Inaug.-Diss.: Philosophische Fakultät: München: 1972. _ Contient des extraits en latin de la règle de St Benoit de Nursie. _ Bibliogr. p. 394-402. Index.

Inaug. _ Diss.: Philosophische Fakultät: Zürich: 1976. _ Bibliogr. p. V.

Doctor of Philosophy / Genetics Interdepartmental Program / Scot H. Hulbert / Frank F. White / Many maize lines carry Rxo1, an NB-LRR gene that confers a rapid hypersensitive response (HR) after infiltration with the rice streak pathogen Xanthomonas oryzae pv. oryzicola (Xoc) or the maize stripe pathogen Burkholderia andropogonis (Ba) carrying the effector genes avrRxo1 or avrRba1 respectively. Interestingly, when expressed as a transgene in rice, Rxo1 also confers a strong and rapid HR to Xoc strains harboring the avrRxo1 type III effector gene. To gain insights into the Rxo1 signaling network, we used a combination of functional genomics and bioinformatics, molecular genetics and reverse genetics. Microarray experiments were carried out to investigate the temporal expression profiles of nonhost and host responses to isogenic strains of Xanthomonas oryzae pv. oryzae (Xoo), the rice bacterial blight pathogen, and Ba with and without the Xoc type III secreted effector gene avrRxo1. Xoc AvrRxo1 induces disease resistance in maize when delivered by Xoo or Ba. We show that recognition of the two bacterial pathogens is translated into similar transcriptional outputs. Cluster analyses revealed that Xoo and Ba co-regulated genes display different kinetics and amplitudes and showed that gene clusters are associated with overrepresentation of known and putative novel DNA cis regulatory elements. One early induced gene, ZmPti1b, is a serine threonine kinase. RNAi-mediated gene silencing of a rice ortholog of ZmPti1b, OsPti1a, revealed that OsPti1a is required for Rxo1-governed resistance. Using a full length coding sequence as bait to screen a yeast-two-hybrid library, we identified 11 rice proteins that interact with RXO1. Functional analysis of two showed that Os1PVOZ, encoding a putative transcription factor, is required for Rxo1-dependent HR whereas OsATL6, a putative RING finger type E3 ubiquitin ligase gene is dispensable. Scanning of the rice genome for putative DNA binding sites suggests that Os1PVOZ is a master regulator of many signal transduction pathways, including those that mediate plant defense responses. Our investigations identified key signaling components that mediate Rxo1-specified resistance and possibly resistance mediated by other R genes.

Doctor of Philosophy / Department of Plant Pathology / Jan E. Leach / Both qualitative and quantitative resistance mechanisms are important contributors to disease resistance in rice. To identify useful sources of durable resistance for Korean breeding programs, the distribution of rice blast isolates compatible to widely used resistance (R) genes was analyzed. Interactions of 3,747 Korean rice Magnaporthe oryzae isolates with eight monogenic lines, each harboring a major blast R gene, were tested. Lines with R gene Pi-9 and Pi-5 were susceptible to the fewest M. oryzae isolates, and therefore, this gene might be applied for blast resistance in breeding programs in Korea. Six major blast resistance genes were susceptible to more than 60 % of the population, suggesting limited utility of these genes in breeding programs. Quantitative trait loci (QTL)-based resistance is predicted to provide durable and broad spectrum resistance to rice diseases. A candidate gene approach was applied to a population of 164 recombinant inbred lines to identify sources of quantitative resistance. Resistance gene analogs and defense response genes were mapped on the rice chromosomes, and analyzed for their association with blast and bacterial blight resistance QTL. A total of 21 putative QTL for blast resistance were identified on chromosomes 1, 4, 5, 6, 8, 9 and 12. Four putative QTL for bacterial blight resistance were identified on chromosome 3, 5 and 10. Thirteen RGA markers were associated with 11 different QTL on chromosome 1, 5, 8, and 9. The role of one disease resistance QTL associated gene, Os02g39330, encoding a chitinase was investigated for contributing to basal defense responses. RNAi silencing was used to evaluate contributions of the gene for the resistance to Rhizoctonia solani and M. oryzae. Five transgenic lines harboring the silencing construct and which differed in the level of expression of Os02g39330 were screened for responses to R. solani and M. oryzae. The chitinase gene expression levels were inversely correlated with sheath blight disease severity, suggesting a role for this defense gene in resistance to R. solani. Rice blast disease was not affected by silencing Os02g39330. Both qualitative and QTL-based resistances provide valuable sources of disease resistance, and a combination of R gene Pi-9 and QTL harboring the Os02g39330 chitinase may help to stabilize resistance.

Dissertation Philosophy Harvard : 1978. / Bibliogr. p. 145-147. Index.

Habilitationsschrift--Philosophische Fakultät--Erlangen-Nürnberg, 1974. / Bibliogr. p. 417-427. Index.

Doctor of Philosophy / Department of Plant Pathology / William W. Bockus / Septoria tritici blotch caused by Mycosphaerella graminicola (anamorph Septoria tritici), is an important disease of wheat worldwide capable of reducing yields by as much as 30 to 40%. In Kansas, the disease is widespread and losses in individual fields can exceed 25%. This study examined the genetic structure of Kansas populations of M. graminicola at different spatial scales (micro-plot, macro-plot, and statewide) using amplified fragment length polymorphism (AFLP) markers. Three primer pairs were used to resolve 174 polymorphic loci from 476 isolates. The results indicated high levels of genotypic variability, which is consistent with a genetically diverse initial inoculum. Genetic identities among populations representing the three spatial scales were >98%. Tests for differentiation among populations due to population subdivision revealed that on average 97.5% of the genetic variability occurred within populations with a correspondingly high migration rate of 16 to 23 individuals per generation. We observed little evidence of linkage disequilibrium, on average, only 4.6% of locus pairs were in disequilibrium. Our results indicate that Kansas populations of M. graminicola are characterized by regular recombination, are genetically diverse, and appear to be homogenous across different spatial scales. These populations are probably components of a larger pathogen pool that is distributed at least across much of Kansas and probably the central Great Plains. Because of the frequent recombination, the risk of adaptation of Kansas populations of M. graminicola to fungicide treatments or resistance genes is high and could be dispersed very quickly, whether these new pathogenic traits occur locally through mutation or by migration from other areas.

la 1ère partie constitue l'éd. commerciale de : Habil.-Schr. : ? : Berlin, Freie Univ. : 1999.

Master of Science / Department of Plant Pathology / John P. Fellers / Harold N. Trick / Wheat streak mosaic virus (WSMV) and Triticum mosaic virus (TriMV), are two of the major viruses in the Great Plains of the United States. Cultural practices and mite vector control are the primary methods of disease management; however, they are not fully effective. Resistant varieties are also deployed, although some of the lines present temperature sensitive resistance or negative agronomic properties are linked to resistance. Alternative approaches to viral resistance are needed. RNAi has been shown to play a role in viral defense response and has been successfully used as a biotechnological tool to preprogram viral resistance in transgenic plants. RNAi reduces the expression of specific genes by targeting the accumulation of mRNA. The mechanism is activated by the presence of dsRNA, which is processed into small non-coding sequence that serves as a guide for degrading RNA in a sequence specific manner. In this work, the RNAi approach was used to elicit resistance against WSMV and TriMV. Immature embryos of the wheat cv "Bobwhite" were independently co-transformed with pAHC20, containing the bar gene for glufosinate selection, and either the hairpin construct targeting the coat protein of WSMV or TriMV. After tissue culture, PCR was used to determined the presence of the RNAi CP transgene in putative transformed plants. Eight WSMV and ten TriMV CP RNAi transgenic plants were obtained from the bombardment experiments. Transgenic T1 and T2 seeds were collected and transgene expression was established through RT-PCR. In order to determine viral resistance, T1 and T2 progeny was mechanically inoculated. ELISA results indicated a differential resistance response among the tillers evaluated in each line in T1 generation for both WSMV and TriMV constructs. In T1 generation resistance was seen in up to 60% of the plants evaluated for both constructs, although some events that showed transgene presence did not exhibited resistant phenotype. Analyses of transgene presence and expression in T2 generation evidenced events of transgene silencing and deletion. Regardless of these phenomena, consistent resistance response in two lines of WSMV CP construct and one TriMV CP transgenic line was found.

Doctor of Philosophy / Department of Plant Pathology / Bernd R. Friebe / Hexaploid wheat (Triticum aestivum L., 2n=6x=42, AABBDD) is a recent polyploid and originates from a limited number of founder genotypes. Domestication bottlenecks further reduced genetic diversity. The wheat gene pool, which consists of landraces and wild relatives such as rye (Secale cereale L.), Leymus racemosus Tien and Elymus tsukushiensis Honda, is a rich source of genetic diversity. Agronomically important traits can be transferred from these gene pools to wheat through chromosome engineering. This dissertation describes chromosome engineering and pre-breeding efforts for resistance to Hessian fly and Fusarium head blight (FHB) in wheat. The germplasm with a whole-arm rye translocation, T2BS.2R#2L, contains the highly effective Hessian fly resistance gene, H21, and an unnamed powdery mildew resistance gene. Directed chromosome engineering was used to shorten the whole-arm rye segment. The recovered wheat-rye recombinant chromosome, T2BS.2BL-2R#2L, had a shorter rye segment but still contained the H21 gene and was transferred through backcrosses to adapted winter and spring wheat cultivars. This study released the germplasm KS09WGGRC51, which is used in wheat breeding programs in the U.S.A. Two novel sources of FHB resistance were identified in L. racemosus and E. tsukushiensis. Fhb3 present in the wheat-L. racemosus T7AL.7Lr#1S Robertsonian translocation was transferred into the adapted Kansas winter wheat cultivar Fuller. The wheat-E. tsukushiensis disomic addition translocation line confers FHB resistance. Ph1b-induced homoeologous recombination was used to produce wheat-E. tsukushiensis recombinants. The distal and interstitial recombinants were identified using molecular markers and genomic in situ hybridization (GISH). A combination of molecular cytogenetic analyses determined that the distal recombinant involved wheat chromosome 1A and a small distal segment originating from the E. tsukushiensis chromosome arm, 1E[superscript]ts#1S, resulting in the recombinant chromosome T1AL.1AS-1E[superscript]ts#1S. The interstitial recombinant involves an unidentified wheat chromosome and appears to be highly rearranged. Both recombinants confer high levels of type II FHB resistance (resistance to spread within the head) based on point inoculations in the greenhouse. To date, these two recombinants are the smallest alien introgression with FHB resistance in common wheat. This germplasm material has been released as KS14WGRC61. The distal recombinant can be used directly for breeding of FHB-resistant cultivars worldwide.