Browsing by Author "James B. Holland, Committee Member"
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- Characterization of Stem Rust Resistance in US Wheat Germplasm(2009-07-23) Olson, Eric Leonard; David Marshall, Committee Member; James B. Holland, Committee Member; Gina Brown-Guedira, Committee ChairIn 1999 in Uganda a race of stem rust, Puccinia gramins f. sp. tritici was identified with virulence to Sr31. This race, designated as TTKS based on the North American nomenclature system, combined Sr31 virulence with virulence to the majority of Triticum aestivum L. derived stem rust resistance genes. The development of resistant cultivars is needed as TTKS may reach global dispersal due to its unique virulence to multiple known and unknown resistance genes and widespread cultivar susceptibility. The ability to detect the presence of specific stem rust resistance genes using molecular markers presents a viable method for identifying resistance to race TTKS in the absence of the pathogen itself. The frequency of DNA markers associated with resistance genes Sr24, Sr26, Sr36, and Sr1RSAmigo which confer resistance to TTKS was assessed in diverse wheat cultivars and breeding lines from breeding programs throughout the United States. The reliability of these markers in predicting the presence of the resistance genes in diverse germplasm was evaluated through comparison with phenotypic data. Introgression of undeployed seedling resistance genes is necessary to improve the availability of resistance to TTKS. The stem rust resistance gene Sr22 confers resistance to TTKS. Sr22 is present on a chromosomal translocation derived from Triticum boeoticum Boiss. which is homoeologous to the A genome of T. aesitivum Linkage analysis of SSR loci on 7AL was done to identify the loci most closely linked to Sr22. Individuals with reduced T. boeoticum segments due to recombination between wheat chromosome 7AL and the Sr22 introgression were identified with SSR markers in F2:3 populations of crosses between the germplasm stock Sr22Tb and the hard winter wheat lines 2174 and Lakin. From analysis of F3:4 populations derived from F2 recombinants, F3:4 individuals with further reduced translocation segments have been identified. Recombinant lines with reduced translocations will provide a more agronomically desirable source of Sr22 stem rust resistance in hard winter wheat germplasm that can be readily deployed utilizing molecular markers. The identification of molecular markers efficacious for the selection of genes for resistance to TTKS will hasten the development of resistant cultivars.
- Enhancing Genetic Gain in Maize with Tropical Germplasm, QTL Mapping, and Spatial Methodologies(2008-05-16) Jines, Michael P.; Major Goodman, Committee Chair; James B. Holland, Committee Member; Cavell Brownie, Committee Member; Paul Murphy, Committee MemberAdvance-cycle breeding is restricting the germplasm base for U.S. maize (Zea Mays L.). Many breeding programs devote efforts to adapt diverse germplasm to U.S. growing conditions, but few are participating in continual enhancement. Incorporating tropical germplasm into U.S. breeding pools could broaden the maize germplasm base, while concomitantly providing favorable alleles for yield and disease resistance. Knowing the genomic regions, or quantitative trait loci (QTL), for disease resistance can enhance gain by permitting selection on marker genotypes in the absence of disease expression. In addition, accounting for spatial variability can improve the precision of experiments and aid breeders in line advancement decisions and QTL mapping. Recombinant inbred (RI) lines were derived from a cross between NC300, a temperate-adapted, all-tropical line, and B104, a Stiff-Stalk-synthetic line. The RI lines were topcrossed to the tester FR615.FR697 (a C103 sister line cross). Resistance QTL for Southern Rust (rust) (Puccinia polysora) were mapped in the topcrosses, while Gray Leaf Spot (GLS) (Cercospora zeae-maydis) QTL were mapped in both the RI lines and topcross populations. A major resistance gene for rust was identified on the short-arm of chromosome 10, while ten GLS QTL mapped to chromosomes 1, 2, 3, 4, 8, and 10. Similar markers on chromosome 1 and 8 flanked three GLS and flowering time QTL pairs, and the resistance alleles were associated with increased flowering time. No flowering time regions co-localized with rust-resistance loci. The major rust-resistance gene and three GLS QTL corresponded to regions mapped in prior populations. The tropical parental allele, NC300, increased resistance at three of these four loci. Extensively haplotyping germplasm at these four consensus regions could aid in forward breeding strategies to efficiently integrate resistance packages into U.S. maize breeding populations. Spatial analyses, such as trend and trend analysis with correlated errors models, can improve precision of genotype means estimates. These analyses often reduce the phenotypic variance among family means, and in doing so, increase the response to selection. A dynamic SAS program, entitled SPATIALPRO, was developed to implement spatial analytical techniques. The program constructs and optimizes several spatial models for each trait and single-environment-trial combination, and chooses a preferred model based on a specified criterion. Results from the preferred model are outputted into SAS data sets. A long term breeding effort was initiated in 1975 to adapt and subsequently enhance tropical germplasm. Founder germplasm included seven double-cross-tropical hybrids. Based on the poor per se performance of the first and second-cycle lines, at least five cycles of S1 recurrent selection (RS) for grain yield has been practiced on two populations derived from these lines. Cycles per se and cycle-topcrosses to LH132.LH51 were grown in separate yield trials to estimate responses to selection. In both instances, grain yield increased linearly across the cycles of selection for each population, but the yield responses across the cycle-topcrosses are approximately half the average annual gains of commercial breeding activities in the U.S. Corn Belt. To determine the current range in combining ability, ninety-six S1 families were sampled from the latest cycles of each population and topcrossed to LH132.LH51. Three topcross families did not differ significantly in yield from the commercial check hybrid average. Variance components estimated from the topcross families suggest that S1 topcross RS is more promising in maintaining relevancy, and appears to be a more favorable method of enhancement, as resources are devoted to families with superior combining ability.
- Evaluation of Elite Exotic Maize Inbreds for Use in Long-term Temperate Breeding(2007-05-10) Nelson, Paul Thomas; Major M. Goodman, Committee Chair; James B. Holland, Committee Member; Cavell Brownie, Committee MemberThe U.S. maize (Zea mays L.) germplasm base is narrow. While maize is a very diverse species, that diversity is not represented in U.S. maize production acreage. Most elite U.S. maize inbreds can be traced back to a small pool of inbreds that were developed decades ago. Increased genetic diversity can be obtained through breeding with exotic germplasm, especially tropical-exotic sources. However, setbacks are often encountered when working with tropical germplasm due to adaptation barriers. Furthermore, the pool of available tropical germplasm is large and diverse, making choices of tropical parents difficult. The maize breeding program at North Carolina State University has begun a large-scale screening effort to evaluate elite exotic maize inbreds, most of which are tropical-exotic in origin. The purpose of this research was to: 1) generate comparative yield-trial data for over 100 elite exotic maize inbreds, 2) determine the relative effectiveness of various testcross regimes, 3) identify sources of gray leaf spot (GLS) resistance among these elite exotic inbreds, and 4) promote the use of exotic maize germplasm to broaden the genetic base of U.S. maize. Over 100 elite exotic maize inbreds were obtained from various international breeding programs. They were tested in replicated yield trials in North Carolina as 50%-exotic testcrosses by crossing them to a broad-base U.S. tester of Stiff Stalk (SS) x non-Stiff Stalk (NSS) origin. The more promising lines additionally entered 25%-tropical testcrosses with SS and NSS testers and were further evaluated in yield-trials. A dozen tropical inbred lines performed well overall—CML10, CML108, CML157Q, CML258, CML264, CML274, CML277, CML341, CML343, CML373, Tzi8, and Tzi9. Inbred lines CML157Q, CML343, CML373, and Tzi9 did not show significant line x tester interaction. Furthermore, it was determined that testcrossing to a single broad-based tester will suffice for initial screening purposes, allowing for elimination of the poorest performing lines. Testcrossing to additional SS and NSS testers may be of value when determining where the better performing materials will fit into a breeding program. It was further determined that most tropical lines can effectively be evaluated at the 50%-tropical level because many of the problems typically associated unadapted tropical material were minimized through a single testcross to an adapted tester. Each of the exotic lines was screened for GLS resistance either as inbreds per se, as testcrosses, or both. Many of the inbreds showed high levels of GLS resistance, including several lines that have good yield potential. These lines include CML108, CML258, CML274, CML277, CML343, and Tzi16. The results presented in this thesis provide temperate breeders with information on a sizable pool of potentially useful exotic maize inbred lines. These lines certainly deserve further attention in breeding efforts to broaden the U.S. maize germplasm base. Many are already being used at North Carolina State University in both exotic x temperate and exotic x exotic breeding crosses and populations.
- 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 MemberABSTRACT 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 × 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.
- Impact of Heterozygosity and Heterogeneity on Cotton Lint Yield Stability(2007-04-26) Cole, Clay Brady; Thomas G. Isleib, Committee Member; James B. Holland, Committee Member; Christina Cowger, Committee Member; Daryl T. Bowman, Committee ChairAdequate stability of cotton (Gossypium hirsutum L.) lint yield is an integral criterion for cultivar release; however, the magnitude of lint yield variation today is close to six times greater than variation observed in the 1920's. Yield stability has often been associated with genetic diversity. Observing cotton lint yield in diverse population types containing various levels and kinds of genetic diversity over many environments could reveal information about stability and how it relates to diversity. An 18-environment field study was undertaken to observe lint yield stability in four population types of cotton. These populations were pure lines grown in pure stands (homozygous⁄homogeneous), pure lines grown in blended stands (homozygous⁄heterogeneous), hybrids grown in pure stands (heterozygous⁄homogeneous), and hybrids grown in blended stands (heterozygous⁄heterogeneous). Lint yield components were also observed to determine the contribution each had towards lint yield stability. Differences were determined by observing the coefficient of variation (CV) for mean yield and yield components of population types and over environments. We found the heterozygous populations to be more stable than the homozygous populations. This was attributed to the hybrids and blends of hybrids out-yielding the parents and blends of parents in the low-yielding environments. This advantage was not observed in the high-yielding environments and, in effect, reduced the amount of variation observed over all environments. The number of bolls/hectare was the only yield component that showed definitive differences for stability between population types with the heterozygous populations having significantly higher stability than the homozygous populations. The superior stability of the heterozygous populations was attributed to an increased lint production in the lower yielding environments stemming from an increased number of bolls/hectare.
- The Physiology and Host Genetics of Quantitative Resistance in Maize to the Fungal Pathogen Cochliobolus heterostrophus.(2009-08-12) Belcher, Araby Ruth; Margaret E. Daub, Committee Member; James B. Holland, Committee Member; Peter J. Balint-Kurti, Committee ChairQuantitative disease resistance, despite widespread use, remains poorly understood. A previous project in the NCSU Maize Disease Resistance Genetics lab has generated 253 near-isogenic lines (NILs) in the background of the historically important maize inbred line B73. B73, although of excellent overall agronomic quality, is highly resistant to a number of common maize diseases. Each NIL is genetically differentiated by its combination of 1-5 of 12 total introgressed regions from the multiple disease-resistant parent NC250P. These 12 NC250P introgressions were selected for study as, following an initial B73 x NC250P cross, they had been retained by a program of recurrent backcrossing to B73 and selection for resistance to the fungal maize pathogen Cochliobolus heterostrophus, causal agent of southern corn leaf blight (SLB). Prior research also evaluated the effect of each NC250P introgression in conferring quantitative resistance or susceptibility against SLB. Introgressions having an effect can be designated as disease resistance quantitative trait loci, or “dQTLs†. Presented here is a 2-phase study with the ultimate aim of characterizing the physiological basis for the effect on disease severity of these NC250P-derived SLB dQTLs. The first phase attempts to determine more precisely how infection is altered by the two largest-effect introgressions, termed dQTL 3.04 and dQTL 6.01 (or 3B and 6A). To do so, it uses growth chamber juvenile plant trials to compare the interactions between C. heterostrophus and 6 select lines - B73, the major-gene resistant line B73rhm (also a B73-background NIL), and four NILs with varying combinations of dQTLs 3.04 and 6.01 - by quantifying spore germination and penetration efficiency, hyphal growth, and host expression of the pathogenesis related genes PR1 and PR5. The second phase investigates dQTL disease specificity by field testing 236 NILs for adult plant resistance to 5 fungal maize pathogens. Based on the results of the first phase, host genotype was not a significant factor for germination or penetration efficiency (P≥0.27). None of the resistance loci had an effect on hyphal growth at 24 hours post-inoculation (hpi), but dQTL 6.01 NILs did have significantly less fungal growth at 48hpi (α=0.05). PR1 and PR5 were significantly upregulated at 15 and 24hpi in all lines (P≤0.01), although relative PR gene expression between lines did not uniformly correspond with the presence of any resistance locus or with the relative resistance between NILs. Moreover, using data from a previous B73rhm1 x NC250A (sister line of NC250P and allelic to NC250P for dQTL 6.01) to test for allelism between rhm and dQTL 6.01, it was determined that the gene underlying dQTL 6.01 is almost certainly rhm itself. In the second phase experiments, correlations for resistance to any given disease pair were low across the NIL population (0.067 ≤ |r| ≤ 0.535). However, eight of the twelve NC250P introgressions represented in the NILs were shown to have significant multiple disease resistance effects (P≤0.058 for all significant effects). A dQTL in bin 3.04 had a significant effect on resistance for 4 diseases; and the dQTLs in bins 2.06, 5.07-5.09, and 6.01 had significant effects on 3 diseases. The dQTLs in bins 3.00-3.01, 9.01, 9.02-9.03, and 10.02 had significant effects on resistance for 2 diseases. The combined results of these experiments, by adding to the current knowledge of the timing and specificity of quantitative disease resistance effects within the infection court, can be used to both 1) help plant breeders better deploy quantitative resistance genes through an increased understanding of their effects and 2) provide quantitative resistance and multiple disease resistance gene candidates for future fine-mapping and cloning efforts.
