Molecular marker diversity and bacterial wilt resistance in wild <Emphasis Type="Italic">Solanum commersonii</Emphasis> accessions from Uruguay

Solanum commersonii is a wild tuber-bearing species native to Uruguay with high potential for use in potato breeding programs. Little is known about the genetic diversity within this wild species and the relationship with the resistance to the bacterial pathogen Ralstonia solanacearum. We studied 30 S. commersonii clonal accessions, 20 of which were collected from geographically different areas across the country, while the other ten were grown from seeds from a single plant. Resistance against R. solanacearum was tested and different levels of resistance were found, ranging from delayed wilting to asymptomatic reactions. The genetic variation and the relationships among individuals in this germplasm collection were studied by different molecular markers: Random Amplified Polymorphic DNA (RAPD), Amplified Fragment Length Polymorphism (AFLP) and Microsatellites or Simple Sequence Repeats (SSR). AFLP markers generated the largest number of total and polymorphic fragments per assay unit while SSR revealed the highest frequency of polymorphic bands (100%), followed by AFLP (96.2%) and RAPD (89.4%). In contrast, when comparing the number of different genetic profiles generated, the SSR markers exhibited the lowest discriminatory power. The clustering pattern obtained with the three marker systems showed a similar distribution of the S. commersonii germplasm revealing a high correlation between the three methods employed. All three dendrograms grouped most of the accessions into two main clusters, containing the same accessions regardless of the marker type. Bacterial wilt resistant accessions were present in both clusters. Accessions originated from different seeds of the same plant were grouped within one of the major clusters, and differed in the response to R. solanacearum revealing segregation of resistance. Furthermore, the distribution in two main clusters showed high correspondence with the geographical origin of the accessions, from the north and south of the country, and with the subspecies malmeanum and commersonii morphologically identified.     

AFLP analysis of introgression in coffee cultivars (Coffea arabica L.) derived from a natural interspecific hybrid

S.288 an offspring of a putative spontaneous interspecific hybrid between tetraploid Coffea Arabica (2n = 4x = 44) and diploid C. liberica(2n = 2x = 22) and 17 arabica coffee introgression lines (representing F₂ and F₄) derived from the cross S.288 x Kent arabica were evaluated for introgression of C. liberica genetic material. In all, 36 AFLP primer combinations were used in the analysis. The AFLP profiles of introgressed lines were compared to five accessions each of C. arabica and C. liberica. A total of 137 polymorphic bands were scored among the 29 accessions analysed. The introgressed genotypes exhibited 102 marker bands consisting of 65 additional bands and 37missing bands associated with introgression of C. liberica genetic material. C. liberica accessions of EA group (C. liberica var liberica of Guinean origin) seemed to be the likely progenitor in the origin of natural hybrid. Analysis of genetic relationships in the introgressed lines suggested that introgression was limited to few fragments. Segregation and wide variation in number of marker fragments in the F₂ and F₄progenies were attributed to chromosome recombinations. The differences in the level of introgression between introgressed parent, F₂ and F₄ groups was not pronounced. Therefore the alien genetic material appeared to be fixed and there was no elimination or counter-selection over generations, from introgressed parent to F₄.In C. arabica accessions, only 35 polymorphic bands were seen confirming the low genetic diversity. On the contrary, although representing a small amount of alien genome introgression, the Liberica-introgressed genotypes provided notable genetic diversity. Considering the fact that the diploid species of Coffea constitute a valuable source of genetic diversity, the potential implications of variability generated by Liberica-introgressed genotypes in C. arabica breeding are discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Population genetic structure of the clonal plant Zingiber zerumbet (L.) Smith (Zingiberaceae), a wild relative of cultivated ginger, and its response to Pythium aphanidermatum

Zingiber zerumbet (L) Smith, a wild clonal species related to the cultivated ginger (Zingiber officinale Roscoe), is a potential resistance donor for soft rot disease in ginger caused by Pythium aphanidermatum (Edson) Fitzp. In this study we evaluated the genetic diversity and P. aphanidermatum resistance of 74 Z. zerumbet accessions belonging to 15 populations from eight districts in Kerala state, India. The disease index (DI) of the accessions varied from 0% to 72.24% and the accessions could be separated into six frequency classes according to their DI values. More than 65% of the accessions had a DI < 20%. Eight accessions were found to be immune to the infection. The relative frequency of resistant accessions was higher in the central and northern regions of Kerala. Amplified fragment length polymorphism (AFLP) analysis of Z. zerumbet accessions using five primer combinations yielded 215 bands in total, of which 175 (81.4%) were polymorphic. Nei’s genetic diversity (h) of 0.2738 and Shannon information index (I) of 0.4012 revealed a high genetic diversity in Z. zerumbet unexpected for a clonal species. In the UPGMA dendrogram, accessions were clustered mostly according to their geographical origin and no clear correspondence was observed between the clustering pattern of accessions and their responses to Pythium aphanidermatum. The study revealed high genetic diversity and variability for pathogen resistance among Z. zerumbet accessions and confirmed the value of Z. zerumbet as a potential donor for soft rot resistance for the genetic improvement of ginger.     

AFLP analysis of genetic variability among Stylosanthes guianensis accessions resistant and susceptible to the stylo anthracnose

Stylosanthes guianensis, belonging to the genus Stylosanthes, is one of the most important tropical forage legumes and is native to South and Central America and Africa. Anthracnose, caused by the fungus Colletotrichum gloeosporioides (Penz.) Sacc., is a major constraint to the extensive use of Stylosanthes as tropical forage. Forty‐two accessions of S. guianensis were assessed with amplified fragment length polymorphism (AFLP) for genetic diversity and for resistance to anthracnose. In AFLP analysis, four selective primer combinations screened from 96 primer combinations were used to analyse these accessions, and a total of 225 clear bands were used for genetic similarity (GS) analysis, showing a 95.5% level of polymorphism on average. GS from 31.0% to 95.0% among the accessions was calculated with ntsys ‐pc software. The dendrogram was constructed with unweighted pair group method of averages (UPGMA) based on the AFLP data, and five clusters were defined at 48% GS. Two typical strains of C. gloeosporioides from Stylosanthes in China were used for anthracnose resistance screening. Most of the plant accessions showed variation in the reaction to two strains, and the correlation of resistance had a value of 0.904 (P < 0.01), suggesting common resistance to the two strains. The resistance accessions were randomly distributed in different groups of UPGMA clustering. These results demonstrate that AFLP analysis is an efficient method for evaluating the genetic diversity among S. guianensis accessions.     

Assessment of genetic diversity in synthetic hexaploid wheats and their Triticum dicoccum and Aegilops tauschii parents using AFLPs and agronomic traits

Synthetic hexaploid wheats are of interest to wheat breeding programs, especially for introducing new genes that confer resistance to biotic and abiotic stresses. A group of 54 synthetic hexaploid wheats derived from crosses between emmer wheat(Triticum dicoccum, source of the A and B genomes) and goat grass (Aegilops tauschii, D genome donor) were investigated for genetic diversity. Using the AFLP technique, dendrograms revealed clear grouping according to geographical origin for the T. dicoccum parents but no clear groups for the Ae. tauschii parents. The geographical clustering of the T. dicoccum parents was also reflected in the dendrogram of their derived synthetic hexaploids. Diversity of the T. dicoccum parents and their derived synthetic hexaploids was further evaluated by measuring 18morphological and agronomic traits on the plants. Clustering based on morphological and agronomic data also reflected geographical origin. However, comparison of genetic distances obtained from AFLP and agronomic data showed no correlation between the two diversity measurements. Nevertheless, similarities among major clusters with the two systems could be identified. Based on percentage of polymorphic markers, the synthetic hexaploids had a considerably higher level of AFLP diversity (39%) than normally observed in cultivated hexaploid wheat (12–21%). This suggests that synthetic hexaploid wheats can be used to introduce new genetic diversity into the bread wheat gene pool. This revised version was published online in July 2006 with corrections to the Cover Date.     

Diversity in the wild potato species Solanum chacoense Bitt.

Summary The morphological and isozyme variation was studied in 22 accessions of Solanum chacoense from Paraguay and Argentina. Clear geographic groups were identified through the use of multivariate analyses. S. chacoense from mountain sites in Argentina could be readily distinguished from plains forms from Paraguay, on the basis of several correlated morphological characters. Three isozyme systems, namely phosphoglucose isomerase (PGI), glutamate-oxaloacetate transaminase (GOT) and peroxidase (PRX) were studied using starch gel electrophoresis. The banding patterns indicated that for each isozyme there were several loci, which were polymorphic. A genetic interpretation of one of the PGI loci was made, and indices of genetic diversity and genetic identity calculated. Principal components analysis, cluster analysis and genetic diversity indicated a close relationship between the geographical groups. These results are discussed in the context of in situ genetic conservation.     

Genetic diversity and relationships in accessions from different cultivar groups and origins in the tree tomato (<Emphasis Type="Italic">Solanum betaceum</Emphasis> Cav.)

Tree tomato (Solanum betaceum) is an Andean small tree cultivated for its juicy fruits. Little information is available on the characterization of genetic resources and breeding of this neglected crop. We have studied the molecular diversity with AFLP markers using 11 combinations of primers of a collection of 25 S. betaceum accessions belonging to four cultivar groups, most of which had been previously morphologically characterized, as well as one accession of the wild relative S. cajanumense. A total of 197 AFLP fragments were scored, of which 84 (43 %) were polymorphic. When excluding S. cajanumense from the analysis, the number of polymorphic AFLP fragments was 78 (40 %). Unique AFLP fingerprints were obtained for every accession, but no AFLP fragments specific and universal to any of the four cultivar groups were found. The total genetic diversity (H _T ) of cultivated accessions was H _T  = 0.2904, while for cultivar groups it ranged from H _T  = 0.1846 in the orange group to H _T  = 0.2498 in the orange pointed group. Genetic differentiation among cultivar groups (G _ST ) was low (G _ST  = 0.2248), which was matched by low values of genetic distance among cultivar groups. The diversity of collections from Ecuador, which we hypothesize is a center of diversity for tree tomato, was similar to that from other origins (H _T  = 0.2884 and H _T  = 0.2645, respectively). Cluster and PCoA analyses clearly separated wild S. cajanumense from the cultivated species. However, materials of different cultivar groups and origins were intermingled in both analyses. The Mantel test correlation coefficient of the matrices of morphological and AFLP distances was low (−0.024) and non-significant. Overall, the results show that a wide diversity is present in each of the cultivar groups, indicate that Ecuador may be regarded as a center of accumulation of diversity for this crop, and confirm that AFLP and morphological characterization data are complementary. The results obtained are of value for the conservation of genetic resources and breeding of tree tomato, as an assessment of the genetic diversity and relationships among different cultivar groups and geographic origins is obtained.     

Genetic diversity among selected Argentinean garlic clones (Allium sativum L.) using AFLP (Amplified Fragment Length Polymorphism)

Genetic diversity of eight selected Argentinean garlic clones (Allium sativum L.) were investigated at the DNA level with the amplified fragment length polymorphism DNA (AFLP) procedure. A total of 405 unambiguous bands were identified by six primer combinations of EcoR I +3 and Mse I +3, of those, 398 showed a clear polymorphism, representing 98% of the total bands. A presence/absence matrix was constructed with the polymorphic bands, and a dendrogram was obtained from it with the UPGMA method. The accessions showed different levels of similarity ranging between 0.24 and 0.97, using the coefficient of Jaccard. The dendrogram showed six arbitrary groups. Accessions typically considered as different clones show similarities between 0.97 and 0.495. The garlic clones were clustered according to the physiological group and bulb color. We could detect an association between AFLP and the geographical origin of the clones. The potential use of AFLP could allow not only the differentiation among species, but also between botanical varieties and well-defined ecotype groups. This is the first report of the use of AFLP to characterize Argentinean garlic clones. This revised version was published online in August 2006 with corrections to the Cover Date.     

Inter and intra-species Inter Simple Sequence Repeat (ISSR) variations in the genus Cicer

Intra and inter-species ISSR variation and use of ISSR markers in determination of genetic relationship were investigated in an accession collection representing twoperennial and six annual Cicerspecies. Screening of Ciceraccessions with SSR primers revealed highly reproducible amplicon profiles with relatively high multiplex ratios. Many of the primers generated amplicon profiles with which not only the differences among species can readily be identified, but also polymorphisms within species could be detected more efficiently. PCR products at 150 gel positions detected using six SSR primers in Cicer accessions were treated as dominant DNA markers and utilized to compute the distances among accessions and species. Cluster analysis of accessions and species revealed groupings that corroborate our previous studies of relationships based on allozyme and AFLP analysis. Consistent with the AFLP analysis carried out in the same accession collection, ISSR-based groupings indicated that perennial C. incisumis genetically close to the annuals of the second crossability group (C. pinnatifidum,C. bijugum, C. judaicum) while C. reticulatum is the closest wild species to the cultivated chickpea. ISSR-based variation estimates were relatively higher when compared to previous estimates computed from RAPD and AFLP data. Technically, ISSR analysis combines the PCR-based targeting of microsatellite-associated polymorphisms with no prior sequence requirement and stringent PCR conditions. Similarly, when compared to AFLP analysis, it is less technically demanding allowing to survey polymorphic loci in the genome. Thus, ISSR-PCR technology is a reliable, fast, and cost-effective marker system that can be used to study genetic variation and genetic relationships in the genusCicer. This revised version was published online in July 2006 with corrections to the Cover Date.     

AFLP分析小豆种(Vigna angularis)内遗传多样性

利用12对AFLP引物,对来自于世界6个国家的146份小豆(Vigna angularis)栽培变种(var. angularis)和野生变种(var. nipponensis)种质的基因组DNA进行扩增,得到580条清晰的显带,其中313(53.93%)条呈多态性,平均每对AFLP引物得到26.08条多态性带;平均遗传距离0.35,变异幅度为0.00～0.87.利用AFLP多态性数据进行的Jaccard''s遗传距     

Assessment of genetic diversity within and among Basmati and non-Basmati rice varieties using AFLP,ISSR and SSR markers

Molecular markers provide novel tools to differentiate between the various grades of Basmati rice, maintain fair-trade practices and to determine its relationship with other rice groups in Oryza sativa. We have evaluated the genetic diversity and patterns of relationships among the 18 rice genotypes representative of the traditional Basmati, cross-bred Basmati and non-Basmati (indica and japonica) rice varieties using AFLP, ISSR and SSR markers. All the three marker systems generated higher levels of polymorphism and could distinguish between all the 18 rice cultivars. The minimum number of assay-units per system needed to distinguish between all the cultivars was one for AFLP, two for ISSR and five for SSR. A total of 171 (110 polymorphic), 240 (188 polymorphic) and 160 (159 polymorphic) bands were detected using five primer combinations of AFLP, 25 UBC ISSR primers and 30 well distributed, mapped SSR markers, respectively. The salient features of AFLP, ISSR and SSR marker data analyzed using clustering algorithms, principal component analysis, Mantel test and AMOVA analysis are as given below: (i) the two traditional Basmati rice varieties were genetically distinct from indica and japonica rice varieties and invariably formed a separate cluster, (ii) the six Basmati varieties developed from various indica × Basmati rice crosses and backcrosses were grouped variably depending upon the marker system employed; CSR30 and Super being more closer to traditional Basmati followed by HKR228, Kasturi, Pusa Basmati 1 and Sabarmati, (iii) AFLP, ISSR and SSR marker data-sets showed moderate levels of positive correlation (Mantel test, r = 0.42–0.50), and (iv) the partitioning of the variance among and within rice groups (traditional Basmati, cross-bred Basmati, indica and japonica) using AMOVA showed greater variation among than within groups using SSR data-set, while reverse was true for both ISSR and AFLP data-sets. The study emphasizes the need for using a combination of different marker systems for a comprehensive genetic analysis of Basmati rice germplasm. The high-level polymorphism generated by SSR, ISSR and AFLP assays described in this study shall provide novel markers to differentiate between traditional Basmati rice supplies from cheaper cross-bred Basmati and long-grain non-Basmati varieties at commercial level.The first two authors have equal contribution     

Evaluation of genetic variation in Lachenalia bulbifera (Hyacinthaceae) using RAPDs

RAPD (randomly amplified polymorphic DNA) analyses were carried out on 21 accessions of Lachenalia bulbifera (Cyrillo) Engl. Five pre-selected primers produced an average of 88% polymorphisms. Fifteen of the 21 accessions could be identified using the five primers. In a pairwise comparison genetic distance values ranging from 0.11 to 1.08 were obtained. These values reveal a high amount of variation within the species. The genetic distance values within the tetraploid and hexaploid groups on the south coast were low, but values were high between the groups on the south coast and those on the west coast. A dendogram was constructed from the RAPD banding profiles, using UPGM cluster analysis. The dendogram clusters certain accessions together. These clusters are supported by their geographical locality and chromosome data. The hexaploid group, tetraploid group and octoploid group on the south coast are respectively clustered together. It is concluded that RAPDs can be used to assess the genetic variation at an intra-specific level in Lachenalia. This revised version was published online in July 2006 with corrections to the Cover Date.     

AFLP in Triticum aestivum L.: patterns of genetic diversity and genome distribution

The amplified fragment length polymorphism (AFLP) procedure was applied to a diverse panel of wheat (Triticum aestivum L. em. Thell.) accessions and sixty-nine of the recombinant inbred lines (RILs) from the widely used genetic mapping population derived from the cross of Opata 85 and W7984. Most (76.8%) bands were monomorphic among T. aestivum accessions. The majority of bands monomorphic in T. aestivum also were present in the synthetic wheat parent (W7984). Ten primer pairs generated 153 polymorphic AFLP bands, 140 of which could be assigned to a chromosome location and were relatively evenly distributed on the genetic linkage map. AFLP loci in T. aestivum were distributed throughout the genome; they generally have only one detectable sequence variant; and they exhibit monogenic dominant mendelian inheritance. Frequencies of polymorphic bands in the germplasm sampled are in the range that enables informative cluster analyses as well as map-based diversity and association analysis studies. AFLP bands mapped to individual loci in the Opata 85/W7984 RIL population will frequently be polymorphic in other crosses or germplasm, irrespective of whether the band arises from the T. aestivum parent or the synthetic wheat parent. This revised version was published online in July 2006 with corrections to the Cover Date.     

采用AFLP和SSR标记对扁蓿豆遗传多样性进行比较分析

为了筛选出优异的扁蓿豆育种新材料,本研究采用AFLP和SSR分子标记技术对来自于中国7个省市自治区的15份扁蓿豆种质资源进行遗传多样性的比较分析,结果表明:18对SSR引物扩增出109个多态位点,8个AFLP引物组合扩增出640条带,其中472条多态带.AFLP标记的平均Nei′s遗传多样性指数、Shannon多样性指数和遗传分化系数均高于SSR标记.15份扁蓿豆种质的遗传距离和遗传相似系数与地理类群很接近.AFLP和SSR数据的聚类分析显示:15份扁蓿豆种质分为4大类,但是聚类结果与地理类群不完全相符,主成分结果与聚类结果相似,Mantel 检测表明:AFLP和SSR数据有较高的显著相关性,AFLP和SSR标记能够有效地对扁蓿豆进行遗传多样性分析,其结果为扁蓿豆育种和资源保护具有指导意义.     

Bulked AFLP analysis for the assessment of genetic diversity in white clover (Trifolium repens L.)

The use of bulked leaf samples from individual plants for amplified fragment length polymorphism (AFLP) analysis was evaluated as a tool for assessment of genetic diversity in white clover (Trifolium repens L.). Bulking of leaf samples produced slightly simpler AFLP profiles compared to the combined profiles of individual plants from the same cultivar. Approximately 90% of bands which were present in individual plants were present in bulked samples of the same cultivar. The majority of those absent were rare bands, shared by less than 25% of individual plants. Replicate bulk samples gave almost identical banding patterns, demonstrating the robustness of the bulked AFLP technique. Cluster analysis of AFLP data derived from individual plants resulted in a phenogram similar to that produced from data derived from bulked samples of the same plants. AFLP analysis of bulked samples detected significant amounts of genetic variability among 52 cultivars and accessions with genetic similarity values ranging from 0.42 to 0.92. However, cluster analysis of AFLP data only partially reflected the geographic origin of cultivars and accessions and was not congruent with cluster analysis based on variation for morphophysiological characters. Bulked AFLP analysis provides a powerful tool for rapid assessment of genetic variability in white clover and may also be used for cultivar identification. This revised version was published online in August 2006 with corrections to the Cover Date.     

RAPD genetic diversity of Albanian olive germplasm and its relationships with other Mediterranean countries

RAPD markers were used for the study of 19Albanian olive cultivars and two wild olives (oleasters). A total of 76polymorphic bands (4.8 polymorphic markers per primer) out of 107 reproducible were obtained using 16 primers. The number of bands per primer ranged from 4 to 10,whereas the number of polymorphic bands ranged from 1 to 9, corresponding to 71%of the total amplification products. All the accessions could be identified by the combination of four primers: OPA-19;OPA-02; OPK-16 and OPP-19. The dendrogram,based on Jaccard's index, included three major groups according to their origin: 1)most of the cultivars from the area of Berat (South of Albania) 2) cultivars from the Centre and Centre-North of Albania and3) cultivars from the Centre and North-West of Albania along with the oleaster from Elbasan. In order to evaluate the origin of Albanian cultivars they were compared to those diffused in other countries like Greece, Italy and Turkey, due to geographical and historical affinity among these countries, by using a one way AMOVA. Although most of the genetic diversity was attributable to differences among cultivars within each country (91.47%) significantφ-values among countries(φ_st = 0.085; p < 0.001)suggested the existence of RAPD phenotypic differentiation. Significant φ-values in all pairs formed by Albania with the other countries were observed. These results are consistent with the autochthonous origin of Albanian cultivars. This revised version was published online in August 2006 with corrections to the Cover Date.     

Inferred origin of several Native American potatoes from the Pacific Northwest and Southeast Alaska using SSR markers

Certain Native Americans from the Pacific Northwest and Alaska of the USA have grown potatoes in their gardens for many generations. In this study, the origin of several potatoes collected from Native gardens was investigated. Fourteen SSR markers covering the 12 potato homologs yielding a total of 199 alleles were amplified and scored in Solanum tuberosum Group Andigena (52 accessions), S. tuberosum Group. Tuberosum (39 accessions) and wild species (6 accessions). “Ozette” from the Makah Nation on the Olympic Peninsula in Washington State was closely related to “Maria’s” and “Kasaan” potatoes collected from Native Alaskan gardens in Southeast Alaska. These three potatoes were more closely related to either two Mexican and one Peruvian andigena accessions or three Chilean Group Tuberosum accessions, while being relatively less related to the old European or modern varieties and most distantly related to Group Andigenum. “To-Le-Ak” was closely related to two Chilean tuberosum accessions and one old European variety. All Native potatoes harbored T-type chloroplast genome indicating that their maternal lineage is shared with Chilean Group Tuberosum. Using genetic relationship as a guide to origin it appears plausible that the Native American/Alaskan cultivars are either directly or indirectly from Mexico and Chile. These Native potato cultivars present a possible second route of diffusion distinct from the South America to Europe transfer which has been assumed to the sole means by which potato was spread out of South America.     

Photomorphogenic mutants of tomato

Summary Two cloned cassava genes (pCAS6, pHNL) and a barley gene (pBLT63) which is highly conserved in higher plants, were evaluated as potential multilocus probes for RFLP analysis of phylogenetic relationships of species within the genus Manihot. For M. rubricaulis, M. chlorosticta and M. esculenta subsp. flabellifolia dendrograms based on 13 probe-restriction enzyme combinations show very little variation between accessions of the same species. A close relationship is demonstrated between the Mexican species M. chlorosticta and the M. esculenta subsp. flabellifolia accessions, which does not support the classification of flabellifolia as a true South American wild species.     

Evaluation of the genetic diversity among elite tea (Camellia sinensis var. sinensis) accessions using RAPD markers

The diversity of 27 superior tea (Camellia sinensis var. sinensis) accessions from Korea, Japan and Taiwan was examined with RAPD-PCR (Random Amplified Polymorphic DNA Polymerase Chain Reaction) markers. Out of the 50 primers screened, 17 primers generated 58 polymorphic and reproducible bands. A minimum of 3 primers was sufficient to distinguish all the 27 accessions studied. The Shannon's index used to partition diversity into inter- and intra-group, revealed that 71 percent of variability resided within groups and 29 percent between groups. Diversity was greatest within the Korean group followed by Taiwan and Japan. The relatively high diversity observed in Korea might reflect the larger genetic base of its plantations while the low diversity in Japan could be explained by the long and intensive tea selection programme in this country. A dendrogram based on the UPGMA-link method using Jaccard's distances and multivariate Factorial correspondence analysis clustered the tea accessions into two main groups, regrouping the Taiwan cultivars on the one side and the Korean and Japanese accessions on the other side. This suggests that the Taiwan tea studied here may have a different origin from that of Korea and Japan. This revised version was published online in July 2006 with corrections to the Cover Date.     

AFLP genetic diversity analysis in Russian wheat aphid resistant wheat accessions

Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko), is an important insect pest which causes severe economic losses in wheat (Triticum spp.). Among the various U.S. RWA biotypes, biotype 1 (RWA1) and biotype 2 (RWA2) are the most prevalent and most virulent on cultivated genotypes. Although many sources of resistance to these biotypes are available among landraces, their relatedness should be characterized to permit their more efficient use in breeding programs. In this study, 38 hexaploid accessions resistant to biotype 1 and/or biotype 2 were evaluated for genetic diversity based on amplified fragment length polymorphisms (AFLP). Fifteen AFLP selective primer combinations were used to genotype these accessions, resulting in 893 amplicons. Of these, 274 (30.6%) informative polymorphic bands were used for genetic diversity analysis. Genetic similarity coefficients ranged from 0.47 to 0.87 among the resistant accessions, indicating high genetic diversity among them. Cluster analysis grouped the 38 accessions into two major clusters, I and II, including resistant lines for RWA1 and RWA2. The study indicated that accessions in the National Small Grains Collection conferring RWA1 or RWA2 resistance comprise a diversified population which should support introgression efforts and provide genetic diversity for future breeding for RWA resistance.