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R.G. Fjellstrom, D.E. Parfitt and G.H. McGranahan

RFLP markers were used to investigate genetic diversity among California walnut (Juglans regia) cultivars and germplasm collected worldwide. Sixteen of 21 RFLP markers were polymorphic in the 48 walnut accessions tested. RFLP markers were useful for identifying walnut cultivars. All genotypes were heterozygous at ≈20% of the loci for both California and worldwide germplasm. California walnut germplasm contained 60% of the worldwide allelic diversity. Cluster analysis of genetic distance between accessions and principal component analysis of allelic genotypes showed two major groups of walnut domestication. California germplasm was associated with germplasm from France, central Europe, and Iran and had less genotypic similarity with germplasm from Nepal, China, Korea, and Japan.

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Mei Guo, David A. Lightfoot, Machteld C. Mok and David W. S. Mok

142 ORAL SESSION (Abstr. 666-672) CROSS-COMMODITY BIOTECHNOLOGY II/RFLPs

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Mei Guo, David A. Lightfoot, Machteld C. Mok and David W. S. Mok

142 ORAL SESSION (Abstr. 666-672) CROSS-COMMODITY BIOTECHNOLOGY II/RFLPs

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Wayne Kennard, Arian Dijkhuizen, Michael Havey and Jack Staub

142 ORAL SESSION (Abstr. 666-672) CROSS-COMMODITY BIOTECHNOLOGY II/RFLPs

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Diane R. Lester, Wayne B. Sherman and Brian J. Atwell

, CSIRO Division of Horticulture, for support and advice; Bruce Topp, Queensland Dept. of Primary Industry, for leaf and fruit samples; and Zeneca Seeds for advice and facilities for the RFLP work. Use of trade names does not imply endorsement of the

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R. Fjellstrom and D.E. Parfitt

RFLP probes were developed to determine the degree of genetic diversity both within and between 12 walnut species (Juglans spp.), including the widely cultivated English walnut (J. regia). One to three kilobase DNA fragments from Pst I digested J. regia nuclear DNA were cloned using the vector pUC18. Inserts corresponding to low copy number walnut genomic sequences were used to assess the genetic variability among walnut species. Extensive polymorphism was found between species and limited polymorphism within species. The inheritances of the RFLP loci are being analyzed to provide a genetic basis for the polymorphisms detected and to establish a RFLP based linkage map in walnuts

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Hong Lin and M. Andrew Walker

probe and primers used in RFLP and SSR analysis and Doug Adams and Sekar Arulsekar for critiquing this manuscript. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must

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M. Hubbard, J. Kelly, S. Rajapakse, A. Abbott and R. Ballard

We have identified cloned rose DNA fragments that detect restriction fragment length polymorphisms (RFLP) in rose (Rosa ×hybrida) cultivars. RFLP can be used as genetic markers for identification, certification, and patent protection. By comparing RFLP patterns for each of six probes, we have been able to characterize eight cultivars. These results confirm that RFLP analyses are useful for rose cultivar identification and may provide a means for protecting patent rights to new cultivars.

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David C. Jarrell and Mikeal L. Roose

We report a preliminary genetic map of citrus based on segregation of 8 isozyme and at least 33 RFLP loci. The segregating population consisted of 60 plants from a cross of two citrus rootstock, `Sacaton' citrumelo × `Troyer' citrange. This cross represents an intergeneric F2 since `Sacaton' is Citrus paradisi (grapefruit) × Poncirus trifoliata (trifoliate orange) and `Troyer' is C. sinensis (sweet orange) × P. trifoliata. RFLPs were identified using anonymous probes from both cDNA and genomic DNA libraries of citrus. About 20% of the loci deviated significantly from Mendelian segregation. Two-point linkage analysis identified 8 linkage groups in which pairs of loci were within 30 centimorgans. This suggests that we have markers on most of the 9 chromosomes of Citrus. A map based on multipoint linkage estimates will be reported. Evidence for structural rearrangements between Citrus and Poncirus and extension of the map to additional marker and disease resistance loci will be discussed.

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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.