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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.
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.
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.
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.
Simple sequence repeats (SSRs) were isolated from a size-fractionated genomic DNA library of watermelon (Citrullus lanatus L. cv. New Hampshire Midget). Screening of the library with five oligonucleotide probes, including (GT)11, (AT)11, (CT)11, (GC)11, and (TAA)8, detected the occurrence of 96 positive colonies among ≈8000 recombinants. Automated DNA sequencing revealed the presence of SSRs. PCR primer pairs homologous to the regions flanking the SSR loci were synthesized commercially and used to screen 56 watermelon genotypes for the occurrence of SSR polymorphisms. Amplification products were separated using nondenaturing PAGE. Eighty percent of the primer pairs produced amplification products of the expected size and detected polymorphisms among the genotypes examined. The use of SSRs for watermelon germplasm characterization is discussed.
Simple sequence repeats (SSRs) were isolated from a size-fractionated genomic DNA library of sweetpotato [Ipomoea batatas (L.) Lam.]. Screening of the library with five oligonucleotide probes, including; (GT)11, (AT)11, (CT)11, (GC)11, and (TAA)8, detected the occurrence of 142 positive colonies among ≈12,000 recombinants. Automated DNA sequencing revealed the presence of simple, compound, perfect, and imperfect SSRs. Five homologous PCR primer pairs were synthesized commercially and used to screen 30 sweetpotato clones for the occurrence of SSR polymorphisms. All primer pairs produced an amplification product of the expected size and detected polymorphisms among the genotypes examined. The potential for the use of SSRs as genetic markers for sweetpotato germplasm characterization is discussed.
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.
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.
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.
Abstract
The fruit ripening behavior of the green ripe mutant (Gr) of tomato (Lycopersicon esculentum Mill.) was examined. Green ripe fruit are climacteric and evolve increasing amounts of ethylene after harvest; however, the time course for these events is dramatically altered in comparison with ‘Rutgers’. Maximal rates of C2H4 evolution from Gr fruit were achieved 20 days after the initial increase, and 7 to 10 days prior to maximal respiratory rates. Fruit age at harvest did not affect either the rate or the magnitude of these processes. Wavelength scans of pigment extracts from 60 day postharvest Gr fruit indicated low levels of carotenoids. Mutant fruit also remain firm a long time after harvest. Polygalacturonase activity in Gr fruit increases with fruit age, but reaches only 3% to 5% of the total activity in ‘Rutgers’. PG activity was only slightly reduced when extracts were heated to 65°C for 5 min, suggesting that a heat stable isoenzyme of PG is predominant in mature mutant fruit in contrast to ‘Rutgers’ in which 90% to 95% of PG activity in ripe fruit is heat labile under these conditions. When heterozygous, the Gr mutation is dominant in its effects on total PG activity and on the time course from the initiation of C2H4 and respiratory increases to their maximal rates of evolution. The magnitude of other changes in heterozygous mutant fruit was intermediate between normal and homozygous Gr.