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Keith Woeste, Gale McGranahan, and Robert Bernatzky

A first backcross population of walnuts {[Juglans hindsii (Jeps.) Jeps. × Juglans regia L.] × J. regia} was used to evaluate the correlation between morphological (statistical) and genetic distance during introgression. Five traits based on leaf morphology were identified to quantitate the morphology of the parental species, their F1 hybrids, and the backcrosses to each parent. These traits were used to evaluate the morphological similarity of first backcrosses to J. regia using Mahalanobis' distance. The amount of genomic introgression of each backcross was estimated using 59 randomly amplified polymorphic DNA (RAPD) and 41 restriction fragment-length polymorphism (RFLP) genetic markers that identify polymorphisms between J. regia and J. hindsii. A smaller scaffold set of markers was also identified using published linkage data. The correlation between the measures of morphological and genomic introgression for the first backcrosses was low (0.23) but significant. The results suggest that selection based on morphology during backcrossing will not be an effective way to recover recurrent parent genome.

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A. Adato, D. Sharon, U. Lavi, J. Hillel, and S. Gazit

DNA fingerprint information was used for identification of mango (Mangifera indica L.) cultivars for genetic relatedness analysis of20 mango cultivars and for genetic analysis of a family structure. Genomic DNA was extracted from young leaves, digested with Hind III or Dra I, and hybridized with 10 different DNA probes. Jeffreys' minisatellite probe 33.6 was the most useful, resulting in well-resolved bands representing highly polymorphic loci. Specific patterns were obtained for each cultivar. The probability of obtaining a similar pattern for two different cultivars was 9.4 × 10-6. Based on DNA fingerprint information, genetic distances between 20 mango cultivars were evaluated and an evolutionary tree was established. Analysis of DNA fingerprint band patterns of 12 progeny resulting from a cross between `Tommy Atkins' and `Keitt' mango revealed neither linked nor allelic bands. Application of the reported results for identification, genetic analyses, and mango breeding is discussed.

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Luping Qu and James F. Hancock

A tetraploid blueberry population resulting from a cross of US 75 {a tetraploid hybrid of Fla 4B [a selection of Vaccinium darrowi Camp (2n = 2x = 24) × `Bluecrop' [(V. corymbosum L. (2n = 4x = 48)]} × `Bluetta' (4x) was used to generate a genetic linkage map of US 75 by randomly amplified polymorphic DNA (RAPD) analysis. One hundred and forty markers unique for Fla 4B that segregated 1:1 in the population were mapped into 29 linkage groups that cover a total genetic distance of 1288.2 cM, with a range of 1.6 to 33.9 cM between adjacent markers. The map is essentially of V. darrowi because US 75 was produced via a 2n gamete from Fla 4B and only unique markers for Fla 4B were used. Therefore, all the chromosomes of V. darrowi could be represented in the map.

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Richard E. Harrison, lames J. Luby, and Glenn R. Furnier

Runners from 318 plants representing 37 populations across the northern tier of US states, from Washington to New York, were collected and planted in two replications in a common greenhouse environment to assess morphological variation among octoploid strawberries (Fragaria chiloensis, F. virginiana spp. glauca and F. v. spp. virginiana). DNA was also extracted from these plants to determine molecular variation using RAPD's (Random Amplified Polymorphic DNA). Preliminary data suggest that the following morphological characters are useful traits in assessing diversity: flowering and runnering date; sex; petiole and peduncle hairs; petiole and peduncle color; leaf color, size, shape and density; and powdery mildew resistance. Preliminary RAPD data has revealed many useful molecular markers capable of detecting variability from the intrapopulation to interspecific level. Analysis of these data will determine relative genetic distances among the populations and provide a more complete understanding of the diversity available to the strawberry breeder in the octoploid taxa native to North America.

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Margaret R. Pooler and John S. Hartung

Xylella fastidiosa is a fastidious gram-negative, xylem-limited leafhopper-transmitted bacterium that has proven to be the causal agent of many economically important horticultural plant diseases, including Pierce's disease of grapevine and citrus variegated chlorosis. Genetic relationships among 11 X. fastidiosa strains isolated from mulberry, almond, ragweed, grape, plum, elm, and citrus were determined using randomized amplified polymorphic DNA (RAPD). Twenty-two 10-base primers amplified a total of 77 discrete polymorphic bands. Phenetic analysis based on a similarity matrix corresponded well with previous reports on RFLP-based similarity relationships, indicating that RAPD-PCR amplification products can be used as a reliable indicator of genetic distance in X. fastidiosa. RAPD products have been cloned and sequenced, and pairs of 21-nucleotide PCR primers have been developed that detect X. fastidiosa in general and the causal agent of citrus variegated chlorosis specifically.

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Angela K. Anderson and Chad E. Finn

The superb flavor of trailing blackberry cultivars, such as `Marion', is derived from Rubus ursinus Cham. & Schlecht. Wild R. ursinus offer a range of horticulturally desirable traits to breeders, from high fruit quality to improved cold hardiness. Current cultivars are derived from relatively few sources of R. ursinus, selected primarily for fruiting characteristics. A replicated field trial of 460 clones, representing 20 populations from southern British Columbia, Washington, and Oregon, was established in 1994. Observations during the planting year have indicated that monitoring variability in the following reproductive traits will be useful in assessing diversity; budbreak, flowering, and fruiting date; lateral length; proportion of reproductive laterals; gender; flower and fruit number; and fruit size. In particular, there are clones that exhibit large fruit size (4 to 5 g), high flower number per lateral, and uniform fruit set. Analysis of these data will contribute to determination of relative genetic distances among the populations and enhance the understanding of the diversity available in R. ursinus.

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Jericó J. Bello-Bello, Lourdes G. Iglesias-Andreu, Susana A. Avilés-Viñas, Eunice Gómez-Uc, Adriana Canto-Flick, and Nancy Santana-Buzzy

Intersimple sequence repeat (ISSR) markers were used to evaluate the effects of in vitro culture on genetic variation in Habanero pepper (Capsicum chinense Jacq.) regeneration protocols. A total of 219 ISSR clear and reproducible fragments were generated with 13 ISSR primers in direct organogenesis, direct and indirect somatic embryos, and the embryogenic callus system. A cluster analysis was performed to express in the form of dendrogram the relationships among different regeneration systems and the genetic variability detected. Genetic distance analysis indicated that our regeneration protocols are inappropriate for micropropagation, conservation, or genetic transformation; however, they may be applicable to breeding. This is the first report on the use of molecular analysis to evaluate genetic variation of in vitro-regenerated plants of Habanero pepper using ISSR markers.

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Julie Villand, James Nienhuis, Paul Skroch, and Jan Tivang

Precise cultivar descriptions are necessary to support Plant Variety Protection and utility applications for patent protection. However, accurate discrimination among cultivars is contingent upon the dependability of the method used to delineate lines. The efficiency and reliability of Amplified Fragment Length Polymorphisms (AFLPs), Random Amplified Polymorphic DNAs (RAPDs), microsatellite polymorphisms, and phenotypic traits were studied in order to determine a method's ability to accurately predict pedigree relationships among a set of 20 California processing tomato cultivars. All molecular marker and phenotypic trait data sets were independently produced using identical cultivar seed sources. Data was reduced to a genetic distance measure and presented as a multidimensional scaling (MDS) plot. Principal component analysis using the scored quantitative phenotypic traits was computed and is compared to molecular marker data results. Experimental error, sampling variance, and independence of scored bands for each molecular marker technique are presented. These estimates should assist breeders to determine a sufficient level of characterization, determine a minimum distance considered to be unique, and defend pedigree relationships.

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James Nienhuis, Paul Skroch, and Steve Beebe

Nuñas are a type of common bean (Phaseolus vulgaris) that possess the unusual characteristic of popping or expanding their cotyledonary tissue when heated. Numerous landraces of nuña beans were domesticated in the Andean region of South America (Peru, Bolivia, and Ecuador) and have been grown and consumed in this region since antiquity. The practical consideration in the domestication of nuñas in the high Andes was likely due to the greater energy efficiency in cooking toasted vs. boiled seeds.The Phaseolus germplasm bank at CIAT (Centro Internacional de Agricultura Tropical) has developed a core collection of Andean beans that includes numerous nuña landraces. Based on the wide range of phaseolin types observed among nuña landraces, it has been hypothesized that nuñas may represent a greater source of genetic diversity compared to other landraces and cultivars of common bean. Eighty nuña accessions and 120 nonpopping common bean accessions were randomly sampled from the CIAT Andean germplasm core collection. The 200 accessions were characterized for 140 mapped RAPD markers. The objectives of our research were to 1) understand the genetic structure of nuña bean accessions relative to other Andean common beans, and 2) to measure the genetic distance and genetic diversity between nuña and other Andean bean populations.

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Mirko Siragusa, Fabio De Pasquale, Loredana Abbate, and Nicasio Tusa

A collection of 18 accessions of sour orange (Citrus aurantium L.) coming from Sicily and other countries was investigated by two polymerase chain reaction (PCR)-based DNA marker technologies. Ten inter-simple sequence repeat (ISSR) primers and fifteen randomly amplified polymorphic DNA (RAPD) primers were used to identify and to evaluate the genetic variability and relationship of accessions. A total of 111 ISSR and 145 RAPD amplified fragments were used to estimate the Dice's coefficient of similarity for cluster analysis using a unweighted pair-group method using an arithmetic averaging (UPGMA) algorithm. The genetic relationships identified using ISSR and RAPD markers were highly concordant, such that the correlation between ISSR and RAPD genetic distance (GD) estimates was r = 0.93. The ISSR and RAPD analysis of 18 sour orange accessions found a high grade of genetic diversity in foreign accessions, while a low variability was detected in local accessions. Sicilian accessions could be grouped in two distinct clusters, including indistinctly plants from three origin regions. Some markers could be linked to the different growing areas. The ISSR and RAPD molecular reference system seems to be suitable for a fine identification of tightly related plants and the obtained results can form the basis for future setting up of Citrus rootstock genetic improvement projects.