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Karen R. Harris, W. Patrick Wechter, and Amnon Levi

.P. 2002 Isolation, sequence analysis, and linkage mapping of resistance-gene analogs in cowpea ( Vigna unguiculata L. Walp.) Euphytica 126 365 377 Guner, N. Wehner, T.C. 2008 Overview of potyvirus resistance in

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L. Eldredge, R. Ballard, W.V. Baird, A. Abbott, P. Morgens, A. Callahan, R. Scorza, and R. Monet

Peach [Prunus persica (L.) Batsch.] is considered the best genetically characterized species of the genus Prunus. We therefore used it as a model in our study of the genome organization in Prunus by means of restriction fragment length polymorphisms (RPLPs). Initial results indicated that 60% of cloned DNA sequences examined occur at low copy number within the peach genome. After selecting and examining these sequences, polymorphisms sufficient for RPLP mapping were found. We determined that ≫33% of our cDNA clones and 20% of our genomic clones detected RPLPs among peach cultivars. Analysis of RPLP segregation in two families, both of which segregate for known morphological characters, revealed segregation in 12 RFLP markers for one family and 16 for the other. Although we have not detected linkage between RFLP and morphological markers, preliminary analyses indicate possible linkage between two RPLP markers.

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Karen R. Harris-Shultz, Brian M. Schwartz, Wayne W. Hanna, and Jeff A. Brady

mapping, a linkage map is generated for each parent separately ( Fregene et al., 1997 ). Four homologous sets were formed for the T89 (tetraploid) parental map using 155 SDRFs ( Bethel et al., 2006 ). For the T574 (diploid) parental map, 77 SDRFs formed

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Minou Hemmat, Norman F. Weeden, Frank S. Cheng, and S.K. Brown

The positions of over 50 SSR loci and other sequence tagged sites (STSs) have been located on the linkage maps of five apple cultivars (Rome Beauty, White Angel, Golden Delicious, Liberty, McIntosh) and two New York accessions. In most cases, the primers used produced single amplification products, permitting identification of homologous loci in the different cultivars and the precise alignment of the linkage maps generated for each. Based on this information, we present a general linkage map for apple with STS markers on each linkage group. The map consists of 17 linkage groups (equal to the haploid chromosome number for the species) with over 500 markers. The positions of several resistant gene analogues have been located on this linkage map. None of these sequences map near genes conferring resistance to scab or powdery mildew. SSR loci exhibited a tendency to cluster in certain regions of the linkage map. This clustering slightly reduces their effectiveness as genome markers for comparative mapping or germplasm diversity. However, the SSR markers definitely displayed a high level of polymorphism, making them particularly useful for genetic studies.

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Rajeswari Srinivasan* and Richard Manshardt

QTL mapping gives an insight into the number, position and effect of loci controlling quantitative traits. Although a few linkage maps already exist for papaya, not many economically important traits have been studied. An investigation was undertaken to map two qualitative traits: 1) fruit flesh color and 2) an isozyme locus, phosphoglucomutase (PGM); as well as two quantitative traits: 1) number of nodes to first flowering and 2) stamen carpellody. An F2 population consisting of 281 plants derived from the parents Kapoho X Saipan Red was used for this study. Field observations suggested that there may be a linkage between PGM locus and one of the major QTLs controlling number of nodes to first flowering. Also, phenotypic data suggested that there may be a linkage between flesh color and carpellody. Marker genotyping was performed on a subset of 84 plants chosen from the phenotypic extremes of the population for node number and carpellody. Using AFLP (Amplified fragment length polymorphism) method, 510 markers were generated with 161 primer pairs. Although papaya has a haploid chromosome number of 9, at LOD score 5.0 and a maximum recombination frequency of 0.25, 25 linkage groups with number of markers ranging from 2 to 109 were generated using the software Mapmaker\EXP. Linkage and QTL maps are being constructed to reveal the molecular markers linked with the traits of interest and the nature of QTLs controlling the quantitative traits.

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Gehendra Bhattarai and Shawn A. Mehlenbacher

) using an Excel macro ( Rinehart, 2004 ). The dendrograms were visualized using Mega7 software ( Kumar et al., 2016 ). Segregation and linkage mapping. For the newly developed SSR marker loci at which the parent genotypes of the mapping population [OSU

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Gehendra Bhattarai, Shawn A. Mehlenbacher, and David C. Smith

was imported into JoinMap software (version 4.1; Kyazma, Wageningen, The Netherlands) and mapping conducted using the BC1 population type. The linkage map was constructed using the maximum likelihood (ML) mapping algorithm with default recombination

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M.R. Foolad, S. Arulsekar, and F. Bliss

A genetic linkage map of Prunus has been constructed using an interspecific F2 population generated from self-pollinating a single F1 plant of a cross between a dwarf peach selection (54P455) and an almond cultivar (Padre). This map consists of approximately 80 markers including 10 isozymes. 12 plum genomic, 19 almond genomic and 40 peach mesocarp specific cDNA clones. The backbone map will be used for identifying the genomic locations and characterization of genes governing important economic traits in the genus Prunus. Of particular interests are those genes associated with fruit ripening and mesocarp development in peach and almond.

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S. Rajapakse, L. E. Belthoff, R. E. Ballard, R. Scorza, W.V. Baird, R. Monet, and A. G. Abbott

We have constructed a genetic linkage map of peach consisting of RFLP, RAPD, and morphological markers, based on 78 F2 individuals derived from the self-fertilization of four F1 individuals originating from a cross between `New Jersey Pillar' and KV 77119. This progeny set was chosen because parental genotypes exhibit variation in canopy shape, fruit flesh color, and flower petal color, size, and number. The segregation of 81 markers comprised of RFLP, RAPD and morphological loci was analyzed. Low copy genomic and cDNA probes were used in the RFLP analysis. The current genetic map for the WV family contains 57 markers assigned to 9 linkage groups, which cover 520 cM of the peach nuclear genome. The average distance between two adjacent markers was 9 cM. Linkage was detected between Pillar (Pi) and double flowers (Dl). RFLP markers loosely linked to Pi, flesh color (Y), and white flower (W) loci were found. Twenty-four markers remain unassigned.

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Pan-chi Liou, Fred G. Gmitter Jr., and Gloria A. Moore

Citrus genetic studies and cultivar improvement have been difficult with conventional techniques. Alternative approaches are needed to enhance efficiency of such studies. Our objectives were to characterize the Citrus genome and to initiate development of a linkage map using RFLP and isozyme analysis. Methods of Citrus DNA extraction were developed to allow the isolation of chromosomal DNA of acceptable quality for recombinant' DNA manipulations. A PstI Citrus genomic library was constructed to create DNA clones for the RFLP survey. A rapid, reliable procedure was developed to facilitate screening of the library for useful clones. The methods used and strategy followed minimized contamination with organelle DNA, increased the frequency of single copy clones, and allowed rapid screening of the newly–constructed library. Linkage relationships of 49. markers, including 36 RFLP and 6 isozyme loci, were analyzed and a map comprised of 8 linkage groups was constructed. Insertions or deletions were responsible for at least 30% of the RFLPs identified. A hypothesis of transposon activity in Citrus was proposed based on our observations.