Browsing by Author "James Holland, Committee Member"

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    Genetic and Quantitative Analysis of Red Raspberry (Rubus idaeus) for Heat Tolerance and Longer Chilling Requirement
    (2009-12-04) Molina Bravo, Ramon; Bryon Sosinski, Committee Co-Chair; James Ballington, Committee Member; Gina Fernandez, Committee Co-Chair; James Holland, Committee Member
    Despite the high level of interest for growing red raspberries (Rubus ideaus) in the southeastern US, production is limited by the lack of adapted, high quality cultivars. Breeding efforts are underway for increasing cultivar availability for this region, however breeding improvements in Rubus are slow and time-consuming. In order to expedite the slow, but effective, breeding process, more molecular breeding tools should be developed. Cultivars adapted to the southeastern US need to tolerate warm summers, and winters with temperature fluctuations. To address this issue, we have developed a genetic linkage mapping population from a cross that segregates for the tolerance of both conditions, (R. parvifolius × ‘Tulameen’) × ‘Qualicum’. This population was used for the construction of a genetic linkage map and for quantitative trait loci (QTL) analysis of heat tolerance, and chilling requirement for tolerance to fluctuating winter temperatures. As expected, seven linkage groups were created and were similar to the already published map. Because heat tolerance is a difficult trait to measure, a protocol was developed using chlorophyll fluorescence to assess heat tolerance. This protocol was used to measure tolerance in the population, and after QTL analysis, 3 QTL explained ~35% of the variation. Chilling requirements in the population were estimated by measuring bud break under greenhouse conditions. Quantitative analysis was performed on these estimates, and 3 QTL were found in two separate season evaluations, and in most cases co-localization occurred in the same region on the map. These regions explained the majority of the variation in the trait (100-64.5%). In summary, this research has established a protocol that measures heat tolerance in red raspberry, without relying on visual assessment, and has mapped important QTL for further molecular studies. Future research should focus on these regions to develop closely linked molecular markers for marker assisted breeding.
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    Genetic Characterization and Mapping of Wheat Powdery Mildew Resistance Genes from Different Wheat Germplasm Sources
    (2008-12-04) Maxwell, Judd Joseph; James Holland, Committee Member; Christina Cowger, Committee Member; David Marshall, Committee Member; Gina Brown-Guedira, Committee Co-Chair; J Paul Murphy, Committee Chair
    Powdery mildew caused by Blumeria graminis f. sp. tritici is a major economic disease in wheat (Triticum aestivum) in cool and humid, or maritime environments. Grain yield loss can reach 48% in susceptible cultivars under sever epidemics. Race-specific host resistance was identified as the most effective, consistent, and economic method of powdery mildew control. However, because of the constant virulence shifts and recombination among powdery mildew isolates, most race-specific resistance genes are ephemeral and are overcome a few years after wide deployment. Incorporation of new and novel resistance genes is imperative to maintain effective control in new wheat cultivars. The wheat germplasm lines NC96BGTD1, NC97BGTAB10, NC06BGTAG12, and NC06BGTAG13 exhibit different virulence spectrums and a high level of powdery mildew resistance in the southeastern United States. The objectives of this study were to characterize the inheritance of the powdery mildew resistance and identify simple sequence repeat (SSR) markers linked to the resistance genes in each line. The NC96BGTD1 and NC97BGTAB10 lines were crossed the cultivar Saluda and F2:3 families were developed for field and greenhouse evaluations. The NC06BGTAG12 and NC06BGTAG13 lines were crossed to the susceptible cultivar Jagger and F2:3 families were developed for greenhouse evaluation. SSR markers were used to development linkage maps to localize the genes to their respective chromosomes in each population. Phenotypic segregation among the F2:3 families indicated monogenic control of the resistance gene in each of the four populations. The resistance in NC96BGTD1 was located to the short arm of chromosome 7D, flanked by the SSR markers Xwmc635 and Xcfd41 at a genetic distance of 5.3 cM distal and 20 cM proximal respectively. Because seed was not made available in a timely fashion, we were unable to determine if the resistance gene in NC96BGTD1 was a novel resistance gene or an allele of the Pm19 locus which is also located on chromosome 7. The gene in NC96BGTD1 was given the temporary designation MlNCD1. The resistance gene in NC97BGTAB10 was located to the terminal tip of chromosome 2BL with the SSR marker Xwmc445 mapping 7 cM proximal to the gene. Again, because seed was not made available in a timely manner we were unable to determine the relationship between the gene in NC97BGTAB10 and the powdery mildew gene MlZec1 also located on chromosome 2BL. The gene in NC97BGTAB10 it was given the temporary designation MlAB10 The resistance genes in NC06BGTAG12 and NC06BGTAG13 mapped to the same region of chromosome 7AL and an allelism test indicated that the genes were likely alleles of each other. Furthermore, the genes mapped to the same region where the Pm1 locus resides, but detached leaf test suggested that the genes were different from each other as well as all five of the alleles at the Pm1 locus. Linkage mapping showed the resistance genes were flanked by the SSR markers Xwmc273 and Xwmc346 by a distance of 7.2 cM distal and 2.4 cM proximal in NC06BGTAG12 respectively, and 8.3 cM distal and 6.6 cM proximal in NC06BGTAG13 respectively. We were unable to determine the linkage or allelic relationship of the resistance genes in NC06BGTAG12 and NC06BGTAG13 with the Pm1 locus at this time. Thus these genes in NC06BGTAG12 and NC06BGTAG13 were give the temporary designation MlAG12 and MlAG13 respectively.
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    Resistance To Powdery Mildew In Wheat Germplasm With Different Resistance Sources
    (2007-09-07) Miranda, Lilian; David Marshall, Committee Member; Steven Leath, Committee Member; J. Paul Murphy, Committee Chair; Cavell Brownie, Committee Member; James Holland, Committee Member
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    Seed Nitrogen Content of Soybean: Mobilization of Nitrogen Reserves and Its Relationship to Seedling Growth.
    (2002-06-17) Naegle, Erin Rochelle; Thomas Rufty, Committee Chair; James Holland, Committee Member; Judith Thomas, Committee Member; Prachuab Kwanyuen, Committee Member
    Leguminous crops such as soybean are commonly grown in the relatively infertile soils of the southeastern U.S. The primary source of N for soybean growth and development in these environments is N2-fixation, which requires a symbiotic relationship that does not develop until 3 to 4 weeks after germination. Prior to N2-fixation, plants are largely dependent on seed reserves and they often experience a period of N stress. The purpose of this thesis was to investigate mobilization of seed N and its impact on soybean seedling development. Sixteen soybean lines differing in seed N content were grown hydroponically for 27 days without external N. Higher seed N was associated with increased seedling growth and reduced expression of N deficiency symptoms. Three of the 16 lines were selected for detailed characterization of seed protein degradation and N mobilization, and their relationship with seedling developmental responses during progression into and recovery from N stress. Leaf expansion and initiation were restricted more severely in soybean lines with lower seed N content. Depressed canopy development was the primary factor leading to decreased shoot:root growth ratios in all 3 lines. The soybean line with the lowest seed N content had a higher S/R ratio as the N stress progressed. The shoot and root growth changes were different than those in previous N deficiency studies, where adjustments have been proportional to the severity of N stress. When external N was supplied to plants deprived of N for 15 or 23 days, the induction period of the nitrate uptake process was extended and growth recovery rates were correlated with initial seed N contents. There was no delay, however, in stimulation of leaf initiation rates, which responded rapidly to the presence of external N. Individual leaf expansion during the recovery from N stress was dependent upon a lea'?s developmental stage. The majority of N was mobilized out of cotyledons within 12 days in three soybean lines with differing seed N contents. Mobilization was complete before differences in seedling growth were measurable. Mobilization rates were lower when external N was present, suggesting the involvement of source/sink relations on the mobilization process. Differences in proteolysis of glycinin and beta-conglycnin, the main storage proteins in soybean seeds, between N treatments were not detectable. Storage protein content and proteolysis rates were proportional to differences in seed N content.