Browsing by Author "J. Paul Murphy, Committee Member"

Now showing 1 - 4 of 4

Allelopathy in Rye (Secale cereale)
(2008-12-05) Brooks, Ashley Meredith; Jeff Thompson, Committee Member; David A. Danehower, Committee Chair; Chris Reberg-Horton, Committee Member; J. Paul Murphy, Committee Member
Allelopathy is an ecological phenomenon in which chemicals produced by and released from a plant affect the germination or growth of another plant. A possible exploitation of allelopathy is the use of allelopathic cover crops for weed management. Organic farming systems can utilize allelopathy as an alternative to synthetic herbicides and conventional farming can reduce reliance upon pre-emergence herbicides. Rye (Secale cereale) is a cover crop species known to be allelopathic to many weeds. In addition to allelopathic activity, rye is a successful cover crop because of prolific biomass, high germinability and winter hardiness. The objective of this research was to investigate the potential to develop a rye cultivar with increased allelopathy through a conventional breeding approach. A population of 150 half-sib families of rye was grown in two North Carolina locations. Above ground tissue was utilized to assess rye allelopathic activity. To assess allelopathy in the population, we aimed to develop a greenhouse bioassay which utilized a rye incorporated soil media and redroot pigweed (Amaranthus retroflexus) as the indicator species. It is necessary to identify a screening protocol to quantify variation in allelopathic activity and to identify high performing lines. The greenhouse bioassay was fast, inexpensive and able to screen the large number of genotypes in the rye population. Results of redroot pigweed fresh weight biomass were reproducible and were utilized to estimate genetic parameters for allelopathy in the rye population. Estimates of genetic variation, genotype x environment interaction and narrow sense heritability help plant breeders develop an appropriate breeding program for the trait of interest. The estimates also give an idea of the rapidity at which progress can be made with selection. Genetic variation for rye allelopathy was not significant across locations but was significant within each location. Redroot pigweed fresh weight biomass was normally distributed indicating that allelopathy in rye is a quantitative trait. Heritability estimates were low on a per-plot basis and moderately low on an entry mean basis. A petri dish bioassay was also utilized to estimate genetic parameters for allelopathy in rye. Redroot pigweed germination and root length measures were utilized to quantify allelopathic activity. Genetic variation was not significant across locations for germination or root length. Analysis of variance within each location detected variation among the genotypes grown at the Kinston location but not at the Clayton location. Measures of redroot pigweed germination and root length were normally distributed. Heritability estimates were low on a per-plot basis and on an entry mean basis. This study demonstrates that allelopathy in rye is under genetic control and that it is a quantitative trait. Results suggest that a conventional breeding approach may be used for the development of a highly allelopathic rye cultivar.
Genetic and Phenotypic Characterization of Maize Germplasm Resources: Ex-PVPA Inbreds, NCSU Inbreds, and Elite Exotic Inbreds
(2008-12-19) Nelson, Paul Thomas; Major M. Goodman, Committee Chair; James B. Holland, Committee Member; J. Paul Murphy, Committee Member; Jason A. Osborne, Committee Member
ABSTRACT NELSON, PAUL THOMAS. Genetic and Phenotypic Characterization of Maize Germplasm Resources: Ex-PVPA Inbreds, NCSU Inbreds, and Elite Exotic Inbreds. (Under the direction of Major M. Goodman.) Maize (Zea maize L.) germplasm resources are characterized to illuminate their usefulness and proper placement for temperate maize breeding. Three germplasm pools are examined: 1) maize inbreds that have expired U.S. plant variety protection certificates (Ex-PVPA), 2) the North Carolina State University maize inbred line releases, and 3) elite unadapted tropical maize inbreds. We have used single nucleotide polymorphism (SNP) markers to evaluate the relationships and population structure among 92 ex-PVPA inbred lines in relation to 17 well-known public inbreds. Based on UPGMA clustering, principal component analysis, and model-based clustering, we identified six primary genetic clusters represented by the prominent inbred lines B73, Mo17, PH207, A632, Oh43, and B37. We also determined the genetic background of ex-PVPA inbreds with conflicting, ambiguous, or undisclosed pedigrees. We assessed genetic diversity across subsets of ex-PVPA lines and concluded that the ex-PVPA lines are no more diverse than the public set evaluated here. The NCSU maize breeding germplasm represents a potentially useful resource for maize improvement and diversity in the U.S. While the NC maize inbreds can generally be classified into five germplasm pools, Lancaster, temperate-adapted all-tropical (TAAT), Lancaster Ã— Tropical, Stiff Stalk, and Southern non-Stiff Stalk, analysis of detailed pedigree records and with molecular markers reveals additional substructure within each of these pools. There is general agreement among the four cluster analyses performed, three on SNP data and one on pedigree-derived coefficients of coancestry, as to the organization of this substructure. We performed topcross yield trial evaluation for 128 elite tropical maize inbreds from these institutions and 15 temperate-adapted all-tropical NC maize inbreds. We report, not only performance for yield and other traits of agronomic importance, but also heterotic patterns among many of these lines. We maintain, as reported in previous studies conducted at NCSU, that tropical germplasm, either adapted or unadapted, generally combines equally well with either Stiff Stalk or non-Stiff Stalk U.S. maize germplasm.
Identification of AFLP markers linked to tomato spotted wilt virus resistance in tobacco
(2006-05-12) Moon, Hyunsook; Jennifer S. Nicholson, Committee Co-Chair; Arthur K. Weissinger, Committee Co-Chair; Jim B. Holland, Committee Member; J. Paul Murphy, Committee Member
Tomato spotted wilt virus (TSWV) is a serious disease in several crops such as tobacco (Nicotiana tabacum.), peanut (Arachis hypogaea.), tomato (Lycopersicon esculentum.), and pepper (Capsicum annuum.). One source of resistance in tobacco is the breeding line Polalta, which contains a TSWV resistance gene introgressed from the wild relative Nicotiana alata. However, the resistance is associated with abnormal plant morphology and traditional backcrossing has been ineffective in producing normal plants with TSWV resistance. Molecular marker-assisted backcrossing allows for rapid identification of the plants that are most genetically similar to the recurrent parent and can be used to reduce the size of an introgressed chromosome segment. We applied AFLP (amplified fragment length polymorphism) technology and bulk segregant analysis to identify markers linked to TSWV resistance. One TSWV resistant bulk and two susceptible bulks were constructed by combining DNA from 5 doubled haploid lines from the cross K326 x Polalta for each bulk. A total of 128 primer combinations were used to screen one resistant and two susceptible bulks, and I found 48 potential markers linked to the TSWV resistance. Thirty two markers were selected for further study based on their reproducibility. A population of 88 F2 plants and 23 doubled haploid lines were screened with 32 markers and a 2.5 cM map with 24 markers was constructed. Eleven AFLP fragments between 100 to 400 bp in size linked in coupling phase to TSWV resistance were isolated and sequenced to develop PCR based markers. Four AFLP fragments were successfully converted to sequence characterized amplified region (SCAR) markers. An F2BC2 population of 160 plants was screened with 5 AFLP coupling phase markers to select resistant plants that have fewer Polalta-derived markers and more K326-derived markers. No resistant line was identified with a reduced introgression from N. alata. In an F2BC3 population of about 200 plants, 8 plants were selected based on an improved phenotype and screened with the 17 AFLP coupling phase markers. Four plants with a reduced introgression were identified and will form the basis for future backcrossing. This approach is expected to facilitate development of a line with TSWV resistance and a normal phenotype.
Structure of the Eastern U.S. Wheat Powdery Mildew Population
(2008-04-23) Parks, Wesley Ryan; J. Paul Murphy, Committee Member; Ignazio Carbone, Committee Member; Christina Cowger, Committee Chair