Browsing by Author "David Marshall, 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 Chair
In 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.
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.
Genetic Characterization of Wheat Germplasm with Resistance to Fusarium Head Blight (FHB) and Powdery Mildew
(2007-12-20) Perugini, Leandro Daniel; Gina Brown-Guedira, Committee Chair; Marc Cubeta, Committee Member; David Marshall, Committee Member; Paul Murphy, Committee Member
A dominant powdery mildew resistance gene transferred to the hexaploid germplasm line NC99BGTAG11 from T. timopheevii subsp. armeniacum was mapped distally on the long arm of chromosome 7A. Differential reactions were observed between the resistance gene in NC99BGTAG11, the resistance gene in NC96BGTA4, and the alleles of the Pm1 locus that are also located on chromosome arm 7AL. Observed segregation in F2:3 lines from the cross NC99BGTAG11 x Axminster (Pm1a) and from the cross NC99BGTAG11 x NC96BGTA4 demonstrate that germplasm line NC99BGTAG11 carries a novel powdery mildew resistance gene, which is now designated as Pm37. Analyses of the population with molecular markers indicate that Pm37 is located 16 cM proximal to the Pm1 complex. However, further identification of linked markers is necessary to resolve the location of the resistance gene in NC96BGTA4. Simple sequence repeat (SSR) markers Xgwm332 and Xwmc790 were located 0.5 cM proximal and distal, respectively, to Pm37. Two new EST-derived STS markers were located distal to Pm37 and one marker was closely linked to the Pm1a region. Quantitative trait loci (QTL) for resistance to Fusarium head blight (FHB) have been mapped in the Chinese cv. Sumai 3 and its derivatives (on 3BS, 5AS, and 6BS), in Wuhan 1 (on 2D and 4B), and in the soft winter (SW) wheat cv. Ernie (on 4BL, 5A, and 3BSc). In this study, we selected 48 molecular markers near or at FHB resistance QTL mapped in Sumai 3, Wuhan 1 and Ernie to haplotype 245 soft winter wheat lines and to evaluate the use of these markers for marker-assisted selection (MAS). Based on the marker data, entries were grouped into 6 main clusters that generally represented breeding programs and/or geographic origin. The Chinese cultivars having the Fhb1 resistance gene were grouped separately from all other entries. The Xsts3B-256 and Xgwm533 markers can be clearly used to identify lines with the Fhb1 resistance gene. The haplotypes at these loci, along with the 3BSc region, suggest that SW wheat cultivars such as Patton, Freedom, and Roane that have been considered important sources of native FHB resistance, may share resistance QTL with Ernie.
New Advances in Fall Sown Oat Winter Hardness
(2009-12-04) Maloney, Peter Vincent; J. Paul Murphy, Committee Chair; Gina Brown-Guedira, Committee Member; David P. Livingston, Committee Member; David Marshall, Committee Member
Fall sown oats (Avena sativa L.) are plagued by a poor ability to tolerate freezing temperatures. Of all the fall sown small grain cereals, oats have the poorest winter field survival. Advances in marker technology and mapping techniques have allowed for more efficient and accurate location of quantitative trait loci (QTL). With these new technologies, breeders can more accurately screen early segregating generations for winter hardiness component traits. The objectives of this research were: (i) screen and validate new microsatellite or simple sequence repeat (SSR), single nucleotide polymorphism (SNP), and cleaved amplified polymorphic sequences (CAPS) markers; (ii) map new SSR, SNP, and CAPS markers to the Fulghum (winter tender) x Norline (winter hardy) recombinant inbred population (iii) screen the Fulghum x Norline population for QTL linked to winter hardiness component traits and (iv) develop a association mapping population to test for marker associations across a wider oat genetic base for winter hardiness component traits and validate marker use in marker assisted selection (MAS). Selected primer pairs derived from oat, including 315 SSR primers, four SNP markers and one CAPS maker were tested on a panel of 11 oat lines. Two hundred fifty two of the 315 primers amplified products in oat, and 168 were polymorphic for at least one of the 11 oat lines tested. Markers supplied by Dr. Joseph Anderson, USDA-ARS (JAO) were screened and PIC scores were generated. Among the JAO primers, 106 were co-dominant and 11 were dominant makers. Polymorphic information content (PIC) scores were generated for JAO primers with an average PIC score of 0.64 and an average of five alleles per primer pair. ii Sixty-five new SSR markers, four SNP markers and one CAPS marker were added to the Fulghum x Norline linkage map. This brought the total number of markers mapped on the population to 101. The map contained 19 different linkage groups for a total distance of 326.9 cM. Four major QTL were identified for winter field survival. Norline contributed three of the QTL and Fulghum contributed one QTL for increased winter field survival. Most of the winter field survival QTLs were located around the TC7-17 translocation event characteristic of Norline. Other QTL were identified for crown freezing tolerance, photoperiod effect, vernalization effect, heading date, and plant height. An association mapping population comprised of 63 fall-sown and spring-sown oats was selected for testing. Cultivars selected were released anywhere from 1775 to 1995 and consisted of two facultative, 25 spring sown and 36 fall sown type cultivars. The cultivars were chosen based on their linage and significance to the oat breeding community. The basis of the research was done on 29 unlinked simple-sequence repeat markers. The population was phenotyped for crown freezing tolerance and winter field survival. An admixture model in Structure v3.2.1, was used for subpopulation analysis, where we showed eight sub populations. Tassel 2.1 was used to conduct all the association mapping techniques including kinship and the mixed linear model. Association mapping yielded six loci linked to traits of interest. The six loci found are readily available to be used in a marker assisted selection program.
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