1 differed genetically from all other accessions examined (P > 0.01), and accessions in Groups 2 and 3 were uniquely associated with several RA accessions. While GD among accessions in Group 1 ranged between 0.52 and 0.90, distances among Group 2 accessions varied between 0.93 and 0.97. The GD between the two accessions in Group 3 was 0.65. An accession from Syria (PI 181874) and from one Turkey (PI 199383) were genetically more similar to accessions in Group 1 than to other accessions in the RA. Likewise, accessions in Group 2 were genetically similar to two RA accessions from China and a European glasshouse cucumber line, and Group 3 accessions showed genetic affinities with the U.S. market class cultivar Dasher II. Data suggest that some Egyptian accessions (Group 1) possess unique genetic variation, that this germplasm has potential for broadening the genetic base of commerical cucumber, and that further collection of African germplasm is likely to enhance genetic diversity of cucumber in NPGS.     

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.     

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.     

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.     

Interrelationships among Coconut (Cocos Nucifera L.) Accessions Using RAPD Technique

The genetic relationships among 33 coconut germplasm accessions were analyzed using RAPD markers. The germplasm accessions were collected from various coconut growing regions viz. South Asia (SA), South East Asia (SEA), South Pacific (SP), Atantic and America, and Africa. Forty-five random primers produced a total of 399 polymorphic markers. The Polymorphism Information Content (PIC) ranged from 0.031 to 0.392 and the Marker Index (MI) ranged from 6.28 to 0.031 among the primers. Based on the MI a set of 5, 10 and 15 informative and reproducible primers were identified. The mantel matrix correlation was calculated to compare the similarity matrices of a set of reproducible informative primers and global primers. There was significant correlation among the similarity matrices (r ≥ 0.50). The similarity matrix based on 399 polymorphic markers was used to construct the dendrogram to show the genetic relationship among the accessions. Similarity values ranged between 0.573 and 0.846. There was less genetic similarity (based on Jaccard's coefficient) among South Pacific and South East Asian accessions. The clustering pattern obtained in the present study was in agreement with the earlier reports based on RFLP, SSRs and AFLPs.     

Genetic variation in radish (Raphanus sativus L.) germplasm from Pakistan using morphological traits and RAPDs

Genetic diversity of 30 radish (Raphanus sativus L.) accessions was investigated at the phenotypic level with morphological characters and at the DNA level using the random amplified polymorphic DNA (RAPD) technique. Thirty-six morpho-physiological traits were recorded from seedling stage to harvest. The 31 primers used generated 202 RAPD bands, of which 158 (78.2%) were polymorphic. Multivariate procedures were used to classify the germplasm on the basis of phenotypic traits and RAPD fragments. Dendrograms were generated for the Euclidean distance from the morphological data and the Nei's genetic distance from the RAPD markers. Phenotypically, all the accessions were classified into four major groups corresponding to the different forms of cultivated radish. The morphological diversity existing within each of these groups suggested that they should be discriminated into the three botanical convarieties, sativusT (large-rooted), caudatus (pod-type) and oleifer (oilseed-type). Clustering of the accessions did not show any pattern of association between the morphological characters and the collection sites. Instead, landrace groups were associated with their morphological similarities and horticultural uses. On the other hand, the intra-specific genetic relationships of several accessions based on RAPD analysis were related primarily to their collection sites rather than to their phenotypic affinities. The level of polymorphism exhibited by the various convarieties could be exploited in genetic mapping populations to tag economically important traits. These genotypes also could serve as a useful germplasm source for root, leaf, pod and seed. This preliminary study of traditional radish landraces from Pakistan provides useful information regarding their horticultural potential.     

Genetic diversity and intra-specific phylogeny of Triticum turgidum L. subsp. dicoccon (Schrank) Thell. revealed by RFLPs and SSRs

Today, emmer wheat, T. turgidum subsp. dicoccon, widely grown in the past is a candidate crop for sustainable agriculture in Italy. As part of a research project aimed at the enhanced use of the hulled wheat germplasm, molecular characterization was carried out to understand the genetic structure of the crop and to identify accessions of interest. A collection of 194 accessions was analyzed with 15 microsatellite loci (SSRs), while only a sample of 38 accessions was tested with 19 RFLP probes. The marker loci were selected on the basis of their independent genomic distribution. Genetic distances and allelic frequencies were calculated for each marker class. The genetic relationships were visualized with dendrograms. RFLP loci were, on average, less polymorphic than SSRs. An average Dice's genetic distance of 0.22 for RFLPs vs 0.38 for SSRs was detected, while an expected average heterozygosity per locus of 0.23 for RFLPs vs 0.26 for SSRs was also estimated. With a least number of 10 loci per marker class it was possible to identify each genotype. The most diverse accessions had different geographic origins. Germplasms from Italy and Ethiopia appear to belong to a more primitive genepool, given that a group of accessions from these countries were genetically differentiated from a Russian-Iranian group.     

RAPD markers in the analysis of genetic diversity among common bean germplasm from Central Himalaya

A set of 99 common bean germplasm collected from central Himalaya was investigated for their genetic variability using random amplified polymorphic DNA (RAPD) markers. Ten oligonucleotide primers, selected from 60 initially screened, generated 123 amplicon products. Of these, two amplicons were shared by all the accessions whereas 112 were polymorphic at least in two pair wise comparison. Nine unique bands identified were as low as 0.32 kb M.W. to as high as 3.5 kb and were confined to eight collections. All primers produced polymorphic amplicons though the extent of polymorphism varied with each primer. The primer OPF-17 was found to be most powerful and efficient as it generated a total of 17 bands of which 15 were polymorphic. RAPD markers data were analysed statistically using NTSYSpc.2.02e software and a dendrogram was generated using Jaccard’s similarity coefficient. The similarity coefficient values varied from 0.19 to 0.91. Grouping analysis revealed the categorization of 99 germplasm into 12 major branches with different level of similarity. Three branches namely branch 2, 3 and 5 out of 12 had only one accession. Branch 1 which consisted of three accessions was the most divergent as revealed by Jaccard’s similarity coefficient. Branching pattern of the accessions did not show any correlation with morphological data or altitudinal alignment of the accessions.     

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.     

Morphological and molecular diversity of an underutilized fruit crop - <Emphasis Type="Italic">Cordia myxa</Emphasis> L. germplasm from the arid region of Rajasthan,India

Twenty two germplasm accessions of Cordia myxa were collected from Rajasthan and established at the field gene bank for conservation and evaluation. Morphological characterization of 10 year-old trees for 17 traits indicated wide variations among the accessions tested. Higher number of flowers per cyme was found in accession ACHM11 and higher pulp:stone ratio in AHCM25. Overall, AHCM22 was found to be a superior germplasm line for most of the horticulturally useful traits among the accessions tested as it had higher percent of fruit set, pulp:stone ratio and fruit weight. High significant positive correlation was obtained between leaf, fruit characters and pulp:stone ratio. However, these characters were found to be negatively correlated with number of flowers per cyme. Out of 50 random decamer primers used for random amplification (RAPD), 25 were polymorphic. Average polymorphism resolved by these markers among these accessions was 69.8% with an average polymorphic information content of 0.43. Genetic diversity revealed by Jaccard’s co-efficient was between 0.44 and 0.94, and three major clusters were identified among these accessions by phylogenetic analysis using NTSYSpc-2.02e software. RAPD markers associated with leaf size and pulp:stone ratio were also identified. This study shows the existence of high genetic diversity among these accessions.     

Genetic diversity in cucumber (Cucumis sativus L.): IV. An evaluation of Chinese germplasm1

Genetic variation in cucumber (Cucumis sativus L. var. sativus) accessions from China was assessed by examining variation at 21 polymorphic isozyme loci. One hundred and forty-six Chinese accessions acquired by the U.S. National Plant Germplasm System (NPGS) before 1994 were compared to 67 recently collected Chinese accessions. Of the 67, 39 were collected during a 1994 U.S.–China expedition and 28 were donated in 1996. Isozymic profiles of all of these Chinese accessions were also compared with 853 previously examined NPGS cucumber accessions. Principal component analysis of allele frequencies identified two distinct groups of Chinese accessions: one containing accessions collected in 1994 (Group 1) and the other containing accessions received by NPGS in 1996 (Group 2) (P<0.01). Variation at Gpi, Gr, Mdh-2, Mpi-2, Pep-gl and Pep-la was important in the detection of this difference. Isozymic variation in U.S. NPGS accessions of Chinese origin acquired before 1994 differed significantly (P<0.01) from those collected during 1994 and those received in 1996. Eleven loci (Fdp-1, Gpi, Gr, Idh, Mpi-2, Pep-gl, Pep-la, Pep-pap, Per, Pgm and Pgd-1), were important in the detection of this difference. When Chinese accessions taken collectively (i.e., those acquired before 1994, and those during 1994 and 1996) were compared with an array of 853 C. s. var. sativus accessions examined previously, relationships between accessions grouped by country or subcontinent differed from those found in the previous work. Accessions from China and India were distinct from each other and from all other groupings and the C. s. var. hardwickii (feral form of C. s. var. sativus) accessions examined. Thus, Chinese and Indian accessions represent the most diverse genetic variation present in the NPGS cucumber collection. Further collection in India and China would be strategically important for increasing genetic diversity of the U.S. NPGS cucumber collection.     

Evaluation of the discriminance capacity of RAPD, isoenzymes and morphologic markers in apple (Malus x domestica Borkh.) and the congruence among classifications

Twenty-one apple accessions were characterised and classified taxonomically with randomly amplified polymorphic DNA (RAPD). The results were compared with morphological and isoenzymatic classifications of the same material by calculating the congruence between similarity matrices. The results confirmed the greater discrimination capacity of RAPD compared with isoenzymes, although the taxonomic clusters obtained with both types of markers were congruent. The genetic relationships calculated using RAPD and isoenzymes showed little congruence with the morphological relationships among accessions. Isoenzymatic markers are useful in germplasm banks to evaluate the diversity of newly introduced accessions. The use of RAPD markers are especially beneficial to discriminate between material that is genetically similar, to evaluate genetic variability within a collection and to choose the components of the core collection.     

Variation and phylogeny of the triploid cultivated potatoSolanum chaucha Juz. et Buk. based on RAPD and isozyme markers

Ninety four accessions of the cultivated triploid potatoS. chaucha were analyzed and classified in genotypic groups using 9 isozyme loci and RAPD markers disclosed by 20 arbitrary 10-mer primers. Eight isozyme loci out of nine were polymorphic. A total of 22 allozymes were analyzed but none of them were specific for any genotypic group. About half (52%) of the 102 RAPD markers scored, were polymorphic, all of them showing polymorphism among groups and rarely within groups. Eighteen RAPD markers were specific for certain genotypes. The isozyme markers showed a certain amount of intra group variation which made classification less reliable than with RAPD markers. A total of 10 triploid genetic groups were discriminated using both techniques together. A single primer was found to be sufficient to distinguish all 10 groups. All varieties of a single group are considered to have been derived from the same cross and then clonally propagated, even though there is a high amount of morphological variation within a single genotypic group due probably to somatic mutations. RAPD markers have been shown to be more reliable in the classification of triploid potato varieties than other genetic markers like isozymes, proteins and morphological traits.     

Genetic identity of three mint accessions stored by different conservation procedures: field collection, in vitro and cryopreservation

At the genebank of IPK (Leibniz Institute of Plant Genetics and Crop Plant Research) in Gatersleben, Germany, three long-term conservation methods (field genebank, in vitro slow-growth and cryopreservation) are used for mint germplasm. The plant material of the field genebank was the source to establish the slow-growth in vitro culture collection, from which the cryopreserved collection was set up, using a droplet-vitrification protocol. The genetic identity of 161 samples of three mint accessions (MEN 198, MEN 166 and MEN 186), stored for several years using those three methods, was studied using RAPD markers. Accession ‘MEN 198’ was the only one with a unique RAPD fragment pattern for all its samples, independently of the conservation procedure employed. The field collections of accessions ‘MEN 166’ and ‘MEN 186’ were made up of different genotypes. None of the genotypes detected in the plots of these accessions was represented in the in vitro and cryopreserved samples analyzed, which showed a unique genotype for each accession. From this work we conclude that, for an appropriate management of a germplasm collection of vegetatively propagated species, the determination of the genetic composition of the donor material and a periodical assessment of the preserved material should be carried out.     

Comparative analysis of genetic diversity using molecular and morphometric markers in Andrographis paniculata (Burm. f.) Nees

Andrographis paniculata is a medicinal plant of immense therapeutic value. The present study was aimed to elucidate its genetic diversity based on morphochemical and RAPD markers from 53 accessions belonging to 5 eco-geographic regions. Analysis of variance and D ² statistics revealed significant differences in all the metric traits and sufficient inter-cluster distances indicating considerable diversity among the accessions. The complementary approach of RAPD was used to evaluate the genetic dissimilarities among all the accessions using 6 highly polymorphic primers. The average proportion of polymorphic loci across primers was 96.28%. The molecular genetic diversity based on Shannon index per primer averaged 5.585 with values ranging from 3.08 to 8.70 indicating towards wide genetic base. RAPD based UPGMA and D ² cluster analysis also revealed that various accessions available in different eco-geographic regions might have originated from native places of wild abundance. Similarity matrices were generated for molecular markers and morphometric data to determine the degree of congruence between the two. A highly significant but low correlation (r = 0.547, P < 0.001) was obtained thus implying the correspondence between the two. The species is hermaphroditic and a habitual inbreeder. The present study yielded a typical triangular congruence between its breeding system, morphometric traits and RAPD markers thus elucidating the usefulness of complementary approaches to make diversity analysis more explanatory and purposeful for optimum genetic amelioration and effective conservation of its genotypic variability.     

Genetic Diversity of Traditional Chinese Mustard Crops Brassica juncea as Revealed by Phenotypic differences and RAPD Markers

This investigation was aimed at exploring the genetic diversity among nine typical accessions of Chinese mustard crops using random amplified polymorphic DNA (RAPD) markers and morphological comparison. Totally, 111 reproducible DNA bands were generated by 16 arbitrary primers, of which 91 bands were proved to be polymorphic. Based on pair-wise comparisons of the amplified bands, genetic similarities were obtained using Nei & Li's similarity coefficients and a dendrogram reflecting their relationships was made using the unweighted pair–group method with arithmetic averages (UPGMA). The result of cluster analysis indicated that the nine accessions were capable of being classified into two primary groups, one including accession 2 with expanded root (root mustard), accession 3 with entirely expanded whole stem (long-stem mustard), accession 6 with edible leaves (leaf mustard), accession 8 with edible seed stalk (seed stalk mustard) and another one including accession 4 with expanded basal stem (short-stem mustard), accession 5 with bulgy petiole (leafy bulgy mustard), and accession 9 with mustard-rich seed (seed mustard). Besides, accession 1 with expanded root (root mustard) and accession 7 with edible leaves and seed stalk (seed stalk mustard) were independent of other accessions in the dendrogram. Additionally, by cluster analysis based on highly reproducible RAPD markers, the accessions with similar edible parts of leaves or roots were not actually in the same phylogenetic groups. This implied that they were probably derived from different geographical origins with dissimilar genetic background and possessed higher genetic diversification. Furthermore, the results indicated that the traditional method for classifying Chinese mustard crops was not much reliable as it was largely dependent on phenotypic behaviors. Meanwhile, the phenotypic differences among individuals did not necessarily mean they must have sharp difference in genetic background as they met in the same group. Undoubtedly, these results aforementioned make this crop quite interesting to researchers for further investigating the molecular evolution of this special AABB group.     

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.     

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.     

Genetic diversity in wild and cultivated black raspberry (Rubus occidentalis L.) evaluated by simple sequence repeat markers

Breeding progress in black raspberry (Rubus occidentalis L.) has been limited by a lack of genetic diversity in elite germplasm. Black raspberry cultivars have been noted for showing very few phenotypic differences and seedlings from crosses between cultivars for a lack of segregation for important traits. Despite these challenges, little molecular work has been done to explore genetic diversity and relationships in wild and cultivated black raspberry germplasm. Microsatellite, or simple sequence repeat (SSR), markers are highly polymorphic codominant markers useful for studying genetic diversity, population genetics, genetic fingerprinting and other applications. We examined genetic diversity in 148 wild and cultivated black raspberry accessions using 21 polymorphic SSR markers. Black raspberry cultivars clustered tightly and showed higher than expected heterozygosity while that of wild accessions was low. Relationships between wild black raspberry accessions were poorly resolved and regional clusters were mostly absent from our analysis. Our results indicated that wild black raspberry germplasm is a relatively untapped resource available for future breeding.