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  • Author or Editor: R. Jarret x
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Fifty-seven accessions of Musa including cultivated clones Of 6 genomic groups (AA, AB, AAA, AAB, ABB, ABBB), M. balbisiana (BB), M. acuminata ssp. banksii (AA), M. acuminata ssp. malaccensis (AA) and M. velutina were examined for random amplified polymorphic DNA (RAPD) genetic markers using PCR with sixty 10-mer random primers. Forty-nine of 60 tested primers gave reproducible DNA amplification patterns. The number of bands resolved per amplification was primer dependent and varied from 1 to a maximum of 24. The size range of the amolification products also differed with the select& primer sequence/genotype and ranged from 0.29 to 3.0 kb. RAPD data were used to generate Jaccard's similarity coefficients which were analyzed phenetically. Phenetic analysis separated clones into distinct groupings that were in agreement with clusterings revealed when data were subsequently analyzed by principal coordinate analysis (PCO). In both the phenetic and the PCO analyses, previously unclassified cultivars grouped with cultivars previously classified for their genomic group based on morphological keys. The implications of RAPD analysis for Musa germplasm classification, clonal identification, and management are discussed.

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The PCR-based DNA amplification fingerprinting (DAF) approach was used to investigate the evolutionary relationships among 30 U.S. sweetpotato cultivars. Phenogram and pairwise similarity matrix based on Jaccard's coefficients showed relationships among U.S. cultivars and their progenitors to be consistent with the pedigree history. The genetic variability of U.S. cultivars was relatively low (compared to a sample of global collection). Many older U.S. cultivars formed a cluster in the principal coordinate analysis, suggesting their narrow genetic base, but new cultivars, such as `Regal' and `Excel', showed greater divergence. Somatic mutants showed close genetic similarity with their wild types and yet distinct in fingerprint profiles (e.g., `Resisto' and `Copper Resisto'; `Redmar' and `Goldmar'). All cultivars showed unique DAF profiles, and thus, the DAF approach enabled cultivar identification. `Centennial' showed high similarity to major U.S. cultivars such as `Jewel' and `Rojo Blanco'. `Regal' and its open-pollinated offspring `Excel' showed high similarity with each other. `Jewel', the most leading sweetpotato cultivar in the United States, clustered closely to its parent `Nugget' (83%). Carver, a selection from a cross `Centennial' × `Jewel', showed 75% similarity with `Jewel' and 63% similarity to `Centennial'. `Scarlet', a mutant of `Jewel', appeared in the same cluster as `Jewel' but showed only 68% similarity. Our results show that DAF may be an useful approach in elucidating evolutionary relationships among sweetpotato cultivars.

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The S-9 Plant Germplasm Collection maintains and distributes germplasm of various horticultural crops, including pepper (Capsicum spp.), watermelon (Citrullus lanatus), okra (Abelmoschus spp.), eggplant (Solanum melongena), miscellaneous Solanum spp., sweetpotato (Ipomoea batatas spp.), luffa (Luffa spp.), gourds (Lagenaria and Momordica spp.), squash (Curcurbita moschata), pumpkin (Curcurbita maxima), marigold (Tagetes spp.), Stokes' aster (Stokesia laevis), hibiscus (Hibiscus spp.), Engelman daisy (Engelmannia pinnatifolia), pampasgrass (Cortaderia selloana), ornamental bamboo (Bambusa spp.), and other ornamental grasses. Seed or other propagules of these plant materials are available for research purposes. Detailed information on individual collections and general information on the USDA National Plant Germplasm System will be presented.

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Twenty-four accessions of Ipomoea, representing 13 species of section Batatas and the outgroup species I. gracilis and I. pes-caprae were analyzed for restriction fragment length polymorphisms. Polymorphisms were detected by probing Southern blots of restriction enzyme-digested genomic DNA with 20 low or moderate copy number sequences isolated from an I. batatas cv. Georgia Red genomic library. Data were analyzed cladistically and phenetically. Ipomoea trifida, I. tabascana, and collection K233 are, of the materials examined, the most closely related to sweetpotato (I. batatas). Ipomoea littoralis, the only Old World species in the section, is a sister species to I. tiliacea. Ipomoea littoralis, I. umbraticola, I. peruviana, I. cynanchifolia, and I. gracilis are shown to be diploid (2n = 2x = 30). In contrast, I. tabascana is tetraploid (2n = 4x = 60). The intrasectional relationships of section Batatas species and the role of tetraploid related species in the evolution of the cultivated I. batatas are discussed.

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Abstract

Asexual embryos arose from callus derived from axillary bud shoot tips of 6 sweet potato [Ipomoea batatas (L.) Lam.] plant introductions (PIs) when cultured on a modified Murashige and Skoog (MS) medium supplemented with various concentrations of 2,4-dichlorophenoxyacetic acid (2,4-D). Transferral of embryogenic callus to auxin-free medium resulted in the continued development and eventual germination of individual somatic embryos and recovery of rooted plantlets.

Open Access

The USDA gene bank currently maintains 668 accessions of cultivated sweetpotato and 219 accessions of related Ipomoea species. Information on the genetic diversity of the collection does not exist due to funding constraints. The development of a core collection would provide a subset of accessions that represent the genetic diversity of the main collection with a minimum of repetitiveness. The small size of the core collection would facilitate the evaluation of the accessions for economically important traits. The objective of this research is to develop a core collection of Papua New Guinea sweetpotato germplasm using the Amplified Fragment Length Polymorphisms (AFLPs) marker system. This approach to quantifying genetic diversity would later serve as a model for the development of a USDA sweetpotato germplasm core collection. The germplasm choosen for this study was collected from this crop's secondary center of genetic diversity based on its potential as a source of new traits. All genotypes were fingerprinted using four primer combinations that generated 224 markers. The molecular data was then analyzed using NTSYSpc 2.0 program to determine the relatedness of the genotypes. The molecular analysis showed a homogeneous genetic constitution. The extent of diversity among accessions was correlated with the geographic origin of the plant material.

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The USDA gene bank currently maintains 668 accessions of cultivated sweetpotato and 219 accessions of related Ipomoea species. Information on the genetic diversity of the collection does not exist due to funding constraints. The development of a core collection would provide a subset of accessions that represent the genetic diversity of the main collection with a minimum of repetitiveness. The small size of the core collection would facilitate the evaluation of the accessions for economically important traits. The objective of this research is to develop a core collection of Papua New Guinea sweetpotato germplasm using the Amplified Fragment Length Polymorphisms (AFLPs) marker system. This approach to quantifying genetic diversity would later serve as a model for the development of a USDA sweetpotato germplasm core collection. The germplasm choosen for this study was collected from this crop's secondary center of genetic diversity based on its potential as a source of new traits. All genotypes were fingerprinted using four primer combinations that generated 224 markers. The molecular data was then analyzed using NTSYSpc 2.0 program to determine the relatedness of the genotypes. The molecular analysis showed a homogeneous genetic constitution. The extent of diversity among accessions was correlated with the geographic origin of the plant material.

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Microsatellites or simple sequence repeats (SSRs) were used to characterize 20 sweetpotato genotypes and to assign paternity for offspring from crosses among them. The PCR amplifications were performed with each of the sweetpotato genotypes and primers flanking a SSR loci previously characterized with the varieties Beauregard and Excel and 20 offspring from a cross among them. The PCR reaction products were separated in nondenaturing 12% acrylamide gels run at 25 V·cm–1 for 5 hours, and DNA fragments were visualized with silver staining. Gels were scanned on a flat bed scanner and analyzed using the Pro-RFLP software package. Three primer pairs were sufficient to produce an allelic profile capable of differentiating the 20 genotypes from each other. More than seven alleles/loci were found using each of the three primer pairs assayed. Occasionally primers produced allelic products clearly localized in two or three regions of the gel. These multiple loci segregated independently in a diploid fashion. This evidence suggests that there is not total homology among the three sweetpotato genomes.

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Deciduous azaleas have been gaining popularity because of their showy floral displays and adaptability to adverse environmental conditions. However, an absence of distinguishing morphological characteristics, combined with the wide variability present in most species, has created difficulties in efforts to unambiguously identify the different species. Various DNA isolation protocols were tested in order to determine the most effective methods for isolation of DNA from 22 taxa of Rhododendron for subsequent PCR amplification. DNA yields from the various isolation methods varied widely. A minimum of 50 ng/μL of template DNA was necessary for PCR amplification under standard amplification conditions. Results indicated that the effect of tissue age on the efficiency of DNA isolation was taxa-dependent. For most species, extraction of DNA from freshly harvested young leaf tissue resulted in the highest DNA yields. However, DNA yields from R. serrulatum, R. atlanticum, and R. viscosum `Lemon Drop' were highest when mature leaf tissue was used. Primers designed to amplify the internal transcribed spacer (ITS) region of the nuclear ribosomal genes and the psbD, trnK, and 16S chloroplast genes were tested in various PCR reaction mixes in order to optimize reaction conditions for amplification. Primers to both the ITS and the psbD gene resulted in satisfactory amplification in the presence of 1.5 mM MgCl2 and 50 ng template DNA.

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Abstract

The chlorophyll intensifíer mutations high pigment (hp) and dark green (dg) of tomato (Lycopersicon esculentum Mill.) were analyzed for their effects on fruit and vegetative characters. These mutations are nonallelic, and differences between them are primarily quantitative. Both mutations increased Vitamin C content at all stages of fruit development, and more than 90% was present in the reduced form in the mature-green and fully ripe mutant types and in normal fruit. Ascorbate levels in all fruit portions were increased by hp and dg, with the largest increase occurring in the outer pericarp. Chlorophyll in outer pericarp tissue of mutant fruit was increased 166% by hp and 320% by dg. Mutant fruit were smaller and more elongate than isogenic normal controls, but ripening was unaffected by either mutation. Vegetative and reproductive development were retarded by both chlorophyll intensifier mutations. The hp and dg mutations significantly reduced total leaf area, internode length, and whole plant fresh and dry weight, but did not reduce the number of nodes present at a particular stage of development. The effects of dg were always quantitatively greater than for hp. The similarity of effects associated with these 2 nonallelic mutants suggests that pleiotropy rather than close linkage accounts for the multiple effects of these genes.

Open Access