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Larry D. Knerr and Jack E. Staub

The available U. S. Cucumis sativus germplasm collection (754 Plant Introductions) was electrophoretically screened for genetic diversity using 39 enzymes representing a total of 57 loci. Polymorphisms were observed at 18 loci which included g2dh, gpi1, gpi2, gr1, gr2, idh, mdh1, mdh2, mdh3, mpi2, pep-la2, pep-pap2, per4, pgd1, pgd2, pgm1, pgm3, and skdh. Appropriate crosses were set up to verify the inheritance of and test linkages among these loci. Four allozyme linkage groups have currently been identified. Representative linkages and their genetic distances include: gpi1 - mdh3 (20); pgm1 - pgd1 (25); and g2dh - pgd2 (19). Additionally, crosses were made to marker stocks to test for linkages between some allozyme loci and loci coding for resistance to downy mildew and anthracnose, long hypocotyl, divided leaf, short petiole, glabrous, compact plant, determinate, little leaf, and bitter free (bi).

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Raymond J. Schnell and Robert J. Knight

Genetic relationships between commercial mango cultivars are often speculative and only the maternal parent is generally known. RAPD™ primers were used with the polymerase chain reaction (PCR) to provide markers useful in determining individual identity, family relationships, and linkage mapping analysis. In mango, 53 RAPD primers were screened for markers and 27 proved useful. Genomic DNA was isolated from 70 clones of mango maintained in the USDA germplasm collection. DNA from these clones was amplified with each of the 27 primers. Data were scored as the presence or absence of bands. Groupings of the clones using UPGMA based on Nei's genetic distance gave distinct clusters. RAPD clusters vs. clusters based on isozyme analysis are compared.

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Robert G. Fjellstrom, Dan E. Parfitt, and Gale H. McGranahan

RFLP markers were used to study genetic diversity among California walnut (Juglans regia L.) cultivars and germplasm collected worldwide. 16 of 21 RFLP markers were polymorphic in the 48 walnut accessions tested. Seven RFLP markers permitted unique identification of all walnut cultivars. All genotypes were heterozygous at approximately 20% of the loci for both California and worldwide germplasm. California walnut germplasm contained 65% 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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Patrick J. Conner and Bruce W. Wood

Genetic variation among pecan [Carya illinoinensis (Wangenh.) K. Koch] cultivars was studied using randomly amplified polymorphic DNA (RAPD) markers. Using a combination of primers, a unique fingerprint was produced for each of the pecan genotypes studied. The genetic relatedness between 44 cultivars was estimated using more than 100 RAPD markers. Genetic distances based on the simple matching coefficient varied from 0.91 to 0.59. The phenetic dendogram developed from cluster analysis showed relatively weak grouping association. However, cultivars with known pedigrees usually grouped with at least one of the parents and genetic similarity estimates appear to agree with known genetic relationships. Using RAPD information in determining genetic relationships among pecan cultivars with unknown or questionable pedigrees and the integration of that knowledge into the breeding program is discussed.

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Kathryn R. Kleiner, John J. Frett, and James Nienhuis

Lima beans are an important vegetable crop to the processing industry in Delaware, but yields in Delaware are below other areas due to heat. The objective was to correlate RAPD markers from heat-tolerant and intolerant cultivars with phenotypic data. Twenty-five primers were used, 10 of which generated 25 polymorphic bands among 11 cultivars. MDS analysis of genetic distance among the cultivars shows segregation into two major clusters, with Kingston as a distant outlier. Kingston's position can be correlated to published data reporting its consistently good yields even when temperatures are high. The results of this study indicate RAPD markers may be used to screen for cultivars that have high yield potentials despite high temperatures. Further studies to screen F, and inbreeds will determine the usefulness of these markers in breeding programs.

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Margaret Pooler and John S. Hartung

Xylella fastidiosa is a fastidious gram-negative, xylem-limited, leafhopper-transmitted bacterium that has proven to be the casual agent of many economically important diseases, including Pierce's disease of grapevine and citrus variegated chlorosis. Genetic relationships among 11 Xylella fastidiosa strains isolated from mulberry, almond, ragweed, grape, plum, elm, and citrus were determined using random 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 X. fastidiosa RFLP-based similarity relationships, indicating that RAPD-PCR amplification products can be used as a reliable indicator of genetic distance in X. fastidiosa. Cladistic analysis suggests the existence of five groups of X. fastidosa: the citrus group, the plum-elm group, the grape-ragweed group, the almond group, and the mulberry group.

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Dapeng Zhang and Wanda Collins

To understand the prospects of applying the RAPD technique to assay genetic diversity in Ipomoea, four species (I. batatas, I. trifida, I. triloba, and I. ×leucantha) were analyzed for RAPD molecular markers. Six accessions of each species were used. Significant RAPD polymorphisms were detected within each species. Of 20 primers used, nine produced clear scorable polymorphic bands. The number of polymorphic bands produced per primer ranged from two to nine. Pair-wide genetic distance was calculated based on “band sharing”. The SAS-CLUSTER procedure was used to build a hierarchical species dendrogram. The four species were clearly separated by the clustering, which agrees with their existing taxonomic relationship. This study shows that RAPD analysis can be a powerful tool for identifying duplicates of germplasm acessions and for assessing genetic diversity. The procedures are relatively inexpensive and easy to perform and could be valuable in preliminary assessment of field genebank collections to separate species and indicate duplications in collected material.

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Zhi-Hong Gao, Zhi-Jun Shen, Zhen-Hai Han, Jing-Gui Fang, Yu-Ming Zhang, and Zhen Zhang

Sequencing amplification fragments produced using simple-sequence repeat (SSR) primer pairs pchgms2 and UDP96008 in `Dayezhugan' japanese apricot showed that SSRs obtained included a microsatellite locus originally identified in peach. The microsatellite sequence homogeneity between UDP96008 in japanese apricot in this study and UDP96008 in the peach in GenBank was 98%. Twenty-four japanese apricot genotypes originating in diverse geographic areas had been identified with 14 SSR primer pairs developed in different species of Prunus. In total, 129 alleles were obtained and per primer pairs detected 2.5 alleles on the average. The results from cluster analysis showed that the genetic distance between `Nanhong' and `Zhonghong' was the closest, and cultivars from China and from Japan could not be separated completely.

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S. Echeverrigaray, R.L. Cansian, A.P.L. Delamare, R.P. Silveira, and V. Barni

A collection of garlic (Allium sativum L.) germplasm, including 11 cultivars currently used in South Brazil, was evaluated using randomly amplified polymorphic DNA (RAPD) markers. Objectives were to assess genetic variations and relationships among cultivars and determine the potential of RAPD markers for the identification of garlic cultivars. One-hundred-twenty-two RAPD bands were scored from 12 oligonucleotide decamer primers selected from Operon Techn. kits B, X, and Y. Of these, 46 bands (37.6%) were polymorphic. Similarity indices between garlic entries were computed from RAPD data, and these range from 0.69 to 1.00. UPGMA cluster analysis of genetic distances showed three groups: one formed by nine cultivars and two formed by single entries. The nine cultivars that form group I had common origin, which explains the high similarity observed between them.

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Lili Zhou, Frank Kappel, Cheryl Hampson, Paul A. Wiersma, and Guus Bakkeren

Amplified fragment length polymorphisms (AFLPs) were used to analyze the relationships between sweet cherry (Prunus avium L.) cultivars and selections from the breeding program at the Pacific Agri-Food Research Centre in Summerland, Canada. Six pairs of preselected primers were used for the analysis of a total of 67 cultivars and selections. Scoring the absence and presence of 118 polymorphic DNA fragments produced a unique binary code for each cultivar and selection. Two phylogenetic trees were constructed using these 118 polymorphic fragments, one tree for 55 related cultivars and selections from the Summerland breeding program and the other for 23 self-incompatible cultivars of differing origins. The reliability of AFLP DNA fingerprints was confirmed by correlating relationships revealed by AFLP profiles with known genetic relationships of some sweet cherry cultivars and by a blind test for cultivar identification. Results indicate that AFLP analysis is a good technique to evaluate genetic distance and relationships in a sweet cherry breeding population.